libstdc++
utility.h
Go to the documentation of this file.
1// Utilities used throughout the library -*- C++ -*-
2
3// Copyright (C) 2004-2026 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/** @file include/bits/utility.h
26 * This is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{utility}
28 *
29 * This file contains the parts of `<utility>` needed by other headers,
30 * so they don't need to include the whole of `<utility>`.
31 */
32
33#ifndef _GLIBCXX_UTILITY_H
34#define _GLIBCXX_UTILITY_H 1
35
36#ifdef _GLIBCXX_SYSHDR
37#pragma GCC system_header
38#endif
39
40#if __cplusplus >= 201103L
41
42#include <type_traits>
43#include <bits/move.h>
44#ifdef __glibcxx_constant_wrapper // C++ >= 26
45# include <bits/invoke.h>
46#endif
47
48namespace std _GLIBCXX_VISIBILITY(default)
49{
50_GLIBCXX_BEGIN_NAMESPACE_VERSION
51
52 /// Finds the size of a given tuple type.
53 template<typename _Tp>
54 struct tuple_size;
55
56 // _GLIBCXX_RESOLVE_LIB_DEFECTS
57 // 2313. tuple_size should always derive from integral_constant<size_t, N>
58 // 2770. tuple_size<const T> specialization is not SFINAE compatible
59
60 template<typename _Tp,
61 typename _Up = typename remove_cv<_Tp>::type,
62 typename = typename enable_if<is_same<_Tp, _Up>::value>::type,
63 size_t = tuple_size<_Tp>::value>
64 using __enable_if_has_tuple_size = _Tp;
65
66 template<typename _Tp>
67 struct tuple_size<const __enable_if_has_tuple_size<_Tp>>
68 : public tuple_size<_Tp> { };
69
70 template<typename _Tp>
71 struct tuple_size<volatile __enable_if_has_tuple_size<_Tp>>
72 : public tuple_size<_Tp> { };
73
74 template<typename _Tp>
75 struct tuple_size<const volatile __enable_if_has_tuple_size<_Tp>>
76 : public tuple_size<_Tp> { };
77
78#if __cplusplus >= 201703L
79 template<typename _Tp>
80 inline constexpr size_t tuple_size_v = tuple_size<_Tp>::value;
81#endif
82
83 /// Gives the type of the ith element of a given tuple type.
84 template<size_t __i, typename _Tp>
85 struct tuple_element;
86
87 // Duplicate of C++14's tuple_element_t for internal use in C++11 mode
88 template<size_t __i, typename _Tp>
89 using __tuple_element_t = typename tuple_element<__i, _Tp>::type;
90
91 template<size_t __i, typename _Tp>
92 struct tuple_element<__i, const _Tp>
93 {
94 using type = const __tuple_element_t<__i, _Tp>;
95 };
96
97 template<size_t __i, typename _Tp>
98 struct tuple_element<__i, volatile _Tp>
99 {
100 using type = volatile __tuple_element_t<__i, _Tp>;
101 };
102
103 template<size_t __i, typename _Tp>
104 struct tuple_element<__i, const volatile _Tp>
105 {
106 using type = const volatile __tuple_element_t<__i, _Tp>;
107 };
108
109#if __cplusplus >= 201402L
110
111 // Return the index of _Tp in _Types, if it occurs exactly once.
112 // Otherwise, return sizeof...(_Types).
113 template<typename _Tp, typename... _Types>
114 constexpr size_t
115 __find_uniq_type_in_pack()
116 {
117 constexpr size_t __sz = sizeof...(_Types);
118 constexpr bool __found[__sz] = { __is_same(_Tp, _Types) ... };
119 size_t __n = __sz;
120 for (size_t __i = 0; __i < __sz; ++__i)
121 {
122 if (__found[__i])
123 {
124 if (__n < __sz) // more than one _Tp found
125 return __sz;
126 __n = __i;
127 }
128 }
129 return __n;
130 }
131#endif // C++14
132
133// The standard says this macro and alias template should be in <tuple> but we
134// define them here, to be available in <array>, <utility> and <ranges> too.
135// _GLIBCXX_RESOLVE_LIB_DEFECTS
136// 3378. tuple_size_v/tuple_element_t should be available when
137// tuple_size/tuple_element are
138#ifdef __glibcxx_tuple_element_t // C++ >= 14
139 template<size_t __i, typename _Tp>
140 using tuple_element_t = typename tuple_element<__i, _Tp>::type;
141#endif
142
143#ifdef __glibcxx_constant_wrapper // C++ >= 26
144 // remove_cvref_t needed due PR115314
145 template<auto _Xv, typename _Vt = remove_cvref_t<decltype(_Xv)>>
146 struct constant_wrapper;
147
148 template<typename _Tp>
149 concept _ConstExprParam = requires
150 {
151 typename constant_wrapper<_Tp::value>;
152 };
153
154 struct _CwOperators
155 {
156 template<_ConstExprParam _Tp>
157 friend constexpr auto
158 operator+(_Tp) noexcept -> constant_wrapper<(+_Tp::value)>
159 { return {}; }
160
161 template<_ConstExprParam _Tp>
162 friend constexpr auto
163 operator-(_Tp) noexcept -> constant_wrapper<(-_Tp::value)>
164 { return {}; }
165
166 template<_ConstExprParam _Tp>
167 friend constexpr auto
168 operator~(_Tp) noexcept -> constant_wrapper<(~_Tp::value)>
169 { return {}; }
170
171 template<_ConstExprParam _Tp>
172 friend constexpr auto
173 operator!(_Tp) noexcept -> constant_wrapper<(!_Tp::value)>
174 { return {}; }
175
176 template<_ConstExprParam _Tp>
177 friend constexpr auto
178 operator&(_Tp) noexcept -> constant_wrapper<(&_Tp::value)>
179 { return {}; }
180
181 template<_ConstExprParam _Tp>
182 friend constexpr auto
183 operator*(_Tp) noexcept -> constant_wrapper<(*_Tp::value)>
184 { return {}; }
185
186 template<_ConstExprParam _Left, _ConstExprParam _Right>
187 friend constexpr auto
188 operator+(_Left, _Right) noexcept
189 -> constant_wrapper<(_Left::value + _Right::value)>
190 { return {}; }
191
192 template<_ConstExprParam _Left, _ConstExprParam _Right>
193 friend constexpr auto
194 operator-(_Left, _Right) noexcept
195 -> constant_wrapper<(_Left::value - _Right::value)>
196 { return {}; }
197
198 template<_ConstExprParam _Left, _ConstExprParam _Right>
199 friend constexpr auto
200 operator*(_Left, _Right) noexcept
201 -> constant_wrapper<(_Left::value * _Right::value)>
202 { return {}; }
203
204 template<_ConstExprParam _Left, _ConstExprParam _Right>
205 friend constexpr auto
206 operator/(_Left, _Right) noexcept
207 -> constant_wrapper<(_Left::value / _Right::value)>
208 { return {}; }
209
210 template<_ConstExprParam _Left, _ConstExprParam _Right>
211 friend constexpr auto
212 operator%(_Left, _Right) noexcept
213 -> constant_wrapper<(_Left::value % _Right::value)>
214 { return {}; }
215
216 template<_ConstExprParam _Left, _ConstExprParam _Right>
217 friend constexpr auto
218 operator<<(_Left, _Right) noexcept
219 -> constant_wrapper<(_Left::value << _Right::value)>
220 { return {}; }
221
222 template<_ConstExprParam _Left, _ConstExprParam _Right>
223 friend constexpr auto
224 operator>>(_Left, _Right) noexcept
225 -> constant_wrapper<(_Left::value >> _Right::value)>
226 { return {}; }
227
228 template<_ConstExprParam _Left, _ConstExprParam _Right>
229 friend constexpr auto
230 operator&(_Left, _Right) noexcept
231 -> constant_wrapper<(_Left::value & _Right::value)>
232 { return {}; }
233
234 template<_ConstExprParam _Left, _ConstExprParam _Right>
235 friend constexpr auto
236 operator|(_Left, _Right) noexcept
237 -> constant_wrapper<(_Left::value | _Right::value)>
238 { return {}; }
239
240 template<_ConstExprParam _Left, _ConstExprParam _Right>
241 friend constexpr auto
242 operator^(_Left, _Right) noexcept
243 -> constant_wrapper<(_Left::value ^ _Right::value)>
244 { return {}; }
245
246 template<_ConstExprParam _Left, _ConstExprParam _Right>
247 requires (!is_constructible_v<bool, decltype(_Left::value)>
248 || !is_constructible_v<bool, decltype(_Right::value)>)
249 friend constexpr auto
250 operator&&(_Left, _Right) noexcept
251 -> constant_wrapper<(_Left::value && _Right::value)>
252 { return {}; }
253
254 template<_ConstExprParam _Left, _ConstExprParam _Right>
255 requires (!is_constructible_v<bool, decltype(_Left::value)>
256 || !is_constructible_v<bool, decltype(_Right::value)>)
257 friend constexpr auto
258 operator||(_Left, _Right) noexcept
259 -> constant_wrapper<(_Left::value || _Right::value)>
260 { return {}; }
261
262 template<_ConstExprParam _Left, _ConstExprParam _Right>
263 friend constexpr auto
264 operator<=>(_Left, _Right) noexcept
265 -> constant_wrapper<(_Left::value <=> _Right::value)>
266 { return {}; }
267
268 template<_ConstExprParam _Left, _ConstExprParam _Right>
269 friend constexpr auto
270 operator<(_Left, _Right) noexcept
271 -> constant_wrapper<(_Left::value < _Right::value)>
272 { return {}; }
273
274 template<_ConstExprParam _Left, _ConstExprParam _Right>
275 friend constexpr auto
276 operator<=(_Left, _Right) noexcept
277 -> constant_wrapper<(_Left::value <= _Right::value)>
278 { return {}; }
279
280 template<_ConstExprParam _Left, _ConstExprParam _Right>
281 friend constexpr auto
282 operator==(_Left, _Right) noexcept
283 -> constant_wrapper<(_Left::value == _Right::value)>
284 { return {}; }
285
286 template<_ConstExprParam _Left, _ConstExprParam _Right>
287 friend constexpr auto
288 operator!=(_Left, _Right) noexcept
289 -> constant_wrapper<(_Left::value != _Right::value)>
290 { return {}; }
291
292 template<_ConstExprParam _Left, _ConstExprParam _Right>
293 friend constexpr auto
294 operator>(_Left, _Right) noexcept
295 -> constant_wrapper<(_Left::value > _Right::value)>
296 { return {}; }
297
298 template<_ConstExprParam _Left, _ConstExprParam _Right>
299 friend constexpr auto
300 operator>=(_Left, _Right) noexcept
301 -> constant_wrapper<(_Left::value >= _Right::value)>
302 { return {}; }
303
304 template<_ConstExprParam _Left, _ConstExprParam _Right>
305 friend constexpr auto
306 operator,(_Left, _Right) noexcept = delete;
307
308 template<_ConstExprParam _Left, _ConstExprParam _Right>
309 friend constexpr auto
310 operator->*(_Left, _Right) noexcept
311 -> constant_wrapper<_Left::value->*(_Right::value)>
312 { return {}; }
313
314 template<_ConstExprParam _Tp>
315 constexpr auto
316 operator++(this _Tp) noexcept
317 -> constant_wrapper<(++_Tp::value)>
318 { return {}; }
319
320 template<_ConstExprParam _Tp>
321 constexpr auto
322 operator++(this _Tp, int) noexcept
323 -> constant_wrapper<(_Tp::value++)>
324 { return {}; }
325
326 template<_ConstExprParam _Tp>
327 constexpr auto
328 operator--(this _Tp) noexcept
329 -> constant_wrapper<(--_Tp::value)>
330 { return {}; }
331
332 template<_ConstExprParam _Tp>
333 constexpr auto
334 operator--(this _Tp, int) noexcept
335 -> constant_wrapper<(_Tp::value--)>
336 { return {}; }
337
338 template<_ConstExprParam _Tp, _ConstExprParam _Right>
339 constexpr auto
340 operator+=(this _Tp, _Right) noexcept
341 -> constant_wrapper<(_Tp::value += _Right::value)>
342 { return {}; }
343
344 template<_ConstExprParam _Tp, _ConstExprParam _Right>
345 constexpr auto
346 operator-=(this _Tp, _Right) noexcept
347 -> constant_wrapper<(_Tp::value -= _Right::value)>
348 { return {}; }
349
350 template<_ConstExprParam _Tp, _ConstExprParam _Right>
351 constexpr auto
352 operator*=(this _Tp, _Right) noexcept
353 -> constant_wrapper<(_Tp::value *= _Right::value)>
354 { return {}; }
355
356 template<_ConstExprParam _Tp, _ConstExprParam _Right>
357 constexpr auto
358 operator/=(this _Tp, _Right) noexcept
359 -> constant_wrapper<(_Tp::value /= _Right::value)>
360 { return {}; }
361
362 template<_ConstExprParam _Tp, _ConstExprParam _Right>
363 constexpr auto
364 operator%=(this _Tp, _Right) noexcept
365 -> constant_wrapper<(_Tp::value %= _Right::value)>
366 { return {}; }
367
368 template<_ConstExprParam _Tp, _ConstExprParam _Right>
369 constexpr auto
370 operator&=(this _Tp, _Right) noexcept
371 -> constant_wrapper<(_Tp::value &= _Right::value)>
372 { return {}; }
373
374 template<_ConstExprParam _Tp, _ConstExprParam _Right>
375 constexpr auto
376 operator|=(this _Tp, _Right) noexcept
377 -> constant_wrapper<(_Tp::value |= _Right::value)>
378 { return {}; }
379
380 template<_ConstExprParam _Tp, _ConstExprParam _Right>
381 constexpr auto
382 operator^=(this _Tp, _Right) noexcept
383 -> constant_wrapper<(_Tp::value ^= _Right::value)>
384 { return {}; }
385
386 template<_ConstExprParam _Tp, _ConstExprParam _Right>
387 constexpr auto
388 operator<<=(this _Tp, _Right) noexcept
389 -> constant_wrapper<(_Tp::value <<= _Right::value)>
390 { return {}; }
391
392 template<_ConstExprParam _Tp, _ConstExprParam _Right>
393 constexpr auto
394 operator>>=(this _Tp, _Right) noexcept
395 -> constant_wrapper<(_Tp::value >>= _Right::value)>
396 { return {}; }
397 };
398
399 template<auto _Xv, typename _Vt>
400 struct constant_wrapper : _CwOperators
401 {
402 // Use decltype((_Xv)) instead of decltype(auto) due PR125188
403 static constexpr decltype((_Xv)) value = (_Xv);
404 using type = constant_wrapper;
405 using value_type = decltype(_Xv);
406 static_assert(is_same_v<value_type, _Vt>);
407
408 template<_ConstExprParam _Right>
409 constexpr auto
410 operator=(_Right) const noexcept
411 -> constant_wrapper<(value = _Right::value)>
412 { return {}; }
413
414 template<typename... _Args,
415 bool _ConstExprInvocable = requires {
416 requires (_ConstExprParam<remove_cvref_t<_Args>> && ...);
417 typename constant_wrapper<std::__invoke(value, remove_cvref_t<_Args>::value...)>;
418 }>
419 requires _ConstExprInvocable || is_invocable_v<const value_type&, _Args...>
420 static constexpr decltype(auto)
421 operator()(_Args&&... __args)
422 noexcept(requires {
423 requires _ConstExprInvocable || is_nothrow_invocable_v<const value_type&, _Args...>;
424 })
425 {
426 if constexpr (_ConstExprInvocable)
427 return constant_wrapper<std::__invoke(value, remove_cvref_t<_Args>::value...)>{};
428 else
429 return std::__invoke(value, std::forward<_Args>(__args)...);
430 }
431
432 template<typename... _Args,
433 bool _ConstExprSubscriptable = requires {
434 requires (_ConstExprParam<remove_cvref_t<_Args>> && ...);
435 typename constant_wrapper<value[remove_cvref_t<_Args>::value...]>;
436 }>
437 requires _ConstExprSubscriptable || requires { value[std::declval<_Args>()...]; }
438 static constexpr decltype(auto)
439 operator[](_Args&&... __args)
440 noexcept(requires {
441 requires _ConstExprSubscriptable || noexcept(value[std::declval<_Args>()...]);
442 })
443 {
444 if constexpr (_ConstExprSubscriptable)
445 return constant_wrapper<value[remove_cvref_t<_Args>::value...]>{};
446 else
447 return value[std::forward<_Args>(__args)...];
448 }
449
450 constexpr
451 operator decltype(value)() const noexcept
452 { return value; }
453 };
454
455 template<typename>
456 constexpr bool __is_constant_wrapper_v = false;
457
458 template<auto __cw, typename _Fn>
459 constexpr bool __is_constant_wrapper_v<constant_wrapper<__cw, _Fn>> = true;
460
461 template<auto _Xv>
462 constexpr auto cw = constant_wrapper<_Xv>{};
463#endif
464
465#ifdef __glibcxx_integer_sequence // C++ >= 14
466
467 /// Class template integer_sequence
468 template<typename _Tp, _Tp... _Idx>
469 struct integer_sequence
470 {
471#if __cplusplus >= 202002L
472 static_assert(is_integral_v<_Tp>);
473#endif
474 typedef _Tp value_type;
475 static constexpr size_t size() noexcept { return sizeof...(_Idx); }
476 };
477
478#if __glibcxx_integer_sequence >= 202511L // C++ >= 26
479 /** @brief Structured binding support for `integer_sequence`
480
481 * @since C++26
482 * @{
483 */
484 /// Structured binding support
485 template<typename _Tp, _Tp... _Idx>
486 struct tuple_size<integer_sequence<_Tp, _Idx...>>
487 : integral_constant<size_t, sizeof...(_Idx)> { };
488
489 template<size_t __i, class _Tp, _Tp... _Idx>
490 struct tuple_element<__i, integer_sequence<_Tp, _Idx...>>
491 {
492 static_assert(__i < sizeof...(_Idx));
493 using type = _Tp;
494 };
495
496 template<size_t __i, class _Tp, _Tp... _Idx>
497 struct tuple_element<__i, const integer_sequence<_Tp, _Idx...>>
498 {
499 static_assert(__i < sizeof...(_Idx));
500 using type = _Tp;
501 };
502
503 template<size_t __i, class _Tp, _Tp... _Idx>
504 [[nodiscard]]
505 constexpr _Tp
506 get(integer_sequence<_Tp, _Idx...>) noexcept
507 {
508 static_assert(__i < sizeof...(_Idx));
509 return _Idx...[__i];
510 }
511 /// @}
512#endif // __glibcxx_integer_sequence >= 202511L
513
514 /// Alias template make_integer_sequence
515 template<typename _Tp, _Tp _Num>
516 using make_integer_sequence
517#if __has_builtin(__make_integer_seq)
518 = __make_integer_seq<integer_sequence, _Tp, _Num>;
519#else
520 = integer_sequence<_Tp, __integer_pack(_Num)...>;
521#endif
522
523 /// Alias template index_sequence
524 template<size_t... _Idx>
525 using index_sequence = integer_sequence<size_t, _Idx...>;
526
527 /// Alias template make_index_sequence
528 template<size_t _Num>
529 using make_index_sequence = make_integer_sequence<size_t, _Num>;
530
531 /// Alias template index_sequence_for
532 template<typename... _Types>
533 using index_sequence_for = make_index_sequence<sizeof...(_Types)>;
534#endif // __glibcxx_integer_sequence
535
536#if __cpp_structured_bindings >= 202411L
537#if __has_builtin(__integer_pack)
538 template <auto _Num, typename _Tp = decltype(_Num)>
539 inline constexpr _Tp
540 _IotaArray[_Num] = {__integer_pack(_Tp(_Num))...};
541#elif defined __glibcxx_integer_sequence
542 template <auto _Num, typename _Tp = decltype(_Num), typename = make_integer_sequence<_Tp, _Num>>
543 inline constexpr _Tp
544 _IotaArray[_Num];
545
546 template <auto _Num, typename _Tp, _Tp... _Is>
547 inline constexpr _Tp
548 _IotaArray<_Num, _Tp, integer_sequence<_Tp, _Is...>>[_Num] = {_Is...};
549#endif // __integer_pack
550#endif // __cpp_structured_bindings >= 202411L
551
552#if __cplusplus >= 201703L
553
554 struct in_place_t {
555 explicit in_place_t() = default;
556 };
557
558 inline constexpr in_place_t in_place{};
559
560 template<typename _Tp> struct in_place_type_t
561 {
562 explicit in_place_type_t() = default;
563 };
564
565 template<typename _Tp>
566 inline constexpr in_place_type_t<_Tp> in_place_type{};
567
568 template<size_t _Idx> struct in_place_index_t
569 {
570 explicit in_place_index_t() = default;
571 };
572
573 template<size_t _Idx>
574 inline constexpr in_place_index_t<_Idx> in_place_index{};
575
576 template<typename>
577 inline constexpr bool __is_in_place_type_v = false;
578
579 template<typename _Tp>
580 inline constexpr bool __is_in_place_type_v<in_place_type_t<_Tp>> = true;
581
582 template<typename>
583 inline constexpr bool __is_in_place_index_v = false;
584
585 template<size_t _Nm>
586 inline constexpr bool __is_in_place_index_v<in_place_index_t<_Nm>> = true;
587
588#endif // C++17
589
590#if _GLIBCXX_USE_BUILTIN_TRAIT(__type_pack_element)
591 template<size_t _Np, typename... _Types>
592 struct _Nth_type
593 { using type = __type_pack_element<_Np, _Types...>; };
594#else
595 template<size_t _Np, typename... _Types>
596 struct _Nth_type
597 { };
598
599 template<typename _Tp0, typename... _Rest>
600 struct _Nth_type<0, _Tp0, _Rest...>
601 { using type = _Tp0; };
602
603 template<typename _Tp0, typename _Tp1, typename... _Rest>
604 struct _Nth_type<1, _Tp0, _Tp1, _Rest...>
605 { using type = _Tp1; };
606
607 template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
608 struct _Nth_type<2, _Tp0, _Tp1, _Tp2, _Rest...>
609 { using type = _Tp2; };
610
611 template<size_t _Np, typename _Tp0, typename _Tp1, typename _Tp2,
612 typename... _Rest>
613#if __cpp_concepts
614 requires (_Np >= 3)
615#endif
616 struct _Nth_type<_Np, _Tp0, _Tp1, _Tp2, _Rest...>
617 : _Nth_type<_Np - 3, _Rest...>
618 { };
619
620#if ! __cpp_concepts // Need additional specializations to avoid ambiguities.
621 template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
622 struct _Nth_type<0, _Tp0, _Tp1, _Tp2, _Rest...>
623 { using type = _Tp0; };
624
625 template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
626 struct _Nth_type<1, _Tp0, _Tp1, _Tp2, _Rest...>
627 { using type = _Tp1; };
628#endif
629#endif
630
631#if __glibcxx_ranges
632 namespace ranges::__detail
633 {
634 template<typename _Range>
635 inline constexpr bool __is_subrange = false;
636 } // namespace __detail
637#endif
638
639 // A class (and instance) which can be used in 'tie' when an element
640 // of a tuple is not required.
641 struct _Swallow_assign
642 {
643 template<class _Tp>
644 constexpr const _Swallow_assign&
645 operator=(const _Tp&) const noexcept
646 { return *this; }
647 };
648
649 // _GLIBCXX_RESOLVE_LIB_DEFECTS
650 // 2773. Making std::ignore constexpr
651 /** Used with `std::tie` to ignore an element of a tuple
652 *
653 * When using `std::tie` to assign the elements of a tuple to variables,
654 * unwanted elements can be ignored by using `std::ignore`. For example:
655 *
656 * ```
657 * int x, y;
658 * std::tie(x, std::ignore, y) = std::make_tuple(1, 2, 3);
659 * ```
660 *
661 * This assignment will perform `x=1; std::ignore=2; y=3;` which results
662 * in the second element being ignored.
663 *
664 * @since C++11
665 */
666 _GLIBCXX17_INLINE constexpr _Swallow_assign ignore{};
667
668#if __glibcxx_flat_map || __glibcxx_flat_set // >= C++23
669 struct sorted_unique_t { explicit sorted_unique_t() = default; };
670 inline constexpr sorted_unique_t sorted_unique{};
671
672 struct sorted_equivalent_t { explicit sorted_equivalent_t() = default; };
673 inline constexpr sorted_equivalent_t sorted_equivalent{};
674#endif
675
676_GLIBCXX_END_NAMESPACE_VERSION
677} // namespace
678
679#endif // C++11
680#endif /* _GLIBCXX_UTILITY_H */
std::declval
auto declval() noexcept -> decltype(__declval< _Tp >(0))
Definition type_traits:2741
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:92
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition move.h:72
std
ISO C++ entities toplevel namespace is std.
std::make_index_sequence
make_integer_sequence< size_t, _Num > make_index_sequence
Alias template make_index_sequence.
Definition utility.h:527
std::index_sequence
integer_sequence< size_t, _Idx... > index_sequence
Alias template index_sequence.
Definition utility.h:523
std::make_integer_sequence
__make_integer_seq< integer_sequence, _Tp, _Num > make_integer_sequence
Alias template make_integer_sequence.
Definition utility.h:516
std::ignore
constexpr _Swallow_assign ignore
Definition utility.h:664
std::index_sequence_for
make_index_sequence< sizeof...(_Types)> index_sequence_for
Alias template index_sequence_for.
Definition utility.h:531
std::integral_constant
integral_constant
Definition type_traits:96
std::enable_if
Define a member typedef type only if a boolean constant is true.
Definition type_traits:137
std::tuple_size
Finds the size of a given tuple type.
Definition utility.h:54
std::tuple_element
Gives the type of the ith element of a given tuple type.
Definition utility.h:85
std::integer_sequence
Class template integer_sequence.
Definition utility.h:470