libstdc++
expected
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1// <expected> -*- 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/expected
26 * This is a Standard C++ Library header.
27 */
28
29#ifndef _GLIBCXX_EXPECTED
30#define _GLIBCXX_EXPECTED
31
32#ifdef _GLIBCXX_SYSHDR
33#pragma GCC system_header
34#endif
35
36#define __glibcxx_want_expected
37#define __glibcxx_want_freestanding_expected
38#define __glibcxx_want_constrained_equality
39#include <bits/version.h>
40
41#ifdef __cpp_lib_expected // C++ >= 23 && __cpp_concepts >= 202002L
42#include <initializer_list>
43#include <bits/exception.h> // exception
44#include <bits/invoke.h> // __invoke
45#include <bits/stl_construct.h> // construct_at
46#include <bits/utility.h> // in_place_t
47
48namespace std _GLIBCXX_VISIBILITY(default)
49{
50_GLIBCXX_BEGIN_NAMESPACE_VERSION
51
52 /**
53 * @defgroup expected_values Expected values
54 * @addtogroup utilities
55 * @since C++23
56 * @{
57 */
58
59 /// Discriminated union that holds an expected value or an error value.
60 /**
61 * @since C++23
62 */
63 template<typename _Tp, typename _Er>
64 class expected;
65
66 /// Wrapper type used to pass an error value to a `std::expected`.
67 /**
68 * @since C++23
69 */
70 template<typename _Er>
71 class unexpected;
72
73 /// Exception thrown by std::expected when the value() is not present.
74 /**
75 * @since C++23
76 */
77 template<typename _Er>
78 class bad_expected_access;
79
80 template<>
81 class bad_expected_access<void> : public exception
82 {
83 protected:
84 bad_expected_access() noexcept { }
85 bad_expected_access(const bad_expected_access&) noexcept = default;
86 bad_expected_access(bad_expected_access&&) noexcept = default;
87 bad_expected_access& operator=(const bad_expected_access&) noexcept = default;
88 bad_expected_access& operator=(bad_expected_access&&) noexcept = default;
89 ~bad_expected_access() = default;
90
91 public:
92
93 [[nodiscard]]
94 const char*
95 what() const noexcept override
96 { return "bad access to std::expected without expected value"; }
97 };
98
99 template<typename _Er>
100 class bad_expected_access : public bad_expected_access<void> {
101 public:
102 explicit
103 bad_expected_access(_Er __e) : _M_unex(std::move(__e)) { }
104
105 // XXX const char* what() const noexcept override;
106
107 [[nodiscard]]
108 _Er&
109 error() & noexcept
110 { return _M_unex; }
111
112 [[nodiscard]]
113 const _Er&
114 error() const & noexcept
115 { return _M_unex; }
116
117 [[nodiscard]]
118 _Er&&
119 error() && noexcept
120 { return std::move(_M_unex); }
121
122 [[nodiscard]]
123 const _Er&&
124 error() const && noexcept
125 { return std::move(_M_unex); }
126
127 private:
128 _Er _M_unex;
129 };
130
131 /// Tag type for constructing unexpected values in a std::expected
132 /**
133 * @since C++23
134 */
135 struct unexpect_t
136 {
137 explicit unexpect_t() = default;
138 };
139
140 /// Tag for constructing unexpected values in a std::expected
141 /**
142 * @since C++23
143 */
144 inline constexpr unexpect_t unexpect{};
145
146/// @cond undocumented
147namespace __expected
148{
149 template<typename _Tp>
150 constexpr bool __is_expected = false;
151 template<typename _Tp, typename _Er>
152 constexpr bool __is_expected<expected<_Tp, _Er>> = true;
153
154 template<typename _Tp>
155 constexpr bool __is_unexpected = false;
156 template<typename _Tp>
157 constexpr bool __is_unexpected<unexpected<_Tp>> = true;
158
159 template<typename _Fn, typename _Tp>
160 using __result = remove_cvref_t<invoke_result_t<_Fn&&, _Tp&&>>;
161 template<typename _Fn, typename _Tp>
162 using __result_xform = remove_cv_t<invoke_result_t<_Fn&&, _Tp&&>>;
163 template<typename _Fn>
164 using __result0 = remove_cvref_t<invoke_result_t<_Fn&&>>;
165 template<typename _Fn>
166 using __result0_xform = remove_cv_t<invoke_result_t<_Fn&&>>;
167
168 template<typename _Er>
169 concept __can_be_unexpected
170 = is_object_v<_Er> && (!is_array_v<_Er>)
171 && (!__expected::__is_unexpected<_Er>)
172 && (!is_const_v<_Er>) && (!is_volatile_v<_Er>);
173
174 // Tag types for in-place construction from an invocation result.
175 struct __in_place_inv { };
176 struct __unexpect_inv { };
177}
178/// @endcond
179
180 template<typename _Er>
181 class unexpected
182 {
183 static_assert( __expected::__can_be_unexpected<_Er> );
184
185 public:
186 constexpr unexpected(const unexpected&) = default;
187 constexpr unexpected(unexpected&&) = default;
188
189 template<typename _Err = _Er>
190 requires (!is_same_v<remove_cvref_t<_Err>, unexpected>)
191 && (!is_same_v<remove_cvref_t<_Err>, in_place_t>)
192 && is_constructible_v<_Er, _Err>
193 constexpr explicit
194 unexpected(_Err&& __e)
195 noexcept(is_nothrow_constructible_v<_Er, _Err>)
196 : _M_unex(std::forward<_Err>(__e))
197 { }
198
199 template<typename... _Args>
200 requires is_constructible_v<_Er, _Args...>
201 constexpr explicit
202 unexpected(in_place_t, _Args&&... __args)
203 noexcept(is_nothrow_constructible_v<_Er, _Args...>)
204 : _M_unex(std::forward<_Args>(__args)...)
205 { }
206
207 template<typename _Up, typename... _Args>
208 requires is_constructible_v<_Er, initializer_list<_Up>&, _Args...>
209 constexpr explicit
210 unexpected(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
211 noexcept(is_nothrow_constructible_v<_Er, initializer_list<_Up>&,
212 _Args...>)
213 : _M_unex(__il, std::forward<_Args>(__args)...)
214 { }
215
216 constexpr unexpected& operator=(const unexpected&) = default;
217 constexpr unexpected& operator=(unexpected&&) = default;
218
219
220 [[nodiscard]]
221 constexpr const _Er&
222 error() const & noexcept { return _M_unex; }
223
224 [[nodiscard]]
225 constexpr _Er&
226 error() & noexcept { return _M_unex; }
227
228 [[nodiscard]]
229 constexpr const _Er&&
230 error() const && noexcept { return std::move(_M_unex); }
231
232 [[nodiscard]]
233 constexpr _Er&&
234 error() && noexcept { return std::move(_M_unex); }
235
236 constexpr void
237 swap(unexpected& __other) noexcept(is_nothrow_swappable_v<_Er>)
238 requires is_swappable_v<_Er>
239 {
240 using std::swap;
241 swap(_M_unex, __other._M_unex);
242 }
243
244 template<typename _Err>
245 [[nodiscard]]
246 friend constexpr bool
247 operator==(const unexpected& __x, const unexpected<_Err>& __y)
248 { return __x._M_unex == __y.error(); }
249
250 friend constexpr void
251 swap(unexpected& __x, unexpected& __y) noexcept(noexcept(__x.swap(__y)))
252 requires is_swappable_v<_Er>
253 { __x.swap(__y); }
254
255 private:
256 _Er _M_unex;
257 };
258
259 template<typename _Er> unexpected(_Er) -> unexpected<_Er>;
260
261/// @cond undocumented
262namespace __expected
263{
264 template<typename _Tp>
265 struct _Guard
266 {
267 static_assert( is_nothrow_move_constructible_v<_Tp> );
268
269 constexpr explicit
270 _Guard(_Tp& __x)
271 : _M_guarded(__builtin_addressof(__x)), _M_tmp(std::move(__x)) // nothrow
272 { std::destroy_at(_M_guarded); }
273
274 constexpr
275 ~_Guard()
276 {
277 if (_M_guarded) [[unlikely]]
278 std::construct_at(_M_guarded, std::move(_M_tmp));
279 }
280
281 _Guard(const _Guard&) = delete;
282 _Guard& operator=(const _Guard&) = delete;
283
284 constexpr _Tp&&
