// Implementation of std::reference_wrapper -*- C++ -*- // Copyright (C) 2004-2020 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