1 // Implementation of std::move_only_function -*- C++ -*-
2
3 // Copyright The GNU Toolchain Authors.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24
25 /** @file include/bits/mofunc_impl.h
26 * This is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{functional}
28 */
29
30 #ifndef _GLIBCXX_MOF_CV
31 # define _GLIBCXX_MOF_CV
32 #endif
33
34 #ifdef _GLIBCXX_MOF_REF
35 # define _GLIBCXX_MOF_INV_QUALS _GLIBCXX_MOF_CV _GLIBCXX_MOF_REF
36 #else
37 # define _GLIBCXX_MOF_REF
38 # define _GLIBCXX_MOF_INV_QUALS _GLIBCXX_MOF_CV &
39 #endif
40
41 #define _GLIBCXX_MOF_CV_REF _GLIBCXX_MOF_CV _GLIBCXX_MOF_REF
42
43 namespace std _GLIBCXX_VISIBILITY(default)
44 {
45 _GLIBCXX_BEGIN_NAMESPACE_VERSION
46
47 /**
48 * @brief Polymorphic function wrapper.
49 * @ingroup functors
50 * @since C++23
51 * @headerfile functional
52 *
53 * The `std::move_only_function` class template is a call wrapper similar
54 * to `std::function`, but does not require the stored target function
55 * to be copyable.
56 *
57 * It also supports const-qualification, ref-qualification, and
58 * no-throw guarantees. The qualifications and exception-specification
59 * of the `move_only_function::operator()` member function are respected
60 * when invoking the target function.
61 */
62 template<typename _Res, typename... _ArgTypes, bool _Noex>
63 class move_only_function<_Res(_ArgTypes...) _GLIBCXX_MOF_CV
64 _GLIBCXX_MOF_REF noexcept(_Noex)>
65 : _Mofunc_base
66 {
67 template<typename _Tp>
68 using __callable
69 = __conditional_t<_Noex,
70 is_nothrow_invocable_r<_Res, _Tp, _ArgTypes...>,
71 is_invocable_r<_Res, _Tp, _ArgTypes...>>;
72
73 // [func.wrap.mov.con]/1 is-callable-from<VT>
74 template<typename _Vt>
75 static constexpr bool __is_callable_from
76 = __and_v<__callable<_Vt _GLIBCXX_MOF_CV_REF>,
77 __callable<_Vt _GLIBCXX_MOF_INV_QUALS>>;
78
79 public:
80 using result_type = _Res;
81
82 /// Creates an empty object.
83 move_only_function() noexcept { }
84
85 /// Creates an empty object.
86 move_only_function(nullptr_t) noexcept { }
87
88 /// Moves the target object, leaving the source empty.
89 move_only_function(move_only_function&& __x) noexcept
90 : _Mofunc_base(static_cast<_Mofunc_base&&>(__x)),
91 _M_invoke(std::__exchange(__x._M_invoke, nullptr))
92 { }
93
94 /// Stores a target object initialized from the argument.
95 template<typename _Fn, typename _Vt = decay_t<_Fn>>
96 requires (!is_same_v<_Vt, move_only_function>)
97 && (!__is_in_place_type_v<_Vt>) && __is_callable_from<_Vt>
98 move_only_function(_Fn&& __f) noexcept(_S_nothrow_init<_Vt, _Fn>())
99 {
100 if constexpr (is_function_v<remove_pointer_t<_Vt>>
101 || is_member_pointer_v<_Vt>
102 || __is_move_only_function_v<_Vt>)
103 {
104 if (__f == nullptr)
105 return;
106 }
107 _M_init<_Vt>(std::forward<_Fn>(__f));
108 _M_invoke = &_S_invoke<_Vt>;
109 }
110
111 /// Stores a target object initialized from the arguments.
112 template<typename _Tp, typename... _Args>
113 requires is_constructible_v<_Tp, _Args...>
114 && __is_callable_from<_Tp>
115 explicit
116 move_only_function(in_place_type_t<_Tp>, _Args&&... __args)
117 noexcept(_S_nothrow_init<_Tp, _Args...>())
118 : _M_invoke(&_S_invoke<_Tp>)
119 {
120 static_assert(is_same_v<decay_t<_Tp>, _Tp>);
121 _M_init<_Tp>(std::forward<_Args>(__args)...);
122 }
123
124 /// Stores a target object initialized from the arguments.
125 template<typename _Tp, typename _Up, typename... _Args>
126 requires is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
127 && __is_callable_from<_Tp>
128 explicit
129 move_only_function(in_place_type_t<_Tp>, initializer_list<_Up> __il,
130 _Args&&... __args)
131 noexcept(_S_nothrow_init<_Tp, initializer_list<_Up>&, _Args...>())
132 : _M_invoke(&_S_invoke<_Tp>)
133 {
134 static_assert(is_same_v<decay_t<_Tp>, _Tp>);
135 _M_init<_Tp>(__il, std::forward<_Args>(__args)...);
136 }
137
138 /// Stores a new target object, leaving `x` empty.
139 move_only_function&
140 operator=(move_only_function&& __x) noexcept
141 {
142 _Mofunc_base::operator=(static_cast<_Mofunc_base&&>(__x));
143 _M_invoke = std::__exchange(__x._M_invoke, nullptr);
144 return *this;
145 }
146
147 /// Destroys the target object (if any).
148 move_only_function&
149 operator=(nullptr_t) noexcept
150 {
151 _Mofunc_base::operator=(nullptr);
152 _M_invoke = nullptr;
153 return *this;
154 }
155
156 /// Stores a new target object, initialized from the argument.
157 template<typename _Fn>
158 requires is_constructible_v<move_only_function, _Fn>
159 move_only_function&
160 operator=(_Fn&& __f)
161 noexcept(is_nothrow_constructible_v<move_only_function, _Fn>)
162 {
163 move_only_function(std::forward<_Fn>(__f)).swap(*this);
164 return *this;
165 }
166
167 ~move_only_function() = default;
168
169 /// True if a target object is present, false otherwise.
170 explicit operator bool() const noexcept { return _M_invoke != nullptr; }
171
172 /** Invoke the target object.
173 *
174 * The target object will be invoked using the supplied arguments,
175 * and as an lvalue or rvalue, and as const or non-const, as dictated
176 * by the template arguments of the `move_only_function` specialization.
177 *
178 * @pre Must not be empty.
179 */
180 _Res
181 operator()(_ArgTypes... __args) _GLIBCXX_MOF_CV_REF noexcept(_Noex)
182 {
183 __glibcxx_assert(*this != nullptr);
184 return _M_invoke(this, std::forward<_ArgTypes>(__args)...);
185 }
186
187 /// Exchange the target objects (if any).
188 void
189 swap(move_only_function& __x) noexcept
190 {
191 _Mofunc_base::swap(__x);
192 std::swap(_M_invoke, __x._M_invoke);
193 }
194
195 /// Exchange the target objects (if any).
196 friend void
197 swap(move_only_function& __x, move_only_function& __y) noexcept
198 { __x.swap(__y); }
199
200 /// Check for emptiness by comparing with `nullptr`.
201 friend bool
202 operator==(const move_only_function& __x, nullptr_t) noexcept
203 { return __x._M_invoke == nullptr; }
204
205 private:
206 template<typename _Tp>
207 using __param_t = __conditional_t<is_scalar_v<_Tp>, _Tp, _Tp&&>;
208
209 using _Invoker = _Res (*)(_Mofunc_base _GLIBCXX_MOF_CV*,
210 __param_t<_ArgTypes>...) noexcept(_Noex);
211
212 template<typename _Tp>
213 static _Res
214 _S_invoke(_Mofunc_base _GLIBCXX_MOF_CV* __self,
215 __param_t<_ArgTypes>... __args) noexcept(_Noex)
216 {
217 using _TpCv = _Tp _GLIBCXX_MOF_CV;
218 using _TpInv = _Tp _GLIBCXX_MOF_INV_QUALS;
219 return std::__invoke_r<_Res>(
220 std::forward<_TpInv>(*_S_access<_TpCv>(__self)),
221 std::forward<__param_t<_ArgTypes>>(__args)...);
222 }
223
224 _Invoker _M_invoke = nullptr;
225 };
226
227 #undef _GLIBCXX_MOF_CV_REF
228 #undef _GLIBCXX_MOF_CV
229 #undef _GLIBCXX_MOF_REF
230 #undef _GLIBCXX_MOF_INV_QUALS
231
232 _GLIBCXX_END_NAMESPACE_VERSION
233 } // namespace std