bslmf_isnothrowswappable.h

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/// @file bslmf_isnothrowswappable.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmf_isnothrowswappable.h                                         -*-C++-*-
#ifndef INCLUDED_BSLMF_ISNOTHROWSWAPPABLE
#define INCLUDED_BSLMF_ISNOTHROWSWAPPABLE
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmf_isnothrowswappable bslmf_isnothrowswappable
/// @brief  Provide metafunction to identify nothrow swappable types.
/// @addtogroup bsl
/// @{
/// @addtogroup bslmf
/// @{
/// @addtogroup bslmf_isnothrowswappable
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmf_isnothrowswappable-purpose"> Purpose</a>
/// * <a href="#bslmf_isnothrowswappable-classes"> Classes </a>
/// * <a href="#bslmf_isnothrowswappable-description"> Description </a>
///   * <a href="#bslmf_isnothrowswappable-usage"> Usage </a>
///     * <a href="#bslmf_isnothrowswappable-example-1-verify-class-types"> Example 1: Verify Class Types </a>
///
/// # Purpose {#bslmf_isnothrowswappable-purpose}
/// Provide metafunction to identify nothrow swappable types.
///
/// # Classes {#bslmf_isnothrowswappable-classes}
///
/// -  bsl::is_nothrow_swappable:   type-traits metafunction
/// -  bsl::is_nothrow_swappable_v: the metafunction's result value
///
/// @see  bslmf_integralconstant
///
/// # Description {#bslmf_isnothrowswappable-description}
/// This component defines a metafunction,
/// `bsl::is_nothrow_swappable`, and a variable template
/// `bsl::is_nothrow_swappable_v` that represents the result value of the
/// `bsl::is_nothrow_swappable` metafunction, which may be used to query whether
/// `swap(x,y);` is well-formed.  Note that this is only implemented for C++11
/// and above.
///
/// `bsl::is_nothrow_swappable` meets the requirements of the
/// `is_nothrow_swappable` template defined in the C++17 standard.
///
/// Note that the template variable `is_nothrow_swappable_v` is defined in the
/// C++17 standard as an inline variable.  If the current compiler supports the
/// inline variable C++17 compiler feature, `bsl::is_nothrow_swappable_v` is
/// defined as an `inline constexpr bool` variable.  Otherwise, if the compiler
/// supports the variable templates C++14 compiler feature,
/// `bsl::is_nothrow_swappable_v` is defined as a non-inline `constexpr bool`
/// variable.  See `BSLS_COMPILERFEATURES_SUPPORT_INLINE_VARIABLES` and
/// `BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES` macros in the
/// bsls_compilerfeatures component for details.
///
/// ## Usage {#bslmf_isnothrowswappable-usage}
///
///
/// In this section we show intended use of this component.
///
/// ### Example 1: Verify Class Types {#bslmf_isnothrowswappable-example-1-verify-class-types}
///
///
/// Suppose that we want to assert whether a particular type is nothrow
/// swappable.
///
/// First, we create two `struct`s -- one nothrow swappable and one not.
/// @code
/// struct MyType1 {
///     // trivial so swappable
/// };
///
/// struct MyType2 {
///     // private assignement, so not swappable
///   private:
///     // NOT IMPLEMENTED
///     MyType2& operator=(const MyType2&);
///         // Assignment operator made private to prevent swappability.
/// };
/// @endcode
/// Now, we instantiate the `bsl::is_nothrow_swappable` template for each of the
/// `struct`s and assert the `value` static data member of each instantiation:
/// @code
/// assert(true  == bsl::is_nothrow_swappable<MyType1>::value);
/// assert(false == bsl::is_nothrow_swappable<MyType2>::value);
/// @endcode
/// Note that if the current compiler supports the variable templates C++14
/// feature then we can re-write the snippet of code above using the
/// `bsl::is_nothrow_swappable_v` variable as follows:
/// @code
/// #ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
///   assert(true  == bsl::is_nothrow_swappable_v<MyType1>);
///   assert(false == bsl::is_nothrow_swappable_v<MyType2>);
/// #endif
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmf
 * @{
 */
/** @addtogroup bslmf_isnothrowswappable
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslmf_assert.h>
#include <bslmf_enableif.h>
#include <bslmf_if.h>
#include <bslmf_integralconstant.h>
#include <bslmf_isswappable.h>
#include <bslmf_util.h>
#include <bslmf_voidtype.h>
 
#include <bsls_compilerfeatures.h>
#include <bsls_keyword.h>
#include <bsls_platform.h>
 
#include <stddef.h>
 
#ifdef BSLS_COMPILERFEATURES_SUPPORT_TRAITS_HEADER
# include <type_traits>
#endif // BSLS_COMPILERFEATURES_SUPPORT_TRAITS_HEADER
 
#ifndef BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
#include <bsls_nativestd.h>
#endif // BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
 
 
// Forward declaration for C++11 and C++14 non-MSVC
#if !defined(BSLS_LIBRARYFEATURES_HAS_CPP17_BASELINE_LIBRARY) &&              \
    !defined(BSLS_PLATFORM_CMP_MSVC)                          &&              \
     defined(BSLS_COMPILERFEATURES_SUPPORT_CONSTEXPR)         &&              \
     defined(BSLS_COMPILERFEATURES_SUPPORT_NOEXCEPT)          &&              \
     defined(BSLS_COMPILERFEATURES_SUPPORT_DECLTYPE)
 
namespace bslmf {
namespace bslmf_is_nothrow_swappable_impl_ns {
// This test requires that 'using std::swap' be executed, hence the use of a
// named namespace to prevent that statement from "leaking" outside of the
// 'bslmf_isnothrowswappable.h' header.
 
template <class TYPE, class = void>
struct IsNoThrowSwappable_Impl;
    // Forward declaration
 
}  // close namespace bslmf_is_nothrow_swappable_impl_ns
}  // close package namespace
 
#endif
 
                        // ===========================
                        // struct is_nothrow_swappable
                        // ===========================
 
namespace bsl {
 
// C++17 alias definition
#if defined(BSLS_LIBRARYFEATURES_HAS_CPP17_BASELINE_LIBRARY)
 
using std::is_nothrow_swappable;
using std::is_nothrow_swappable_v;
 
// Windows non-C++17 definition
#elif defined(BSLS_PLATFORM_CMP_MSVC)
// For MSVC before 2019 and all MSVC versions building C++14 (C++14 is the
// lowest supported by MSVC), a combination of MSVC's name lookup and sfinae
// peculiarities means we cannot reproduce this behaviour.  Under these
// unfortunate circumstances, it is therefore safest to assume nothing is
// nothrow swappable.
 
#define BSLMF_ISNOTHROWSWAPPABLE_ALWAYS_FALSE 1
 
template <class TYPE>
struct is_nothrow_swappable : bsl::false_type {};
 
template <class TYPE>
BSLS_KEYWORD_INLINE_VARIABLE
constexpr bool is_nothrow_swappable_v = is_nothrow_swappable<TYPE>::value;
    // This template variable represents the result value of the
    // 'bsl::is_nothrow_swappable' metafunction.
 
// C++11 implementation
#elif defined(BSLS_COMPILERFEATURES_SUPPORT_CONSTEXPR) \
   && defined(BSLS_COMPILERFEATURES_SUPPORT_NOEXCEPT)  \
   && defined(BSLS_COMPILERFEATURES_SUPPORT_DECLTYPE)
// We are compiling C++11 or C++14 on a conformant compiler, so we can
// replicate the is_swappable trait.
 
