bslstl_unorderedmap.h

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/// @file bslstl_unorderedmap.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslstl_unorderedmap.h                                              -*-C++-*-
#ifndef INCLUDED_BSLSTL_UNORDEREDMAP
#define INCLUDED_BSLSTL_UNORDEREDMAP
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslstl_unorderedmap bslstl_unorderedmap
/// @brief  Provide an STL-compliant `unordered_map` container.
/// @addtogroup bsl
/// @{
/// @addtogroup bslstl
/// @{
/// @addtogroup bslstl_unorderedmap
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslstl_unorderedmap-purpose"> Purpose</a>
/// * <a href="#bslstl_unorderedmap-classes"> Classes </a>
/// * <a href="#bslstl_unorderedmap-canonical-header"> Canonical Header </a>
/// * <a href="#bslstl_unorderedmap-description"> Description </a>
///   * <a href="#bslstl_unorderedmap-requirements-on-value_type"> Requirements on value_type </a>
///   * <a href="#bslstl_unorderedmap-glossary"> Glossary </a>
///   * <a href="#bslstl_unorderedmap-requirements-on-hash-and-equal"> Requirements on HASH and EQUAL </a>
///   * <a href="#bslstl_unorderedmap-memory-allocation"> Memory Allocation </a>
///     * <a href="#bslstl_unorderedmap-bslma-style-allocators"> bslma-Style Allocators </a>
///   * <a href="#bslstl_unorderedmap-operations"> Operations </a>
///   * <a href="#bslstl_unorderedmap-iterator-pointer-and-reference-invalidation"> Iterator, Pointer, and Reference Invalidation </a>
///   * <a href="#bslstl_unorderedmap-unordered-map-configuration"> Unordered Map Configuration </a>
///   * <a href="#bslstl_unorderedmap-practical-requirements-on-hash"> Practical Requirements on HASH </a>
///   * <a href="#bslstl_unorderedmap-usage"> Usage </a>
///     * <a href="#bslstl_unorderedmap-example-1-gathering-document-statistics"> Example 1: Gathering Document Statistics </a>
///     * <a href="#bslstl_unorderedmap-example-2-examining-and-setting-unordered-map-configuration"> Example 2: Examining and Setting Unordered Map Configuration </a>
///     * <a href="#bslstl_unorderedmap-example-3-inverse-concordance"> Example 3: Inverse Concordance </a>
///
/// # Purpose {#bslstl_unorderedmap-purpose}
/// Provide an STL-compliant `unordered_map` container.
///
/// # Classes {#bslstl_unorderedmap-classes}
///
/// -   bsl::unordered_map : STL-compliant `unordered_map` container
///
/// # Canonical Header {#bslstl_unorderedmap-canonical-header}
/// bsl_unordered_map.h
///
/// @see  package bos+stdhdrs in the bos package group
///
/// # Description {#bslstl_unorderedmap-description}
/// This component defines a single class template,
/// `bsl::unordered_map`, implementing the standard container holding a
/// collection of unique keys, each mapped to an associated value with no
/// guarantees on ordering.
///
/// An instantiation of `unordered_map` is an allocator-aware, value-semantic
/// type whose salient attributes are its size (number of keys) and the set of
/// `KEY-VALUE` pairs the `unordered_map` contains, without regard to their
/// order.  If `unordered_map` is instantiated with a key type or mapped type
/// that is not itself value-semantic, then it will not retain all of its
/// value-semantic qualities.  In particular, if the key or mapped type cannot
/// be tested for equality, then an `unordered_map` containing that type cannot
/// be tested for equality.  It is even possible to instantiate `unordered_map`
/// with types that do not have an accessible copy-constructor, in which case
/// the `unordered_map` will not be copyable.  Note if a hasher and/or
/// equality-comparison functor are supplied at container construction, they are
/// copied to the container, and those copies, rather than the object(s)
/// supplied, are used for hashing and equality comparison of keys.
///
/// When comparing unordered map containers for equality, the keys are compared
/// using `operator==`, rather than the `EQUALS` parameter function type.
///
/// An `unordered_map` meets the requirements of an unordered associative
/// container with forward iterators in the C++11 standard [23.2.5].  The
/// `unordered_map` implemented here adheres to the C++11 standard when compiled
/// with a C++11 compiler, and makes the best approximation when compiled with a
/// C++03 compiler.  In particular, for C++03 we emulate move semantics, but
/// limit forwarding (in `emplace`) to `const` lvalues, and make no effort to
/// emulate `noexcept` or initializer-lists.  The `unordered_map` implemented
/// here adheres to the C++ standard, except that it may rehash when setting the
/// @ref max_load_factor  in order to preserve the property that the factor is
/// always respected (which is a potentially throwing operation).
///
/// ## Requirements on value_type {#bslstl_unorderedmap-requirements-on-value_type}
///
///
/// An `unordered_map` is a fully Value-Semantic Type (see @ref bsldoc_glossary )
/// only if the supplied `KEY` and `VALUE` template parameters are themselves
/// fully value-semantic.  The alias `value_type` is defined as
/// `pair<const KEY, VALUE>`.  It is possible to instantiate an `unordered_map`
/// with `KEY` and `VALUE` parameter arguments that do not provide a full set of
/// value-semantic operations, but then some methods of the container may not be
/// instantiable.  The following terminology, adopted from the C++11 standard,
/// is used in the function documentation of `map` to describe a function's
/// requirements for the `KEY` and `VALUE` template parameters.  These terms are
/// also defined in section [17.6.3.1] of the C++11 standard.
///
/// ## Glossary {#bslstl_unorderedmap-glossary}
///
///
/// @code
/// Legend
/// ------
/// 'X'    - denotes an allocator-aware container type (e.g., 'map')
/// 'T'    - 'value_type' associated with 'X'
/// 'A'    - type of the allocator used by 'X'
/// 'm'    - lvalue of type 'A' (allocator)
/// 'p',   - address ('T *') of uninitialized storage for a 'T' within an 'X'
/// 'rv'   - rvalue of type (non-'const') 'T'
/// 'v'    - rvalue or lvalue of type (possibly 'const') 'T'
/// 'args' - 0 or more arguments
/// @endcode
/// The following terms are used to more precisely specify the requirements on
/// template parameter types in function-level documentation.
///
///  *default-insertable*: `T` has a default constructor.  More precisely, `T`
///    is `default-insertable` into `X` means that the following expression is
///    well-formed:
///    `allocator_traits<A>::construct(m, p)`
/// 
///  *move-insertable*: `T` provides a constructor that takes an rvalue of type
///    (non-`const`) `T`.  More precisely, `T` is `move-insertable` into `X`
///    means that the following expression is well-formed:
///    `allocator_traits<A>::construct(m, p, rv)`
///    Note that since the `first` field of `T` is `const`, `T` is not
///    *move-insertable* unless `key_type` is *copy-insertable*.
/// 
///  *copy-insertable*: `T` provides a constructor that takes an lvalue or
///    rvalue of type (possibly `const`) `T`.  More precisely, `T` is
///    `copy-insertable` into `X` means that the following expression is
///    well-formed:
///    `allocator_traits<A>::construct(m, p, v)`
/// 
///  *move-assignable*: `T` provides an assignment operator that takes an rvalue
///    of type (non-`const`) `T`.  Note that since the `first` element of
///    `value_type` is `const`, `value_type` is not `move-assignable`.
///    Note that since the `first` field of `T` is `const`, `T` is not
///    *move-assignable* unless `key_type` is *copy-assignable*.
/// 
///  *copy-assignable*: `T` provides an assignment operator that takes an lvalue
///    or rvalue of type (possibly `const`) `T`.
/// 
///  *emplace-constructible*: `T` is `emplace-constructible` into `X` from
///    `args` means that the following expression is well-formed:
///    `allocator_traits<A>::construct(m, p, args)`
/// 
///  *erasable*: `T` provides a destructor.  More precisely, `T` is `erasable`
///    from `X` means that the following expression is well-formed:
///    `allocator_traits<A>::destroy(m, p)`
/// 
///  *equality-comparable*: The type provides an equality-comparison operator
///    that defines an equivalence relationship and is both reflexive and
///    transitive.
///
/// ## Requirements on HASH and EQUAL {#bslstl_unorderedmap-requirements-on-hash-and-equal}
///
///
/// The (template parameter) types `HASH` and `EQUAL` must be copy-constructible
/// function-objects.  Note that this requirement is somewhat stronger than the
/// requirement currently in the standard; see the discussion for Issue 2215
/// (http://cplusplus.github.com/LWG/lwg-active.html#2215);
///
/// Naturally, if either `HASH` or `EQUAL` is to be the default for its type, it
/// must be default-constructible as well.
///
/// `HASH` shall support a function call operator compatible with the following
/// statements:
/// @code
/// HASH        hash;
/// KEY         key;
/// std::size_t result = hash(key);
/// @endcode
/// where the definition of the called function meets the requirements of a
/// hash function as specified in {@ref bslstl_hash |Standard Hash Function}.
///
/// `EQUAL` shall support the a function call operator compatible with the
///  following statements:
/// @code
/// EQUAL equal;
/// KEY   key1, key2;
/// bool  result = equal(key1, key2);
/// @endcode
/// where the definition of the called function defines an equivalence
/// relationship on keys that is both reflexive and transitive.
///
/// The `HASH` and `EQUAL` function-objects are further constrained, such that
/// for any two objects whose keys compare equivalent by the comparator, shall
/// also produce the same return value from the hasher.
///
/// ## Memory Allocation {#bslstl_unorderedmap-memory-allocation}
///
///
/// The type supplied as the `ALLOCATOR` template parameter determines how
/// memory will be allocated.  The `unordered_map` template supports allocators
/// meeting the requirements of the C++11 standard [allocator.requirements],
/// and, in addition, it supports scoped-allocators derived from the
/// `bslma::Allocator` memory allocation protocol.  Clients intending to use
/// `bslma` style allocators should use the template's default `ALLOCATOR` type.
/// The default type for the `ALLOCATOR` template parameter, `bsl::allocator`,
/// provides a C++11 standard-compatible adapter for a `bslma::Allocator`
/// object.
///
/// ### bslma-Style Allocators {#bslstl_unorderedmap-bslma-style-allocators}
///
///
/// If the (template parameter) type `ALLOCATOR` of an `unordered_map`
/// instantiation is `bsl::allocator`, then objects of that unordered map type
/// will conform to the standard behavior of a `bslma`-allocator-enabled type.
/// Such an unordered map accepts an optional `bslma::Allocator` argument at
/// construction.  If the address of a `bslma::Allocator` object is explicitly
/// supplied at construction, it is used to supply memory for the
/// `unordered_map` throughout its lifetime; otherwise, the `unordered_map` will
/// use the default allocator installed at the time of the `unordered_map`s
/// construction (see @ref bslma_default ).  In addition to directly allocating
/// memory from the indicated `bslma::Allocator`, an `unordered_map` supplies
/// that allocator's address to the constructors of contained objects of the
/// (template parameter) types `KEY` and `VALUE` if, respectively, those types
/// define the `bslma::UsesBslmaAllocator` trait to `true`.
///
/// ## Operations {#bslstl_unorderedmap-operations}
///
///
/// This section describes the run-time complexity of operations on instances
/// of `unordered_map`:
/// @code
/// Legend
/// ------
/// 'K'                 - template parameter type 'KEY' of the unordered map
/// 'M'                 - template parameter type 'VALUE' of the unordered map
/// 'a', 'b'            - two distinct objects of type 'unordered_map<K, V>'
/// 'n', 'm'            - number of elements in 'a' and 'b', respectively
/// 'w'                 - number of buckets of 'a'
/// 'hf'                - hash functor hashing objects of type 'K'
/// 'eq'                - equality functor comparing objects of type 'K'
/// 'A'                 - STL-style memory allocator
/// 'i1', 'i2'          - two iterators defining a sequence of 'value_type'
///                       objects
/// 'rg'                - range of objects convertable to `value_type' objects
/// 'k'                 - object of type 'K'
/// 'vt'                - object of type 'bsl::pair<const K, M>'
/// 'Args&&...'         - variable number of arguments
/// 't&&'               - movable reference to variable 't'
/// 'ai1', 'ai2'        - two iterators belonging to 'a'
/// 'idx'               - bucket index
/// '{*}'               - C++11 std::initializer_list
/// 'distance(i1, i2)'  - number of elements in the range '[i1 .. i2)'
/// 'distance(ai1,ai2)' - number of elements in the range '[ai1 .. ai2)'
/// 'distance({*})'     - number of elements in the initializer list
/// 'z'                 - floating point value representing a load factor
///
/// +----------------------------------------------------+--------------------+
/// | Operation                                          | Complexity         |
/// +====================================================+====================+
/// | unordered_map<K, M> a;    (default construction)   | O[1]               |
/// | unordered_map<K, M> a(A);                          |                    |
/// +----------------------------------------------------+--------------------+
/// | unordered_map<K, M> a(b); (copy construction)      | Average: O[m]      |
/// | unordered_map<K, M> a(b, A);                       | Worst:   O[m^2]    |
/// +----------------------------------------------------+--------------------+
/// | unordered_map<K, M> a(b&&); (move construction)    | O[1]
/// +----------------------------------------------------+--------------------+
/// | unordered_map<K, M> a(b&&, A); (move construction) | Best:    O[1]
/// |                                                    | Worst:   O[m^2]    |
/// +----------------------------------------------------+--------------------+
/// | unordered_map<K, M> a(w);                          | O[n]               |
/// | unordered_map<K, M> a(w, A);                       |                    |
/// | unordered_map<K, M> a(w, hf);                      |                    |
/// | unordered_map<K, M> a(w, hf, A);                   |                    |
/// | unordered_map<K, M> a(w, hf, eq);                  |                    |
/// | unordered_map<K, M> a(w, hf, eq, A);               |                    |
/// +----------------------------------------------------+--------------------+
/// | unordered_map<K, M> a(i1, i2);                     | Average: O[N]      |
/// | unordered_map<K, M> a(i1, i2, A);                  | Worst:   O[N^2]    |
/// | unordered_map<K, M> a(i1, i2, w);                  | where N =          |
/// | unordered_map<K, M> a(i1, i2, w, A);               |  distance(i1, i2)] |
/// | unordered_map<K, M> a(i1, i2, w, hf);              |                    |
/// | unordered_map<K, M> a(i1, i2, w, hf, A);           |                    |
/// | unordered_map<K, M> a(i1, i2, w, hf, eq);          |                    |
/// | unordered_map<K, M> a(i1, i2, w, hf, eq, A);       |                    |
/// +----------------------------------------------------+--------------------+
/// | unordered_map<K, M> a(from_range, rg);             | Average: O[N]      |
/// | unordered_map<K, M> a(from_range, rg, A);          | Worst:   O[N^2]    |
/// | unordered_map<K, M> a(from_range, rg, w);          | where N = range::  |
/// | unordered_map<K, M> a(from_range, rg, w, A);       |      distance(rg)] |
/// | unordered_map<K, M> a(from_range, rg, w, hf);      |                    |
/// | unordered_map<K, M> a(from_range, rg, w, hf, A);   |                    |
/// | unordered_map<K, M> a(from_range, rg, w, hf, eq);  |                    |
/// | unordered_map<K, M> a(from_range, rg, w, hf, eq, A)|                    |
/// +----------------------------------------------------+--------------------+
/// | unordered_map<K, M> a({*});                        | Average: O[N]      |
/// | unordered_map<K, M> a({*}, A);                     | Worst:   O[N^2]    |
/// | unordered_map<K, M> a({*}, w);                     | where N =          |
/// | unordered_map<K, M> a({*}, w, A);                  |       'distance{*}'|
/// | unordered_map<K, M> a({*}, w, hf);                 |                    |
/// | unordered_map<K, M> a({*}, w, hf, A);              |                    |
/// | unordered_map<K, M> a({*}, w, hf, eq);             |                    |
/// | unordered_map<K, M> a({*}, w, hf, eq, A);          |                    |
/// +----------------------------------------------------+--------------------+
/// | a.~unordered_map<K, M>(); (destruction)            | O[n]               |
/// +----------------------------------------------------+--------------------+
/// | a = b;          (assignment)                       | Average: O[n+m]    |
/// |                                                    | Worst:   O[n+m^2]  |
/// +----------------------------------------------------+--------------------+
/// | a = {*};        (assignment)                       | Average: O[n+N]    |
/// |                                                    | Worst:   O[n+N^2]  |
/// |                                                    | where N =          |
/// |                                                    |       distance({*})|
/// +----------------------------------------------------+--------------------+
/// | a.begin(), a.end(), a.cbegin(), a.cend()           | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.begin(idx), a.end(idx), a.cbegin(idx),           | O[1]               |
/// | a.cend(idx)                                        |                    |
/// +----------------------------------------------------+--------------------+
/// | a == b, a != b                                     | Best:  O[n]        |
/// |                                                    | Worst: O[n^2]      |
/// +----------------------------------------------------+--------------------+
/// | a.swap(b), swap(a, b)                              | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.key_eq()                                         | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.hash_function()                                  | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.size()                                           | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.max_size()                                       | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.empty()                                          | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.get_allocator()                                  | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a[k]                                               | Average: O[1]      |
/// |                                                    | Worst:   O[n]      |
/// +----------------------------------------------------+--------------------+
/// | a.at(k)                                            | Average: O[1]      |
/// |                                                    | Worst:   O[n]      |
/// +----------------------------------------------------+--------------------+
/// | a.insert(vt), a.insert(ai1, vt)                    | Average: O[1]      |
/// | a.emplace(Args&&...)                               | Worst:   O[n]      |
/// | a.emplace_hint(ai1, Args&&...)                     |                    |
/// +----------------------------------------------------+--------------------+
/// | a.insert(vt&&), a.insert(ai1, vt&&)                | Average: O[1]      |
/// |                                                    | Worst:   O[n]      |
/// +----------------------------------------------------+--------------------+
/// | a.insert(i1, i2)                                   | Average: O[        |
/// |                                                    |   distance(i1, i2)]|
/// |                                                    | Worst:   O[n *     |
/// |                                                    |   distance(i1, i2)]|
/// +----------------------------------------------------+--------------------+
/// | a.insert({*})                                      | Average: O[        |
/// |                                                    |      distance({*})]|
/// |                                                    | Worst:   O[        |
/// |                                                    |  (n+distance{*})^2]|
/// +----------------------------------------------------+--------------------+
/// | a.insert_range(rg)                                 | Average: O[        |
/// |                                                    |   ranges::         |
/// |                                                    |       distance(rg)]|
/// |                                                    | Worst:   O[n *     |
/// |                                                    |   ranges::         |
/// |                                                    |       distance(rg)]|
/// +----------------------------------------------------+--------------------+
/// | a.erase(ai1)                                       | Average: O[1]      |
/// |                                                    | Worst:   O[n]      |
/// +----------------------------------------------------+--------------------+
/// | a.erase(k)                                         | Average:           |
/// |                                                    |       O[a.count(k)]|
/// |                                                    | Worst:             |
/// |                                                    |       O[n]         |
/// +----------------------------------------------------+--------------------+
/// | a.erase(ai1, ai2)                                  | Average: O[        |
/// |                                                    | distance(ai1, ai2)]|
/// |                                                    | Worst:   O[n]      |
/// +----------------------------------------------------+--------------------+
/// | a.clear()                                          | O[n]               |
/// +----------------------------------------------------+--------------------+
/// | a.contains(k)                                      | Average: O[1]      |
/// |                                                    | Worst:   O[n]      |
/// +----------------------------------------------------+--------------------+
/// | a.find(k)                                          | Average: O[1]      |
/// |                                                    | Worst:   O[n]      |
/// +----------------------------------------------------+--------------------+
/// | a.count(k)                                         | Average: O[1]      |
/// |                                                    | Worst:   O[n]      |
/// +----------------------------------------------------+--------------------+
/// | a.equal_range(k)                                   | Average: O[1]      |
/// |                                                    | Worst:   O[n]      |
/// +----------------------------------------------------+--------------------+
/// | a.bucket_count()                                   | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.max_bucket_count()                               | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.bucket(k)                                        | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.bucket_size(idx)                                 | O[a.bucket_size(   |
/// |                                                    |               idx)]|
/// +----------------------------------------------------+--------------------+
/// | a.load_factor()                                    | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.max_load_factor()                                | O[1]               |
/// | a.max_load_factor(z)                               | O[1]               |
/// +----------------------------------------------------+--------------------+
/// | a.rehash(k)                                        | Average: O[n]      |
/// |                                                    | Worst:   O[n^2]    |
/// +----------------------------------------------------+--------------------+
/// | a.reserve(k)                                       | Average: O[n]      |
/// |                                                    | Worst:   O[n^2]    |
/// +----------------------------------------------------+--------------------+
/// @endcode
///
/// ## Iterator, Pointer, and Reference Invalidation {#bslstl_unorderedmap-iterator-pointer-and-reference-invalidation}
///
///
/// No method of `unordered_map` invalidates a pointer or reference to an
/// element in the unordered map, unless it also erases that element, such as
/// any `erase` overload, `clear`, or the destructor (that erases all elements).
/// Pointers and references are stable through a rehash.
///
/// Iterators to elements in the container are invalidated by any rehash, so
/// iterators may be invalidated by an `insert` or `emplace` call if it triggers
/// a rehash (but not otherwise).  Iterators to specific elements are also
/// invalidated when that element is erased.  Note that although the `end`
/// iterator is not an iterator referring to any element in the container, it
/// may be invalidated by any non-`const` method.
///
/// ## Unordered Map Configuration {#bslstl_unorderedmap-unordered-map-configuration}
///
///
/// The unordered map has interfaces that can provide insight into and control
/// of its inner workings.  The unordered map is implemented using a hash table
/// (see @ref bslstl_hashtable ), a dynamically sized array of "buckets".  If two
/// elements hash to the same bucket (termed a "collision"), then that bucket
/// will house multiple elements.  As elements are added to the unordered map,
/// the number of buckets is increased (and the existing elements redistributed)
/// to keep the average number of elements per bucket (the "loading factor")
/// below the specified maximum (the "maximum load factor", 1 by default).
/// {Example 2: Examining and Setting Unordered Map Configuration} illustrates
/// the use of these interfaces.
///
/// ## Practical Requirements on HASH {#bslstl_unorderedmap-practical-requirements-on-hash}
///
///
/// An important factor in the performance an unordered map (and any of the
/// other unordered containers) is the choice of hash function.  In general, one
/// wants the hash function to return uniformly distributed values that can be
/// assigned to buckets (see {Unordered Map Configuration}) with few collisions.
///
/// The `bsl` package provides general purpose, default hash functions for
/// `bsl::string`, `bslstl::StringRef`, and the arithmetic types (e.g., `int`);
/// however, custom defined hash functions may do better, especially if one has
/// information about the distribution of keys; there is considerable literature
/// on designing hash functions.
///
/// When a user-defined class is used as a key, hasher must be provided (and
/// equality functor, if equality is not otherwise defined).  Two examples,
/// {Example 3} and {@ref bslstl_unorderedset |Example 1}, address this issue by
/// adapting the existing default hash functions for primitive types, an
/// approach that may not always prove adequate.
///
/// ## Usage {#bslstl_unorderedmap-usage}
///
///
/// In this section we show intended use of this component.
///
/// ### Example 1: Gathering Document Statistics {#bslstl_unorderedmap-example-1-gathering-document-statistics}
///
///
/// Unordered maps are useful in situations when there is no meaningful way to
/// order the key values, when the order of the keys is irrelevant to the
/// problem domain (see {Example 3}), and (even if there is a meaningful
/// ordering) the value of ordering the results is outweighed by the higher
/// performance provided by unordered maps (compared to ordered maps).
///
/// Suppose one wished to gather statistics on the words appearing in a large
/// set of documents on disk or in a data base.  Gathering those statistics is
/// intrusive (as one is competing for access to the documents with the regular
/// users) and must be done as quickly as possible.  Moreover, the set of unique
/// words appearing in those documents may be high.  The English language has in
/// excess of a million words (albeit many appear infrequently), and, if the
/// documents contain serial numbers, or Social Security numbers, or chemical
/// formulas, etc., then the `O[log(n)]` insertion time of ordered maps may well
/// be inadequate.  The unordered map, having an `O[1]` typical insertion cost,
/// is a viable alternative.  In many problem domains, sorting, if needed, can
/// be done after the data is gathered.
///
/// This example illustrates the use of `bsl::unordered_map` to gather one
/// simple statistic (counts of unique words) on a single document.  To avoid
/// irrelevant details of acquiring the data, several modestly sized documents
/// are stored in static arrays:
/// @code
/// static char document0[] =
/// " IN CONGRESS, July 4, 1776.\n"
/// "\n"
/// " The unanimous Declaration of the thirteen united States of America,\n"
/// "\n"
/// " When in the Course of human events, it becomes necessary for one\n"
/// " people to dissolve the political bands which have connected them with\n"
/// " another, and to assume among the powers of the earth, the separate\n"
/// " and equal station to which the Laws of Nature and of Nature's God\n"
/// " entitle them, a decent respect to the opinions of mankind requires\n"
/// " that they should declare the causes which impel them to the\n"
/// " separation.  We hold these truths to be self-evident, that all men\n"
/// " are created equal, that they are endowed by their Creator with\n"
/// " certain unalienable Rights, that among these are Life, Liberty and\n"
/// " the pursuit of Happiness.--That to secure these rights, Governments\n"
/// " are instituted among Men, deriving their just powers from the consent\n"
/// " of the governed, --That whenever any Form of Government becomes\n"
/// ...
/// " States may of right do.  And for the support of this Declaration,\n"
/// " with a firm reliance on the protection of divine Providence, we\n"
/// " mutually pledge to each other our Lives, our Fortunes and our sacred\n"
/// " Honor.\n";
///
/// static char document1[] =
/// "/The Universal Declaration of Human Rights\n"
/// "/-----------------------------------------\n"
/// "/Preamble\n"
/// "/ - - - -\n"
/// " Whereas recognition of the inherent dignity and of the equal and\n"
/// " inalienable rights of all members of the human family is the\n"
/// " foundation of freedom, justice and peace in the world,\n"
/// ...
/// "/Article 30\n"
/// "/ - - - - -\n"
/// " Nothing in this Declaration may be interpreted as implying for any\n"
/// " State, group or person any right to engage in any activity or to\n"
/// " perform any act aimed at the destruction of any of the rights and\n"
/// " freedoms set forth herein.\n";
///
/// static char document2[] =
/// "/CHARTER OF FUNDAMENTAL RIGHTS OF THE EUROPEAN UNION\n"
/// "/---------------------------------------------------\n"
/// " PREAMBLE\n"
/// "\n"
/// " The peoples of Europe, in creating an ever closer union among them,\n"
/// " are resolved to share a peaceful future based on common values.\n"
/// ...
/// "/Article 54\n"
/// "/-  -  -  -\n"
/// " Prohibition of abuse of rights\n"
/// "\n"
/// " Nothing in this Charter shall be interpreted as implying any right to\n"
/// " engage in any activity or to perform any act aimed at the destruction\n"
/// " of any of the rights and freedoms recognized in this Charter or at\n"
/// " their limitation to a greater extent than is provided for herein.\n";
///
/// static char * const documents[] = { document0,
///                                     document1,
///                                     document2
///                                   };
/// const int           numDocuments = sizeof documents / sizeof *documents;
/// @endcode
/// First, we define an alias to make our code more comprehensible.
/// @code
/// typedef bsl::unordered_map<bsl::string, int> WordTally;
/// @endcode
/// Next, we create an (empty) unordered map to hold our word tallies.  The
/// output from the `printf` statements will be discussed in {Example 2}.
/// @code
/// WordTally wordTally;
///
/// printf("size             %4d initial\n", wordTally.size());
/// printf("bucket_count     %4d initial\n", wordTally.bucket_count());
/// printf("load_factor      %f  initial\n", wordTally.load_factor());
/// printf("max_load_factor  %f  initial\n", wordTally.max_load_factor());
/// @endcode
/// Then, we define the set of characters that define word boundaries:
/// @code
/// const char *delimiters = " \n\t,:;.()[]?!/";
/// @endcode
/// Next, we extract the words from our documents.  Note that `strtok` modifies
/// the document arrays (which were not made `const`).
///
/// For each iteration of the inner loop, that method looks for a map entry
/// matching the given key value.  On the first occurrence of a word, the map
/// has no such entry, so one is created with a default value of the mapped
/// value (0, just what we want in this case) and inserted into the map where it
/// is found on any subsequent occurrences of the word.  The `operator[]` method
/// returns a reference providing modifiable access to the mapped value.  Here,
/// we apply the `++` operator to that reference to maintain a tally for the
/// word.
/// @code
/// for (int idx = 0; idx < numDocuments; ++idx) {
///     for (char *cur = strtok(documents[idx], delimiters);
///                cur;
///                cur = strtok(NULL,     delimiters)) {
///         ++wordTally[bsl::string(cur)];
///     }
/// }
/// @endcode
/// Now that the data has been (quickly) gathered, we can indulge in analysis
/// that is more time consuming.  For example, we can define a comparison
/// function, copy the data to another container (e.g., `bsl::vector`), sort the
/// entries, and determine the 20 most commonly used words in the given
/// documents:
/// @code
/// /// Assignable equivalent to `WordTally::value_type`.  Note that
/// /// `bsl::vector` requires assignable types.
/// typedef bsl::pair<bsl::string, int> WordTallyEntry;
///
/// struct WordTallyEntryCompare {
///     static bool lessValue(const WordTallyEntry& a,
///                           const WordTallyEntry& b) {
///         return a.second < b.second;
///     }
///     static bool moreValue(const WordTallyEntry& a,
///                           const WordTallyEntry& b) {
///         return !lessValue(a, b);
///     }
/// };
///
/// bsl::vector<WordTallyEntry> array(wordTally.cbegin(), wordTally.cend());
///
/// assert(20 <= array.size());
///
/// std::partial_sort(array.begin(),
///                   array.begin() + 20,
///                   array.end(),
///                   WordTallyEntryCompare::moreValue);
/// @endcode
/// Notice that @ref partial_sort  suffices here since we seek only the 20 most used
/// words, not a complete distribution of word counts.
///
/// Finally, we print the sorted portion of `array`:
/// @code
/// for (bsl::vector<WordTallyEntry>::const_iterator cur  = array.begin(),
///                                                  end  = cur + 20;
///                                                  end != cur; ++cur) {
///     printf("%-10s %4d\n", cur->first.c_str(), cur->second);
/// }
/// @endcode
/// and standard output shows:
/// @code
/// the         463
/// -           398
/// of          361
/// and         349
/// to          306
/// in          141
/// or          106
/// right        93
/// be           90
/// Article      86
/// has          79
/// a            76
/// shall        69
/// for          69
/// by           62
/// with         50
/// Everyone     49
/// rights       44
/// their        44
/// is           43
/// @endcode
/// Notice that "-" (used as an header underscore in our markup) appears in the
/// word count.  That could be eliminated by adding `-` to the set of
/// delimiters; however, that would partition hyphenated words into separate
/// words.  In practice, one defines a "stop list" of common words (e.g., "the",
/// "of", "and", "is") that one does not wish to tally.  We could easily add "-"
/// to the stop list.
///
/// ### Example 2: Examining and Setting Unordered Map Configuration {#bslstl_unorderedmap-example-2-examining-and-setting-unordered-map-configuration}
///
///
/// Suppose we wish to examine (and possibly influence) the performance of an
/// unordered map.  The unordered map provides several interfaces that allow us
/// to do so.  Several of these were used in {Example 1} (code repeated below):
/// @code
/// WordTally wordTally;
///
/// printf("size             %4d initial\n", wordTally.size());
/// printf("bucket_count     %4d initial\n", wordTally.bucket_count());
/// printf("load_factor      %f  initial\n", wordTally.load_factor());
/// printf("max_load_factor  %f  initial\n", wordTally.max_load_factor());
/// @endcode
/// First, we examine the metrics of this newly created (empty) unordered map:
/// @code
/// size                0 initial
/// bucket_count        1 initial
/// load_factor      0.000000  initial
/// max_load_factor  1.000000  initial
/// @endcode
/// Notice that even when there are no elements (`size` is 0) there is one
/// bucket.  Since there are no elements, the average number of elements per
/// bucket (the @ref load_factor  above) must be 0.
///
/// Next, after `wordTally` has been loaded, we examine its metrics:
/// @code
/// printf("size             %4d\n", wordTally.size());
/// printf("bucket_count     %4d\n", wordTally.bucket_count());
/// printf("load_factor      %f\n",  wordTally.load_factor());
/// printf("max_load_factor  %f\n",  wordTally.max_load_factor());
/// @endcode
/// and find at standard output:
/// @code
/// size             1504
/// bucket_count     2099
/// load_factor      0.716532
/// max_load_factor  1.000000
/// @endcode
/// Notice how the number of buckets has increased.  (Sampling this metric as
/// the map was loaded would show that the increase was done in several stages.)
///
/// Then, we see that the load factor is indeed below the specified maximum;
/// however we obtain further details of how the buckets are used.
///
/// Using the @ref bucket_count  method, the unordered map's interface for the
/// number of elements in each bucket, we can easily determine the bucket with
/// the greatest number of elements (i.e., the greatest number of collisions):
/// @code
/// bsl::vector<int> bucketSizes;
/// bucketSizes.reserve(wordTally.bucket_count());
///
/// for (size_t idx = 0; idx < wordTally.bucket_count(); ++idx) {
///    bucketSizes.push_back(static_cast<int>(wordTally.bucket_size(idx)));
/// }
///
/// assert(0 < bucketSizes.size());
/// int maxBucketSize = *std::max_element(bucketSizes.begin(),
///                                       bucketSizes.end());
/// printf("maxBucketSize    %4d\n", maxBucketSize);
/// @endcode
/// and find on standard output:
/// @code
/// maxBucketSize       5
/// @endcode
/// We can also count the number of empty buckets, and the number of buckets at
/// `maxBucketSize`.
/// @code
/// int numEmptyBuckets = static_cast<int>(std::count(bucketSizes.begin(),
///                                                   bucketSizes.end(),
///                                                   0));
/// printf("numEmptyBuckets  %4d\n", numEmptyBuckets);
///
/// int numMaxBuckets = static_cast<int>(std::count(bucketSizes.begin(),
///                                                 bucketSizes.end(),
///                                                 maxBucketSize));
/// printf("numMaxBuckets    %4d\n", numMaxBuckets);
/// @endcode
/// which shows on standard output:
/// @code
/// numEmptyBuckets  1031
/// numMaxBuckets       3
/// @endcode
/// Suppose we are not satisfied with this distribution.  (Perhaps the load
/// factor is too high.)  We can create a second, differently configured table.
///
/// Next, create a new table `wordTally2` with twice the bucket count shown by
/// the first table (`wordTally`), and examine its initial metrics.
/// @code
/// WordTally wordTally2(wordTally.bucket_count() * 2);
///
/// printf("size2            %4d initial\n", wordTally2.size());
/// printf("bucket_count2    %4d initial\n", wordTally2.bucket_count());
/// printf("load_factor2     %f  initial\n", wordTally2.load_factor());
/// printf("max_load_factor2 %f  initial\n", wordTally2.max_load_factor());
/// @endcode
/// Standard output shows:
/// @code
/// size2               0 initial
/// bucket_count2    4201 initial
/// load_factor2     0.000000  initial
/// max_load_factor2 1.000000  initial
/// @endcode
/// Notice that although we requested 4198 buckets (2 * 2099), we created a
/// table with 4201 buckets.  (4201 is the smallest prime number greater than
/// 4198).
///
/// Then, we load our new table and examine its metrics.  For simplicity, we
/// load data from the first table rather than re-tokenize our documents.
/// @code
/// wordTally2 = wordTally;
///
/// printf("size2            %4d\n", wordTally2.size());
/// printf("bucket_count2    %4d\n", wordTally2.bucket_count());
/// printf("load_factor2     %f\n",  wordTally2.load_factor());
/// printf("max_load_factor2 %f\n",  wordTally2.max_load_factor());
///
/// bsl::vector<int> bucketSizes2;
/// bucketSizes2.reserve(wordTally2.bucket_count());
///
/// for (size_t idx = 0; idx < wordTally2.bucket_count(); ++idx) {
///    bucketSizes2.push_back(static_cast<int>(wordTally2.bucket_size(idx)));
/// }
///
/// assert(0 < bucketSizes2.size());
/// int maxBucketSize2 = *std::max_element(bucketSizes2.begin(),
///                                        bucketSizes2.end());
/// printf("maxBucketSize2   %4d\n", maxBucketSize2);
///
/// int numEmptyBuckets2 = static_cast<int>(std::count(bucketSizes2.begin(),
///                                         bucketSizes2.end(),
///                                         0));
/// printf("numEmptyBuckets2 %4d\n", numEmptyBuckets2);
///
/// int numMaxBuckets2 = static_cast<int>(std::count(bucketSizes2.begin(),
///                                       bucketSizes2.end(),
///                                       maxBucketSize2));
/// printf("numMaxBuckets2   %4d\n", numMaxBuckets2);
/// @endcode
/// Finally, we see on standard output:
/// @code
/// size2            1504
/// bucket_count2    4201
/// load_factor2     0.358010
/// max_load_factor2 1.000000
/// maxBucketSize2      4
/// numEmptyBuckets2 2971
/// numMaxBuckets2      5
/// @endcode
/// Notice that the loading factor has been (roughly) cut in half; we have
/// achieved our goal.  Also notice that the bucket count is unchanged since
/// construction; thus, there were no rehashes during the loading this unordered
/// map.  Finally, notice that the number of empty (unused) buckets is
/// significantly higher, and there's been a modest decrease in the largest
/// bucket size, but more instances of them.
///
/// Thus, the unordered map provides facilities by which we can make trade-offs
/// in performance characteristics of the containers we create.
///
/// ### Example 3: Inverse Concordance {#bslstl_unorderedmap-example-3-inverse-concordance}
///
///
/// If one has a concordance for a set of documents (an index of the position of
/// every unique word in those documents), then words of interest can be
/// efficiently located.  Suppose after locating a word of interest one also
/// needs the surrounding words (for context).  Searching in the original
/// document requires re-tokenization (time consuming).  Alternatively, one can
/// use the concordance to create an inverse concordance to provide a fast
/// lookup of the words at given locations in a document and then examine words
/// near the word of interest.
///
/// First, we define the types required (and convenient aliases) to create an
/// unordered map from a word location to the corresponding word.  The "key"
/// value will be `WordLocation`, a pair of `int` values: the first being the
/// document code number (arbitrarily assigned), and second the word offset in
/// that document (the first word of the document is at offset 0).  The "mapped"
/// value of each entry is a `bsl::string` containing the word at that location.
/// @code
/// /// Document code number (`first`) and word offset (`second`) in that
/// /// document specify a word location.  The first word in the document
/// /// is at word offset 0.
/// typedef bsl::pair<int, int> WordLocation;
/// @endcode
/// Notice that the `WordLocation`, the type of the key value, has no natural
/// ordering.  The assignment of document codes is arbitrary so there is no
/// reason to consider the words on one document to sort below those in any
/// another.
///
/// Then, since there is no default hash function for the `WordLocation` type,
/// we define one.  The document code and the word offset are individually
/// hashed using the default hasher for the `int` type and those results bitwise
/// exclusive OR-ed a combined result.  This trivial combination formula
/// suffices for this problem, but is *not* a general solution for combining
/// hashes; see {Practical Requirements on `HASH`}.
/// @code
/// class WordLocationHash
/// {
///   private:
///     WordLocationHash& operator=(const WordLocationHash& rhs);
///
///   public:
///     // CREATORS
///
///     /// Create a `WordLocationHash` object.
///     //! WordLocationHash() = default;
///
///     /// Create a `WordLocationHash` object.  Note that as
///     /// `WordLocationHash` is an empty (stateless) type, this operation
///     /// has no observable effect.
///     //! WordLocationHash(const WordLocationHash& original) = default;
///
///     /// Destroy this object.
///     //! ~WordLocationHash() = default;
///
///     // ACCESSORS
///
///     /// Return a hash value computed using the specified `x`.
///     std::size_t operator()(WordLocation x) const
///     {
///         bsl::hash<int> hasher;
///         return hasher(x.first) ^ hasher(x.second);
///     }
/// };
/// @endcode
/// Notice that many of the required methods of the hash type are compiler
/// generated.  (The declaration of those methods are commented out and suffixed
/// by an `= default` comment.)
///
/// In addition to a hash functor, the unordered map requires an equality
/// comparison functor.  In this example, the unordered map uses `operator==`
/// method of `std::pair` by default.  If the mapped type has no such method, a
/// equality-comparison functor must be provided explicitly.
///
/// Next, we define the type of the unordered map and associated convenience
/// aliases:
/// @code
/// typedef bsl::unordered_map<WordLocation, bsl::string, WordLocationHash>
///                                              InverseConcordance;
///
/// typedef InverseConcordance::const_iterator   InverseConcordanceConstItr;
/// @endcode
/// Next, we obtain a concordance for the document set (see
/// {@ref bslstl_unorderedmultimap |Example 1}).  Here, the concordance is provided
/// as a statically initialized array:
/// @code
/// const static struct {
///     const char *d_word;
///     int         d_documentCode;
///     int         d_wordOffset;
/// } concordance[] = {
///     { "extent",             2,  3597 }, { "to",                 2,  1225 },
///     ...
///     { "to",                 2,  1252 }, { "Every",              2,  1049 }
/// };
/// const int numConcordance = sizeof concordance/sizeof *concordance;
/// @endcode
/// Then, we create `inverseConcordance`, an unordered map, and initialize it
/// with values obtained from `concordance`.
/// @code
/// InverseConcordance inverseConcordance;
///
/// for (int idx = 0; idx < numConcordance; ++idx) {
///     bsl::string word         = concordance[idx].d_word;
///     int         documentCode = concordance[idx].d_documentCode;
///     int         wordOffset   = concordance[idx].d_wordOffset;
///
///     WordLocation                   location(documentCode, wordOffset);
///     InverseConcordance::value_type value(location, word);
///     bool                           status =
///                                    inverseConcordance.insert(value).second;
///     assert(status);
/// }
/// @endcode
/// Notice that we expect every `insert` to be successful, as the concordance
/// should not show more than one word at any location.
///
/// Next, suppose we knew the location of the word "unalienable" in the document
/// set (see {@ref bslstl_unorderedmultimap |Example 1}) and want to know its
/// context?
/// @code
/// "unalienable",  0,  109
/// @endcode
/// We use the `find` method of `inverseConcordance` to determine the words
/// within offset `delta` of "unalienable".  Note that we must check the
/// validity of the returned iterator, in case we probe beyond the boundaries of
/// the document.
/// @code
/// const int docCode =   0;
/// const int origin  = 109;
/// const int delta   =  16;
///
/// for (int offset = origin - delta; offset < origin + delta; ++offset) {
///     WordLocation               location(docCode, offset);
///     InverseConcordanceConstItr itr = inverseConcordance.find(location);
///
///     if (inverseConcordance.end() != itr) {
///         printf("%d %4d: %s\n",
///                itr->first.first,
///                itr->first.second,
///                itr->second.c_str());
///         assert(origin != offset
///             || bsl::string("unalienable") == itr->second);
///     }
/// }
/// @endcode
/// Notice that the assertion confirms that "unalienable" is found in our
/// inverse location at the location we obtained from the concordance.
///
/// Finally, we find on standard output:
/// @code
/// 0   93: evident
/// 0   94: that
/// 0   95: all
/// 0   96: men
/// 0   97: are
/// 0   98: created
/// 0   99: equal
/// 0  100: that
/// 0  101: they
/// 0  102: are
/// 0  103: endowed
/// 0  104: by
/// 0  105: their
/// 0  106: Creator
/// 0  107: with
/// 0  108: certain
/// 0  109: unalienable
/// 0  110: Rights
/// 0  111: that
/// 0  112: among
/// 0  113: these
/// 0  114: are
/// 0  115: Life
/// 0  116: Liberty
/// 0  117: and
/// 0  118: the
/// 0  119: pursuit
/// 0  120: of
/// 0  121: Happiness
/// 0  122: That
/// 0  123: to
/// 0  124: secure
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslstl
 * @{
 */
/** @addtogroup bslstl_unorderedmap
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslstl_algorithm.h>
#include <bslstl_equalto.h>
#include <bslstl_hash.h>
#include <bslstl_hashtable.h>
#include <bslstl_hashtablebucketiterator.h>
#include <bslstl_hashtableiterator.h>
#include <bslstl_iteratorutil.h>
#include <bslstl_pair.h>
#include <bslstl_ranges.h>
#include <bslstl_stdexceptutil.h>
#include <bslstl_unorderedmapkeyconfiguration.h>
 
#include <bslalg_bidirectionallink.h>
#include <bslalg_typetraithasstliterators.h>
 
#include <bslma_allocatortraits.h>
#include <bslma_allocatortraits.h>
#include <bslma_destructorguard.h>
#include <bslma_isstdallocator.h>
#include <bslma_bslallocator.h>
#include <bslma_usesbslmaallocator.h>
 
#include <bslmf_addlvaluereference.h>
#include <bslmf_assert.h>
#include <bslmf_containercompatiblerange.h>
#include <bslmf_enableif.h>
#include <bslmf_isbitwisemoveable.h>
#include <bslmf_isconvertible.h>
#include <bslmf_movableref.h>
#include <bslmf_nestedtraitdeclaration.h>
#include <bslmf_typeidentity.h>
#include <bslmf_util.h>    // 'forward(V)'
 
#include <bsls_assert.h>
#include <bsls_compilerfeatures.h>
#include <bsls_keyword.h>
#include <bsls_libraryfeatures.h>
#include <bsls_objectbuffer.h>
#include <bsls_performancehint.h>
#include <bsls_platform.h>
#include <bsls_util.h>     // 'forward<T>(V)'
 
#include <cstddef> // NULL
 
#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
# include <initializer_list>
#endif
 
#ifdef BSLS_COMPILERFEATURES_SUPPORT_TRAITS_HEADER
#include <type_traits>  // 'std::is_constructible'
    #ifndef BSLS_COMPILERFEATURES_SUPPORT_RVALUE_REFERENCES
    #error Rvalue references curiously absent despite native 'type_traits'.
    #endif
#endif
 
#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)
# define BSLSTL_UNORDEREDMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(R, T) \
                  requires ::BloombergLP::bslmf::ContainerCompatibleRange<R, T>
#else
# define BSLSTL_UNORDEREDMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(R, T)
#endif
 
#if BSLS_COMPILERFEATURES_SIMULATE_CPP11_FEATURES
// clang-format off
// Include version that can be compiled with C++03
// Generated on Mon Jan 13 08:31:39 2025
// Command line: sim_cpp11_features.pl bslstl_unorderedmap.h
 
# define COMPILING_BSLSTL_UNORDEREDMAP_H
# include <bslstl_unorderedmap_cpp03.h>
# undef COMPILING_BSLSTL_UNORDEREDMAP_H
 
// clang-format on
#else
 
namespace bsl {
 
                           // ===================
                           // class unordered_map
                           // ===================
 
/// This class template implements a value-semantic container type holding
/// an unordered set of `KEY-VALUE` pairs having unique keys that provide a
/// mapping from keys (of template parameter type `KEY`) to their associated
/// mapped values (of template parameter type `VALUE`).
///
/// This class:
/// * supports a complete set of *value-semantic* operations
/// * is *exception-neutral* (agnostic except for the `at` method)
/// * is *alias-safe*
/// * is `const` *thread-safe*
/// For terminology see @ref bsldoc_glossary .
///
/// See @ref bslstl_unorderedmap 
template <class KEY,
          class VALUE,
          class HASH      = bsl::hash<KEY>,
          class EQUAL     = bsl::equal_to<KEY>,
          class ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE> > >
class unordered_map {
 
  private:
    // PRIVATE TYPES
 
    /// This `typedef` is an alias for the allocator traits type associated
    /// with this container.
    typedef bsl::allocator_traits<ALLOCATOR> AllocatorTraits;
 
    /// This `typedef` is an alias for the type of key-value pair objects
    /// maintained by this unordered map.
    typedef bsl::pair<const KEY, VALUE>  ValueType;
 
    /// This `typedef` is an alias for the policy used internally by this
    /// unordered map to extract the `KEY` value from the key-value pair
    /// objects maintained by this unordered map.
    typedef BloombergLP::bslstl::UnorderedMapKeyConfiguration<const KEY,
                                                              ValueType>
                                                        ListConfiguration;
 
    /// This typedef is an alias for the template instantiation of the
    /// underlying `bslstl::HashTable` used to implement this container.
    typedef BloombergLP::bslstl::HashTable<ListConfiguration,
                                             HASH,
                                             EQUAL,
                                             ALLOCATOR> HashTable;
 
    /// This typedef is an alias for the type of links maintained by the
    /// linked list of elements held by the underlying `bslstl::HashTable`.
    typedef BloombergLP::bslalg::BidirectionalLink HashTableLink;
 
    /// This typedef is an alias for the type of nodes that hold the values
    /// in this unordered map.
    typedef typename HashTable::NodeType HashTableNode;
 
    /// This typedef is a convenient alias for the utility associated with
    /// movable references.
    typedef BloombergLP::bslmf::MovableRefUtil    MoveUtil;
 
    // FRIENDS
    template <class KEY2,
              class VALUE2,
              class HASH2,
              class EQUAL2,
              class ALLOCATOR2>
    friend bool operator==(
                const unordered_map<KEY2, VALUE2, HASH2, EQUAL2, ALLOCATOR2>&,
                const unordered_map<KEY2, VALUE2, HASH2, EQUAL2, ALLOCATOR2>&);
 
    // PRIVATE MANIPULATORS
 
    /// Insert the values between the specified `first` and `last` into an
    /// initially empty set.
    template <class INPUT_ITERATOR, class SENTINEL>
    void constructFromRange(INPUT_ITERATOR first, SENTINEL last);
 
#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)
 
    /// Insert the values between the specified `first` and `last` into an
    /// initially empty set.  The specified `numElements` is used to improve performance.  
    /// 
    /// \pre The behavior is undefined   if the iterators support
    /// the calculation of distance and `numElements` is not the distance
    /// from `first` to `last`.
    template <class INPUT_ITERATOR, class SENTINEL>
    void constructFromRange(INPUT_ITERATOR first,
                            SENTINEL       last,
                            size_t         numElements);
#endif
 
    /// Insert the values between the specified `first` and `last` into this
    /// set.
    template <class INPUT_ITERATOR, class SENTINEL>
    void insertFromRange(INPUT_ITERATOR first, SENTINEL last);
 
#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)
 
    /// Insert the values between the specified `first` and `last` into this
    /// set.  The specified `numElements` is used to improve performance. 
    /// 
    /// \pre The behavior is undefined   if the iterators support the calculation of
    /// distance and `numElements` is not the distance from `first` to `last`.
    template <class INPUT_ITERATOR, class SENTINEL>
    void insertFromRange(INPUT_ITERATOR first,
                         SENTINEL       last,
                         size_t         numElements);
#endif
 
  public:
    // TRAITS
 
    // PUBLIC TYPES
    typedef KEY                                        key_type;
    typedef VALUE                                      mapped_type;
    typedef bsl::pair<const KEY, VALUE>                value_type;
    typedef HASH                                       hasher;
    typedef EQUAL                                      key_equal;
    typedef ALLOCATOR                                  allocator_type;
 
    typedef value_type&                                reference;
    typedef const value_type&                          const_reference;
 
    typedef typename AllocatorTraits::size_type        size_type;
    typedef typename AllocatorTraits::difference_type  difference_type;
    typedef typename AllocatorTraits::pointer          pointer;
    typedef typename AllocatorTraits::const_pointer    const_pointer;
 
    typedef BloombergLP::bslstl::HashTableIterator<
                             value_type, difference_type> iterator;
    typedef BloombergLP::bslstl::HashTableIterator<
                       const value_type, difference_type> const_iterator;
    typedef BloombergLP::bslstl::HashTableBucketIterator<
                             value_type, difference_type> local_iterator;
    typedef BloombergLP::bslstl::HashTableBucketIterator<
                       const value_type, difference_type> const_local_iterator;
 
  private:
    // DATA
    HashTable d_impl;  // underlying hash table used by this unordered map
 
  public:
    // CREATORS
 
    /// Create an empty unordered map having a @ref max_load_factor  of 1.0.
    /// Optionally specify an `initialNumBuckets` indicating the minimum
    /// initial size of the array of buckets of this unordered map.  If
    /// `initialNumBuckets` is not supplied, one empty bucket shall be used
    /// and no memory allocated.  Optionally specify a `hashFunction` used
    /// to generate the hash values associated with the `KEY-VALUE` pairs
    /// contained in this unordered map.  If `hashFunction` is not supplied,
    /// a default-constructed object of the (template parameter) type `HASH`
    /// is used.  Optionally specify a key-equality functor `keyEqual` used
    /// to determine whether two keys are equivalent.  If `keyEqual` is not
    /// supplied, a default-constructed object of the (template parameter)
    /// type `EQUAL` is used.  Optionally specify the `basicAllocator` used
    /// to supply memory.  If `basicAllocator` is not supplied, a
    /// default-constructed object of the (template parameter) type
    /// `ALLOCATOR` is used.  If the `ALLOCATOR` type is `bsl::allocator`
    /// (the default), then `basicAllocator` shall be convertible to
    /// `bslma::Allocator *`.  If the `ALLOCATOR` type is `bsl::allocator`
    /// and `basicAllocator` is not supplied, the currently installed default allocator is used to supply memory.  
    /// 
    /// \note Note that   more than
    /// `initialNumBuckets` buckets may be created in order to preserve the
    /// bucket allocation strategy of the hash-table (but never fewer).
    explicit
    unordered_map(size_type        initialNumBuckets,
                  const HASH&      hashFunction      = HASH(),
                  const EQUAL&     keyEqual          = EQUAL(),
                  const ALLOCATOR& basicAllocator    = ALLOCATOR());
    unordered_map(size_type        initialNumBuckets,
                  const HASH&      hashFunction,
                  const ALLOCATOR& basicAllocator);
    unordered_map(size_type        initialNumBuckets,
                  const ALLOCATOR& basicAllocator);
    explicit
    unordered_map(const ALLOCATOR& basicAllocator);
    unordered_map();
 
    /// Create an empty unordered map, having a @ref max_load_factor  of 1.0,
    /// and then create a `value_type` object for each iterator in the range
    /// starting at the specified `first` iterator and ending immediately
    /// before the specified `last` iterator, by converting from the object
    /// referred to by each iterator.  Insert into this unordered map each
    /// such object, ignoring those having a key that appears earlier in the
    /// sequence.  Optionally specify a minimum `initialNumBuckets`
    /// indicating the minimum initial size of the array of buckets of this
    /// unordered map.  If `initialNumBuckets` is 0 or not supplied, and
    /// `first` and `last` denote an empty range, a single empty bucket
    /// shall be supplied.  The actual number of buckets the unordered_map
    /// is created with shall always be enough to accommodate the number of
    /// elements of the range without exceeding the @ref max_load_factor .
    /// Optionally specify a `hashFunction` used to generate hash values
    /// associated with the `KEY-VALUE` pairs contained in this unordered
    /// map.  If `hashFunction` is not supplied, a default-constructed
    /// object of the (template parameter) type `HASH` is used.  Optionally
    /// specify a key-equality functor `keyEqual` used to verify that two
    /// keys are equivalent.  If `keyEqual` is not supplied, a
    /// default-constructed object of the (template parameter) type `EQUAL`
    /// is used.  Optionally specify a `basicAllocator` used to supply
    /// memory.  If `basicAllocator` is not supplied, a default-constructed
    /// object of the (template parameter) type `ALLOCATOR` is used.  If
    /// `ALLOCATOR` type is `bsl::allocator` (the default), then
    /// `basicAllocator` shall be convertible to `bslma::Allocator *`.  If
    /// the `ALLOCATOR` type is `bsl::allocator` and `basicAllocator` is not
    /// supplied, the currently installed default allocator is used to
    /// supply memory.  The (template parameter) type `INPUT_ITERATOR` shall
    /// meet the requirements of an input iterator defined in the C++11
    /// standard [24.2.3] providing access to values of a type convertible to `value_type`.  
    /// 
    /// \pre The behavior is undefined   unless `first` and
    /// `last` refer to a sequence of valid values where `first` is at a position at or before `last`.  
    /// 
    /// \note Note that   more than
    /// `initialNumBuckets` buckets may be created in order to preserve the
    /// bucket allocation strategy of the hash-table (but never fewer).
    template <class INPUT_ITERATOR>
    unordered_map(INPUT_ITERATOR   first,
                  INPUT_ITERATOR   last,
                  size_type        initialNumBuckets = 0,
                  const HASH&      hashFunction      = HASH(),
                  const EQUAL&     keyEqual          = EQUAL(),
                  const ALLOCATOR& basicAllocator    = ALLOCATOR());
    template <class INPUT_ITERATOR>
    unordered_map(INPUT_ITERATOR   first,
                  INPUT_ITERATOR   last,
                  size_type        initialNumBuckets,
                  const HASH&      hashFunction,
                  const ALLOCATOR& basicAllocator);
    template <class INPUT_ITERATOR>
    unordered_map(INPUT_ITERATOR   first,
                  INPUT_ITERATOR   last,
                  size_type        initialNumBuckets,
                  const ALLOCATOR& basicAllocator);
    template <class INPUT_ITERATOR>
    unordered_map(INPUT_ITERATOR   first,
                  INPUT_ITERATOR   last,
                  const ALLOCATOR& basicAllocator);
 
#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
# ifdef BSLS_COMPILERFEATURES_SUPPORT_CTAD
    template <
    class = bsl::enable_if_t<std::is_invocable_v<HASH, const KEY &>>,
    class = bsl::enable_if_t<
                         std::is_invocable_v<EQUAL, const KEY &, const KEY &>>,
    class = bsl::enable_if_t< bsl::IsStdAllocator_v<ALLOCATOR>>
    >
# endif
    unordered_map(
            std::initializer_list<value_type> values,
            size_type                         initialNumBuckets = 0,
            const HASH&                       hashFunction      = HASH(),
            const EQUAL&                      keyEqual          = EQUAL(),
            const ALLOCATOR&                  basicAllocator    = ALLOCATOR());
# ifdef BSLS_COMPILERFEATURES_SUPPORT_CTAD
    template <
    class = bsl::enable_if_t<std::is_invocable_v<HASH, const KEY &>>,
    class = bsl::enable_if_t< bsl::IsStdAllocator_v<ALLOCATOR>>
    >
# endif
    unordered_map(std::initializer_list<value_type> values,
                  size_type                         initialNumBuckets,
                  const HASH&                       hashFunction,
                  const ALLOCATOR&                  basicAllocator);
# ifdef BSLS_COMPILERFEATURES_SUPPORT_CTAD
    template <
    class = bsl::enable_if_t< bsl::IsStdAllocator_v<ALLOCATOR>>
    >
# endif
    unordered_map(std::initializer_list<value_type> values,
                  size_type                         initialNumBuckets,
                  const ALLOCATOR&                  basicAllocator);
# ifdef BSLS_COMPILERFEATURES_SUPPORT_CTAD
    /// Create an empty unordered map, having a @ref max_load_factor  of 1.0,
    /// and then create a `value_type` object for each in the range
    /// specified by `values` argument, ignoring elements having a key that
    /// appears earlier in the sequence.  Optionally specify a minimum
    /// `initialNumBuckets` indicating the minimum initial size of the array
    /// of buckets of this unordered map.  If `initialNumBuckets` is not
    /// supplied and `values` is an empty list, a single empty bucket shall
    /// be created.  The actual number of buckets the unordered_map is
    /// created with shall always be enough to accommodate the number of
    /// elements in `values` without exceeding the @ref max_load_factor .
    /// Optionally specify a `hashFunction` used to generate hash values
    /// associated with the `KEY-VALUE` pairs contained in this unordered
    /// map.  If `hashFunction` is not supplied, a default-constructed
    /// object of the (template parameter) type `HASH` is used.  Optionally
    /// specify a key-equality functor `keyEqual` used to verify that two
    /// keys are equivalent.  If `keyEqual` is not supplied, a
    /// default-constructed object of the (template parameter) type `EQUAL`
    /// is used.  Optionally specify a `basicAllocator` used to supply
    /// memory.  If `basicAllocator` is not supplied, a default-constructed
    /// object of the (template parameter) type `ALLOCATOR` is used.  If the
    /// `ALLOCATOR` type is `bsl::allocator` (the default), then
    /// `basicAllocator` shall be convertible to `bslma::Allocator *`.  If
    /// the `ALLOCATOR` type is `bsl::allocator` and `basicAllocator` is not
    /// supplied, the currently installed default allocator is used to supply memory.  
    /// 
    /// \note Note that   more than `initialNumBuckets` buckets may
    /// be created in order to preserve the bucket allocation strategy of
    /// the hash-table (but never fewer).
    template <
    class = bsl::enable_if_t< bsl::IsStdAllocator_v<ALLOCATOR>>
    >
# endif
    unordered_map(std::initializer_list<value_type> values,
                  const ALLOCATOR&                  basicAllocator);
#endif
 
    /// Create an unordered set, and insert each `value_type` object in the
    /// specified `range`, ignoring those keys having a key equivalent to
    /// that which appears earlier in the `range`.  Optionally specify an
    /// `initialNumBuckets` indicating the initial size of the array of
    /// buckets of this container.  If `initialNumBuckets` is not supplied,
    /// an implementation-defined value is used.  Optionally specify a
    /// `hashFunction` used to generate the hash values for each key value
    /// contained in this set.  If `hashFunction` is not supplied, a
    /// default-constructed object of the (template parameter) type `HASH`
    /// is used.  Optionally specify a key-equality functor `keyEqual` used
    /// to determine whether two keys have the same value.  If `keyEqual` is
    /// not supplied, a default-constructed object of the (template
    /// parameter) type `EQUAL` is used.  Optionally specify a
    /// `basicAllocator` used to supply memory.  If `basicAllocator` is not
    /// supplied, a default-constructed object of the (template parameter)
    /// type `ALLOCATOR` is used.  If the type `ALLOCATOR` is
    /// `bsl::allocator` (the default), then `basicAllocator`, if supplied,
    /// shall be convertible to `bslma::Allocator *`.  If the type
    /// `ALLOCATOR` is `bsl::allocator` and `basicAllocator` is not
    /// supplied, the currently installed default allocator is used.  This
    /// operation has `O[N]` complexity, where `N` is the number of elements in `range`.  
    /// 
    /// \note Note that   `RANGE` must meet the requirements of an
    /// input range and the values from `range` must have a type matching or
    /// convertible to `value_type`.
    template <class RANGE>
    BSLSTL_UNORDEREDMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(RANGE, value_type)
    unordered_map(
         bsl::from_range_t                        ,
         BSLS_COMPILERFEATURES_FORWARD_REF(RANGE) range,
         size_type                                initialNumBuckets = 0,
         const HASH&                              hashFunction = HASH(),
         const EQUAL&                             keyEqual = EQUAL(),
         const ALLOCATOR&                         basicAllocator = ALLOCATOR())
    : d_impl(hashFunction,
             keyEqual,
             initialNumBuckets,
             1.0f,
             basicAllocator)
    {
        // Defined inline to avoid `clang` and Windows errors.
#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)
        if constexpr (ranges::sized_range<RANGE>) {
            constructFromRange(bsl::ranges::begin(range),
                               bsl::ranges::end  (range),
                               bsl::ranges::size (range));
        } else // ...
#endif
        {
            constructFromRange(bsl::ranges::begin(range),
                               bsl::ranges::end  (range));
        }
    }
 
    template <class RANGE>
    BSLSTL_UNORDEREDMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(RANGE, value_type)
    unordered_map(bsl::from_range_t                        ,
                  BSLS_COMPILERFEATURES_FORWARD_REF(RANGE) range,
                  size_type                                initialNumBuckets,
                  const HASH&                              hashFunction,
                  const ALLOCATOR&                         basicAllocator)
    : d_impl(hashFunction, EQUAL(), initialNumBuckets, 1.0f, basicAllocator)
    {
        // Defined inline to avoid `clang` error.
 
        unordered_map other(bsl::from_range,
                            range,
                            initialNumBuckets,
                            hashFunction,
                            EQUAL(),
                            basicAllocator);
        this->swap(other);
    }
 
    template <class RANGE>
    BSLSTL_UNORDEREDMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(RANGE, value_type)
    unordered_map(bsl::from_range_t                        ,
                  BSLS_COMPILERFEATURES_FORWARD_REF(RANGE) range,
                  size_type                                initialNumBuckets,
                  const ALLOCATOR&                         basicAllocator)
    : d_impl(HASH(), EQUAL(), initialNumBuckets, 1.0f, basicAllocator)
    {
        // Defined inline to avoid `clang` error.
 
        unordered_map other(bsl::from_range,
                            range,
                            initialNumBuckets,
                            HASH(),
                            EQUAL(),
                            basicAllocator);
        this->swap(other);
    }
 
    template <class RANGE>
    BSLSTL_UNORDEREDMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(RANGE, value_type)
    unordered_map(bsl::from_range_t                        ,
                  BSLS_COMPILERFEATURES_FORWARD_REF(RANGE) range,
                  const ALLOCATOR&                         basicAllocator)
    : d_impl(HASH(), EQUAL(), 0, 1.0f, basicAllocator)
    {
        // Defined inline to avoid `clang` error.
 
        unordered_map other(bsl::from_range,
                            range,
                            0,
                            HASH(),
                            EQUAL(),
                            basicAllocator);
        this->swap(other);
    }
 
    /// Create an unordered map having the same value, hasher, key-equality
    /// comparator, and @ref max_load_factor  as the specified `original`.  Use
    /// the allocator returned by 'bsl::allocator_traits<ALLOCATOR>::
    /// select_on_container_copy_construction(original.get_allocator())' to
    /// supply memory.  If the `ALLOCATOR` type is `bsl::allocator` (the
    /// default), the currently installed default allocator is used to
    /// supply memory.
    unordered_map(const unordered_map& original);
 
    /// Create an unordered map having the same value, hasher, key-equality
    /// comparator, and @ref max_load_factor  as the specified `original`, and
    /// using the specified `basicAllocator` to supply memory.  If the
    /// `ALLOCATOR` type is `bsl::allocator` (the default), then
    /// `basicAllocator` shall be convertible to `bslma::Allocator *`.
    unordered_map(
                const unordered_map&                           original,
                const typename type_identity<ALLOCATOR>::type& basicAllocator);
 
    /// Create an unordered map having the same value as the specified
    /// `original` object by moving (in constant time) the contents of
    /// `original` to the new unordered map.  Use a copy of
    /// `original.hash_function()` to generate hash values for the keys
    /// contained in this unordered map.  Use a copy of `original.key_eq()`
    /// to verify that two keys are equivalent.  The allocator associated
    /// with `original` is propagated for use in the newly-created unordered
    /// map.  `original` is left in a valid but unspecified state.
    unordered_map(
          BloombergLP::bslmf::MovableRef<unordered_map> original);  // IMPLICIT
 
    /// Create an unordered map having the same value, hasher, key-equality
    /// comparator, and @ref max_load_factor  as the specified `original`.  Use
    /// the specified `basicAllocator` to supply memory.  This method
    /// requires that the (template parameter) type `value_type` be
    /// `move-insertable` into this `unordered_map` (see {Requirements on `value_type`}).  
    /// 
    /// \note Note that   a `bslma::Allocator *` can be supplied
    /// for `basicAllocator` if the (template parameter) `ALLOCATOR` type is
    /// `bsl::allocator` (the default).
    unordered_map(
                BloombergLP::bslmf::MovableRef<unordered_map>  original,
                const typename type_identity<ALLOCATOR>::type& basicAllocator);
 
    /// Destroy this object and each of its elements.
    ~unordered_map();
 
    // MANIPULATORS
 
    /// Assign to this object the value, hasher, key-equality functor, and
    /// @ref max_load_factor  of the specified `rhs` object, propagate to this
    /// object the allocator of `rhs` if the `ALLOCATOR` type has trait
    /// @ref propagate_on_container_copy_assignment , and return a reference providing modifiable access to this object.  
    /// 
    /// \note Note that   this method
    /// requires that the (template parameter) types `KEY` and `VALUE` both
    /// be `copy-constructible` (see {Requirements on `value_type`}).
    unordered_map& operator=(const unordered_map& rhs);
 
    /// Assign to this object the value, hash function, and key-equality
    /// comparator of the specified `rhs` object, propagate to this object
    /// the allocator of `rhs` if the `ALLOCATOR` type has trait
    /// @ref propagate_on_container_move_assignment , and return a reference
    /// providing modifiable access to this object.  The contents of `rhs`
    /// are moved (in constant time) to this unordered map if
    /// `get_allocator() == rhs.get_allocator()` (after accounting for the
    /// aforementioned trait); otherwise, all elements in this container are
    /// either destroyed or move-assigned to, and each additional element in
    /// `rhs` is move-inserted into this unordered_map.  `rhs` is left in a
    /// valid but unspecified state, and if an exception is thrown, `*this`
    /// is left in a valid but unspecified state.  This method requires that
    /// the type `value_type` be `move-constructible` (see {Requirements on
    /// `value_type`}).
    unordered_map&
    operator=(BloombergLP::bslmf::MovableRef<unordered_map> rhs)
        BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(
                                AllocatorTraits::is_always_equal::value &&
                                std::is_nothrow_move_assignable<HASH>::value &&
                                std::is_nothrow_move_assignable<EQUAL>::value);
 
#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
    /// Assign to this unordered map the value of the of the specified
    /// initializer list `rhs`, and return a reference providing modifiable
    /// access to this object.  This method requires that the (template
    /// parameter) type `value_type` be `copy-insertable` into this list.
    unordered_map& operator=(std::initializer_list<value_type> rhs);
#endif
 
    /// Return a reference providing modifiable access to the mapped-value
    /// associated with the specified `key` in this unordered map; if this
    /// unordered map does not already contain a `value_type` object with
    /// `key`, first insert a new `value_type` object having `key` and a default-constructed `VALUE` object.  
    /// 
    /// \note Note that   this method requires
    /// that the (template parameter) type `KEY` is `copy-constructible` and
    /// the (template parameter) `VALUE` is "default-constructible" (see
    /// {Requirements on `value_type`}).
    typename add_lvalue_reference<VALUE>::type operator[](const key_type& key);
 
    /// Return a reference providing modifiable access to the mapped-value
    /// associated with the specified `key` in this unordered map; if this
    /// unordered map does not already contain a `value_type` object with
    /// `key`, first insert a new `value_type` object having `key` and a default-constructed `VALUE` object.  
    /// 
    /// \note Note that   this method requires
    /// that the (template parameter) `VALUE` is "default-constructible" (see {Requirements on `value_type`}).  
    /// 
    /// \note Note that   `key` may be
    /// modified; it is guaranteed to be left in a valid state.
    typename add_lvalue_reference<VALUE>::type operator[](
                                 BloombergLP::bslmf::MovableRef<key_type> key);
 
#if !BSLS_COMPILERFEATURES_SIMULATE_CPP11_FEATURES
    /// Return a reference providing modifiable access to the mapped-value
    /// associated with a key that is equivalent with the specified `key`; if
    /// this `map` does not already contain a `value_type` object having an
    /// equivalent key, first insert a new `value_type` object having the
    /// move-inserted `key` and a default-constructed `VALUE` object, and
    /// return a reference to the newly mapped (default) value.  This method
    /// requires that the (template parameter) type `KEY` be `move-insertable`
    /// into this map and the (template parameter) type `VALUE` be
    /// `default-insertable` into this map (see {Requirements on `KEY` and
    /// `VALUE`}).
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
           BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value,
        typename add_lvalue_reference<VALUE>::type>::type
    operator [](LOOKUP_KEY&& key)
    {
        return try_emplace(
                 BSLS_COMPILERFEATURES_FORWARD(LOOKUP_KEY, key)).first->second;
    }
#endif
 
    /// Return a reference providing modifiable access to the mapped-value
    /// associated with the specified `key`, if such an entry exists; otherwise throw `std::out_of_range` exception.  
    /// 
    /// \note Note that   this
    /// method is not exception-neutral.
    typename add_lvalue_reference<VALUE>::type at(const key_type& key);
 
    /// Return a reference providing modifiable access to the
    /// mapped-value associated with a key that is equivalent to the
    /// specified `key`, if such an entry exists; otherwise, throw a `std::out_of_range` exception.  
    /// 
    /// \note Note that   this method may also throw
    /// a different kind of exception if the (user-supplied) comparator
    /// throws.
    ///
    /// Note: implemented inline due to Sun CC compilation error
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
           BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value,
        typename add_lvalue_reference<VALUE>::type>::type
    at(const LOOKUP_KEY& key) {
        HashTableLink *node = d_impl.find(key);
 
        if (!node) {
            BloombergLP::bslstl::StdExceptUtil::throwOutOfRange(
                      "unordered_map<...>::at(LOOKUP_KEY): invalid key value");
        }
        return static_cast<HashTableNode *>(node)->value().second;
    }
 
    /// Return an iterator providing modifiable access to the first
    /// `value_type` object in the sequence of `value_type` objects
    /// maintained by this unordered map, or the `end` iterator if this
    /// unordered map is empty.
    iterator begin() BSLS_KEYWORD_NOEXCEPT;
 
    /// Return an iterator providing modifiable access to the past-the-end
    /// position in the sequence of `value_type` objects maintained by this
    /// unordered map.
    iterator end() BSLS_KEYWORD_NOEXCEPT;
 
    /// Return a local iterator providing modifiable access to the first
    /// `value_type` object in the sequence of `value_type` objects of the
    /// bucket having the specified `index` in the array of buckets
    /// maintained by this unordered map, or the `end(index)` iterator if the bucket is empty.  
    /// 
    /// \pre The behavior is undefined   unless 'index <
    /// bucket_count()'.
    local_iterator begin(size_type index);
 
    /// Return a local iterator providing modifiable access to the
    /// past-the-end position in the sequence of `value_type` objects of the
    /// bucket having the specified `index` in the array of buckets maintained by this unordered map.  
    /// 
    /// \pre The behavior is undefined   unless
    /// `index < bucket_count()`.
    local_iterator end(size_type index);
 
    /// Remove all entries from this unordered map.  
    /// \note Note that  this
    /// unordered map will be empty after calling this method, but allocated
    /// memory may be retained for future use.
    void clear() BSLS_KEYWORD_NOEXCEPT;
 
#if !BSLS_COMPILERFEATURES_SIMULATE_CPP11_FEATURES
    /// Insert into this unordered map a newly-created `value_type` object,
    /// constructed by forwarding `get_allocator()` (if required) and the
    /// specified (variable number of) `args` to the corresponding
    /// constructor of `value_type`, if a key equivalent to such a value
    /// does not already exist in this map; otherwise, this method has no
    /// effect (other than possibly creating a temporary `value_type`
    /// object).  Return a pair whose `first` member is an iterator
    /// referring to the (possibly newly created and inserted) object in
    /// this map whose key is equivalent to that of an object constructed
    /// from `args`, and whose `second` member is `true` if a new value was
    /// inserted, and `false` if an equivalent key was already present.
    /// This method requires that the (template parameter) types `KEY` and
    /// `VALUE` both be `emplace-constructible` from `args` (see
    /// {Requirements on `value_type`}).
    template <class... Args>
    pair<iterator, bool> emplace(Args&&... args);
 
    /// Insert into this unordered map a newly-created `value_type` object,
    /// constructed by forwarding `get_allocator()` (if required) and the
    /// specified (variable number of) `args` to the corresponding
    /// constructor of `value_type`, if a key equivalent to such a value
    /// does not already exist in this map; otherwise, this method has no
    /// effect (other than possibly creating a temporary `value_type`
    /// object).  Return an iterator referring to the (possibly newly
    /// created and inserted) object in this map whose key is equivalent to
    /// that of an object constructed from `args`.  The average and worst
    /// case complexity of this operation is not affected by the specified
    /// `hint`.  This method requires that the (template parameter) types
    /// `KEY` and `VALUE` both be `emplace-constructible` from `args` (see {Requirements on `value_type`}).  
    /// 
    /// \pre The behavior is undefined   unless
    /// `hint` is an iterator in the range `[begin() .. end()]` (both endpoints included).  
    /// 
    /// \note Note that   `hint` is ignored (other than
    /// possibly asserting its validity in some build modes).
    template <class... Args>
    iterator emplace_hint(const_iterator hint, Args&&... args);
#endif
 
    /// Insert into this map the value of each `value_type` object in the
    /// specified `range` if a key equivalent to the object is not already
    /// contained in this set.  The (template parameter) type `RANGE` must
    /// meet the requirements the C++20 standard [ranges] providing access
    /// to values of a type convertible to `value_type`, and `value_type`
    /// must be `emplace-constructible` from `*i` into this set, where `i`
    /// is a dereferenceable iterator obtained from `range` (see {Requirements on `KEY`}).  
    /// 
    /// \pre The behavior is undefined   if `range`
    /// overlaps this map.
    template <class RANGE>
    BSLSTL_UNORDEREDMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(RANGE, value_type)
    void insert_range(BSLS_COMPILERFEATURES_FORWARD_REF(RANGE) range)
    {
        // Defined inline to avoid `clang` and Windows errors.
#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)
        if constexpr (ranges::sized_range<RANGE>) {
            insertFromRange(bsl::ranges::begin(range),
                            bsl::ranges::end  (range),
                            bsl::ranges::size (range));
        } else // ...
#endif
        {
            insertFromRange(bsl::ranges::begin(range),
                            bsl::ranges::end  (range));
        }
    }
 
    /// Remove from this unordered map the `value_type` object at the
    /// specified `position`, and return an iterator referring to the
    /// element immediately following the removed element, or to the
    /// past-the-end position if the removed element was the last element in
    /// the sequence of elements maintained by this unordered map.  This
    /// method invalidates only iterators and references to the removed
    /// element and previously saved values of the `end()` iterator, and
    /// preserves the relative order of the elements not removed.  
    /// 
    /// \pre The behavior is undefined   unless `position` refers to a `value_type`
    /// object in this unordered map.
    iterator erase(const_iterator position);
    iterator erase(iterator position);
 
    /// Remove from this unordered map the `value_type` object having the
    /// specified `key`, if it exists, and return 1; otherwise (there is no
    /// object with a key equivalent to `key` in this unordered map) return
    /// 0 with no other effect.  This method invalidates only iterators and
    /// references to the removed element and previously saved values of the
    /// `end()` iterator, and preserves the relative order of the elements
    /// not removed.
    size_type erase(const key_type& key);
    template <class t_KEY>
    typename enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<HASH, t_KEY>::value &&
        BloombergLP::bslmf::IsTransparentPredicate<EQUAL,t_KEY>::value &&
        !is_convertible<BSLS_COMPILERFEATURES_FORWARD_REF(t_KEY),
                        iterator>::value &&
        !is_convertible<BSLS_COMPILERFEATURES_FORWARD_REF(t_KEY),
                        const_iterator>::value,
    size_type>::type erase(BSLS_COMPILERFEATURES_FORWARD_REF(t_KEY) key)
    {
        // Implemented inline due to Sun CC compilation error.
        iterator it = this->find(key);
        if (it == end()) {
            return 0;                                                 // RETURN
        }
        erase(it);
        return 1;
    }
 
    /// Remove from this unordered map the `value_type` objects starting at
    /// the specified `first` position up to, but not including, the
    /// specified `last` position, and return `last`.  This method
    /// invalidates only iterators and references to the removed element and
    /// previously saved values of the `end()` iterator, and preserves the
    /// relative order of the elements not removed.  
    /// 
    /// \pre The behavior is undefined   unless `first` and `last` either refer to elements in this
    /// unordered map or are the `end` iterator, and the `first` position is
    /// at or before the `last` position in the iteration sequence provided
    /// by this container.
    iterator erase(const_iterator first, const_iterator last);
 
    /// Return an iterator providing modifiable access to the `value_type`
    /// object in this unordered map with a key equivalent to the specified
    /// `key`, if such an entry exists, and the past-the-end iterator (`end`) otherwise.  
    /// 
    /// \pre The behavior is undefined   unless `key` is
    /// equivalent to the key of at most one element in this unordered map.
    template <class LOOKUP_KEY>
    typename enable_if<
           BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value,
                      iterator>::type
    find(const LOOKUP_KEY& key)
        {
            // Note: implemented inline due to Sun CC compilation error.
            return iterator(d_impl.find(key));
        }
 
    /// Return an iterator providing modifiable access to the `value_type`
    /// object in this unordered map with a key equivalent to the specified
    /// `key`, if such an entry exists, and the past-the-end iterator
    /// (`end`) otherwise.
    iterator find(const key_type& key);
 
    /// Insert the specified `value` into this unordered map if the key (the
    /// `first` element) of the object referred to by `value` does not
    /// already exist in this unordered map; otherwise, this method has no
    /// effect (a `value_type` object having the key equivalent to the key
    /// of `value` already exists in this unordered map).  Return a `pair`
    /// whose `first` member is an iterator referring to the (possibly newly
    /// inserted) `value_type` object in this unordered map whose key is
    /// equivalent to that of the object to be inserted, and whose `second`
    /// member is `true` if a new value was inserted, and `false` if a value having an equivalent key was already present.  
    /// 
    /// \note Note that   this method
    /// requires that the (template parameter) types `KEY` and `VALUE` both
    /// be `copy-insertable` into this unordered map (see {Requirements on
    /// `value_type`}).
    pair<iterator, bool> insert(const value_type& value);
 
#if defined(BSLS_PLATFORM_CMP_SUN) && BSLS_PLATFORM_CMP_VERSION < 0x5130
    template <class ALT_VALUE_TYPE>
    pair<iterator, bool>
#elif !defined(BSLS_COMPILERFEATURES_SUPPORT_TRAITS_HEADER)
    template <class ALT_VALUE_TYPE>
    typename enable_if<is_convertible<ALT_VALUE_TYPE, value_type>::value,
                       pair<iterator, bool> >::type
#else
    /// Insert the specified `value` into this unordered map if the key (the
    /// `first` element) of the object referred to by `value` does not
    /// already exist in this unordered map; otherwise, this method has no
    /// effect (a `value_type` object having the same key as the converted
    /// `value` already exists in this unordered map) .  Return a `pair`
    /// whose `first` member is an iterator referring to the (possibly newly
    /// inserted) `value_type` object in this unordered map whose key is the
    /// equivalent to that of the object to be inserted, and whose `second`
    /// member is `true` if a new value was inserted, and `false` if a value having an equivalent key was already present.  
    /// 
    /// \note Note that   this method
    /// requires that the (template parameter) types `KEY` and `VALUE` both
    /// be `move-constructible` (see {Requirements on `value_type`}), and
    /// that the `value_type` be constructible from the (template parameter)
    /// `ALT_VALUE_TYPE`.  Also note that this one template stands in for
    /// three `insert` functions in the C++11 standard.
    template <class ALT_VALUE_TYPE>
    typename enable_if<std::is_constructible<value_type,
                                             ALT_VALUE_TYPE&&>::value,
                       pair<iterator, bool> >::type
#endif
    insert(BSLS_COMPILERFEATURES_FORWARD_REF(ALT_VALUE_TYPE) value)
    {
        // Note that some compilers require functions declared with `enable_if`
        // to be defined inline.
 
        typedef bsl::pair<iterator, bool> ResultType;
 
        bool isInsertedFlag = false;
 
        HashTableLink *result = d_impl.insertIfMissing(
                         &isInsertedFlag,
                         BSLS_COMPILERFEATURES_FORWARD(ALT_VALUE_TYPE, value));
 
        return ResultType(iterator(result), isInsertedFlag);
    }
 
    /// Insert the specified `value` into this unordered map if the key (the
    /// `first` element) of the object referred to by `value` does not
    /// already exist in this unordered map; otherwise, this method has no
    /// effect (a `value_type` object having the key equivalent to the key
    /// of `value` already exists in this unordered map).  Return an
    /// iterator referring to ether the newly inserted `value_type` object
    /// or to the existing object whose key is equivalent to the key of
    /// `value`.  The average and worst case complexity of this operation is
    /// not affected by the specified `hint`.  This method requires that the
    /// (template parameter) types `KEY` and `VALUE` both be
    /// `copy-insertable` into this unordered map (see {Requirements on `value_type`}).  
    /// 
    /// \pre The behavior is undefined   unless `hint` is an
    /// iterator in the range `[begin() .. end()]` (both endpoints included).  
    /// 
    /// \note Note that   `hint` is ignored (other than possibly
    /// asserting its validity in some build modes).
    iterator insert(const_iterator hint, const value_type& value);
 
#if defined(BSLS_PLATFORM_CMP_SUN) && BSLS_PLATFORM_CMP_VERSION < 0x5130
    template <class ALT_VALUE_TYPE>
    iterator
#elif !defined(BSLS_COMPILERFEATURES_SUPPORT_TRAITS_HEADER)
    template <class ALT_VALUE_TYPE>
    typename enable_if<is_convertible<ALT_VALUE_TYPE, value_type>::value,
                       iterator>::type
#else
    /// Insert the specified `value` into this unordered map if the key (the
    /// `first` element) of the object referred to by `value` does not
    /// already exist in this unordered map; otherwise, this method has no
    /// effect (a `value_type` object having the same key as the converted
    /// `value` already exists in this unordered map) .  Return an iterator
    /// referring to ether the newly inserted) `value_type` object or to the
    /// existing object whose key is equivalent to the key of `value`.  The
    /// average and worst case complexity of this operation is not affected
    /// by the specified `hint`.  This method requires that the (template
    /// parameter) types `KEY` and `VALUE` both be `move-constructible` (see
    /// {Requirements on `value_type`}) and that the `value_type` be
    /// constructible from the (template parameter) `ALT_VALUE_TYPE`.  
    /// 
    /// \pre The behavior is undefined   unless `hint` is an iterator in the range `[begin() .. end()]` (both endpoints included).  
    /// 
    /// \note Note that   `hint` is
    /// ignored (other than possibly asserting its validity in some build
    /// modes).  Also note that this one template stands in for three
    /// `insert` functions in the C++11 standard.
    template <class ALT_VALUE_TYPE>
    typename enable_if<std::is_constructible<value_type,
                                             ALT_VALUE_TYPE&&>::value,
                       iterator>::type
#endif
    insert(const_iterator                                    hint,
           BSLS_COMPILERFEATURES_FORWARD_REF(ALT_VALUE_TYPE) value)
    {
        // Note that some compilers require functions declared with 'enable_if'
        // to be defined inline.
 
        // There is no realistic use-case for the 'hint' in an 'unordered_map'
        // of unique values.  We could quickly test for a duplicate key, and
        // have a fast return path for when the method fails, but in the
        // typical use case where a new element is inserted, we are adding an
        // extra key check for no benefit.  In order to insert an element into
        // a bucket, we need to walk the whole bucket looking for duplicates,
        // and the hint is no help in finding the start of a bucket.
 
        (void)hint;  // suppress 'unused' warnings
 
        bool isInsertedFlag;  // not used
 
        HashTableLink *result = d_impl.insertIfMissing(
                         &isInsertedFlag,
                         BSLS_COMPILERFEATURES_FORWARD(ALT_VALUE_TYPE, value));
 
        return iterator(result);
    }
 
    /// Create a `value_type` object for each iterator in the range starting
    /// at the specified `first` iterator and ending immediately before the
    /// specified `last` iterator, by converting from the object referred to
    /// by each iterator.  Insert into this unordered map each such object
    /// whose key is not already contained.  The (template parameter) type
    /// `INPUT_ITERATOR` shall meet the requirements of an input iterator
    /// defined in the C++11 standard [24.2.3] providing access to values of
    /// a type convertible to `value_type`.  
    /// 
    /// \pre The behavior is undefined   unless `first` and `last` refer to a sequence of valid values where `first` is at a position at or before `last`.  
    /// 
    /// \note Note that   this method
    /// requires that the (template parameter) types `KEY` and `VALUE` both
    /// be `copy-constructible` (see {Requirements on `value_type`}).
    template <class INPUT_ITERATOR>
    void insert(INPUT_ITERATOR first, INPUT_ITERATOR last);
 
#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
    /// Create a `value_type` object for each element in the specified
    /// `values`.  Insert into this unordered map each such object whose key is not already contained.  
    /// 
    /// \note Note that   this method requires that the
    /// (template parameter) types `KEY` and `VALUE` both be
    /// `copy-constructible` (see {Requirements on `value_type`}).
    void insert(std::initializer_list<value_type> values);
#endif
 
#if !BSLS_COMPILERFEATURES_SIMULATE_CPP11_FEATURES
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, assign the specified `obj` to the value associated
    /// with that key, and return a pair containing an iterator referring to
    /// the existing item and `false`.  Otherwise, insert into this map a
    /// newly-created `value_type` object, constructed from
    /// `(key, std::forward<BDE_OTHER_TYPE>(obj)...))`, and return a pair
    /// containing an iterator referring to the newly-created entry and
    /// `true`.
    template <class BDE_OTHER_TYPE>
    pair<iterator, bool> insert_or_assign(const KEY&       key,
                                          BDE_OTHER_TYPE&& obj);
 
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, assign the specified `obj` to the value associated
    /// with that key, and return a pair containing an iterator referring to
    /// the existing item and `false`.  Otherwise, insert into this map a
    /// newly-created `value_type` object, constructed from
    /// `(std::forward<KEY>(key), std::forward<BDE_OTHER_TYPE>(obj)...))`,
    /// and return a pair containing an iterator referring to the
    /// newly-created entry and `true`.
    template <class BDE_OTHER_TYPE>
    pair<iterator, bool> insert_or_assign(
                                      BloombergLP::bslmf::MovableRef<KEY> key,
                                      BDE_OTHER_TYPE&&                    obj);
 
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, assign the specified `obj` to the value associated
    /// with that key, and return a pair containing an iterator referring to
    /// the existing item and `false`.  Otherwise, insert into this map a
    /// newly-created `value_type` object, constructed from
    /// `(std::forward<KEY>(key), std::forward<BDE_OTHER_TYPE>(obj)...))`,
    /// and return a pair containing an iterator referring to the
    /// newly-created entry and `true`.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template<class LOOKUP_KEY, class BDE_OTHER_TYPE>
    typename bsl::enable_if<
            BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
         && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value
         , pair<iterator, bool> >::type
    insert_or_assign(LOOKUP_KEY&& key, BDE_OTHER_TYPE&& obj)
    {
        typedef bsl::pair<iterator, bool> ResultType;
        bool isInsertedFlag = false;
        HashTableLink *result = d_impl.insertOrAssignTransparent(
                           &isInsertedFlag,
                           NULL,
                           BSLS_COMPILERFEATURES_FORWARD(LOOKUP_KEY, key),
                           BSLS_COMPILERFEATURES_FORWARD(BDE_OTHER_TYPE, obj));
        return ResultType(iterator(result), isInsertedFlag);
    }
 
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, assign the specified `obj` to the value associated
    /// with that key, and return an iterator referring to the existing
    /// item.  Otherwise, insert into this map a newly-created `value_type`
    /// object, constructed from
    /// `(std::forward<KEY>(key), std::forward<BDE_OTHER_TYPE>(obj)...))`,
    /// and return a pair containing an iterator referring to the
    /// newly-created entry and `true`.  Use the specified `hint` as a
    /// starting point for checking to see if the key already in the
    /// unordered_map.
    template <class BDE_OTHER_TYPE>
    iterator insert_or_assign(const_iterator   hint,
                              const KEY&       key,
                              BDE_OTHER_TYPE&& obj);
 
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, assign the specified `obj` to the value associated
    /// with that key, and return an iterator referring to the existing
    /// item.  Otherwise, insert into this map a newly-created `value_type`
    /// object, constructed from
    /// `(std::forward<KEY>(key), std::forward<BDE_OTHER_TYPE>(obj)...))`,
    /// and return an iterator referring to the newly-created entry.  Use
    /// the specified `hint` as a starting point for checking to see if the
    /// key already in the unordered_map.
    template <class BDE_OTHER_TYPE>
    iterator insert_or_assign(const_iterator                      hint,
                              BloombergLP::bslmf::MovableRef<KEY> key,
                              BDE_OTHER_TYPE&&                    obj);
 
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, assign the specified `obj` to the value associated
    /// with that key, and return an iterator referring to the existing
    /// item.  Otherwise, insert into this map a newly-created `value_type`
    /// object, constructed from
    /// `(std::forward<KEY>(key), std::forward<BDE_OTHER_TYPE>(obj)...))`,
    /// and return an iterator referring to the newly-created entry.  Use
    /// the specified `hint` as a starting point for checking to see if the
    /// key already in the unordered_map.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template<class LOOKUP_KEY, class BDE_OTHER_TYPE>
    typename bsl::enable_if<
            BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
         && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value
         , iterator>::type
    insert_or_assign(const_iterator   hint,
                     LOOKUP_KEY&&     key,
                     BDE_OTHER_TYPE&& obj)
    {
        bool isInsertedFlag = false;
        HashTableLink *result = d_impl.insertOrAssignTransparent(
                           &isInsertedFlag,
                           hint.node(),
                           BSLS_COMPILERFEATURES_FORWARD(LOOKUP_KEY, key),
                           BSLS_COMPILERFEATURES_FORWARD(BDE_OTHER_TYPE, obj));
        return iterator(result);
    }
#endif
 
    /// Return a pair of iterators providing modifiable access to the
    /// sequence of `value_type` objects in this unordered map having the
    /// specified `key`, where the first iterator is positioned at the start
    /// of the sequence, and the second is positioned one past the end of
    /// the sequence.  If this unordered map contains no `value_type` object
    /// having `key`, then the two returned iterators will have the same value, `end()`.  
    /// 
    /// \pre The behavior is undefined   unless `key` is
    /// equivalent to at most one key in this unordered map.  
    /// 
    /// \note Note that   since an unordered map maintains unique keys, the range will contain
    /// at most one element.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename enable_if<
           BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value,
                       pair<iterator, iterator> >::type
    equal_range(const LOOKUP_KEY& key)
        {
            typedef bsl::pair<iterator, iterator> ResultType;
 
            HashTableLink *first = d_impl.find(key);
            return first
                     ? ResultType(iterator(first), iterator(first->nextLink()))
                     : ResultType(iterator(0),     iterator(0));
        }
 
    /// Return a pair of iterators providing modifiable access to the
    /// sequence of `value_type` objects in this unordered map having the
    /// specified `key`, where the first iterator is positioned at the start
    /// of the sequence, and the second is positioned one past the end of
    /// the sequence.  If this unordered map contains no `value_type` object
    /// having `key`, then the two returned iterators will have the same value, `end()`.  
    /// 
    /// \note Note that   since an unordered map maintains unique
    /// keys, the range will contain at most one element.
    pair<iterator, iterator> equal_range(const key_type& key);
 
    /// Set the maximum load factor of this unordered map to the specified
    /// `newMaxLoadFactor`.  If `newMaxLoadFactor < loadFactor()`, this
    /// operator will cause an immediate rehash (in violation of the C++11
    /// standard); otherwise, it has a constant-time cost.  
    /// 
    /// \pre The behavior is undefined   unless `0 < newMaxLoadFactor`.
    void max_load_factor(float newMaxLoadFactor);
 
    /// Change the size of the array of buckets maintained by this unordered
    /// map to at least the specified `numBuckets`, and redistribute all the
    /// contained elements into the new sequence of buckets, according to
    /// their hash values.  After this call, @ref load_factor  will be less than
    /// or equal to @ref max_load_factor .  This operation has no effect if
    /// rehashing the elements into `numBuckets` would cause this map to
    /// exceed its @ref max_load_factor .
    void rehash(size_type numBuckets);
 
    /// Increase the number of buckets of this set to a quantity such that
    /// the ratio between the specified `numElements` and this quantity does not exceed `max_load_factor`.  
    /// 
    /// \note Note that   this guarantees that, after
    /// the reserve, elements can be inserted to grow the container to
    /// `size() == numElements` without rehashing.  Also note that memory
    /// allocations may still occur when growing the container to `size() ==
    /// numElements`.  Also note that this operation has no effect if
    /// `numElements <= size()`.
    void reserve(size_type numElements);
 
    /// Exchange the value, hasher, key-equality functor, and
    /// @ref max_load_factor  of this object with those of the specified `other`
    /// object; also exchange the allocator of this object with that of
    /// `other` if the (template parameter) type `ALLOCATOR` has the
    /// @ref propagate_on_container_swap  trait, and do not modify either
    /// allocator otherwise.  This method provides the no-throw
    /// exception-safety guarantee if and only if both the (template
    /// parameter) types `HASH` and `EQUAL` provide no-throw swap
    /// operations; if an exception is thrown, both objects are left in
    /// valid but unspecified states.  This operation guarantees `O[1]` complexity.  
    /// 
    /// \pre The behavior is undefined   unless either this object was
    /// created with the same allocator as `other` or `ALLOCATOR` has the
    /// @ref propagate_on_container_swap  trait.
    void swap(unordered_map& other) BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(
                                     AllocatorTraits::is_always_equal::value &&
                                     bsl::is_nothrow_swappable<HASH>::value &&
                                     bsl::is_nothrow_swappable<EQUAL>::value);
 
#if !BSLS_COMPILERFEATURES_SIMULATE_CPP11_FEATURES
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, return a pair containing an iterator referring to the
    /// existing item, and `false`.  Otherwise, insert into this map a
    /// newly-created `value_type` object, constructed from `key` and the
    /// specified `args`, and return a pair containing an iterator referring
    /// to the newly-created entry and `true`.  This method requires that
    /// the (template parameter) types `KEY` and `VALUE` are
    /// `emplace-constructible` from `key` and `args` respectively.  For
    /// C++03, `VALUE` must also be `copy-constructible`.
    template <class... Args>
    pair<iterator, bool> try_emplace(const KEY& key, Args&&... args);
 
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, return a pair containing an iterator referring to the
    /// existing item and `false`.  Otherwise, insert into this map a
    /// newly-created `value_type` object, constructed from
    /// `std::forward<KEY>(key)` and the specified `args`, and return a pair
    /// containing an iterator referring to the newly-created entry, and
    /// `true`.  This method requires that the (template parameter) types
    /// `KEY` and `VALUE` are `emplace-constructible` from `key` and `args`
    /// respectively.  For C++03, `VALUE` must also be `copy-constructible`.
    template <class... Args>
    pair<iterator, bool> try_emplace(
                              BloombergLP::bslmf::MovableRef<KEY> key,
                              Args&&...                           args);
 
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, return a pair containing an iterator referring to the
    /// existing item and `false`.  Otherwise, insert into this map a
    /// newly-created `value_type` object, constructed from
    /// `std::forward<LOOKUP_KEY>(key)` and the specified `args`, and return
    /// a pair containing an iterator referring to the newly-created entry,
    /// and `true`.  This method requires that the (template parameter)
    /// types `KEY` and `VALUE` are `emplace-constructible` from `key` and
    /// `args` respectively.  For C++03, `VALUE` must also be
    /// `copy-constructible`.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template<class LOOKUP_KEY, class... Args>
    typename bsl::enable_if<
           BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value
        && !bsl::is_convertible<LOOKUP_KEY&&, const_iterator>::value
        && !bsl::is_convertible<LOOKUP_KEY&&, iterator>::value,
           pair<iterator, bool> >::type
    try_emplace(LOOKUP_KEY&& key, Args&&... args)
    {
        typedef bsl::pair<iterator, bool> ResultType;
        bool isInsertedFlag = false;
        HashTableLink *result = d_impl.tryEmplace(
                                &isInsertedFlag,
                                NULL,
                                BSLS_COMPILERFEATURES_FORWARD(LOOKUP_KEY, key),
                                BSLS_COMPILERFEATURES_FORWARD(Args, args)...);
 
        return ResultType(iterator(result), isInsertedFlag);
    }
 
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, return an iterator referring to the existing item.
    /// Otherwise, insert into this map a newly-created `value_type` object,
    /// constructed from `key` and the specified `args`, and return an
    /// iterator referring to the newly-created entry.  Use the specified
    /// `hint` as a starting point for checking to see if the key already
    /// in the unordered_map.  This method requires that the
    /// (template parameter) types `KEY` and `VALUE` are
    /// `emplace-constructible` from `key` and `args` respectively.  For
    /// C++03, `VALUE` must also be `copy-constructible`.
    template<class... Args>
    iterator
    try_emplace(const_iterator hint, const KEY& key, Args&&... args);
 
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, return an iterator referring to the existing item.
    /// Otherwise, insert into this map a newly-created `value_type` object,
    /// constructed from `std::forward<KEY>(key)` and the specified `args`,
    /// and return an iterator referring to the newly-created entry.  Use
    /// the specified `hint` as a starting point for checking to see if the
    /// key already in the unordered_map.  This method requires that the
    /// (template parameter) types `KEY` and `VALUE` are
    /// `emplace-constructible` from `key` and `args` respectively.  For
    /// C++03, `VALUE` must also be `copy-constructible`.
    template <class... Args>
    iterator try_emplace(const_iterator                      hint,
                         BloombergLP::bslmf::MovableRef<KEY> key,
                         Args&&...                           args);
 
    /// If a key equivalent to the specified `key` already exists in this
    /// unordered_map, return an iterator referring to the existing item.
    /// Otherwise, insert into this map a newly-created `value_type` object,
    /// constructed from `std::forward<LOOKUP_KEY>(key)` and the specified
    /// `args`, and return an iterator referring to the newly-created entry.
    /// Use the specified `hint` as a starting point for checking to see if
    /// the key already in the unordered_map.  This method requires that the
    /// (template parameter) types `KEY` and `VALUE` are
    /// `emplace-constructible` from `key` and `args` respectively.  For
    /// C++03, `VALUE` must also be `copy-constructible`.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template<class LOOKUP_KEY, class... Args>
    typename bsl::enable_if<
           BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value,
           iterator>::type
    try_emplace(const_iterator hint, LOOKUP_KEY&& key, Args&&... args)
    {
        bool isInsertedFlag = false;
        HashTableLink *result = d_impl.tryEmplace(
                                &isInsertedFlag,
                                hint.node(),
                                BSLS_COMPILERFEATURES_FORWARD(LOOKUP_KEY, key),
                                BSLS_COMPILERFEATURES_FORWARD(Args, args)...);
 
        return iterator(result);
    }
#endif
 
  public:
    // ACCESSORS
 
    /// Return a reference providing non-modifiable access to the
    /// mapped-value associated with the specified `key`, if such an entry
    /// exists; otherwise throw a `std::out_of_range` exception.  
    /// 
    /// \note Note that   this method is not exception-neutral.
    typename add_lvalue_reference<const VALUE>::type at(const key_type& key)
                                                                         const;
 
    /// Return a reference providing non-modifiable access to the
    /// mapped-value associated with a key that is equivalent to the
    /// specified `key`, if such an entry exists; otherwise, throw a `std::out_of_range` exception.  
    /// 
    /// \note Note that   this method may also throw
    /// a different kind of exception if the (user-supplied) comparator
    /// throws.
    ///
    /// Note: implemented inline due to Sun CC compilation error
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
           BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value,
        typename add_lvalue_reference<const VALUE>::type>::type
    at(const LOOKUP_KEY& key) const {
        HashTableLink *node = d_impl.find(key);
 
        if (!node) {
            BloombergLP::bslstl::StdExceptUtil::throwOutOfRange(
                "unordered_map<...>::at(LOOKUP_KEY) const: invalid key value");
        }
        return static_cast<HashTableNode *>(node)->value().second;
    }
 
    const_iterator  begin() const BSLS_KEYWORD_NOEXCEPT;
 
    /// Return an iterator providing non-modifiable access to the first
    /// `value_type` object in the sequence of `value_type` objects
    /// maintained by this unordered map, or the `end` iterator if this
    /// unordered map is empty.
    const_iterator cbegin() const BSLS_KEYWORD_NOEXCEPT;
 
    const_iterator  end() const BSLS_KEYWORD_NOEXCEPT;
 
    /// Return an iterator providing non-modifiable access to the
    /// past-the-end position in the sequence of `value_type` objects
    /// maintained by this unordered map.
    const_iterator cend() const BSLS_KEYWORD_NOEXCEPT;
 
    const_local_iterator  begin(size_type index) const;
 
    /// Return a local iterator providing non-modifiable access to the first
    /// `value_type` object in the sequence of `value_type` objects of the
    /// bucket having the specified `index` in the array of buckets
    /// maintained by this unordered map, or the `end(index)` iterator if the bucket is empty.  
    /// 
    /// \pre The behavior is undefined   unless
    /// `index < bucket_count()`.
    const_local_iterator cbegin(size_type index) const;
 
    const_local_iterator  end(size_type index) const;
 
    /// Return a local iterator providing non-modifiable access to the
    /// past-the-end position in the sequence of `value_type` objects of the
    /// bucket having the specified `index` in the array of buckets maintained by this unordered map.  
    /// 
    /// \pre The behavior is undefined   unless
    /// `index < bucket_count()`.
    const_local_iterator cend(size_type index) const;
 
    /// Return the index of the bucket, in the array of buckets maintained
    /// by this unordered map, where values having a key equivalent to the
    /// specified `key` would be inserted.
    size_type bucket(const key_type& key) const;
 
    /// Return the index of the bucket, in the array of buckets maintained
    /// by this unordered map, where values having a key equivalent to the
    /// specified `key` would be inserted.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename enable_if<
           BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value,
                      size_type>::type
    bucket(const LOOKUP_KEY& key) const
    {
        return d_impl.bucketIndexForKey(key);
    }
 
    /// Return the number of buckets in the array of buckets maintained by
    /// this unordered map.
    size_type bucket_count() const BSLS_KEYWORD_NOEXCEPT;
 
    /// Return a theoretical upper bound on the largest number of buckets that this unordered map could possibly manage.  
    /// 
    /// \note Note that   there is
    /// no guarantee that the unordered map can successfully grow to the
    /// returned size, or even close to that size, without running out of
    /// resources.
    size_type max_bucket_count() const BSLS_KEYWORD_NOEXCEPT;
 
    /// Return the number of elements contained in the bucket at the
    /// specified `index` in the array of buckets maintained by this unordered map.  
    /// 
    /// \pre The behavior is undefined   unless
    /// `index < bucket_count()`.
    size_type bucket_size(size_type index) const;
 
    /// Return the number of `value_type` objects within this unordered map
    /// that have a key equivalent to the specified `key`.  
    /// 
    /// \pre The behavior is undefined   unless `key` is equivalent to at most one key in this unordered map.  
    /// 
    /// \note Note that   since an unordered map maintains unique
    /// keys, the returned value will be either 0 or 1.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename enable_if<
           BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value,
                      size_type>::type
    count(const LOOKUP_KEY& key) const
        {
            return d_impl.find(key) != 0;
        }
 
    /// Return the number of `value_type` objects contained within this unordered map having the specified `key`.  
    /// 
    /// \note Note that   since an
    /// unordered map maintains unique keys, the returned value will be
    /// either 0 or 1.
    size_type count(const key_type& key) const;
 
    /// Return `true` if this unordered map contains an element whose key is
    /// equivalent to the specified `key`.
    bool contains(const key_type &key) const;
 
    /// Return `true` if this unordered map contains an element whose key is
    /// equivalent to the specified `key`.
    ///
    /// Note: implemented inline due to Sun CC compilation error
    template <class LOOKUP_KEY>
    typename enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value &&
            BloombergLP::bslmf::IsTransparentPredicate<EQUAL,
                                                       LOOKUP_KEY>::value,
        bool>::type
    contains(const LOOKUP_KEY& key) const
    {
        return find(key) != end();
    }
 
    /// Return `true` if this unordered map contains no elements, and
    /// `false` otherwise.
    bool empty() const BSLS_KEYWORD_NOEXCEPT;
 
    /// Return a pair of iterators providing non-modifiable access to the
    /// sequence of `value_type` objects in this unordered map with a key
    /// equivalent to specified `key`, where the first iterator is
    /// positioned at the start of the sequence, and the second is
    /// positioned one past the end of the sequence.  If this unordered map
    /// contains no `value_type` objects having a key equivalent to `key`,
    /// then the two returned iterators will have the same value, `end()`. 
    /// 
    /// \pre The behavior is undefined   unless `key` is equivalent to at most one key in this unordered map.  
    /// 
    /// \note Note that   since an unordered map
    /// maintains unique keys, the range will contain at most one element.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename enable_if<
           BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value,
                      pair<const_iterator, const_iterator> >::type
    equal_range(const LOOKUP_KEY& key) const
        {
            typedef bsl::pair<const_iterator, const_iterator> ResultType;
 
            HashTableLink *first = d_impl.find(key);
            return first
                     ? ResultType(iterator(first), iterator(first->nextLink()))
                     : ResultType(iterator(0),     iterator(0));
        }
 
    /// Return a pair of iterators providing non-modifiable access to the
    /// sequence of `value_type` objects in this unordered map having the
    /// specified `key`, where the first iterator is positioned at the start
    /// of the sequence, and the second is positioned one past the end of
    /// the sequence.  If this unordered map contains no `value_type` object
    /// having `key`, then the two returned iterators will have the same value, `end()`.  
    /// 
    /// \note Note that   since an unordered map maintains unique
    /// keys, the range will contain at most one element.
    pair<const_iterator, const_iterator> equal_range(
                                                    const key_type& key) const;
 
    /// Return an iterator providing non-modifiable access to the
    /// `value_type` object in this unordered map with a key equivalent to
    /// the specified `key`, if such an entry exists, and the past-the-end iterator (`end`) otherwise.  
    /// 
    /// \pre The behavior is undefined   unless `key`
    /// is equivalent to at most one key in this unordered map.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename enable_if<
           BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value,
                      const_iterator>::type
    find(const LOOKUP_KEY& key) const
        {
            return const_iterator(d_impl.find(key));
        }
 
    /// Return an iterator providing non-modifiable access to the
    /// `value_type` object in this unordered map with a key equivalent to
    /// the specified `key`, if such an entry exists, and the past-the-end
    /// iterator (`end`) otherwise.
    const_iterator find(const key_type& key) const;
 
    /// Return (a copy of) the allocator used for memory allocation by this
    /// unordered map.
    allocator_type get_allocator() const BSLS_KEYWORD_NOEXCEPT;
 
    /// Return (a copy of) the unary hash functor used by this unordered map
    /// to generate a hash value (of type `size_type`) for a `key_type`
    /// object.
    HASH hash_function() const;
 
    /// Return (a copy of) binary the key-equality functor used by this
    /// unordered map that returns `true` if two `key_type` objects are
    /// equivalent, and `false` otherwise.
    EQUAL key_eq() const;
 
    /// Return the current ratio between the `size` of this unordered map
    /// and the number of buckets.  The load factor is a measure of how
    /// full the container is, and a higher load factor typically leads to
    /// an increased number of collisions, thus resulting in a loss of
    /// performance.
    float load_factor() const BSLS_KEYWORD_NOEXCEPT;
 
    /// Return the maximum load factor allowed for this unordered map.  
    /// 
    /// \note Note that   if an insert operation would cause the load factor to exceed
    /// the @ref max_load_factor , that same insert operation will increase the
    /// number of buckets and rehash the elements of the container into
    /// those buckets (see `rehash`).
    float max_load_factor() const BSLS_KEYWORD_NOEXCEPT;
 
    /// Return the number of elements in this unordered map.
    size_type size() const BSLS_KEYWORD_NOEXCEPT;
 
    /// Return a theoretical upper bound on the largest number of elements that this unordered map could possibly hold.  
    /// 
    /// \note Note that   there is no
    /// guarantee that the unordered map can successfully grow to the
    /// returned size, or even close to that size, without running out of
    /// resources.
    size_type max_size() const BSLS_KEYWORD_NOEXCEPT;
};
 
#ifdef BSLS_COMPILERFEATURES_SUPPORT_CTAD
// CLASS TEMPLATE DEDUCTION GUIDES
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `unordered_map`.  Deduce
/// the template parameters `HASH`, `EQUAL` and `ALLOCATOR` from the other
/// parameters passed to the constructor of `unordered_map`.  This deduction
/// guide does not participate unless: (1) the supplied `HASH` is invokable
/// with a `KEY`, (2) the supplied `EQUAL` is invokable with two `KEY`s, and
/// (3) the supplied allocator meets the requirements of a standard
/// allocator.
template <
    class INPUT_ITERATOR,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class HASH = bsl::hash<KEY>,
    class EQUAL = bsl::equal_to<KEY>,
    class ALLOCATOR = bsl::allocator<pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<std::is_invocable_v<HASH, const KEY &>>,
    class = bsl::enable_if_t<
                         std::is_invocable_v<EQUAL, const KEY &, const KEY &>>,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
unordered_map(INPUT_ITERATOR,
              INPUT_ITERATOR,
              typename bsl::allocator_traits<ALLOCATOR>::size_type = 0,
              HASH = HASH(),
              EQUAL = EQUAL(),
              ALLOCATOR = ALLOCATOR())
-> unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `unordered_map`.  Deduce
/// the template parameters `HASH` and "EQUAL' from the other parameters
/// passed to the constructor of `unordered_map`.  This deduction guide does
/// not participate unless the supplied allocator is convertible to
/// `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class INPUT_ITERATOR,
    class HASH,
    class EQUAL,
    class ALLOC,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class DEFAULT_ALLOCATOR = bsl::allocator<pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
unordered_map(INPUT_ITERATOR,
              INPUT_ITERATOR,
              typename bsl::allocator_traits<DEFAULT_ALLOCATOR>::size_type,
              HASH,
              EQUAL,
              ALLOC *)
-> unordered_map<KEY, VALUE, HASH, EQUAL>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `unordered_map`.  Deduce
/// the template parameters `HASH` and `ALLOCATOR` from the other
/// parameters passed to the constructor of `unordered_map`.  This deduction
/// guide does not participate unless the supplied hash is invokable with a
/// `KEY` and the supplied allocator meets the requirements of a standard
/// allocator.
template <
    class INPUT_ITERATOR,
    class HASH,
    class ALLOCATOR,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class = bsl::enable_if_t<std::is_invocable_v<HASH, const KEY &>>,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
unordered_map(INPUT_ITERATOR,
              INPUT_ITERATOR,
              typename bsl::allocator_traits<ALLOCATOR>::size_type,
              HASH,
              ALLOCATOR)
-> unordered_map<KEY, VALUE, HASH, bsl::equal_to<KEY>, ALLOCATOR>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `unordered_map`.  Deduce
/// the template parameter `HASH` from the other parameters passed to the
/// constructor of `unordered_map`.  This deduction guide does not
/// participate unless the supplied allocator is convertible to
/// `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class INPUT_ITERATOR,
    class HASH,
    class ALLOC,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class DEFAULT_ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
unordered_map(INPUT_ITERATOR,
              INPUT_ITERATOR,
              typename bsl::allocator_traits<DEFAULT_ALLOCATOR>::size_type,
              HASH,
              ALLOC *)
-> unordered_map<KEY, VALUE, HASH>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `unordered_map`.  Deduce
/// the template parameter `ALLOCATOR` from the other parameter passed to
/// the constructor of `unordered_map`.  This deduction guide does not
/// participate unless the supplied allocator meets the requirements of a
/// standard allocator.
template <
    class INPUT_ITERATOR,
    class ALLOCATOR,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
unordered_map(INPUT_ITERATOR,
              INPUT_ITERATOR,
              typename bsl::allocator_traits<ALLOCATOR>::size_type,
              ALLOCATOR)
-> unordered_map<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `unordered_map`.  This
/// deduction guide does not participate unless the supplied allocator is
/// convertible to `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class INPUT_ITERATOR,
    class ALLOC,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class DEFAULT_ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
unordered_map(INPUT_ITERATOR,
              INPUT_ITERATOR,
              typename bsl::allocator_traits<DEFAULT_ALLOCATOR>::size_type,
              ALLOC *)
-> unordered_map<KEY, VALUE>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `unordered_map`.  Deduce
/// the template parameter `ALLOCATOR` from the other parameter passed to
/// the constructor of `unordered_map`.  This deduction guide does not
/// participate unless the supplied allocator meets the requirements of a
/// standard allocator.
template <
    class INPUT_ITERATOR,
    class ALLOCATOR,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
unordered_map(INPUT_ITERATOR, INPUT_ITERATOR, ALLOCATOR)
-> unordered_map<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `unordered_map`.  This
/// deduction guide does not participate unless the supplied allocator is
/// convertible to `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class INPUT_ITERATOR,
    class ALLOC,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class DEFAULT_ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
unordered_map(INPUT_ITERATOR, INPUT_ITERATOR, ALLOC *)
-> unordered_map<KEY, VALUE>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `unordered_map`.
/// Deduce the template parameters `HASH`, `EQUAL` and `ALLOCATOR` from the
/// other parameters supplied to the constructor of `unordered_map`.  This
/// deduction guide does not participate unless: (1) the supplied `HASH` is
/// invokable with a `KEY`, (2) the supplied `EQUAL` is invokable with two
/// `KEY`s, and (3) the supplied allocator meets the requirements of a
/// standard allocator.
template <
    class KEY,
    class VALUE,
    class HASH = bsl::hash<KEY>,
    class EQUAL = bsl::equal_to<KEY>,
    class ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<std::is_invocable_v<HASH, const KEY &>>,
    class = bsl::enable_if_t<
                         std::is_invocable_v<EQUAL, const KEY &, const KEY &>>,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
unordered_map(std::initializer_list<bsl::pair<const KEY, VALUE>>,
              typename bsl::allocator_traits<ALLOCATOR>::size_type = 0,
              HASH      = HASH(),
              EQUAL     = EQUAL(),
              ALLOCATOR = ALLOCATOR())
-> unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `unordered_map`.
/// Deduce the template parameters `HASH` and `EQUAL` from the other
/// parameters supplied to the constructor of `unordered_map`.  This
/// deduction guide does not participate unless the supplied allocator is
/// convertible to `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class KEY,
    class VALUE,
    class HASH,
    class EQUAL,
    class ALLOC,
    class DEFAULT_ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
unordered_map(std::initializer_list<bsl::pair<const KEY, VALUE>>,
              typename bsl::allocator_traits<DEFAULT_ALLOCATOR>::size_type,
              HASH,
              EQUAL,
              ALLOC *)
-> unordered_map<KEY, VALUE, HASH, EQUAL>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `unordered_map`.
/// Deduce the template parameters `HASH` and `ALLOCATOR` from the other
/// parameters supplied to the constructor of `unordered_map`.  This
/// deduction guide does not participate unless the supplied `HASH` is
/// invokable with a `KEY`, and the supplied allocator meets the
/// requirements of a standard allocator.
template <
    class KEY,
    class VALUE,
    class HASH,
    class ALLOCATOR,
    class = bsl::enable_if_t<std::is_invocable_v<HASH, const KEY &>>,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
unordered_map(std::initializer_list<bsl::pair<const KEY, VALUE>>,
              typename bsl::allocator_traits<ALLOCATOR>::size_type,
              HASH,
              ALLOCATOR)
-> unordered_map<KEY, VALUE, HASH, bsl::equal_to<KEY>, ALLOCATOR>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `unordered_map`.
/// Deduce the template parameter `HASH` from the other parameters supplied
/// to the constructor of `unordered_map`.  This deduction guide does not
/// participate unless the supplied allocator is convertible to
/// `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class KEY,
    class VALUE,
    class HASH,
    class ALLOC,
    class DEFAULT_ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
unordered_map(std::initializer_list<bsl::pair<const KEY, VALUE>>,
              typename bsl::allocator_traits<DEFAULT_ALLOCATOR>::size_type,
              HASH,
              ALLOC *)
-> unordered_map<KEY, VALUE, HASH>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `unordered_map`.
/// This deduction guide does not participate unless the supplied allocator
/// meets the requirements of a standard allocator.
template <
    class KEY,
    class VALUE,
    class ALLOCATOR,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
unordered_map(std::initializer_list<bsl::pair<const KEY, VALUE>>,
              typename bsl::allocator_traits<ALLOCATOR>::size_type,
              ALLOCATOR)
-> unordered_map<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `unordered_map`.
/// This deduction guide does not participate unless the supplied allocator
/// is convertible to `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class KEY,
    class VALUE,
    class ALLOC,
    class DEFAULT_ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
unordered_map(std::initializer_list<bsl::pair<const KEY, VALUE>>,
              typename bsl::allocator_traits<DEFAULT_ALLOCATOR>::size_type,
              ALLOC *)
-> unordered_map<KEY, VALUE>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `unordered_map`.
/// Deduce the template parameter `ALLOCATOR` from the other parameters
/// supplied to the constructor of `unordered_map`.  This deduction guide
/// does not participate unless the supplied allocator meets the
/// requirements of a standard allocator.
template <
    class KEY,
    class VALUE,
    class ALLOCATOR,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
unordered_map(std::initializer_list<bsl::pair<const KEY, VALUE>>, ALLOCATOR)
-> unordered_map<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>;
 
/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `unordered_map`.
/// This deduction guide does not participate unless the supplied allocator
/// is convertible to `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class KEY,
    class VALUE,
    class ALLOC,
    class DEFAULT_ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
unordered_map(std::initializer_list<bsl::pair<const KEY, VALUE>>, ALLOC *)
-> unordered_map<KEY, VALUE>;
#endif
 
// FREE OPERATORS
 
/// Return `true` if the specified `lhs` and `rhs` objects have the same
/// value, and `false` otherwise.  Two `unordered_map` objects have the
/// same value if they have the same number of key-value pairs, and for each
/// key-value pair that is contained in `lhs` there is a key-value pair
/// contained in `rhs` having the same value, and vice versa.  
/// 
/// \note Note that   this method requires that the (template parameter) types `KEY` and
/// `VALUE` both be `equality-comparable` (see {Requirements on
/// `value_type`}).
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
bool operator==(const unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& lhs,
                const unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& rhs);
 
#ifndef BSLS_COMPILERFEATURES_SUPPORT_THREE_WAY_COMPARISON
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
bool operator!=(const unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& lhs,
                const unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& rhs);
    // Return 'true' if the specified 'lhs' and 'rhs' objects do not have the
    // same value, and 'false' otherwise.  Two 'unordered_map' objects do not
    // have the same value if they do not have the same number of key-value
    // pairs, or for some key-value pair that is contained in 'lhs' there is
    // not a key-value pair in 'rhs' having the same value or vice-versa.  Note
    // that this method requires that the (template parameter) types 'KEY' and
    // 'VALUE' both be 'equality-comparable' (see {Requirements on
    // 'value_type'}).
#endif
 
// FREE FUNCTIONS
 
/// Erase all the elements in the specified unordered_map `m` that satisfy
/// the specified predicate `predicate`.  Return the number of elements
/// erased.
template <class KEY,
          class VALUE,
          class HASH,
          class EQUAL,
          class ALLOCATOR,
          class PREDICATE>
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::size_type
erase_if(unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>&         m,
                                                          PREDICATE predicate);
 
/// Exchange the value, hasher, key-equality functor, and @ref max_load_factor 
/// of the specified `a` object with those of the specified `b` object; also
/// exchange the allocator of `a` with that of `b` if the (template
/// parameter) type `ALLOCATOR` has the @ref propagate_on_container_swap  trait,
/// and do not modify either allocator otherwise.  This function provides
/// the no-throw exception-safety guarantee if and only if both the
/// (template parameter) types `HASH` and `EQUAL` provide no-throw swap
/// operations; if an exception is thrown, both objects are left in valid
/// but unspecified states.  This operation guarantees `O[1]` complexity. 
/// 
/// \pre The behavior is undefined   unless either `a` was created with the same
/// allocator as `b` or `ALLOCATOR` has the @ref propagate_on_container_swap 
/// trait.
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
void swap(unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& a,
          unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& b)
                                    BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(false);
 
}  // close namespace bsl
 
// ============================================================================
//                  TEMPLATE AND INLINE FUNCTION DEFINITIONS
// ============================================================================
 
namespace bsl {
                        //--------------------
                        // class unordered_map
                        //--------------------
 
// PRIVATE MANIPULATORS
template <class KEY, class VALUE,  class HASH, class EQUAL, class ALLOCATOR>
template <class INPUT_ITERATOR, class SENTINEL>
inline
void unordered_map<KEY, VALUE,  HASH, EQUAL, ALLOCATOR>::constructFromRange(
                                                          INPUT_ITERATOR first,
                                                          SENTINEL       last)
{
    ///Implementation Notes
    ///--------------------
    // If we can calculate the number of elements, reserve space for them
    // upfront to reduce rehashing.  The calculation is done once since
    // `IteratorUtil::insertdistance` may be expensive for non-random-access
    // iterators.
 
    if (first == last) {
        return;                                                       // RETURN
    }
 
    if BSLS_KEYWORD_CONSTEXPR_CPP17 (
        BloombergLP::bslstl::IteratorUtil::
                       canCalculateInsertDistance<INPUT_ITERATOR,SENTINEL>()) {
        this->reserve(
               BloombergLP::bslstl::IteratorUtil::insertDistance(first, last));
    }
 
    bool isInsertedFlag;  // value is not used
 
    while (first != last) {
        d_impl.insertIfMissing(&isInsertedFlag, *first);
        ++first;
    }
}
 
#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)
 
template <class KEY, class VALUE,  class HASH, class EQUAL, class ALLOCATOR>
template <class INPUT_ITERATOR, class SENTINEL>
inline
void unordered_map<KEY, VALUE,  HASH, EQUAL, ALLOCATOR>::constructFromRange(
                                                    INPUT_ITERATOR first,
                                                    SENTINEL       last,
                                                    size_t         numElements)
{
    BSLS_ASSERT_SAFE((
        !BloombergLP::bslstl::IteratorUtil
                       ::canCalculateInsertDistance<INPUT_ITERATOR, SENTINEL>()
        || numElements == static_cast<size_t>(
             BloombergLP::bslstl::IteratorUtil::insertDistance(first, last))));
 
    if (0 < numElements) {
        this->reserve(numElements);
    }
 
    bool isInsertedFlag;  // value is not used
 
    while (first != last) {
        d_impl.insertIfMissing(&isInsertedFlag, *first);
        ++first;
    }
}
 
#endif
 
// CREATORS
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::
unordered_map(size_type        initialNumBuckets,
              const HASH&      hashFunction,
              const EQUAL&     keyEqual,
              const ALLOCATOR& basicAllocator)
: d_impl(hashFunction, keyEqual, initialNumBuckets, 1.0f, basicAllocator)
{
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                                            size_type        initialNumBuckets,
                                            const HASH&      hashFunction,
                                            const ALLOCATOR& basicAllocator)
: d_impl(hashFunction, EQUAL(), initialNumBuckets, 1.0f, basicAllocator)
{
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                                            size_type        initialNumBuckets,
                                            const ALLOCATOR& basicAllocator)
: d_impl(HASH(), EQUAL(), initialNumBuckets, 1.0f, basicAllocator)
{
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                                               const ALLOCATOR& basicAllocator)
: d_impl(basicAllocator)
{
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map()
: d_impl()
{
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class INPUT_ITERATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                                            INPUT_ITERATOR   first,
                                            INPUT_ITERATOR   last,
                                            size_type        initialNumBuckets,
                                            const HASH&      hashFunction,
                                            const EQUAL&     keyEqual,
                                            const ALLOCATOR& basicAllocator)
: d_impl(hashFunction, keyEqual, initialNumBuckets, 1.0f, basicAllocator)
{
    constructFromRange(first, last);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class INPUT_ITERATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                                            INPUT_ITERATOR   first,
                                            INPUT_ITERATOR   last,
                                            size_type        initialNumBuckets,
                                            const HASH&      hashFunction,
                                            const ALLOCATOR& basicAllocator)
: d_impl(hashFunction, EQUAL(), initialNumBuckets, 1.0f, basicAllocator)
{
    this->insert(first, last);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class INPUT_ITERATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                                            INPUT_ITERATOR   first,
                                            INPUT_ITERATOR   last,
                                            size_type        initialNumBuckets,
                                            const ALLOCATOR& basicAllocator)
: d_impl(HASH(), EQUAL(), initialNumBuckets, 1.0f, basicAllocator)
{
    this->insert(first, last);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class INPUT_ITERATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                                               INPUT_ITERATOR   first,
                                               INPUT_ITERATOR   last,
                                               const ALLOCATOR& basicAllocator)
: d_impl(basicAllocator)
{
    this->insert(first, last);
}
 
#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
# ifdef BSLS_COMPILERFEATURES_SUPPORT_CTAD
template <class, class, class>
# endif
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                           std::initializer_list<value_type> values,
                           size_type                         initialNumBuckets,
                           const HASH&                       hashFunction,
                           const EQUAL&                      keyEqual,
                           const ALLOCATOR&                  basicAllocator)
: d_impl(hashFunction, keyEqual, initialNumBuckets, 1.0f, basicAllocator)
{
    insert(values.begin(), values.end());
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
# ifdef BSLS_COMPILERFEATURES_SUPPORT_CTAD
template <class, class>
# endif
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                           std::initializer_list<value_type> values,
                           size_type                         initialNumBuckets,
                           const HASH&                       hashFunction,
                           const ALLOCATOR&                  basicAllocator)
: d_impl(hashFunction, EQUAL(), initialNumBuckets, 1.0f, basicAllocator)
{
    insert(values.begin(), values.end());
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
# ifdef BSLS_COMPILERFEATURES_SUPPORT_CTAD
template <class>
# endif
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                           std::initializer_list<value_type> values,
                           size_type                         initialNumBuckets,
                           const ALLOCATOR&                  basicAllocator)
: d_impl(HASH(), EQUAL(), initialNumBuckets, 1.0f, basicAllocator)
{
    insert(values.begin(), values.end());
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
# ifdef BSLS_COMPILERFEATURES_SUPPORT_CTAD
template <class>
# endif
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                              std::initializer_list<value_type> values,
                              const ALLOCATOR&                  basicAllocator)
: d_impl(basicAllocator)
{
    insert(values.begin(), values.end());
}
#endif
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                                                 const unordered_map& original)
: d_impl(original.d_impl,
         AllocatorTraits::select_on_container_copy_construction(
                                                     original.get_allocator()))
{
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                 const unordered_map&                           original,
                 const typename type_identity<ALLOCATOR>::type& basicAllocator)
: d_impl(original.d_impl, basicAllocator)
{
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                        BloombergLP::bslmf::MovableRef<unordered_map> original)
: d_impl(MoveUtil::access(original).get_allocator())
{
    unordered_map& lvalue = original;
 
    this->swap(lvalue);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::unordered_map(
                 BloombergLP::bslmf::MovableRef<unordered_map>  original,
                 const typename type_identity<ALLOCATOR>::type& basicAllocator)
: d_impl(MoveUtil::move(MoveUtil::access(original).d_impl), basicAllocator)
{
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::~unordered_map()
{
    // All memory management is handled by the base 'd_impl' member.
}
 
// MANIPULATORS
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>&
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::operator=(
                                                      const unordered_map& rhs)
{
    // Note that we have delegated responsibility for correct handling of
    // allocator propagation to the 'HashTable' implementation.
 
    d_impl = rhs.d_impl;
 
    return *this;
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>&
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::operator=(
                             BloombergLP::bslmf::MovableRef<unordered_map> rhs)
    BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(
                                AllocatorTraits::is_always_equal::value &&
                                std::is_nothrow_move_assignable<HASH>::value &&
                                std::is_nothrow_move_assignable<EQUAL>::value)
{
    // Note that we have delegated responsibility for correct handling of
    // allocator propagation to the 'HashTable' implementation.
 
    unordered_map& lvalue = rhs;
 
    d_impl = MoveUtil::move(lvalue.d_impl);
 
    return *this;
}
 
#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>&
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::operator=(
                                         std::initializer_list<value_type> rhs)
{
    unordered_map tmp(rhs.begin(), rhs.end(), d_impl.allocator());
 
    this->swap(tmp);
 
    return *this;
}
#endif
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename add_lvalue_reference<VALUE>::type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::operator[](
                                                           const key_type& key)
{
    HashTableLink *node = d_impl.insertIfMissing(key);
    return static_cast<HashTableNode *>(node)->value().second;
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename add_lvalue_reference<VALUE>::type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::operator[](
                                  BloombergLP::bslmf::MovableRef<key_type> key)
{
    HashTableLink *node = d_impl.insertIfMissing(
                                        MoveUtil::move(MoveUtil::access(key)));
    return static_cast<HashTableNode *>(node)->value().second;
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename add_lvalue_reference<VALUE>::type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::at(const key_type& key)
{
    HashTableLink *node = d_impl.find(key);
 
    if (!node) {
        BloombergLP::bslstl::StdExceptUtil::throwOutOfRange(
                        "unordered_map<...>::at(key_type): invalid key value");
    }
 
    return static_cast<HashTableNode *>(node)->value().second;
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::begin()
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return iterator(d_impl.elementListRoot());
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::end() BSLS_KEYWORD_NOEXCEPT
{
    return iterator();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::local_iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::begin(size_type index)
{
    BSLS_ASSERT_SAFE(index < this->bucket_count());
 
    return local_iterator(&d_impl.bucketAtIndex(index));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::local_iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::end(size_type index)
{
    BSLS_ASSERT_SAFE(index < this->bucket_count());
 
    return local_iterator(0, &d_impl.bucketAtIndex(index));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
void
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::clear()
                                                          BSLS_KEYWORD_NOEXCEPT
{
    d_impl.removeAll();
}
 
#if !BSLS_COMPILERFEATURES_SIMULATE_CPP11_FEATURES
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class... Args>
bsl::pair<
         typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator,
         bool>
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::emplace(Args&&... args)
{
    typedef bsl::pair<iterator, bool> ResultType;
 
    bool isInsertedFlag = false;
 
    HashTableLink *result = d_impl.emplaceIfMissing(
                                 &isInsertedFlag,
                                 BSLS_COMPILERFEATURES_FORWARD(Args, args)...);
 
    return ResultType(iterator(result), isInsertedFlag);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class... Args>
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::emplace_hint(
                                                const_iterator, Args&&... args)
{
    // There is no realistic use-case for the 'hint' in an 'unordered_map' of
    // unique values.  We could quickly test for a duplicate key, and have a
    // fast return path for when the method fails, but in the typical use case
    // where a new element is inserted, we are adding an extra key check for no
    // benefit.  In order to insert an element into a bucket, we need to walk
    // the whole bucket looking for duplicates, and the hint is no help in
    // finding the start of a bucket.
 
    bool isInsertedFlag = false;
 
    HashTableLink *result = d_impl.emplaceIfMissing(
                                 &isInsertedFlag,
                                 BSLS_COMPILERFEATURES_FORWARD(Args, args)...);
 
    return iterator(result);
}
#endif
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::erase(
                                                       const_iterator position)
{
    BSLS_ASSERT_SAFE(position != this->end());
 
    return iterator(d_impl.remove(position.node()));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::erase(iterator position)
{
    return erase(const_iterator(position));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::size_type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::erase(const key_type& key)
{
    HashTableLink *target = d_impl.find(key);
    if (target) {
        d_impl.remove(target);
        return 1;                                                     // RETURN
    }
    else {
        return 0;                                                     // RETURN
    }
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::erase(const_iterator first,
                                                         const_iterator last)
{
 
#if defined BDE_BUILD_TARGET_SAFE_2
    if (first != last) {
        iterator it        = this->begin();
        const iterator end = this->end();
        for (; it != first; ++it) {
            BSLS_ASSERT(last != it);
            BSLS_ASSERT(end  != it);
        }
        for (; it != last; ++it) {
            BSLS_ASSERT(end  != it);
        }
    }
#endif
 
    while (first != last) {
        first = this->erase(first);
    }
 
    return iterator(first.node()); // convert from const_iterator
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
bool unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::contains(
                                                     const key_type& key) const
{
    return find(key) != end();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::find(const key_type& key)
{
    return iterator(d_impl.find(key));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
pair<typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator,
     bool>
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::insert(
                                                       const value_type& value)
{
    typedef bsl::pair<iterator, bool> ResultType;
 
    bool isInsertedFlag = false;
 
    HashTableLink *result = d_impl.insertIfMissing(&isInsertedFlag, value);
 
    return ResultType(iterator(result), isInsertedFlag);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::insert(
                                                       const_iterator,
                                                       const value_type& value)
{
    bool   isInsertedFlag;    // not used
 
    HashTableLink *result = d_impl.insertIfMissing(&isInsertedFlag, value);
 
    return iterator(result);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class INPUT_ITERATOR>
void unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::insert(
                                                          INPUT_ITERATOR first,
                                                          INPUT_ITERATOR last)
{
    insertFromRange(first, last);
}
 
#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
void unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::insert(
                                      std::initializer_list<value_type> values)
{
    insert(values.begin(), values.end());
}
#endif
 
#if !BSLS_COMPILERFEATURES_SIMULATE_CPP11_FEATURES
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class BDE_OTHER_TYPE>
bsl::pair<typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator,
          bool>
bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::insert_or_assign(
    const KEY&       key,
    BDE_OTHER_TYPE&& obj)
{
    typedef bsl::pair<iterator, bool> ResultType;
    bool           isInsertedFlag = false;
    HashTableLink *result = d_impl.insertOrAssign(
                           &isInsertedFlag,
                           NULL,
                           key,
                           BSLS_COMPILERFEATURES_FORWARD(BDE_OTHER_TYPE, obj));
    return ResultType(iterator(result), isInsertedFlag);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class BDE_OTHER_TYPE>
bsl::pair<typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator,
          bool>
bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::insert_or_assign(
    BloombergLP::bslmf::MovableRef<KEY> key,
    BDE_OTHER_TYPE&&                    obj)
{
    typedef bsl::pair<iterator, bool> ResultType;
    bool           isInsertedFlag = false;
    HashTableLink *result = d_impl.insertOrAssign(
                           &isInsertedFlag,
                           NULL,
                           BSLS_COMPILERFEATURES_FORWARD(KEY, key),
                           BSLS_COMPILERFEATURES_FORWARD(BDE_OTHER_TYPE, obj));
    return ResultType(iterator(result), isInsertedFlag);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class BDE_OTHER_TYPE>
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::insert_or_assign(
                                                         const_iterator   hint,
                                                         const KEY&       key,
                                                         BDE_OTHER_TYPE&& obj)
{
    bool isInsertedFlag = false;
    HashTableLink *result         = d_impl.insertOrAssign(
                &isInsertedFlag,
                hint.node(),
                key,
                BSLS_COMPILERFEATURES_FORWARD(BDE_OTHER_TYPE, obj));
    return iterator(result);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class BDE_OTHER_TYPE>
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::insert_or_assign(
                                      const_iterator                      hint,
                                      BloombergLP::bslmf::MovableRef<KEY> key,
                                      BDE_OTHER_TYPE&&                    obj)
{
    bool isInsertedFlag = false;
    HashTableLink *result         = d_impl.insertOrAssign(
                &isInsertedFlag,
                hint.node(),
                BSLS_COMPILERFEATURES_FORWARD(KEY, key),
                BSLS_COMPILERFEATURES_FORWARD(BDE_OTHER_TYPE, obj));
    return iterator(result);
}
#endif
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
bsl::pair<
         typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator,
         typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator>
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::equal_range(
                                                           const key_type& key)
{
    typedef bsl::pair<iterator, iterator> ResultType;
 
    HashTableLink *first = d_impl.find(key);
    return first ? ResultType(iterator(first), iterator(first->nextLink()))
                 : ResultType(iterator(0),     iterator(0));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
void
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::max_load_factor(
                                                        float newMaxLoadFactor)
{
    d_impl.setMaxLoadFactor(newMaxLoadFactor);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
void
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::rehash(
                                                          size_type numBuckets)
{
    d_impl.rehashForNumBuckets(numBuckets);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
void
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::reserve(
                                                         size_type numElements)
{
    d_impl.reserveForNumElements(numElements);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
void
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::swap(unordered_map& other)
    BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(
                                     AllocatorTraits::is_always_equal::value &&
                                     bsl::is_nothrow_swappable<HASH>::value &&
                                     bsl::is_nothrow_swappable<EQUAL>::value)
{
    d_impl.swap(other.d_impl);
}
 
#if !BSLS_COMPILERFEATURES_SIMULATE_CPP11_FEATURES
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class... Args>
inline
bsl::pair<
     typename bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator,
     bool>
bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::try_emplace(
                                                               const KEY& key,
                                                               Args&&...  args)
{
    typedef bsl::pair<iterator, bool> ResultType;
    bool isInsertedFlag = false;
    HashTableLink *result = d_impl.tryEmplace(
                                &isInsertedFlag,
                                NULL,
                                key,
                                BSLS_COMPILERFEATURES_FORWARD(Args, args)...);
 
    return ResultType(iterator(result), isInsertedFlag);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class... Args>
inline
bsl::pair<
     typename bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator,
     bool>
bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::try_emplace(
                                      BloombergLP::bslmf::MovableRef<KEY> key,
                                      Args&&...                           args)
{
    typedef bsl::pair<iterator, bool> ResultType;
    bool isInsertedFlag = false;
    HashTableLink *result = d_impl.tryEmplace(
                                &isInsertedFlag,
                                NULL,
                                BSLS_COMPILERFEATURES_FORWARD(KEY, key),
                                BSLS_COMPILERFEATURES_FORWARD(Args, args)...);
 
    return ResultType(iterator(result), isInsertedFlag);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class... Args>
inline
typename bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::try_emplace(
                                                           const_iterator hint,
                                                           const KEY&     key,
                                                           Args&&...      args)
{
    bool isInsertedFlag = false;
    HashTableLink *result = d_impl.tryEmplace(
                                &isInsertedFlag,
                                hint.node(),
                                key,
                                BSLS_COMPILERFEATURES_FORWARD(Args, args)...);
 
    return iterator(result);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
template <class... Args>
inline
typename bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::iterator
bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::try_emplace(
                                 const_iterator                           hint,
                                 BloombergLP::bslmf::MovableRef<KEY>      key,
                                 Args&&...                                args)
{
    bool isInsertedFlag = false;
    HashTableLink *result = d_impl.tryEmplace(
                                &isInsertedFlag,
                                hint.node(),
                                BSLS_COMPILERFEATURES_FORWARD(KEY, key),
                                BSLS_COMPILERFEATURES_FORWARD(Args, args)...);
 
    return iterator(result);
}
#endif
 
template <class KEY, class VALUE,  class HASH, class EQUAL, class ALLOCATOR>
template <class INPUT_ITERATOR, class SENTINEL>
inline
void unordered_map<KEY, VALUE,  HASH, EQUAL, ALLOCATOR>::insertFromRange(
                                                          INPUT_ITERATOR first,
                                                          SENTINEL       last)
{
    ///Implementation Notes
    ///--------------------
    // If we can calculate the number of elements, reserve space for them
    // upfront to reduce rehashing.  The calculation is done once since
    // `IteratorUtil::insertDistance` may be expensive for non-random-access
    // iterators.
 
    if BSLS_KEYWORD_CONSTEXPR_CPP17 (BloombergLP::bslstl::IteratorUtil
                    ::canCalculateInsertDistance<INPUT_ITERATOR, SENTINEL>()) {
        this->reserve(this->size()
             + BloombergLP::bslstl::IteratorUtil::insertDistance(first, last));
    }
 
    bool isInsertedFlag;  // value is not used
 
    while (first != last) {
        d_impl.insertIfMissing(&isInsertedFlag, *first);
        ++first;
    }
}
 
#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)
 
template <class KEY, class VALUE,  class HASH, class EQUAL, class ALLOCATOR>
template <class INPUT_ITERATOR, class SENTINEL>
inline
void unordered_map<KEY, VALUE,  HASH, EQUAL, ALLOCATOR>::insertFromRange(
                                                    INPUT_ITERATOR first,
                                                    SENTINEL       last,
                                                    size_t         numElements)
{
    BSLS_ASSERT_SAFE((
        !BloombergLP::bslstl::IteratorUtil
                       ::canCalculateInsertDistance<INPUT_ITERATOR, SENTINEL>()
        || numElements == static_cast<size_t>(
             BloombergLP::bslstl::IteratorUtil::insertDistance(first, last))));
 
    this->reserve(this->size() + numElements);
 
    bool isInsertedFlag;  // value is not used
 
    while (first != last) {
        d_impl.insertIfMissing(&isInsertedFlag, *first);
        ++first;
    }
}
 
#endif
 
// ACCESSORS
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
typename add_lvalue_reference<const VALUE>::type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::at(
                                                     const key_type& key) const
{
    HashTableLink *target = d_impl.find(key);
    if (!target ){
        BloombergLP::bslstl::StdExceptUtil::throwOutOfRange(
                        "unordered_map<...>::at(key_type): invalid key value");
    }
    return static_cast<HashTableNode *>(target)->value().second;
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::const_iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::begin() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return const_iterator(d_impl.elementListRoot());
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::const_iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::end() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return const_iterator();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::const_iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::cbegin() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return const_iterator(d_impl.elementListRoot());
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::const_iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::cend() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return const_iterator();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::const_local_iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::begin(size_type index) const
{
    BSLS_ASSERT_SAFE(index < this->bucket_count());
 
    return const_local_iterator(&d_impl.bucketAtIndex(index));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::const_local_iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::end(size_type index) const
{
    BSLS_ASSERT_SAFE(index < this->bucket_count());
 
    return const_local_iterator(0, &d_impl.bucketAtIndex(index));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::const_local_iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::cbegin(
                                                         size_type index) const
{
    BSLS_ASSERT_SAFE(index < this->bucket_count());
 
    return const_local_iterator(&d_impl.bucketAtIndex(index));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::const_local_iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::cend(size_type index) const
{
    BSLS_ASSERT_SAFE(index < this->bucket_count());
 
    return const_local_iterator(0, &d_impl.bucketAtIndex(index));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::size_type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::bucket(
                                                     const key_type& key) const
{
    return d_impl.bucketIndexForKey(key);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::size_type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::bucket_count() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return d_impl.numBuckets();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::size_type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::max_bucket_count() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return d_impl.maxNumBuckets();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::size_type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::bucket_size(
                                                         size_type index) const
{
    BSLS_ASSERT_SAFE(index < this->bucket_count());
 
    return d_impl.countElementsInBucket(index);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::size_type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::count(
                                                     const key_type& key) const
{
    return d_impl.find(key) != 0;
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
bool
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::empty() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return 0 == d_impl.size();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
bsl::pair<typename unordered_map<KEY,
                                 VALUE,
                                 HASH,
                                 EQUAL,
                                 ALLOCATOR>::const_iterator,
          typename unordered_map<KEY,
                                 VALUE,
                                 HASH,
                                 EQUAL,
                                 ALLOCATOR>::const_iterator>
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::equal_range(
                                                     const key_type& key) const
{
    typedef bsl::pair<const_iterator, const_iterator> ResultType;
 
    HashTableLink *first = d_impl.find(key);
    return first
         ? ResultType(const_iterator(first), const_iterator(first->nextLink()))
         : ResultType(const_iterator(0),     const_iterator(0));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename
       unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::const_iterator
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::find(
                                                     const key_type& key) const
{
    return const_iterator(d_impl.find(key));
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
ALLOCATOR
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::get_allocator() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return d_impl.allocator();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
HASH unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::hash_function() const
{
    return d_impl.hasher();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
EQUAL unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::key_eq() const
{
    return d_impl.comparator();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
float
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::load_factor() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return d_impl.loadFactor();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
float
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::max_load_factor() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return d_impl.maxLoadFactor();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::size_type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::size() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return d_impl.size();
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
typename unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::size_type
unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::max_size() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return d_impl.maxSize();
}
 
}  // close namespace bsl
 
// FREE OPERATORS
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
bool bsl::operator==(
             const bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& lhs,
             const bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& rhs)
{
    return lhs.d_impl == rhs.d_impl;
}
 
#ifndef BSLS_COMPILERFEATURES_SUPPORT_THREE_WAY_COMPARISON
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
bool bsl::operator!=(
             const bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& lhs,
             const bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& rhs)
{
    return !(lhs == rhs);
}
#endif
 
// FREE FUNCTIONS
template <class KEY,
          class VALUE,
          class HASH,
          class EQUAL,
          class ALLOCATOR,
          class PREDICATE>
inline
typename bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>::size_type
bsl::erase_if(unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>&     m,
                                                           PREDICATE predicate)
{
    return BloombergLP::bslstl::AlgorithmUtil::containerEraseIf(m, predicate);
}
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
inline
void
bsl::swap(bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& a,
          bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>& b)
                                     BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(false)
{
    a.swap(b);
}
 
// ============================================================================
//                                TYPE TRAITS
// ============================================================================
 
// Type traits for STL *unordered* *associative* containers:
//: o An unordered associative container defines STL iterators.
//: o An unordered associative container is bit-wise movable if both functors
//:   and the allocator are bit-wise movable.
//: o An unordered associative container uses 'bslma' allocators if the
//:   (template parameter) type 'ALLOCATOR' is convertible from
//:   'bslma::Allocator *'.
 
 
namespace bslalg {
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
struct HasStlIterators<bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR> >
     : bsl::true_type
{};
 
}  // close namespace bslalg
 
namespace bslma {
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
struct UsesBslmaAllocator<bsl::unordered_map<KEY,
                                             VALUE,
                                             HASH,
                                             EQUAL,
                                             ALLOCATOR> >
     : bsl::is_convertible<Allocator*, ALLOCATOR>::type
{};
 
}  // close namespace bslma
 
namespace bslmf {
 
template <class KEY, class VALUE, class HASH, class EQUAL, class ALLOCATOR>
struct IsBitwiseMoveable<
    bsl::unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR> >
    : ::BloombergLP::bslmf::IsBitwiseMoveable<BloombergLP::bslstl::HashTable<
          ::BloombergLP::bslstl::
               UnorderedMapKeyConfiguration<KEY, bsl::pair<const KEY, VALUE> >,
          HASH,
          EQUAL,
          ALLOCATOR> >::type
{};
 
}  // close namespace bslma
 
 
#endif // End C++11 code
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2013 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------
 
/** @} */
/** @} */
/** @} */