bslstl_ownerequal.h

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/// @file bslstl_ownerequal.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslstl_ownerequal.h                                                -*-C++-*-
#ifndef INCLUDED_BSLSTL_OWNEREQUAL
#define INCLUDED_BSLSTL_OWNEREQUAL
 
#include <bsls_ident.h>
BSLS_IDENT("$Id$ $CSID$")
 
/// @defgroup bslstl_ownerequal bslstl_ownerequal
/// @brief  Provide an ownership comparison for shared and weak pointers.
/// @addtogroup bsl
/// @{
/// @addtogroup bslstl
/// @{
/// @addtogroup bslstl_ownerequal
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslstl_ownerequal-purpose"> Purpose</a>
/// * <a href="#bslstl_ownerequal-classes"> Classes </a>
/// * <a href="#bslstl_ownerequal-description"> Description </a>
///   * <a href="#bslstl_ownerequal-usage"> Usage </a>
///     * <a href="#bslstl_ownerequal-example-1-basic-use-of-ref-owner_equal"> Example 1: Basic Use of @ref owner_equal  </a>
///
/// # Purpose {#bslstl_ownerequal-purpose}
/// Provide an ownership comparison for shared and weak pointers.
///
/// # Classes {#bslstl_ownerequal-classes}
///
/// -  bsl::owner_equal: owner equality comparator for `shared_ptr` and `weak_ptr`
///
/// **Canonical header:**  bsl_memory.h
///
/// @see  bslstl_sharedptr
///
/// # Description {#bslstl_ownerequal-description}
/// This component provides the C++26 standard binary comparison
/// functor, `bsl::owner_equal`, that determines the equality of two smart
/// pointer objects by the address of their `bslma::SharedPtrRep` data.  Note
/// that this class is an empty POD type.
///
/// ## Usage {#bslstl_ownerequal-usage}
///
///
/// This section illustrates intended use of this component.
///
/// ### Example 1: Basic Use of @ref owner_equal  {#bslstl_ownerequal-example-1-basic-use-of-ref-owner_equal}
///
///
/// 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 create a container and populate it:
/// @code
///     typedef bsl::unordered_map<
///         bsl::shared_ptr<int>,
///         int,
///         bsl::owner_hash,
///         bsl::owner_equal> 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
/// Then we make sure that shared pointers can be used to perform lookup, and
/// verify that the results are correct.
/// @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 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_ownerequal
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslstl_sharedptr.h>
 
#include <bsls_keyword.h> // 'BSLS_KEYWORD_NOEXCEPT'
 
namespace bsl {
 
                        // C++26 Compatibility
 
struct owner_equal {
 
    // TYPES
 
    /// Type alias indicating this is a transparent comparator.
    typedef void is_transparent;
 
    // CREATORS
     owner_equal() = default;
        // Create an @ref owner_equal  object.
 
     owner_equal(const owner_equal& original) = default;
        // Create an @ref owner_equal  object.  Note that as @ref owner_equal  is an
        // empty (stateless) type, this operation has no observable effect.
 
     ~owner_equal() = default;
        // Destroy this object.
 
    // MANIPULATORS
     owner_equal& operator=(const owner_equal& 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_equal  is an empty (stateless) type, this operation
        // has no observable effect.
 
    // ACCESSORS
    template<class ELEMENT_TYPE_X, class ELEMENT_TYPE_Y>
    bool operator()(const shared_ptr<ELEMENT_TYPE_X>& x,
                    const shared_ptr<ELEMENT_TYPE_Y>& y) const
                                                         BSLS_KEYWORD_NOEXCEPT;
    template<class ELEMENT_TYPE_X, class ELEMENT_TYPE_Y>
    bool operator()(const shared_ptr<ELEMENT_TYPE_X>& x,
                    const weak_ptr<  ELEMENT_TYPE_Y>& y) const
                                                         BSLS_KEYWORD_NOEXCEPT;
    template<class ELEMENT_TYPE_X, class ELEMENT_TYPE_Y>
    bool operator()(const weak_ptr<  ELEMENT_TYPE_X>& x,
                    const shared_ptr<ELEMENT_TYPE_Y>& y) const
                                                         BSLS_KEYWORD_NOEXCEPT;
 
    /// Return `true` if the address of the
    /// `BloombergLP::bslma::SharedPtrRep` object used by the specified `x`
    /// is equal to the address of the `BloombergLP::bslma::SharedPtrRep`
    /// object used by the specified `y`, and `false` otherwise.
    template<class ELEMENT_TYPE_X, class ELEMENT_TYPE_Y>
    bool operator()(const weak_ptr<ELEMENT_TYPE_X>& x,
                    const weak_ptr<ELEMENT_TYPE_Y>& y) const
                                                         BSLS_KEYWORD_NOEXCEPT;
};
 
// ============================================================================
//                           INLINE DEFINITIONS
// ============================================================================
 
                             // ------------------
                             // struct owner_equal
                             // ------------------
 
template<class ELEMENT_TYPE_X, class ELEMENT_TYPE_Y>
inline
bool owner_equal::operator()(
               const shared_ptr<ELEMENT_TYPE_X>& x,
               const shared_ptr<ELEMENT_TYPE_Y>& y) const BSLS_KEYWORD_NOEXCEPT
{
    return x.owner_equal(y);
}
 
template<class ELEMENT_TYPE_X, class ELEMENT_TYPE_Y>
inline
bool owner_equal::operator()(
               const shared_ptr<ELEMENT_TYPE_X>& x,
               const weak_ptr<  ELEMENT_TYPE_Y>& y) const BSLS_KEYWORD_NOEXCEPT
{
    return x.owner_equal(y);
}
 
template<class ELEMENT_TYPE_X, class ELEMENT_TYPE_Y>
inline
bool owner_equal::operator()(
               const weak_ptr<  ELEMENT_TYPE_X>& x,
               const shared_ptr<ELEMENT_TYPE_Y>& y) const BSLS_KEYWORD_NOEXCEPT
{
    return x.owner_equal(y);
}
 
template<class ELEMENT_TYPE_X, class ELEMENT_TYPE_Y>
inline
bool owner_equal::operator()(
                 const weak_ptr<ELEMENT_TYPE_X>& x,
                 const weak_ptr<ELEMENT_TYPE_Y>& y) const BSLS_KEYWORD_NOEXCEPT
{
    return x.owner_equal(y);
}
 
// ============================================================================
//                                TYPE TRAITS
// ============================================================================
 
// Type traits for @ref owner_equal 
//: o @ref owner_equal  is a stateless POD, trivially constructible and copyable.
 
template <>
struct is_trivially_default_constructible<owner_equal> : bsl::true_type {};
 
template <>
struct is_trivially_copyable<owner_equal> : 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */