bdld_manageddatum.h

Go to the documentation of this file.

/// @file bdld_manageddatum.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bdld_manageddatum.h                                                -*-C++-*-
#ifndef INCLUDED_BDLD_MANAGEDDATUM
#define INCLUDED_BDLD_MANAGEDDATUM
 
#include <bsls_ident.h>
BSLS_IDENT("$Id$ $CSID$")
 
/// @defgroup bdld_manageddatum bdld_manageddatum
/// @brief  Provide a smart-pointer-like manager for a `Datum` object.
/// @addtogroup bdl
/// @{
/// @addtogroup bdld
/// @{
/// @addtogroup bdld_manageddatum
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bdld_manageddatum-purpose"> Purpose</a>
/// * <a href="#bdld_manageddatum-classes"> Classes </a>
/// * <a href="#bdld_manageddatum-description"> Description </a>
///   * <a href="#bdld_manageddatum-value-semantics"> Value Semantics </a>
///   * <a href="#bdld_manageddatum-resource-management"> Resource Management </a>
///   * <a href="#bdld_manageddatum-usage"> Usage </a>
///     * <a href="#bdld_manageddatum-example-1-basic-use-of-bdld-manageddatum"> Example 1: Basic Use of bdld::ManagedDatum </a>
///
/// # Purpose {#bdld_manageddatum-purpose}
/// Provide a smart-pointer-like manager for a `Datum` object.
///
/// # Classes {#bdld_manageddatum-classes}
///
/// -  bdld::ManagedDatum: a smart-pointer-like manager for a `Datum` object
///
/// @see  bdld_datum
///
/// # Description {#bdld_manageddatum-description}
/// This component implements a type, `bdld::ManagedDatum`, that
/// provides two important services for `Datum` objects:
///
/// 1. `ManagedDatum` provides value-semantic-like operations for `Datum`.
/// 2. `ManagedDatum` is a resource manager, similar to a smart pointer, for
///    `Datum`.
///
/// These services allow clients to use a `ManagedDatum` object in most contexts
/// where an object of a value-semantic type can be used (passed by value,
/// stored in containers, and so on), even though `ManagedDatum` is not strictly
/// value-semantic.  These services are explored in subsequent sections.
///
/// The `Datum` type maintained by a `ManagedDatum` provides a space-efficient
/// discriminated union (i.e., a variant) holding the value of a scalar type
/// (e.g., `int`, `double`, `string`) or an aggregate of other `Datum` objects.
/// See @ref bdld_datum  for more details.
///
/// ## Value Semantics {#bdld_manageddatum-value-semantics}
///
///
/// `ManagedDatum`, while not strictly a value-semantic type, provides the full
/// set of value-semantic-like operations for `Datum` (see
/// @ref bsldoc_glossary-value-semantic-operations :
///
/// * Equality and Non-Equality Comparisons
/// * Copy Construction
/// * Copy Assignment
/// * Default Construction
/// * `ostream` Printing
///
/// In other words, the syntax of `ManagedDatum` is *regular*, but not all of
/// its copy behavior is value-semantic.  Specifically, for User Defined Types
/// (i.e., those that `bdld::Datum::clone` does not deep-copy) `ManagedDatum`
/// performs a shallow copy (copying the reference rather than the value), which
/// is inconsistent with value-semantics.  For *all* other types `ManagedDatum`
/// copy operations (copy construction, copy assignment, and non-member `swap`
/// when the allocators differ) will deep-copy the value using `Datum::clone`,
/// which creates a completely independent copy, with independent lifetime, by
/// duplicating all data, even referenced data (except for UDTs).
///
/// Note that a default constructed `ManagedDatum`, or a `ManagedDatum` on which
/// `release` has been called, will have the null `Datum` value.
///
/// ## Resource Management {#bdld_manageddatum-resource-management}
///
///
/// A `Datum` object's relationship to memory can be seen as analogous to a raw
/// pointer, requiring calls to static functions `Datum::create*` and
/// `Datum::destroy` to initialize and release resources (see the @ref bdld_datum 
/// component documentation).  A `ManagedDatum`, by extension, provides a
/// resource manager for a `Datum` that is analogous to a smart pointer.
///
/// The `adopt` method of a `ManagedDatum` is used to take ownership of a
/// supplied `Datum` object, after which point the `ManagedDatum` object's
/// destructor will free the resources of the managed `Datum` (unless `release`
/// is subsequently called).  Similar to a smart pointer, a `ManagedDatum`
/// provides dereference operators to access the `Datum` object under
/// management.
///
/// ## Usage {#bdld_manageddatum-usage}
///
///
/// This section illustrates intended use of this component.
///
/// ### Example 1: Basic Use of bdld::ManagedDatum {#bdld_manageddatum-example-1-basic-use-of-bdld-manageddatum}
///
///
/// This example demonstrates the basic construction and manipulation of a
/// `ManagedDatum` object.
///
/// First, we create a `ManagedDatum` object that manages a `Datum` holding a
/// `double` and verify that the managed object has the expected type and value:
/// @code
/// bslma::TestAllocator ta("test", veryVeryVerbose);
///
/// const ManagedDatum realObj(Datum::createDouble(-3.4375), &ta);
///
/// assert(realObj->isDouble());
/// assert(-3.4375 == realObj->theDouble());
/// @endcode
/// Next, we create a `ManagedDatum` object that holds a string and again verify
/// that it has the expected type and value:
/// @code
/// const char         *str = "This is a string";
/// const ManagedDatum  strObj(Datum::copyString(str, &ta), &ta);
///
/// assert(strObj->isString());
/// assert(str == strObj->theString());
/// @endcode
/// Then, we assign this `ManagedDatum` object to another object and verify both
/// objects have the same value:
/// @code
/// ManagedDatum strObj1(&ta);
/// strObj1 = strObj;
/// assert(strObj == strObj1);
/// @endcode
/// Next, copy-construct this `ManagedDatum` object and verify that the copy has
/// the same value as the original:
/// @code
/// const ManagedDatum strObj2(strObj, &ta);
/// assert(strObj == strObj2);
/// @endcode
/// Then, we create a `ManagedDatum` object that holds an opaque pointer to a
/// `bdlt::Date` object and verify that the managed `Date` has the expected
/// value:
/// @code
/// bdlt::Date   udt;
/// ManagedDatum udtObj(Datum::createUdt(&udt, UDT_TYPE), &ta);
///
/// assert(udtObj->isUdt());
/// assert(&udt == udtObj->theUdt().data());
/// assert(UDT_TYPE == udtObj->theUdt().type());
/// @endcode
/// Next, we assign a boolean value to this `ManagedDatum` object and verify
/// that it has the new type and value:
/// @code
/// udtObj.adopt(Datum::createBoolean(true));
/// assert(udtObj->isBoolean());
/// assert(true == udtObj->theBoolean());
/// @endcode
/// Then, we create a `ManagedDatum` object having an array and verify that it
/// has the same array value.  Note that in practice we would use
/// @ref bdld_datumarraybuilder , but do not do so here for dependency reasons:
/// @code
/// const Datum datumArray[2] = {
///     Datum::createInteger(12),
///     Datum::copyString("A long string", &ta)
/// };
///
/// DatumMutableArrayRef arr;
/// Datum::createUninitializedArray(&arr, 2, &ta);
/// for (int i = 0; i < 2; ++i) {
///     arr.data()[i] = datumArray[i];
/// }
/// *(arr.length()) = 2;
/// const ManagedDatum arrayObj(Datum::adoptArray(arr), &ta);
///
/// assert(arrayObj->isArray());
/// assert(DatumArrayRef(datumArray, 2) == arrayObj->theArray());
/// @endcode
/// Next, we create a `ManagedDatum` object having a map and verify that it has
/// the same map value.  Note that in practice we would use
/// @ref bdld_datummapbuilder , but do not do so here to for dependency reasons.
/// @code
/// const DatumMapEntry datumMap[2] = {
///     DatumMapEntry(StringRef("first", static_cast<int>(strlen("first"))),
///                   Datum::createInteger(12)),
///     DatumMapEntry(StringRef("second", static_cast<int>(strlen("second"))),
///                   Datum::copyString("A very long string", &ta))
/// };
///
/// DatumMutableMapRef mp;
/// Datum::createUninitializedMap(&mp, 2, &ta);
/// for (int i = 0; i < 2; ++i) {
///     mp.data()[i] = datumMap[i];
/// }
/// *(mp.size()) = 2;
/// const ManagedDatum mapObj(Datum::adoptMap(mp), &ta);
///
/// assert(mapObj->isMap());
/// assert(DatumMapRef(datumMap, 2, false, false) == mapObj->theMap());
/// @endcode
/// Then, we create a `Datum` object and assign its ownership to a
/// `ManagedDatum` object and verify that the ownership was transferred:
/// @code
/// const Datum  rcObj = Datum::copyString("This is a string", &ta);
/// ManagedDatum obj(Datum::createInteger(1), &ta);
/// obj.adopt(rcObj);
/// assert(obj.datum() == rcObj);
/// @endcode
/// Next, we release the `Datum` object managed by `obj` and verify that it was
/// released:
/// @code
/// const Datum internalObj = obj.release();
/// assert(obj->isNull());
/// assert(internalObj == rcObj);
/// @endcode
/// Finally, we destroy the released `Datum` object:
/// @code
/// Datum::destroy(internalObj, obj.get_allocator());
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bdl
 * @{
 */
/** @addtogroup bdld
 * @{
 */
/** @addtogroup bdld_manageddatum
 * @{
 */
 
#include <bdlscm_version.h>
 
#include <bdld_datum.h>
 
#include <bslma_allocator.h>
#include <bslma_allocatorutil.h>
#include <bslma_bslallocator.h>
#include <bslma_usesbslmaallocator.h>
 
#include <bslmf_isbitwisemoveable.h>
#include <bslmf_nestedtraitdeclaration.h>
 
#include <bsls_assert.h>
#include <bsls_review.h>
 
#include <bsl_algorithm.h>
#include <bsl_iosfwd.h>
 
 
namespace bdld {
 
                            // ==================
                            // class ManagedDatum
                            // ==================
 
/// This class implements a smart-pointer-like resource manager for a
/// `Datum` object.
///
/// See @ref bdld_manageddatum 
class ManagedDatum {
 
  public:
    // TYPES
    typedef bsl::allocator<> allocator_type;
 
  private:
    // DATA
    Datum          d_data;       // storage for data
    allocator_type d_allocator;  // allocator of dynamic memory
 
  public:
    // TRAITS
 
    /// 'ManagedDatum' objects are allocator-aware and bitwise movable.
    BSLMF_NESTED_TRAIT_DECLARATION(ManagedDatum, bslmf::IsBitwiseMoveable);
 
    // CREATORS
 
    ManagedDatum();
    /// Create a `ManagedDatum` object having the default (null) value, and
    /// the specified `allocator` (e.g., the address of a `bslma::Allocator`
    /// object) to supply memory.  Calling `isNull` on the resulting managed
    /// `Datum` object returns `true`.
    explicit ManagedDatum(const allocator_type& allocator);
 
    /// Create a `ManagedDatum` object that assumes ownership of the
    /// specified `datum`.  Optionally specify an `allocator` (e.g., the
    /// address of a `bslma::Allocator` object) to supply memory; otherwise,
    /// the default allocator is used.  The behavior is undefined unless
    /// `datum` was allocated using the indicated allocator and is not
    /// subsequently destroyed externally using `Datum::destroy`.
    explicit ManagedDatum(const Datum&          datum,
                          const allocator_type& allocator = allocator_type());
 
    /// Create a `ManagedDatum` object having the same value as the
    /// specified `original` object.  Optionally specify an `allocator`
    /// (e.g., the address of a `bslma::Allocator` object) used to supply
    /// memory; otherwise, the default allocator is used.  This operation
    /// performs a `clone` of the underlying `Datum`, see {Value Semantics}
    /// for more detail.
    ManagedDatum(const ManagedDatum&   original,
                 const allocator_type& allocator = allocator_type());
 
    /// Destroy this object and release all dynamically allocated memory
    /// managed by this object.
    ~ManagedDatum();
 