template <class TYPE>
struct is_nothrow_swappable
: BloombergLP::bslmf::If<
      BloombergLP::bslmf::bslmf_is_nothrow_swappable_impl_ns::
          IsNoThrowSwappable_Impl<TYPE>::isNoexcept(),
      bsl::true_type,
      bsl::false_type>::Type {
    // This 'struct' template implements a metafunction to determine whether
    // the (template parameter) 'TYPE' is nothrow swappable.  This 'struct'
    // derives from 'bsl::true_type' if the 'TYPE' is nothrow swappable, and
    // from 'bsl::false_type' otherwise.  This metafunction has the same syntax
    // as the 'is_nothrow_swappable' metafunction defined in the C++17 standard
    // [meta.unary.prop]; on C++03 platforms this metafunction is not
    // implemented; on C++11 platforms, it is implemented where it is possible
    // to do so given compiler support, with the notable exception of MSVC.
};
 
#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
template <class TYPE>
BSLS_KEYWORD_INLINE_VARIABLE
constexpr bool is_nothrow_swappable_v =
                           is_nothrow_swappable<TYPE>::value;
    // This template variable represents the result value of the
    // 'bsl::is_nothrow_swappable' metafunction.
#endif // BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
 
#endif
 
}  // close namespace bsl
 
// ============================================================================
//                              TEMPLATE IMPLEMENTATIONS
// ============================================================================
 
// Template implementation only for C++11 and C++14 non-MSVC
#if !defined(BSLS_LIBRARYFEATURES_HAS_CPP17_BASELINE_LIBRARY) &&              \
    !defined(BSLS_PLATFORM_CMP_MSVC)                          &&              \
     defined(BSLS_COMPILERFEATURES_SUPPORT_CONSTEXPR)         &&              \
     defined(BSLS_COMPILERFEATURES_SUPPORT_NOEXCEPT)          &&              \
     defined(BSLS_COMPILERFEATURES_SUPPORT_DECLTYPE)
 
namespace bslmf {
namespace bslmf_is_nothrow_swappable_impl_ns {
// This test requires that 'using std::swap' be executed, hence the use of a
// named namespace to prevent that statement from "leaking" outside of the
// 'bslmf_isnothrowswappable.h' header.
 
using std::swap;
 
template <class TYPE, class BDE_OTHER_TYPE>
struct IsNoThrowSwappable_Impl {
    // This 'struct' template implements a 'constexpr' 'evaluate' function to
    // determine whether the (template parameter) 'TYPE' is nothrow swappable.
    // The default implementation is for non-swappable types, which are, by
    // definition, not nothrow swappable.  Note that the partial
    // specializations below will provide the determination for swappable
    // types.
 
    // CLASS METHODS
    static constexpr bool isNoexcept();
        // 'constexpr' method to determine whether the (template) parameter
        // 'TYPE' is nothrow swappable.
};
 
template <class TYPE>
struct IsNoThrowSwappable_Impl<
    TYPE,
    typename bsl::enable_if<bsl::is_swappable<TYPE>::value, void>::type> {
    // This 'struct' template implements a 'constexpr' 'evaluate' to determine
    // whether the (template parameter) 'TYPE' is nothrow swappable.  Note that
    // this partial specialization provides the determination for swappable
    // types.
 
    // CLASS METHODS
    static constexpr bool isNoexcept();
        // 'constexpr' method to determine whether the (template) parameter
        // 'TYPE' is nothrow swappable.
};
 
 
template <class TYPE, class BDE_OTHER_TYPE>
constexpr bool
IsNoThrowSwappable_Impl<TYPE, BDE_OTHER_TYPE>
::isNoexcept()
{
    return false;
}
 
template <class TYPE>
constexpr bool
IsNoThrowSwappable_Impl<
    TYPE,
    typename bsl::enable_if<bsl::is_swappable<TYPE>::value, void>::type>
::isNoexcept()
{
    return noexcept(swap(BloombergLP::bslmf::Util::declval<TYPE&>(),
                         BloombergLP::bslmf::Util::declval<TYPE&>()));
}
 
}  // close namespace bslmf_is_nothrow_swappable_impl_ns
}  // close package namespace
 
#endif
 
#endif // INCLUDED_BSLMF_ISNOTHROWSWAPPABLE
 
// ----------------------------------------------------------------------------
// Copyright 2022 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */