1 | // Implementation of std::reference_wrapper -*- C++ -*-
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2 |
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3 | // Copyright (C) 2004-2021 Free Software Foundation, Inc.
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4 | //
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5 | // This file is part of the GNU ISO C++ Library. This library is free
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6 | // software; you can redistribute it and/or modify it under the
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7 | // terms of the GNU General Public License as published by the
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8 | // Free Software Foundation; either version 3, or (at your option)
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9 | // any later version.
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10 |
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11 | // This library is distributed in the hope that it will be useful,
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12 | // but WITHOUT ANY WARRANTY; without even the implied warranty of
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13 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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14 | // GNU General Public License for more details.
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15 |
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16 | // Under Section 7 of GPL version 3, you are granted additional
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17 | // permissions described in the GCC Runtime Library Exception, version
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18 | // 3.1, as published by the Free Software Foundation.
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19 |
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20 | // You should have received a copy of the GNU General Public License and
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21 | // a copy of the GCC Runtime Library Exception along with this program;
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22 | // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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23 | // <http://www.gnu.org/licenses/>.
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24 |
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25 | /** @file include/bits/refwrap.h
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26 | * This is an internal header file, included by other library headers.
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27 | * Do not attempt to use it directly. @headername{functional}
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28 | */
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29 |
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30 | #ifndef _GLIBCXX_REFWRAP_H
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31 | #define _GLIBCXX_REFWRAP_H 1
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32 |
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33 | #pragma GCC system_header
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34 |
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35 | #if __cplusplus < 201103L
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36 | # include <bits/c++0x_warning.h>
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37 | #else
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38 |
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39 | #include <bits/move.h>
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40 | #include <bits/invoke.h>
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41 | #include <bits/stl_function.h> // for unary_function and binary_function
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42 |
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43 | namespace std _GLIBCXX_VISIBILITY(default)
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44 | {
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45 | _GLIBCXX_BEGIN_NAMESPACE_VERSION
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46 |
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47 | /// @cond undocumented
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48 |
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49 | /**
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50 | * Derives from @c unary_function or @c binary_function, or perhaps
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51 | * nothing, depending on the number of arguments provided. The
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52 | * primary template is the basis case, which derives nothing.
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53 | */
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54 | template<typename _Res, typename... _ArgTypes>
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55 | struct _Maybe_unary_or_binary_function { };
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56 |
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57 | /// Derives from @c unary_function, as appropriate.
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58 | template<typename _Res, typename _T1>
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59 | struct _Maybe_unary_or_binary_function<_Res, _T1>
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60 | : std::unary_function<_T1, _Res> { };
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61 |
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62 | /// Derives from @c binary_function, as appropriate.
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63 | template<typename _Res, typename _T1, typename _T2>
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64 | struct _Maybe_unary_or_binary_function<_Res, _T1, _T2>
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65 | : std::binary_function<_T1, _T2, _Res> { };
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66 |
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67 | template<typename _Signature>
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68 | struct _Mem_fn_traits;
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69 |
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70 | template<typename _Res, typename _Class, typename... _ArgTypes>
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71 | struct _Mem_fn_traits_base
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72 | {
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73 | using __result_type = _Res;
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74 | using __maybe_type
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75 | = _Maybe_unary_or_binary_function<_Res, _Class*, _ArgTypes...>;
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76 | using __arity = integral_constant<size_t, sizeof...(_ArgTypes)>;
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77 | };
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78 |
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79 | #define _GLIBCXX_MEM_FN_TRAITS2(_CV, _REF, _LVAL, _RVAL) \
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80 | template<typename _Res, typename _Class, typename... _ArgTypes> \
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81 | struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes...) _CV _REF> \
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82 | : _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...> \
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83 | { \
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84 | using __vararg = false_type; \
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85 | }; \
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86 | template<typename _Res, typename _Class, typename... _ArgTypes> \
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87 | struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes... ...) _CV _REF> \
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88 | : _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...> \
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89 | { \
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90 | using __vararg = true_type; \
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91 | };
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92 |
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93 | #define _GLIBCXX_MEM_FN_TRAITS(_REF, _LVAL, _RVAL) \
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94 | _GLIBCXX_MEM_FN_TRAITS2( , _REF, _LVAL, _RVAL) \
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95 | _GLIBCXX_MEM_FN_TRAITS2(const , _REF, _LVAL, _RVAL) \
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96 | _GLIBCXX_MEM_FN_TRAITS2(volatile , _REF, _LVAL, _RVAL) \
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97 | _GLIBCXX_MEM_FN_TRAITS2(const volatile, _REF, _LVAL, _RVAL)
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98 |
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99 | _GLIBCXX_MEM_FN_TRAITS( , true_type, true_type)
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100 | _GLIBCXX_MEM_FN_TRAITS(&, true_type, false_type)
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101 | _GLIBCXX_MEM_FN_TRAITS(&&, false_type, true_type)
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102 |
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103 | #if __cplusplus > 201402L
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104 | _GLIBCXX_MEM_FN_TRAITS(noexcept, true_type, true_type)
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105 | _GLIBCXX_MEM_FN_TRAITS(& noexcept, true_type, false_type)
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106 | _GLIBCXX_MEM_FN_TRAITS(&& noexcept, false_type, true_type)
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107 | #endif
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108 |
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109 | #undef _GLIBCXX_MEM_FN_TRAITS
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110 | #undef _GLIBCXX_MEM_FN_TRAITS2
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111 |
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112 | /// If we have found a result_type, extract it.
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113 | template<typename _Functor, typename = __void_t<>>
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114 | struct _Maybe_get_result_type
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115 | { };
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116 |
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117 | template<typename _Functor>
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118 | struct _Maybe_get_result_type<_Functor,
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119 | __void_t<typename _Functor::result_type>>
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120 | { typedef typename _Functor::result_type result_type; };
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121 |
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122 | /**
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123 | * Base class for any function object that has a weak result type, as
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124 | * defined in 20.8.2 [func.require] of C++11.
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125 | */
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126 | template<typename _Functor>
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127 | struct _Weak_result_type_impl
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128 | : _Maybe_get_result_type<_Functor>
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129 | { };
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130 |
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131 | /// Retrieve the result type for a function type.
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132 | template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
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133 | struct _Weak_result_type_impl<_Res(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL>
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134 | { typedef _Res result_type; };
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135 |
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136 | /// Retrieve the result type for a varargs function type.
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137 | template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
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138 | struct _Weak_result_type_impl<_Res(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL>
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139 | { typedef _Res result_type; };
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140 |
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141 | /// Retrieve the result type for a function pointer.
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142 | template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
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143 | struct _Weak_result_type_impl<_Res(*)(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL>
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144 | { typedef _Res result_type; };
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145 |
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146 | /// Retrieve the result type for a varargs function pointer.
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147 | template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
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148 | struct
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149 | _Weak_result_type_impl<_Res(*)(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL>
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150 | { typedef _Res result_type; };
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151 |
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152 | // Let _Weak_result_type_impl perform the real work.
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153 | template<typename _Functor,
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154 | bool = is_member_function_pointer<_Functor>::value>
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155 | struct _Weak_result_type_memfun
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156 | : _Weak_result_type_impl<_Functor>
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157 | { };
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158 |
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159 | // A pointer to member function has a weak result type.
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160 | template<typename _MemFunPtr>
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161 | struct _Weak_result_type_memfun<_MemFunPtr, true>
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162 | {
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163 | using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type;
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164 | };
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165 |
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166 | // A pointer to data member doesn't have a weak result type.
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167 | template<typename _Func, typename _Class>
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168 | struct _Weak_result_type_memfun<_Func _Class::*, false>
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169 | { };
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170 |
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171 | /**
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172 | * Strip top-level cv-qualifiers from the function object and let
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173 | * _Weak_result_type_memfun perform the real work.
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174 | */
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175 | template<typename _Functor>
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176 | struct _Weak_result_type
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177 | : _Weak_result_type_memfun<typename remove_cv<_Functor>::type>
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178 | { };
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179 |
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180 | #if __cplusplus <= 201703L
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181 | // Detect nested argument_type.
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182 | template<typename _Tp, typename = __void_t<>>
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183 | struct _Refwrap_base_arg1
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184 | { };
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185 |
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186 | // Nested argument_type.
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187 | template<typename _Tp>
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188 | struct _Refwrap_base_arg1<_Tp,
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189 | __void_t<typename _Tp::argument_type>>
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190 | {
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191 | typedef typename _Tp::argument_type argument_type;
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192 | };
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193 |
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194 | // Detect nested first_argument_type and second_argument_type.
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195 | template<typename _Tp, typename = __void_t<>>
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196 | struct _Refwrap_base_arg2
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197 | { };
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198 |
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199 | // Nested first_argument_type and second_argument_type.
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200 | template<typename _Tp>
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201 | struct _Refwrap_base_arg2<_Tp,
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202 | __void_t<typename _Tp::first_argument_type,
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203 | typename _Tp::second_argument_type>>
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204 | {
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205 | typedef typename _Tp::first_argument_type first_argument_type;
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206 | typedef typename _Tp::second_argument_type second_argument_type;
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207 | };
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208 |
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209 | /**
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210 | * Derives from unary_function or binary_function when it
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211 | * can. Specializations handle all of the easy cases. The primary
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212 | * template determines what to do with a class type, which may
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213 | * derive from both unary_function and binary_function.
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214 | */
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215 | template<typename _Tp>
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216 | struct _Reference_wrapper_base
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217 | : _Weak_result_type<_Tp>, _Refwrap_base_arg1<_Tp>, _Refwrap_base_arg2<_Tp>
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218 | { };
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219 |
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220 | // - a function type (unary)
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221 | template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM>
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222 | struct _Reference_wrapper_base<_Res(_T1) _GLIBCXX_NOEXCEPT_QUAL>
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223 | : unary_function<_T1, _Res>
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224 | { };
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225 |
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226 | template<typename _Res, typename _T1>
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227 | struct _Reference_wrapper_base<_Res(_T1) const>
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228 | : unary_function<_T1, _Res>
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229 | { };
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230 |
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231 | template<typename _Res, typename _T1>
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232 | struct _Reference_wrapper_base<_Res(_T1) volatile>
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233 | : unary_function<_T1, _Res>
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234 | { };
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235 |
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236 | template<typename _Res, typename _T1>
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237 | struct _Reference_wrapper_base<_Res(_T1) const volatile>
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238 | : unary_function<_T1, _Res>
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239 | { };
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240 |
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241 | // - a function type (binary)
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242 | template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM>
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243 | struct _Reference_wrapper_base<_Res(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL>
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244 | : binary_function<_T1, _T2, _Res>
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245 | { };
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246 |
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247 | template<typename _Res, typename _T1, typename _T2>
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248 | struct _Reference_wrapper_base<_Res(_T1, _T2) const>
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249 | : binary_function<_T1, _T2, _Res>
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250 | { };
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251 |
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252 | template<typename _Res, typename _T1, typename _T2>
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253 | struct _Reference_wrapper_base<_Res(_T1, _T2) volatile>
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254 | : binary_function<_T1, _T2, _Res>
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255 | { };
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256 |
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257 | template<typename _Res, typename _T1, typename _T2>
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258 | struct _Reference_wrapper_base<_Res(_T1, _T2) const volatile>
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259 | : binary_function<_T1, _T2, _Res>
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260 | { };
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261 |
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262 | // - a function pointer type (unary)
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263 | template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM>
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264 | struct _Reference_wrapper_base<_Res(*)(_T1) _GLIBCXX_NOEXCEPT_QUAL>
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265 | : unary_function<_T1, _Res>
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266 | { };
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267 |
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268 | // - a function pointer type (binary)
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269 | template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM>
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270 | struct _Reference_wrapper_base<_Res(*)(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL>
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271 | : binary_function<_T1, _T2, _Res>
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272 | { };
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273 |
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274 | template<typename _Tp, bool = is_member_function_pointer<_Tp>::value>
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275 | struct _Reference_wrapper_base_memfun
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276 | : _Reference_wrapper_base<_Tp>
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277 | { };
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278 |
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279 | template<typename _MemFunPtr>
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280 | struct _Reference_wrapper_base_memfun<_MemFunPtr, true>
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281 | : _Mem_fn_traits<_MemFunPtr>::__maybe_type
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282 | {
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283 | using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type;
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284 | };
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285 | #endif // ! C++20
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286 |
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287 | /// @endcond
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288 |
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289 | /**
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290 | * @brief Primary class template for reference_wrapper.
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291 | * @ingroup functors
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292 | */
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293 | template<typename _Tp>
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294 | class reference_wrapper
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295 | #if __cplusplus <= 201703L
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296 | // In C++20 std::reference_wrapper<T> allows T to be incomplete,
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297 | // so checking for nested types could result in ODR violations.
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298 | : public _Reference_wrapper_base_memfun<typename remove_cv<_Tp>::type>
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299 | #endif
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300 | {
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301 | _Tp* _M_data;
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302 |
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303 | _GLIBCXX20_CONSTEXPR
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304 | static _Tp* _S_fun(_Tp& __r) noexcept { return std::__addressof(__r); }
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305 |
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306 | static void _S_fun(_Tp&&) = delete;
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307 |
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308 | template<typename _Up, typename _Up2 = __remove_cvref_t<_Up>>
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309 | using __not_same
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310 | = typename enable_if<!is_same<reference_wrapper, _Up2>::value>::type;
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311 |
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312 | public:
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313 | typedef _Tp type;
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314 |
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315 | // _GLIBCXX_RESOLVE_LIB_DEFECTS
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316 | // 2993. reference_wrapper<T> conversion from T&&
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317 | // 3041. Unnecessary decay in reference_wrapper
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318 | template<typename _Up, typename = __not_same<_Up>, typename
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319 | = decltype(reference_wrapper::_S_fun(std::declval<_Up>()))>
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320 | _GLIBCXX20_CONSTEXPR
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321 | reference_wrapper(_Up&& __uref)
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322 | noexcept(noexcept(reference_wrapper::_S_fun(std::declval<_Up>())))
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323 | : _M_data(reference_wrapper::_S_fun(std::forward<_Up>(__uref)))
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324 | { }
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325 |
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326 | reference_wrapper(const reference_wrapper&) = default;
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327 |
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328 | reference_wrapper&
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329 | operator=(const reference_wrapper&) = default;
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330 |
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331 | _GLIBCXX20_CONSTEXPR
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332 | operator _Tp&() const noexcept
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333 | { return this->get(); }
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334 |
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335 | _GLIBCXX20_CONSTEXPR
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336 | _Tp&
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337 | get() const noexcept
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338 | { return *_M_data; }
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339 |
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340 | template<typename... _Args>
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341 | _GLIBCXX20_CONSTEXPR
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342 | typename result_of<_Tp&(_Args&&...)>::type
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343 | operator()(_Args&&... __args) const
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344 | {
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345 | #if __cplusplus > 201703L
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346 | if constexpr (is_object_v<type>)
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347 | static_assert(sizeof(type), "type must be complete");
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348 | #endif
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349 | return std::__invoke(get(), std::forward<_Args>(__args)...);
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350 | }
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351 | };
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352 |
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353 | #if __cpp_deduction_guides
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354 | template<typename _Tp>
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355 | reference_wrapper(_Tp&) -> reference_wrapper<_Tp>;
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356 | #endif
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357 |
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358 | /// @relates reference_wrapper @{
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359 |
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360 | /// Denotes a reference should be taken to a variable.
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361 | template<typename _Tp>
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362 | _GLIBCXX20_CONSTEXPR
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363 | inline reference_wrapper<_Tp>
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364 | ref(_Tp& __t) noexcept
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365 | { return reference_wrapper<_Tp>(__t); }
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366 |
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367 | /// Denotes a const reference should be taken to a variable.
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368 | template<typename _Tp>
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369 | _GLIBCXX20_CONSTEXPR
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370 | inline reference_wrapper<const _Tp>
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371 | cref(const _Tp& __t) noexcept
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372 | { return reference_wrapper<const _Tp>(__t); }
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373 |
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374 | template<typename _Tp>
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375 | void ref(const _Tp&&) = delete;
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376 |
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377 | template<typename _Tp>
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378 | void cref(const _Tp&&) = delete;
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379 |
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380 | /// std::ref overload to prevent wrapping a reference_wrapper
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381 | template<typename _Tp>
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382 | _GLIBCXX20_CONSTEXPR
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383 | inline reference_wrapper<_Tp>
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384 | ref(reference_wrapper<_Tp> __t) noexcept
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385 | { return __t; }
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386 |
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387 | /// std::cref overload to prevent wrapping a reference_wrapper
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388 | template<typename _Tp>
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389 | _GLIBCXX20_CONSTEXPR
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390 | inline reference_wrapper<const _Tp>
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391 | cref(reference_wrapper<_Tp> __t) noexcept
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392 | { return { __t.get() }; }
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393 |
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394 | /// @}
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395 |
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396 | _GLIBCXX_END_NAMESPACE_VERSION
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397 | } // namespace std
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398 |
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399 | #endif // C++11
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400 |
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401 | #endif // _GLIBCXX_REFWRAP_H
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