// bslmf_isnothrowswappable.h -*-C++-*-
#ifndef INCLUDED_BSLMF_ISNOTHROWSWAPPABLE
#define INCLUDED_BSLMF_ISNOTHROWSWAPPABLE
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
//@PURPOSE: Provide metafunction to identify nothrow swappable types.
//
//@CLASSES:
// bsl::is_nothrow_swappable: type-traits metafunction
// bsl::is_nothrow_swappable_v: the metafunction's result value
//
//@SEE_ALSO: bslmf_integralconstant
//
//@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
///-----
// In this section we show intended use of this component.
//
///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.
//..
// 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.
// };
//..
// 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:
//..
// assert(true == bsl::is_nothrow_swappable<MyType1>::value);
// assert(false == bsl::is_nothrow_swappable<MyType2>::value);
//..
// 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:
//..
//#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
// assert(true == bsl::is_nothrow_swappable_v<MyType1>);
// assert(false == bsl::is_nothrow_swappable_v<MyType2>);
//#endif
//..
#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 BloombergLP {
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
} // close enterprise 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 BloombergLP {
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
} // close enterprise 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 ----------------------------------