    // MANIPULATORS
 
    /// Assign to this object the value of the specified `rhs` object, and
    /// return a non-`const` reference to this object.  This operation
    /// performs a `clone` of the underlying `Datum`, see {Value Semantics}
    /// for more detail.
    ManagedDatum& operator=(const ManagedDatum& rhs);
 
    /// Take ownership of the specified `obj` and destroy the `Datum`
    /// object previously managed by this object.  The behavior is undefined
    /// unless `obj` was allocated using the same allocator used by this
    /// object and is not subsequently destroyed externally using
    /// `Datum::destroy`.
    void adopt(const Datum& obj);
 
    /// Assign to this object the specified `value` by making a "deep copy"
    /// of `value`, so that any dynamically allocated memory managed by
    /// `value` is cloned and not shared with `value`.
    void clone(const Datum& value);
 
    /// Make the `Datum` object managed by this object null and release all
    /// dynamically allocated memory managed by this object.
    void makeNull();
 
    /// Return, *by* *value*, the `Datum` object managed by this object and
    /// set the managed object to null.  Ownership of the previously managed
    /// `Datum` object is transferred to the caller.
    Datum release();
 
    /// Efficiently exchange the value of this object with the value of the
    /// specified `other` object.  This method provides the no-throw
    /// exception-safety guarantee.  The behavior is undefined unless this
    /// object was created with the same allocator as `other`.
    void swap(ManagedDatum& other);
 
    // ACCESSORS
 
    /// Return an address providing non-modifiable access to the `Datum`
    /// object managed by this object.
    const Datum *operator->() const;
 
    /// Return a `const` reference to the `Datum` object managed by this
    /// object.
    const Datum& operator*() const;
 
    /// Return a `const` reference to the `Datum` object managed by this
    /// object.
    const Datum& datum() const;
 
                                  // Aspects
 
    /// @deprecated  Use @ref get_allocator() instead.
    ///
    /// Return `get_allocator().mechanism()`.
    bslma::Allocator *allocator() const;
 
    /// Return the allocator used by this object to supply memory.  Note
    /// that if no allocator was supplied at construction the default
    /// allocator in effect at construction is used.
    allocator_type get_allocator() const;
 
    /// Format this object to the specified output `stream` at the (absolute
    /// value of) the optionally specified indentation `level` and return a
    /// reference to the modifiable `stream`.  If `level` is specified,
    /// optionally specify `spacesPerLevel`, the number of spaces per
    /// indentation level for this and all of its nested objects.  If
    /// `level` is negative, suppress indentation of the first line.  If
    /// `spacesPerLevel` is negative, format the entire output on one line,
    /// suppressing all but the initial indentation (as governed by
    /// `level`).  If `stream` is not valid on entry, this operation has no
    /// effect.
    bsl::ostream& print(bsl::ostream& stream,
                        int           level          = 0,
                        int           spacesPerLevel = 4) const;
};
 
// FREE OPERATORS
 
/// Return `true` if the specified `lhs` and `rhs` `ManagedDatum` objects
/// have the same value, and `false` otherwise.  Two `ManagedDatum` objects
/// have the same value if their corresponding managed `Datum` objects have
/// the same value.  See the function-level documentation of the `Datum`
/// equality-comparison operators for details.
bool operator==(const ManagedDatum& lhs, const ManagedDatum& rhs);
 
/// Return `true` if the specified `lhs` and `rhs` `ManagedDatum` objects do
/// not have the same value, and `false` otherwise.  Two `ManagedDatum`
/// objects do not have the same value if their corresponding managed
/// `Datum` objects do not have the same value.  See the function-level
/// documentation of the `Datum` equality-comparison operators for details.
bool operator!=(const ManagedDatum& lhs, const ManagedDatum& rhs);
 
/// Write the specified `rhs` value to the specified output `stream` and
/// return a reference to the modifiable `stream`.  This function has no
/// effect if `stream` is not valid on entry.  Note that this method invokes
/// `operator<<` defined for `Datum`.  See the function-level documentation
/// of the `operator<<` defined for `Datum` for details of the format of the
/// output.
bsl::ostream& operator<<(bsl::ostream& stream, const ManagedDatum& rhs);
 