285 release() noexcept
286 {
287 _M_guarded = nullptr;
288 return std::move(_M_tmp);
289 }
290
291 private:
292 _Tp* _M_guarded;
293 _Tp _M_tmp;
294 };
295
296 // reinit-expected helper from [expected.object.assign]
297 template<typename _Tp, typename _Up, typename _Vp>
298 constexpr void
299 __reinit(_Tp* __newval, _Up* __oldval, _Vp&& __arg)
300 noexcept(is_nothrow_constructible_v<_Tp, _Vp>)
301 {
302 if constexpr (is_nothrow_constructible_v<_Tp, _Vp>)
303 {
304 std::destroy_at(__oldval);
305 std::construct_at(__newval, std::forward<_Vp>(__arg));
306 }
307 else if constexpr (is_nothrow_move_constructible_v<_Tp>)
308 {
309 _Tp __tmp(std::forward<_Vp>(__arg)); // might throw
310 std::destroy_at(__oldval);
311 std::construct_at(__newval, std::move(__tmp));
312 }
313 else
314 {
315 _Guard<_Up> __guard(*__oldval);
316 std::construct_at(__newval, std::forward<_Vp>(__arg)); // might throw
317 __guard.release();
318 }
319 }
320
321 // _GLIBCXX_RESOLVE_LIB_DEFECTS
322 // 3836. std::expected<bool, E1> conversion constructor
323 // expected(const expected<U, G>&) should take precedence over
324 // expected(U&&) with operator bool
325
326 // If T is cv bool, remove_cvref_t<U> is not a specialization of expected.
327 template<typename _Tp, typename _Up>
328 concept __not_constructing_bool_from_expected
329 = ! is_same_v<remove_cv_t<_Tp>, bool>
330 || ! __is_expected<remove_cvref_t<_Up>>;
331}
332/// @endcond
333
334 template<typename _Tp, typename _Er>
335 class expected
336 {
337 static_assert( ! is_reference_v<_Tp> );
338 static_assert( ! is_function_v<_Tp> );
339 static_assert( ! is_same_v<remove_cv_t<_Tp>, in_place_t> );
340 static_assert( ! is_same_v<remove_cv_t<_Tp>, unexpect_t> );
341 static_assert( ! __expected::__is_unexpected<remove_cv_t<_Tp>> );
342 static_assert( __expected::__can_be_unexpected<_Er> );
343
344 // If T is not cv bool, converts-from-any-cvref<T, expected<U, G>> and
345 // is_constructible<unexpected<E>, cv expected<U, G> ref-qual> are false.
346 template<typename _Up, typename _Gr, typename _Unex = unexpected<_Er>,
347 typename = remove_cv_t<_Tp>>
348 static constexpr bool __cons_from_expected
349 = __or_v<is_constructible<_Tp, expected<_Up, _Gr>&>,
350 is_constructible<_Tp, expected<_Up, _Gr>>,
351 is_constructible<_Tp, const expected<_Up, _Gr>&>,
352 is_constructible<_Tp, const expected<_Up, _Gr>>,
353 is_convertible<expected<_Up, _Gr>&, _Tp>,
354 is_convertible<expected<_Up, _Gr>, _Tp>,
355 is_convertible<const expected<_Up, _Gr>&, _Tp>,
356 is_convertible<const expected<_Up, _Gr>, _Tp>,
357 is_constructible<_Unex, expected<_Up, _Gr>&>,
358 is_constructible<_Unex, expected<_Up, _Gr>>,
359 is_constructible<_Unex, const expected<_Up, _Gr>&>,
360 is_constructible<_Unex, const expected<_Up, _Gr>>
361 >;
362
363 // _GLIBCXX_RESOLVE_LIB_DEFECTS
364 // If t is cv bool, we know it can be constructed from expected<U, G>,
365 // but we don't want to cause the expected(U&&) constructor to be used,
366 // so we only check the is_constructible<unexpected<E>, ...> cases.
