refwrap.h
Go to the documentation of this file.
// Implementation of std::reference_wrapper -*- C++ -*-
// Copyright (C) 2004-2021 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/** @file include/bits/refwrap.h
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{functional}
*/
#ifndef _GLIBCXX_REFWRAP_H
#define _GLIBCXX_REFWRAP_H 1
#pragma GCC system_header
#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else
#include <bits/move.h>
#include <bits/invoke.h>
#include <bits/stl_function.h> // for unary_function and binary_function
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/// @cond undocumented
/**
* Derives from @c unary_function or @c binary_function, or perhaps
* nothing, depending on the number of arguments provided. The
* primary template is the basis case, which derives nothing.
*/
template<typename _Res, typename... _ArgTypes>
struct _Maybe_unary_or_binary_function { };
/// Derives from @c unary_function, as appropriate.
template<typename _Res, typename _T1>
struct _Maybe_unary_or_binary_function<_Res, _T1>
: std::unary_function<_T1, _Res> { };
/// Derives from @c binary_function, as appropriate.
template<typename _Res, typename _T1, typename _T2>
struct _Maybe_unary_or_binary_function<_Res, _T1, _T2>
: std::binary_function<_T1, _T2, _Res> { };
template<typename _Signature>
struct _Mem_fn_traits;
template<typename _Res, typename _Class, typename... _ArgTypes>
struct _Mem_fn_traits_base
{
using __result_type = _Res;
using __maybe_type
= _Maybe_unary_or_binary_function<_Res, _Class*, _ArgTypes...>;
using __arity = integral_constant<size_t, sizeof...(_ArgTypes)>;
};
#define _GLIBCXX_MEM_FN_TRAITS2(_CV, _REF, _LVAL, _RVAL) \
template<typename _Res, typename _Class, typename... _ArgTypes> \
struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes...) _CV _REF> \
: _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...> \
{ \
using __vararg = false_type; \
}; \
template<typename _Res, typename _Class, typename... _ArgTypes> \
struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes... ...) _CV _REF> \
: _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...> \
{ \
using __vararg = true_type; \
};
#define _GLIBCXX_MEM_FN_TRAITS(_REF, _LVAL, _RVAL) \
_GLIBCXX_MEM_FN_TRAITS2( , _REF, _LVAL, _RVAL) \
_GLIBCXX_MEM_FN_TRAITS2(const , _REF, _LVAL, _RVAL) \
_GLIBCXX_MEM_FN_TRAITS2(volatile , _REF, _LVAL, _RVAL) \
_GLIBCXX_MEM_FN_TRAITS2(const volatile, _REF, _LVAL, _RVAL)
_GLIBCXX_MEM_FN_TRAITS( , true_type, true_type)
_GLIBCXX_MEM_FN_TRAITS(&, true_type, false_type)
_GLIBCXX_MEM_FN_TRAITS(&&, false_type, true_type)
#if __cplusplus > 201402L
_GLIBCXX_MEM_FN_TRAITS(noexcept, true_type, true_type)
_GLIBCXX_MEM_FN_TRAITS(& noexcept, true_type, false_type)
_GLIBCXX_MEM_FN_TRAITS(&& noexcept, false_type, true_type)
#endif
#undef _GLIBCXX_MEM_FN_TRAITS
#undef _GLIBCXX_MEM_FN_TRAITS2
/// If we have found a result_type, extract it.
template<typename _Functor, typename = __void_t<>>
struct _Maybe_get_result_type
{ };
template<typename _Functor>
struct _Maybe_get_result_type<_Functor,
__void_t<typename _Functor::result_type>>
{ typedef typename _Functor::result_type result_type; };
/**
* Base class for any function object that has a weak result type, as
* defined in 20.8.2 [func.require] of C++11.
*/
template<typename _Functor>
struct _Weak_result_type_impl
: _Maybe_get_result_type<_Functor>
{ };
/// Retrieve the result type for a function type.
template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
struct _Weak_result_type_impl<_Res(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL>
{ typedef _Res result_type; };
/// Retrieve the result type for a varargs function type.
template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
struct _Weak_result_type_impl<_Res(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL>
{ typedef _Res result_type; };
/// Retrieve the result type for a function pointer.
template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
struct _Weak_result_type_impl<_Res(*)(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL>
{ typedef _Res result_type; };
/// Retrieve the result type for a varargs function pointer.
template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
struct
_Weak_result_type_impl<_Res(*)(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL>
{ typedef _Res result_type; };
// Let _Weak_result_type_impl perform the real work.
template<typename _Functor,
bool = is_member_function_pointer<_Functor>::value>
struct _Weak_result_type_memfun
: _Weak_result_type_impl<_Functor>
{ };
// A pointer to member function has a weak result type.
template<typename _MemFunPtr>
struct _Weak_result_type_memfun<_MemFunPtr, true>
{
using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type;
};
// A pointer to data member doesn't have a weak result type.
template<typename _Func, typename _Class>
struct _Weak_result_type_memfun<_Func _Class::*, false>
{ };
/**
* Strip top-level cv-qualifiers from the function object and let
* _Weak_result_type_memfun perform the real work.
*/
template<typename _Functor>
struct _Weak_result_type
: _Weak_result_type_memfun<typename remove_cv<_Functor>::type>
{ };
#if __cplusplus <= 201703L
// Detect nested argument_type.
template<typename _Tp, typename = __void_t<>>
struct _Refwrap_base_arg1
{ };
// Nested argument_type.
template<typename _Tp>
struct _Refwrap_base_arg1<_Tp,
__void_t<typename _Tp::argument_type>>
{
typedef typename _Tp::argument_type argument_type;
};
// Detect nested first_argument_type and second_argument_type.
template<typename _Tp, typename = __void_t<>>
struct _Refwrap_base_arg2
{ };
// Nested first_argument_type and second_argument_type.
template<typename _Tp>
struct _Refwrap_base_arg2<_Tp,
__void_t<typename _Tp::first_argument_type,
typename _Tp::second_argument_type>>
{
typedef typename _Tp::first_argument_type first_argument_type;
typedef typename _Tp::second_argument_type second_argument_type;
};
/**
* Derives from unary_function or binary_function when it
* can. Specializations handle all of the easy cases. The primary
* template determines what to do with a class type, which may
* derive from both unary_function and binary_function.
*/
template<typename _Tp>
struct _Reference_wrapper_base
: _Weak_result_type<_Tp>, _Refwrap_base_arg1<_Tp>, _Refwrap_base_arg2<_Tp>
{ };
// - a function type (unary)
template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM>
struct _Reference_wrapper_base<_Res(_T1) _GLIBCXX_NOEXCEPT_QUAL>
: unary_function<_T1, _Res>
{ };
template<typename _Res, typename _T1>
struct _Reference_wrapper_base<_Res(_T1) const>
: unary_function<_T1, _Res>
{ };
template<typename _Res, typename _T1>
struct _Reference_wrapper_base<_Res(_T1) volatile>
: unary_function<_T1, _Res>
{ };
template<typename _Res, typename _T1>
struct _Reference_wrapper_base<_Res(_T1) const volatile>
: unary_function<_T1, _Res>
{ };
// - a function type (binary)
template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM>
struct _Reference_wrapper_base<_Res(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL>
: binary_function<_T1, _T2, _Res>
{ };
template<typename _Res, typename _T1, typename _T2>
struct _Reference_wrapper_base<_Res(_T1, _T2) const>
: binary_function<_T1, _T2, _Res>
{ };
template<typename _Res, typename _T1, typename _T2>
struct _Reference_wrapper_base<_Res(_T1, _T2) volatile>
: binary_function<_T1, _T2, _Res>
{ };
template<typename _Res, typename _T1, typename _T2>
struct _Reference_wrapper_base<_Res(_T1, _T2) const volatile>
: binary_function<_T1, _T2, _Res>
{ };
// - a function pointer type (unary)
template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM>
struct _Reference_wrapper_base<_Res(*)(_T1) _GLIBCXX_NOEXCEPT_QUAL>
: unary_function<_T1, _Res>
{ };
// - a function pointer type (binary)
template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM>
struct _Reference_wrapper_base<_Res(*)(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL>
: binary_function<_T1, _T2, _Res>
{ };
template<typename _Tp, bool = is_member_function_pointer<_Tp>::value>
struct _Reference_wrapper_base_memfun
: _Reference_wrapper_base<_Tp>
{ };
template<typename _MemFunPtr>
struct _Reference_wrapper_base_memfun<_MemFunPtr, true>
: _Mem_fn_traits<_MemFunPtr>::__maybe_type
{
using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type;
};
#endif // ! C++20
/// @endcond
/**
* @brief Primary class template for reference_wrapper.
* @ingroup functors
*/
template<typename _Tp>
class reference_wrapper
#if __cplusplus <= 201703L
// In C++20 std::reference_wrapper<T> allows T to be incomplete,
// so checking for nested types could result in ODR violations.