// FREE FUNCTIONS
 
/// Exchange the values of the specified `a` and `b` objects.  This function
/// provides the no-throw exception-safety guarantee if the two objects were
/// created with the same allocator and the basic guarantee otherwise.  Note
/// that in case the allocators are different this function places a *clone*
/// of `a` into `b`, and vice versa.  See {Value Semantics} on details of
/// the cloning that may happen.
void swap(ManagedDatum& a, ManagedDatum& b);
 
// ============================================================================
//                             INLINE DEFINITIONS
// ============================================================================
 
                            // ------------------
                            // class ManagedDatum
                            // ------------------
 
// CREATORS
inline
ManagedDatum::ManagedDatum()
: d_data(Datum::createNull())
, d_allocator()
{
}
 
inline
ManagedDatum::ManagedDatum(const allocator_type& allocator)
: d_data(Datum::createNull())
, d_allocator(allocator)
{
}
 
inline
ManagedDatum::ManagedDatum(const Datum& datum, const allocator_type& allocator)
: d_data(datum)
, d_allocator(allocator)
{
}
 
inline
ManagedDatum::ManagedDatum(const ManagedDatum&   original,
                           const allocator_type& allocator)
: d_allocator(allocator)
{
    d_data = original.d_data.clone(d_allocator);
}
 
inline
ManagedDatum::~ManagedDatum()
{
    Datum::destroy(d_data, d_allocator);
}
 
// MANIPULATORS
inline
ManagedDatum& ManagedDatum::operator=(const ManagedDatum& rhs)
{
    ManagedDatum copy(rhs, d_allocator);
    swap(copy);
    return *this;
}
 
inline
void ManagedDatum::adopt(const Datum& obj)
{
    if (&obj != &d_data) {
        ManagedDatum(obj, d_allocator).swap(*this);
    }
}
 
inline
void ManagedDatum::clone(const Datum& value)
{
    Datum data = value.clone(d_allocator);
    ManagedDatum(data, d_allocator).swap(*this);
}
 
inline
void ManagedDatum::makeNull()
{
    ManagedDatum(d_allocator).swap(*this);
}
 
inline
Datum ManagedDatum::release()
{
    Datum temp = d_data;
    d_data = Datum::createNull();
    return temp;
}
 
inline
void ManagedDatum::swap(ManagedDatum& other)
{
    BSLS_ASSERT(d_allocator == other.get_allocator());
 
    using bsl::swap;
    swap(d_data, other.d_data);
}
 
// ACCESSORS
inline
const Datum *ManagedDatum::operator->() const
{
    return &d_data;
}
 
inline
const Datum& ManagedDatum::operator*() const
{
    return d_data;
}
 
inline
const Datum& ManagedDatum::datum() const
{
    return d_data;
}
 
                                  // Aspects
 
inline
bslma::Allocator *ManagedDatum::allocator() const
{
    return get_allocator().mechanism();
}
 
inline
ManagedDatum::allocator_type ManagedDatum::get_allocator() const
{
    return d_allocator;
}
 
inline
bsl::ostream& ManagedDatum::print(bsl::ostream& stream,
                                  int           level,
                                  int           spacesPerLevel) const
{
    return d_data.print(stream, level, spacesPerLevel);
}
 
}  // close package namespace
 
// FREE OPERATORS
inline
bool bdld::operator==(const ManagedDatum& lhs, const ManagedDatum& rhs)
{
    return (lhs.datum() == rhs.datum());
}
 
inline
bool bdld::operator!=(const ManagedDatum& lhs, const ManagedDatum& rhs)
{
    return (lhs.datum() != rhs.datum());
}
 
inline
bsl::ostream& bdld::operator<<(bsl::ostream& stream, const ManagedDatum& rhs)
{
    return (stream << rhs.datum());
}
 
// FREE FUNCTIONS
inline
void bdld::swap(ManagedDatum& a, ManagedDatum& b)
{
    if (a.get_allocator() == b.get_allocator()) {
        a.swap(b);
    }
    else {
        ManagedDatum tempA(a, b.get_allocator());
        ManagedDatum tempB(b, a.get_allocator());
 
        a.swap(tempB);
        b.swap(tempA);
    }
}
 
 
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2020 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */