bslstl_ownerhash.h

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/// @file bslstl_ownerhash.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslstl_ownerhash.h                                                 -*-C++-*-
#ifndef INCLUDED_BSLSTL_OWNERHASH
#define INCLUDED_BSLSTL_OWNERHASH
 
#include <bsls_ident.h>
BSLS_IDENT("$Id$ $CSID$")
 
/// @defgroup bslstl_ownerhash bslstl_ownerhash
/// @brief  Provide an ownership hash functor for shared and weak pointers.
/// @addtogroup bsl
/// @{
/// @addtogroup bslstl
/// @{
/// @addtogroup bslstl_ownerhash
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslstl_ownerhash-purpose"> Purpose</a>
/// * <a href="#bslstl_ownerhash-classes"> Classes </a>
/// * <a href="#bslstl_ownerhash-canonical-header"> Canonical Header </a>
/// * <a href="#bslstl_ownerhash-description"> Description </a>
///   * <a href="#bslstl_ownerhash-usage"> Usage </a>
///     * <a href="#bslstl_ownerhash-example-1-basic-use-of-ref-owner_hash"> Example 1: Basic Use of @ref owner_hash  </a>
///
/// # Purpose {#bslstl_ownerhash-purpose}
/// Provide an ownership hash functor for shared and weak pointers.
///
/// # Classes {#bslstl_ownerhash-classes}
///
/// -  bsl::owner_hash: owner hash functor for `shared_ptr` and `weak_ptr`
///
/// # Canonical Header {#bslstl_ownerhash-canonical-header}
/// bsl_memory.h
///
/// @see  bslstl_sharedptr
///
/// # Description {#bslstl_ownerhash-description}
/// This component provides the C++26 standard functor,
/// `bsl::owner_hash`, that calculates the hash of a smart pointer object by the
/// address of their `bslma::SharedPtrRep` data.  Note that this class is an
/// empty POD type.
///
/// ## Usage {#bslstl_ownerhash-usage}
///
///
/// This section illustrates intended use of this component.
///
/// ### Example 1: Basic Use of @ref owner_hash  {#bslstl_ownerhash-example-1-basic-use-of-ref-owner_hash}
///
///
/// Suppose we need an unordered map accepting shared pointers as keys.  We also
/// expect that this container will be accessible from multiple threads and some
/// of them will store weak versions of smart pointers to break reference
/// cycles.
///
/// First, we define an owner-based equality predicate, that is required by the
/// `bsl::unordered_map` along with this owner-based hash.
/// @code
/// struct TestOwnerEqual {
///     // TYPES
///     typedef void is_transparent;
///
///     template <class T1, class T2>
///     bool operator()(const bsl::shared_ptr<T1>& lhs,
///                     const bsl::shared_ptr<T2>& rhs) const
///         // For the specified 'lhs' and 'rhs', return the result of
///         // 'lhs.owner_equal(rhs)'
///     {
///         return lhs.owner_equal(rhs);
///     }
///
///     template <class T1, class T2>
///     bool operator()(const bsl::shared_ptr<T1>& lhs,
///                     const bsl::weak_ptr<T2>&   rhs) const
///         // For the specified 'lhs' and 'rhs', return the result of
///         // 'lhs.owner_equal(rhs)'
///     {
///         return lhs.owner_equal(rhs);
///     }
///
///     template <class T1, class T2>
///     bool operator()(const bsl::weak_ptr<T1>&   lhs,
///                     const bsl::shared_ptr<T2>& rhs) const
///         // For the specified 'lhs' and 'rhs', return the result of
///         // 'lhs.owner_equal(rhs)'
///     {
///         return lhs.owner_equal(rhs);
///     }
///
///     template <class T1, class T2>
///     bool operator()(const bsl::weak_ptr<T1>& lhs,
///                     const bsl::weak_ptr<T2>& rhs) const
///         // For the specified 'lhs' and 'rhs', return the result of
///         // 'lhs.owner_equal(rhs)'
///     {
///         return lhs.owner_equal(rhs);
///     }
/// };
/// @endcode
/// Note that this struct is defined only to avoid cycle dependencies between
/// BDE components.  In real code for these purposes it is recommended to use
/// `bsl::owner_equal`.
///
/// Then, we create a container and populate it:
/// @code
///     typedef bsl::unordered_map<
///         bsl::shared_ptr<int>,
///         int,
///         bsl::owner_hash,
///         TestOwnerEqual> Map;
///
///     Map                  container;
///
///     bsl::shared_ptr<int> sharedPtr1 = bsl::make_shared<int>(1);
///     bsl::shared_ptr<int> sharedPtr2 = bsl::make_shared<int>(2);
///     bsl::weak_ptr<int>   weakPtr1(sharedPtr1);
///
///     container[sharedPtr1] = 1;
///     container[sharedPtr2] = 2;
/// @endcode
/// Now, we make sure, that shared pointers can be used to perform lookup:
/// @code
///     Map::const_iterator iter = container.find(sharedPtr1);
///     assert(container.end() != iter        );
///     assert(1               == iter->second);
///
///     iter = container.find(sharedPtr2);
///     assert(container.end() != iter);
///     assert(2               == iter->second);
/// @endcode
/// Finally, we simulate the situation of accessing the container from another
/// thread and perform lookup using weak pointers:
/// @code
///     iter = container.find(weakPtr1);
///     assert(container.end() != iter        );
///     assert(1               == iter->second);
///
///     bsl::weak_ptr<int> weakPtr3(bsl::make_shared<int>(3));
///     iter = container.find(weakPtr3);
///     assert(container.end() == iter);
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslstl
 * @{
 */
/** @addtogroup bslstl_ownerhash
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslstl_sharedptr.h>
 
#include <bsls_keyword.h> // 'BSLS_KEYWORD_NOEXCEPT'
 
#include <stddef.h>             // 'size_t'
 
namespace bsl {
 
                        // C++26 Compatibility
 
struct owner_hash {
 
    // TYPES
 
    /// Type alias indicating this is a transparent hash functor.
    typedef void is_transparent;
 
    // CREATORS
     owner_hash() = default;
        // Create an @ref owner_hash  object.
 
     owner_hash(const owner_hash& original) = default;
        // Create an @ref owner_hash  object.  Note that as @ref owner_hash  is an
        // empty (stateless) type, this operation has no observable effect.
 
     ~owner_hash() = default;
        // Destroy this object.
 
    // MANIPULATORS
     owner_hash& operator=(const owner_hash& rhs) = default;
        // Assign to this object the value of the specified 'rhs' object, and
        // return a reference providing modifiable access to this object.  Note
        // that as @ref owner_hash  is an empty (stateless) type, this operation
        // has no observable effect.
 
    // ACCESSORS
    template <class ELEMENT_TYPE>
    size_t operator()(const shared_ptr<ELEMENT_TYPE>& x) const
                                                         BSLS_KEYWORD_NOEXCEPT;
 
    /// Return the result of calling `owner_hash()` on the specified `x`.  
    /// 
    /// \note Note that   for any object `y` where `x.owner_equal(y)` is true,
    /// `x.owner_hash() == y.owner_hash()` is true.
    template <class ELEMENT_TYPE>
    size_t operator()(const weak_ptr<  ELEMENT_TYPE>& x) const
                                                         BSLS_KEYWORD_NOEXCEPT;
};
 
// ============================================================================
//                           INLINE DEFINITIONS
// ============================================================================
 
                             // -----------------
                             // struct owner_hash
                             // -----------------
 
template <class ELEMENT_TYPE>
inline
size_t owner_hash::operator()(
                 const shared_ptr<ELEMENT_TYPE>& x) const BSLS_KEYWORD_NOEXCEPT
{
    return x.owner_hash();
}
 
template <class ELEMENT_TYPE>
inline
size_t owner_hash::operator()(
                   const weak_ptr<ELEMENT_TYPE>& x) const BSLS_KEYWORD_NOEXCEPT
{
    return x.owner_hash();
}
 
// ============================================================================
//                                TYPE TRAITS
// ============================================================================
 
// Type traits for @ref owner_hash 
//: o @ref owner_hash  is a stateless POD, trivially constructible and copyable.
 
template<>
struct is_trivially_default_constructible<owner_hash>
: bsl::true_type
{};
 
template<>
struct is_trivially_copyable<owner_hash>
: bsl::true_type
{};
 
}  // close namespace bsl
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2024 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */