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 template<typename _Tp>
145 struct _CwFixedValue
146 {
147 using __type = _Tp;
148
149 constexpr
150 _CwFixedValue(__type __v) noexcept
151 : _M_data(__v) { }
152
153 __type _M_data;
154 };
155
156 template<typename _Tp, size_t _Extent>
157 struct _CwFixedValue<_Tp[_Extent]>
158 {
159 using __type = _Tp[_Extent];
160
161 constexpr
162 _CwFixedValue(_Tp (&__arr)[_Extent]) noexcept
163 : _CwFixedValue(__arr, typename _Build_index_tuple<_Extent>::__type())
164 { }
165
166 template<size_t... _Indices>
167 constexpr
168 _CwFixedValue(_Tp (&__arr)[_Extent], _Index_tuple<_Indices...>) noexcept
169 : _M_data{__arr[_Indices]...}
170 { }
171
172 _Tp _M_data[_Extent];
173 };
174
175 template<typename _Tp, size_t _Extent>
176 _CwFixedValue(_Tp (&)[_Extent]) -> _CwFixedValue<_Tp[_Extent]>;
177
178 template<_CwFixedValue _Xv,
179 typename = typename decltype(_CwFixedValue(_Xv))::__type>
180 struct constant_wrapper;
181
182 template<typename _Tp>
183 concept _ConstExprParam = requires
184 {
185 typename constant_wrapper<_Tp::value>;
186 };
187
188 struct _CwOperators
189 {
190 template<_ConstExprParam _Tp>
191 friend constexpr auto
192 operator+(_Tp) noexcept -> constant_wrapper<(+_Tp::value)>
193 { return {}; }
194
195 template<_ConstExprParam _Tp>
196 friend constexpr auto
197 operator-(_Tp) noexcept -> constant_wrapper<(-_Tp::value)>
198 { return {}; }
199
200 template<_ConstExprParam _Tp>
201 friend constexpr auto
202 operator~(_Tp) noexcept -> constant_wrapper<(~_Tp::value)>
203 { return {}; }
204
205 template<_ConstExprParam _Tp>
206 friend constexpr auto
207 operator!(_Tp) noexcept -> constant_wrapper<(!_Tp::value)>
208 { return {}; }
209
210 template<_ConstExprParam _Tp>
211 friend constexpr auto
212 operator&(_Tp) noexcept -> constant_wrapper<(&_Tp::value)>
213 { return {}; }
214
215 template<_ConstExprParam _Tp>
216 friend constexpr auto
217 operator*(_Tp) noexcept -> constant_wrapper<(*_Tp::value)>
218 { return {}; }
219
220 template<_ConstExprParam _Left, _ConstExprParam _Right>
221 friend constexpr auto
222 operator+(_Left, _Right) noexcept
223 -> constant_wrapper<(_Left::value + _Right::value)>
224 { return {}; }
225
226 template<_ConstExprParam _Left, _ConstExprParam _Right>
227 friend constexpr auto
228 operator-(_Left, _Right) noexcept
229 -> constant_wrapper<(_Left::value - _Right::value)>
230 { return {}; }
231
232 template<_ConstExprParam _Left, _ConstExprParam _Right>
233 friend constexpr auto
234 operator*(_Left, _Right) noexcept
235 -> constant_wrapper<(_Left::value * _Right::value)>
236 { return {}; }
237
238 template<_ConstExprParam _Left, _ConstExprParam _Right>
239 friend constexpr auto
240 operator/(_Left, _Right) noexcept
241 -> constant_wrapper<(_Left::value / _Right::value)>
242 { return {}; }
243
244 template<_ConstExprParam _Left, _ConstExprParam _Right>
245 friend constexpr auto
246 operator%(_Left, _Right) noexcept
247 -> constant_wrapper<(_Left::value % _Right::value)>
248 { return {}; }
249
250 template<_ConstExprParam _Left, _ConstExprParam _Right>
251 friend constexpr auto
252 operator<<(_Left, _Right) noexcept
253 -> constant_wrapper<(_Left::value << _Right::value)>
254 { return {}; }
255
256 template<_ConstExprParam _Left, _ConstExprParam _Right>
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 requires (!is_constructible_v<bool, decltype(_Left::value)>
282 || !is_constructible_v<bool, decltype(_Right::value)>)
283 friend constexpr auto
284 operator&&(_Left, _Right) noexcept
285 -> constant_wrapper<(_Left::value && _Right::value)>
286 { return {}; }
287
288 template<_ConstExprParam _Left, _ConstExprParam _Right>
289 requires (!is_constructible_v<bool, decltype(_Left::value)>
290 || !is_constructible_v<bool, decltype(_Right::value)>)
291 friend constexpr auto
292 operator||(_Left, _Right) noexcept
293 -> constant_wrapper<(_Left::value || _Right::value)>
294 { return {}; }
295
296 template<_ConstExprParam _Left, _ConstExprParam _Right>
297 friend constexpr auto
298 operator<=>(_Left, _Right) noexcept
299 -> constant_wrapper<(_Left::value <=> _Right::value)>
300 { return {}; }
301
302 template<_ConstExprParam _Left, _ConstExprParam _Right>
303 friend constexpr auto
304 operator<(_Left, _Right) noexcept
305 -> constant_wrapper<(_Left::value < _Right::value)>
306 { return {}; }
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 _Left, _ConstExprParam _Right>
315 friend constexpr auto
316 operator==(_Left, _Right) noexcept
317 -> constant_wrapper<(_Left::value == _Right::value)>
318 { return {}; }
319
320 template<_ConstExprParam _Left, _ConstExprParam _Right>
321 friend constexpr auto
322 operator!=(_Left, _Right) noexcept
323 -> constant_wrapper<(_Left::value != _Right::value)>
324 { return {}; }
325
326 template<_ConstExprParam _Left, _ConstExprParam _Right>
327 friend constexpr auto
328 operator>(_Left, _Right) noexcept
329 -> constant_wrapper<(_Left::value > _Right::value)>
330 { return {}; }
331
332 template<_ConstExprParam _Left, _ConstExprParam _Right>
333 friend constexpr auto
334 operator>=(_Left, _Right) noexcept
335 -> constant_wrapper<(_Left::value >= _Right::value)>
336 { return {}; }
337
338 template<_ConstExprParam _Left, _ConstExprParam _Right>
339 friend constexpr auto
340 operator,(_Left, _Right) noexcept = delete;
341
342 template<_ConstExprParam _Left, _ConstExprParam _Right>
343 friend constexpr auto
344 operator->*(_Left, _Right) noexcept
345 -> constant_wrapper<_Left::value->*(_Right::value)>
346 { return {}; }
347
348 template<_ConstExprParam _Tp>
349 constexpr auto
350 operator++(this _Tp) noexcept
351 -> constant_wrapper<(++_Tp::value)>
352 { return {}; }
353
354 template<_ConstExprParam _Tp>
355 constexpr auto
356 operator++(this _Tp, int) noexcept
357 -> constant_wrapper<(_Tp::value++)>
358 { return {}; }
359
360 template<_ConstExprParam _Tp>
361 constexpr auto
362 operator--(this _Tp) noexcept
363 -> constant_wrapper<(--_Tp::value)>
364 { return {}; }
365
366 template<_ConstExprParam _Tp>
367 constexpr auto
368 operator--(this _Tp, int) noexcept
369 -> constant_wrapper<(_Tp::value--)>
370 { return {}; }
371
372 template<_ConstExprParam _Tp, _ConstExprParam _Right>
373 constexpr auto
374 operator+=(this _Tp, _Right) noexcept
375 -> constant_wrapper<(_Tp::value += _Right::value)>
376 { return {}; }
377
378 template<_ConstExprParam _Tp, _ConstExprParam _Right>
379 constexpr auto
380 operator-=(this _Tp, _Right) noexcept
381 -> constant_wrapper<(_Tp::value -= _Right::value)>
382 { return {}; }
383
384 template<_ConstExprParam _Tp, _ConstExprParam _Right>
385 constexpr auto
386 operator*=(this _Tp, _Right) noexcept
387 -> constant_wrapper<(_Tp::value *= _Right::value)>
388 { return {}; }
389
390 template<_ConstExprParam _Tp, _ConstExprParam _Right>
391 constexpr auto
392 operator/=(this _Tp, _Right) noexcept
393 -> constant_wrapper<(_Tp::value /= _Right::value)>
394 { return {}; }
395
396 template<_ConstExprParam _Tp, _ConstExprParam _Right>
397 constexpr auto
398 operator%=(this _Tp, _Right) noexcept
399 -> constant_wrapper<(_Tp::value %= _Right::value)>
400 { return {}; }
401
402 template<_ConstExprParam _Tp, _ConstExprParam _Right>
403 constexpr auto
404 operator&=(this _Tp, _Right) noexcept
405 -> constant_wrapper<(_Tp::value &= _Right::value)>
406 { return {}; }
407
408 template<_ConstExprParam _Tp, _ConstExprParam _Right>
409 constexpr auto
410 operator|=(this _Tp, _Right) noexcept
411 -> constant_wrapper<(_Tp::value |= _Right::value)>
412 { return {}; }
413
414 template<_ConstExprParam _Tp, _ConstExprParam _Right>
415 constexpr auto
416 operator^=(this _Tp, _Right) noexcept
417 -> constant_wrapper<(_Tp::value ^= _Right::value)>
418 { return {}; }
419
420 template<_ConstExprParam _Tp, _ConstExprParam _Right>
421 constexpr auto
422 operator<<=(this _Tp, _Right) noexcept
423 -> constant_wrapper<(_Tp::value <<= _Right::value)>
424 { return {}; }
425
426 template<_ConstExprParam _Tp, _ConstExprParam _Right>
427 constexpr auto
428 operator>>=(this _Tp, _Right) noexcept
429 -> constant_wrapper<(_Tp::value >>= _Right::value)>
430 { return {}; }
431 };
432
433 template<_CwFixedValue _Xv, typename>
434 struct constant_wrapper : _CwOperators
435 {
436 static constexpr const auto& value = _Xv._M_data;
437 using type = constant_wrapper;
438 using value_type = typename decltype(_Xv)::__type;
439
440 template<_ConstExprParam _Right>
441 constexpr auto
442 operator=(_Right) const noexcept
443 -> constant_wrapper<(value = _Right::value)>
444 { return {}; }
445
446 template<typename... _Args,
447 bool _ConstExprInvocable = requires {
448 requires (_ConstExprParam<remove_cvref_t<_Args>> && ...);
449 typename constant_wrapper<std::__invoke(value, remove_cvref_t<_Args>::value...)>;
450 }>
451 requires _ConstExprInvocable || is_invocable_v<const value_type&, _Args...>
452 static constexpr decltype(auto)
453 operator()(_Args&&... __args)
454 noexcept(requires {
455 requires _ConstExprInvocable || is_nothrow_invocable_v<const value_type&, _Args...>;
456 })
457 {
458 if constexpr (_ConstExprInvocable)
459 return constant_wrapper<std::__invoke(value, remove_cvref_t<_Args>::value...)>{};
460 else
461 return std::__invoke(value, std::forward<_Args>(__args)...);
462 }
463
464 template<typename... _Args,
465 bool _ConstExprSubscriptable = requires {
466 requires (_ConstExprParam<remove_cvref_t<_Args>> && ...);
467 typename constant_wrapper<value[remove_cvref_t<_Args>::value...]>;
468 }>
469 requires _ConstExprSubscriptable || requires { value[std::declval<_Args>()...]; }
470 static constexpr decltype(auto)
471 operator[](_Args&&... __args)
472 noexcept(requires {
473 requires _ConstExprSubscriptable || noexcept(value[std::declval<_Args>()...]);
474 })
475 {
476 if constexpr (_ConstExprSubscriptable)
477 return constant_wrapper<value[remove_cvref_t<_Args>::value...]>{};
478 else
479 return value[std::forward<_Args>(__args)...];
480 }
481
482 constexpr
483 operator decltype(value)() const noexcept
484 { return value; }
485 };
486
487 template<typename>
488 constexpr bool __is_constant_wrapper_v = false;
489
490 template<auto __cw, typename _Fn>
491 constexpr bool __is_constant_wrapper_v<constant_wrapper<__cw, _Fn>> = true;
492
493 template<_CwFixedValue _Tp>
494 constexpr auto cw = constant_wrapper<_Tp>{};
495#endif
496
497#ifdef __glibcxx_integer_sequence // C++ >= 14
498
499 /// Class template integer_sequence
500 template<typename _Tp, _Tp... _Idx>
501 struct integer_sequence
502 {
503#if __cplusplus >= 202002L
504 static_assert(is_integral_v<_Tp>);
505#endif
506 typedef _Tp value_type;
507 static constexpr size_t size() noexcept { return sizeof...(_Idx); }
508 };
509
510#if __glibcxx_integer_sequence >= 202511L // C++ >= 26
511 /** @brief Structured binding support for `integer_sequence`
512
513 * @since C++26
514 * @{
515 */
516 /// Structured binding support
517 template<typename _Tp, _Tp... _Idx>
518 struct tuple_size<integer_sequence<_Tp, _Idx...>>
519 : integral_constant<size_t, sizeof...(_Idx)> { };
520
521 template<size_t __i, class _Tp, _Tp... _Idx>
522 struct tuple_element<__i, integer_sequence<_Tp, _Idx...>>
523 {
524 static_assert(__i < sizeof...(_Idx));
525 using type = _Tp;
526 };
527
528 template<size_t __i, class _Tp, _Tp... _Idx>
529 struct tuple_element<__i, const integer_sequence<_Tp, _Idx...>>
530 {
531 static_assert(__i < sizeof...(_Idx));
532 using type = _Tp;
533 };
534
535 template<size_t __i, class _Tp, _Tp... _Idx>
536 [[nodiscard]]
537 constexpr _Tp
538 get(integer_sequence<_Tp, _Idx...>) noexcept
539 {
540 static_assert(__i < sizeof...(_Idx));
541 return _Idx...[__i];
542 }
543 /// @}
544#endif // __glibcxx_integer_sequence >= 202511L
545
546 /// Alias template make_integer_sequence
547 template<typename _Tp, _Tp _Num>
548 using make_integer_sequence
549#if __has_builtin(__make_integer_seq)
550 = __make_integer_seq<integer_sequence, _Tp, _Num>;
551#else
552 = integer_sequence<_Tp, __integer_pack(_Num)...>;
553#endif
554
555 /// Alias template index_sequence
556 template<size_t... _Idx>
557 using index_sequence = integer_sequence<size_t, _Idx...>;
558
559 /// Alias template make_index_sequence
560 template<size_t _Num>
561 using make_index_sequence = make_integer_sequence<size_t, _Num>;
562
563 /// Alias template index_sequence_for
564 template<typename... _Types>
565 using index_sequence_for = make_index_sequence<sizeof...(_Types)>;
566#endif // __glibcxx_integer_sequence
567
568#if __cpp_structured_bindings >= 202411L
569#if __has_builtin(__integer_pack)
570 template <auto _Num, typename _Tp = decltype(_Num)>
571 inline constexpr _Tp
572 _IotaArray[_Num] = {__integer_pack(_Tp(_Num))...};
573#elif defined __glibcxx_integer_sequence
574 template <auto _Num, typename _Tp = decltype(_Num), typename = make_integer_sequence<_Tp, _Num>>
575 inline constexpr _Tp
576 _IotaArray[_Num];
577
578 template <auto _Num, typename _Tp, _Tp... _Is>
579 inline constexpr _Tp
580 _IotaArray<_Num, _Tp, integer_sequence<_Tp, _Is...>>[_Num] = {_Is...};
581#endif // __integer_pack
582#endif // __cpp_structured_bindings >= 202411L
583
584#if __cplusplus >= 201703L
585
586 struct in_place_t {
587 explicit in_place_t() = default;
588 };
589
590 inline constexpr in_place_t in_place{};
591
592 template<typename _Tp> struct in_place_type_t
593 {
594 explicit in_place_type_t() = default;
595 };
596
597 template<typename _Tp>
598 inline constexpr in_place_type_t<_Tp> in_place_type{};
599
600 template<size_t _Idx> struct in_place_index_t
601 {
602 explicit in_place_index_t() = default;
603 };
604
605 template<size_t _Idx>
606 inline constexpr in_place_index_t<_Idx> in_place_index{};
607
608 template<typename>
609 inline constexpr bool __is_in_place_type_v = false;
610
611 template<typename _Tp>
612 inline constexpr bool __is_in_place_type_v<in_place_type_t<_Tp>> = true;
613
614 template<typename>
615 inline constexpr bool __is_in_place_index_v = false;
616
617 template<size_t _Nm>
618 inline constexpr bool __is_in_place_index_v<in_place_index_t<_Nm>> = true;
619
620#endif // C++17
621
622#if _GLIBCXX_USE_BUILTIN_TRAIT(__type_pack_element)
623 template<size_t _Np, typename... _Types>
624 struct _Nth_type
625 { using type = __type_pack_element<_Np, _Types...>; };
626#else
627 template<size_t _Np, typename... _Types>
628 struct _Nth_type
629 { };
630
631 template<typename _Tp0, typename... _Rest>
632 struct _Nth_type<0, _Tp0, _Rest...>
633 { using type = _Tp0; };
634
635 template<typename _Tp0, typename _Tp1, typename... _Rest>
636 struct _Nth_type<1, _Tp0, _Tp1, _Rest...>
637 { using type = _Tp1; };
638
639 template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
640 struct _Nth_type<2, _Tp0, _Tp1, _Tp2, _Rest...>
641 { using type = _Tp2; };
642
643 template<size_t _Np, typename _Tp0, typename _Tp1, typename _Tp2,
644 typename... _Rest>
645#if __cpp_concepts
646 requires (_Np >= 3)
647#endif
648 struct _Nth_type<_Np, _Tp0, _Tp1, _Tp2, _Rest...>
649 : _Nth_type<_Np - 3, _Rest...>
650 { };
651
652#if ! __cpp_concepts // Need additional specializations to avoid ambiguities.
653 template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
654 struct _Nth_type<0, _Tp0, _Tp1, _Tp2, _Rest...>
655 { using type = _Tp0; };
656
657 template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
658 struct _Nth_type<1, _Tp0, _Tp1, _Tp2, _Rest...>
659 { using type = _Tp1; };
660#endif
661#endif
662
663#if __glibcxx_ranges
664 namespace ranges::__detail
665 {
666 template<typename _Range>
667 inline constexpr bool __is_subrange = false;
668 } // namespace __detail
669#endif
670
671 // A class (and instance) which can be used in 'tie' when an element
672 // of a tuple is not required.
673 struct _Swallow_assign
674 {
675 template<class _Tp>
676 constexpr const _Swallow_assign&
677 operator=(const _Tp&) const noexcept
678 { return *this; }
679 };
680
681 // _GLIBCXX_RESOLVE_LIB_DEFECTS
682 // 2773. Making std::ignore constexpr
683 /** Used with `std::tie` to ignore an element of a tuple
684 *
685 * When using `std::tie` to assign the elements of a tuple to variables,
686 * unwanted elements can be ignored by using `std::ignore`. For example:
687 *
688 * ```
689 * int x, y;
690 * std::tie(x, std::ignore, y) = std::make_tuple(1, 2, 3);
691 * ```
692 *
693 * This assignment will perform `x=1; std::ignore=2; y=3;` which results
694 * in the second element being ignored.
695 *
696 * @since C++11
697 */
698 _GLIBCXX17_INLINE constexpr _Swallow_assign ignore{};
699
700#if __glibcxx_flat_map || __glibcxx_flat_set // >= C++23
701 struct sorted_unique_t { explicit sorted_unique_t() = default; };
702 inline constexpr sorted_unique_t sorted_unique{};
703
704 struct sorted_equivalent_t { explicit sorted_equivalent_t() = default; };
705 inline constexpr sorted_equivalent_t sorted_equivalent{};
706#endif
707
708_GLIBCXX_END_NAMESPACE_VERSION
709} // namespace
710
711#endif // C++11
712#endif /* _GLIBCXX_UTILITY_H */
713