libstdc++
utility
Go to the documentation of this file.
1// <utility> -*- C++ -*-
2
3// Copyright (C) 2001-2025 Free Software Foundation, Inc.
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/*
26 *
27 * Copyright (c) 1994
28 * Hewlett-Packard Company
29 *
30 * Permission to use, copy, modify, distribute and sell this software
31 * and its documentation for any purpose is hereby granted without fee,
32 * provided that the above copyright notice appear in all copies and
33 * that both that copyright notice and this permission notice appear
34 * in supporting documentation. Hewlett-Packard Company makes no
35 * representations about the suitability of this software for any
36 * purpose. It is provided "as is" without express or implied warranty.
37 *
38 *
39 * Copyright (c) 1996,1997
40 * Silicon Graphics Computer Systems, Inc.
41 *
42 * Permission to use, copy, modify, distribute and sell this software
43 * and its documentation for any purpose is hereby granted without fee,
44 * provided that the above copyright notice appear in all copies and
45 * that both that copyright notice and this permission notice appear
46 * in supporting documentation. Silicon Graphics makes no
47 * representations about the suitability of this software for any
48 * purpose. It is provided "as is" without express or implied warranty.
49 */
50
51/** @file include/utility
52 * This is a Standard C++ Library header.
53 */
54
55#ifndef _GLIBCXX_UTILITY
56#define _GLIBCXX_UTILITY 1
57
58#ifdef _GLIBCXX_SYSHDR
59#pragma GCC system_header
60#endif
61
62/**
63 * @defgroup utilities Utilities
64 *
65 * Basic function and class templates used with the rest of the library.
66 * Includes pair, swap, forward/move helpers, declval, integer_sequence.
67 */
68
69#include <bits/c++config.h>
70#include <bits/stl_relops.h>
71#include <bits/stl_pair.h>
72
73#if __cplusplus >= 201103L
74
75#include <initializer_list>
76#include <type_traits>
77#include <bits/move.h>
78#include <bits/utility.h>
79
80#if __cplusplus >= 202002L
81#include <ext/numeric_traits.h> // __is_standard_integer, __int_traits
82#endif
83
84#if __cplusplus > 202302L
85# include <bits/monostate.h>
86#endif
87
88#define __glibcxx_want_addressof_constexpr
89#define __glibcxx_want_as_const
90#define __glibcxx_want_constexpr_algorithms
91#define __glibcxx_want_constexpr_utility
92#define __glibcxx_want_exchange_function
93#define __glibcxx_want_forward_like
94#define __glibcxx_want_integer_comparison_functions
95#define __glibcxx_want_integer_sequence
96#define __glibcxx_want_ranges_zip
97#define __glibcxx_want_to_underlying
98#define __glibcxx_want_tuple_element_t
99#define __glibcxx_want_tuples_by_type
100#define __glibcxx_want_unreachable
101#define __glibcxx_want_observable_checkpoint
102#define __glibcxx_want_tuple_like
103#define __glibcxx_want_constrained_equality
104#include <bits/version.h>
105
106namespace std _GLIBCXX_VISIBILITY(default)
107{
108_GLIBCXX_BEGIN_NAMESPACE_VERSION
109
110#ifdef __cpp_lib_exchange_function // C++ >= 14
111 /// Assign @p __new_val to @p __obj and return its previous value.
112 template <typename _Tp, typename _Up = _Tp>
113 _GLIBCXX20_CONSTEXPR
114 inline _Tp
115 exchange(_Tp& __obj, _Up&& __new_val)
116 noexcept(__and_<is_nothrow_move_constructible<_Tp>,
117 is_nothrow_assignable<_Tp&, _Up>>::value)
118 { return std::__exchange(__obj, std::forward<_Up>(__new_val)); }
119#endif
120
121#ifdef __cpp_lib_as_const // C++ >= 17
122 template<typename _Tp>
123 [[nodiscard]]
124 constexpr add_const_t<_Tp>&
125 as_const(_Tp& __t) noexcept
126 { return __t; }
127
128 template<typename _Tp>
129 void as_const(const _Tp&&) = delete;
130#endif
131
132#ifdef __cpp_lib_integer_comparison_functions // C++ >= 20
133 template<typename _Tp, typename _Up>
134 constexpr bool
135 cmp_equal(_Tp __t, _Up __u) noexcept
136 {
137 static_assert(__is_standard_integer<_Tp>::value);
138 static_assert(__is_standard_integer<_Up>::value);
139
140 if constexpr (is_signed_v<_Tp> == is_signed_v<_Up>)
141 return __t == __u;
142 else if constexpr (is_signed_v<_Tp>)
143 return __t >= 0 && make_unsigned_t<_Tp>(__t) == __u;
144 else
145 return __u >= 0 && __t == make_unsigned_t<_Up>(__u);
146 }
147
148 template<typename _Tp, typename _Up>
149 constexpr bool
150 cmp_not_equal(_Tp __t, _Up __u) noexcept
151 { return !std::cmp_equal(__t, __u); }
152
153 template<typename _Tp, typename _Up>
154 constexpr bool
155 cmp_less(_Tp __t, _Up __u) noexcept
156 {
157 static_assert(__is_standard_integer<_Tp>::value);
158 static_assert(__is_standard_integer<_Up>::value);
159
160 if constexpr (is_signed_v<_Tp> == is_signed_v<_Up>)
161 return __t < __u;
162 else if constexpr (is_signed_v<_Tp>)
163 return __t < 0 || make_unsigned_t<_Tp>(__t) < __u;
164 else
165 return __u >= 0 && __t < make_unsigned_t<_Up>(__u);
166 }
167
168 template<typename _Tp, typename _Up>
169 constexpr bool
170 cmp_greater(_Tp __t, _Up __u) noexcept
171 { return std::cmp_less(__u, __t); }
172
173 template<typename _Tp, typename _Up>
174 constexpr bool
175 cmp_less_equal(_Tp __t, _Up __u) noexcept
176 { return !std::cmp_less(__u, __t); }
177
178 template<typename _Tp, typename _Up>
179 constexpr bool
180 cmp_greater_equal(_Tp __t, _Up __u) noexcept
181 { return !std::cmp_less(__t, __u); }
182
183 template<typename _Res, typename _Tp>
184 constexpr bool
185 in_range(_Tp __t) noexcept
186 {
187 static_assert(__is_standard_integer<_Res>::value);
188 static_assert(__is_standard_integer<_Tp>::value);
189 using __gnu_cxx::__int_traits;
190
191 if constexpr (is_signed_v<_Tp> == is_signed_v<_Res>)
192 return __int_traits<_Res>::__min <= __t
193 && __t <= __int_traits<_Res>::__max;
194 else if constexpr (is_signed_v<_Tp>)
195 return __t >= 0
196 && make_unsigned_t<_Tp>(__t) <= __int_traits<_Res>::__max;
197 else
198 return __t <= make_unsigned_t<_Res>(__int_traits<_Res>::__max);
199 }
200#endif // __cpp_lib_integer_comparison_functions
201
202#ifdef __cpp_lib_to_underlying // C++ >= 23
203 /// Convert an object of enumeration type to its underlying type.
204 template<typename _Tp>
205 [[nodiscard, __gnu__::__always_inline__]]
206 constexpr underlying_type_t<_Tp>
207 to_underlying(_Tp __value) noexcept
208 { return static_cast<underlying_type_t<_Tp>>(__value); }
209#endif
210
211#ifdef __cpp_lib_unreachable // C++ >= 23
212 /// Informs the compiler that program control flow never reaches this point.
213 /**
214 * Evaluating a call to this function results in undefined behaviour.
215 * This can be used as an assertion informing the compiler that certain
216 * conditions are impossible, for when the compiler is unable to determine
217 * that by itself.
218 *
219 * For example, it can be used to prevent warnings about reaching the
220 * end of a non-void function without returning.
221 *
222 * @since C++23
223 */
224 [[noreturn,__gnu__::__always_inline__]]
225 inline void
226 unreachable()
227 {
228#ifdef _GLIBCXX_DEBUG
229 std::__glibcxx_assert_fail(nullptr, 0, "std::unreachable()", nullptr);
230#elif defined _GLIBCXX_ASSERTIONS
231 __builtin_trap();
232#else
233 __builtin_unreachable();
234#endif
235 }
236#endif
237
238
239#ifdef __cpp_lib_observable_checkpoint // C++ >= 26
240 /// Informs the compiler that prior actions are considered observable.
241 /**
242 * This may be used to limit the extent to which optimisations based on the
243 * assumed unreachability of undefined behaviour can propagate to earlier
244 * code.
245 *
246 * @since C++26
247 */
248 [[__gnu__::__always_inline__]]
249 inline void
250 observable_checkpoint() noexcept
251 {
252 return __builtin_observable_checkpoint();
253 }
254#endif
255
256_GLIBCXX_END_NAMESPACE_VERSION
257} // namespace
258
259#endif
260
261#endif /* _GLIBCXX_UTILITY */