: public _Reference_wrapper_base_memfun<typename remove_cv<_Tp>::type>
#endif
{
_Tp* _M_data;
_GLIBCXX20_CONSTEXPR
static _Tp* _S_fun(_Tp& __r) noexcept { return std::__addressof(__r); }
static void _S_fun(_Tp&&) = delete;
template<typename _Up, typename _Up2 = __remove_cvref_t<_Up>>
using __not_same
= typename enable_if<!is_same<reference_wrapper, _Up2>::value>::type;
public:
typedef _Tp type;
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2993. reference_wrapper<T> conversion from T&&
// 3041. Unnecessary decay in reference_wrapper
template<typename _Up, typename = __not_same<_Up>, typename
= decltype(reference_wrapper::_S_fun(std::declval<_Up>()))>
_GLIBCXX20_CONSTEXPR
reference_wrapper(_Up&& __uref)
noexcept(noexcept(reference_wrapper::_S_fun(std::declval<_Up>())))
: _M_data(reference_wrapper::_S_fun(std::forward<_Up>(__uref)))
{ }
reference_wrapper(const reference_wrapper&) = default;
reference_wrapper&
operator=(const reference_wrapper&) = default;
_GLIBCXX20_CONSTEXPR
operator _Tp&() const noexcept
{ return this->get(); }
_GLIBCXX20_CONSTEXPR
_Tp&
get() const noexcept
{ return *_M_data; }
template<typename... _Args>
_GLIBCXX20_CONSTEXPR
typename result_of<_Tp&(_Args&&...)>::type
operator()(_Args&&... __args) const
{
#if __cplusplus > 201703L
if constexpr (is_object_v<type>)
static_assert(sizeof(type), "type must be complete");
#endif
return std::__invoke(get(), std::forward<_Args>(__args)...);
}
};
#if __cpp_deduction_guides
template<typename _Tp>
reference_wrapper(_Tp&) -> reference_wrapper<_Tp>;
#endif
/// @relates reference_wrapper @{
/// Denotes a reference should be taken to a variable.
template<typename _Tp>
_GLIBCXX20_CONSTEXPR
inline reference_wrapper<_Tp>
ref(_Tp& __t) noexcept
{ return reference_wrapper<_Tp>(__t); }
/// Denotes a const reference should be taken to a variable.
template<typename _Tp>
_GLIBCXX20_CONSTEXPR
inline reference_wrapper<const _Tp>
cref(const _Tp& __t) noexcept
{ return reference_wrapper<const _Tp>(__t); }
template<typename _Tp>
void ref(const _Tp&&) = delete;
template<typename _Tp>
void cref(const _Tp&&) = delete;
/// std::ref overload to prevent wrapping a reference_wrapper
template<typename _Tp>
_GLIBCXX20_CONSTEXPR
inline reference_wrapper<_Tp>
ref(reference_wrapper<_Tp> __t) noexcept
{ return __t; }
/// std::cref overload to prevent wrapping a reference_wrapper
template<typename _Tp>
_GLIBCXX20_CONSTEXPR
inline reference_wrapper<const _Tp>
cref(reference_wrapper<_Tp> __t) noexcept
{ return { __t.get() }; }
/// @}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // C++11
#endif // _GLIBCXX_REFWRAP_H
c++0x_warning.h
invoke.h
move.h
stl_function.h
std::true_type
integral_constant< bool, true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:83
std::false_type
integral_constant< bool, false > false_type
The type used as a compile-time boolean with false value.
Definition: type_traits:86
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:49
std::__invoke
constexpr __invoke_result< _Callable, _Args... >::type __invoke(_Callable &&__fn, _Args &&... __args) noexcept(__is_nothrow_invocable< _Callable, _Args... >::value)
Invoke a callable object.
Definition: invoke.h:90
std
ISO C++ entities toplevel namespace is std.
std::reference_wrapper
Primary class template for reference_wrapper.
Definition: refwrap.h:300
std::reference_wrapper::ref
constexpr reference_wrapper< _Tp > ref(_Tp &__t) noexcept
Definition: refwrap.h:364
std::reference_wrapper::ref
constexpr reference_wrapper< _Tp > ref(reference_wrapper< _Tp > __t) noexcept
std::ref overload to prevent wrapping a reference_wrapper
Definition: refwrap.h:384
std::reference_wrapper::cref
constexpr reference_wrapper< const _Tp > cref(const _Tp &__t) noexcept
Denotes a const reference should be taken to a variable.
Definition: refwrap.h:371
std::reference_wrapper::cref
constexpr reference_wrapper< const _Tp > cref(reference_wrapper< _Tp > __t) noexcept
std::cref overload to prevent wrapping a reference_wrapper
Definition: refwrap.h:391
std::enable_if
Define a member typedef type only if a boolean constant is true.
Definition: type_traits:2200
std::result_of
result_of
Definition: type_traits:2373
std::unary_function
Definition: stl_function.h:118
std::binary_function
Definition: stl_function.h:132