367 template<typename _Up, typename _Gr, typename _Unex>
368 static constexpr bool __cons_from_expected<_Up, _Gr, _Unex, bool>
369 = __or_v<is_constructible<_Unex, expected<_Up, _Gr>&>,
370 is_constructible<_Unex, expected<_Up, _Gr>>,
371 is_constructible<_Unex, const expected<_Up, _Gr>&>,
372 is_constructible<_Unex, const expected<_Up, _Gr>>
373 >;
374
375 template<typename _Up, typename _Gr>
376 constexpr static bool __explicit_conv
377 = __or_v<__not_<is_convertible<_Up, _Tp>>,
378 __not_<is_convertible<_Gr, _Er>>
379 >;
380
381 template<typename _Up>
382 static constexpr bool __same_val
383 = is_same_v<typename _Up::value_type, _Tp>;
384
385 template<typename _Up>
386 static constexpr bool __same_err
387 = is_same_v<typename _Up::error_type, _Er>;
388
389 public:
390 using value_type = _Tp;
391 using error_type = _Er;
392 using unexpected_type = unexpected<_Er>;
393
394 template<typename _Up>
395 using rebind = expected<_Up, error_type>;
396
397 constexpr
398 expected()
399 noexcept(is_nothrow_default_constructible_v<_Tp>)
400 requires is_default_constructible_v<_Tp>
401 : _M_val(), _M_has_value(true)
402 { }
403
404 expected(const expected&) = default;
405
406 constexpr
407 expected(const expected& __x)
408 noexcept(__and_v<is_nothrow_copy_constructible<_Tp>,
409 is_nothrow_copy_constructible<_Er>>)
410 requires is_copy_constructible_v<_Tp> && is_copy_constructible_v<_Er>
411 && (!is_trivially_copy_constructible_v<_Tp>
412 || !is_trivially_copy_constructible_v<_Er>)
413 : _M_has_value(__x._M_has_value)
414 {
415 if (_M_has_value)
416 std::construct_at(__builtin_addressof(_M_val), __x._M_val);
417 else
418 std::construct_at(__builtin_addressof(_M_unex), __x._M_unex);
419 }
420
421 expected(expected&&) = default;
422
423 constexpr
424 expected(expected&& __x)
425 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
426 is_nothrow_move_constructible<_Er>>)
427 requires is_move_constructible_v<_Tp> && is_move_constructible_v<_Er>
428 && (!is_trivially_move_constructible_v<_Tp>
429 || !is_trivially_move_constructible_v<_Er>)
430 : _M_has_value(__x._M_has_value)
431 {
432 if (_M_has_value)
433 std::construct_at(__builtin_addressof(_M_val),
434 std::move(__x)._M_val);
435 else
436 std::construct_at(__builtin_addressof(_M_unex),
437 std::move(__x)._M_unex);
438 }
439
440 template<typename _Up, typename _Gr>
441 requires is_constructible_v<_Tp, const _Up&>
442 && is_constructible_v<_Er, const _Gr&>
443 && (!__cons_from_expected<_Up, _Gr>)
444 constexpr explicit(__explicit_conv<const _Up&, const _Gr&>)
445 expected(const expected<_Up, _Gr>& __x)
446 noexcept(__and_v<is_nothrow_constructible<_Tp, const _Up&>,
447 is_nothrow_constructible<_Er, const _Gr&>>)
448 : _M_has_value(__x._M_has_value)
449 {
450 if (_M_has_value)
451 std::construct_at(__builtin_addressof(_M_val), __x._M_val);
452 else
453 std::construct_at(__builtin_addressof(_M_unex), __x._M_unex);
454 }
455
456 template<typename _Up, typename _Gr>
457 requires is_constructible_v<_Tp, _Up>
458 && is_constructible_v<_Er, _Gr>
459 && (!__cons_from_expected<_Up, _Gr>)
460 constexpr explicit(__explicit_conv<_Up, _Gr>)
461 expected(expected<_Up, _Gr>&& __x)
462 noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
463 is_nothrow_constructible<_Er, _Gr>>)
464 : _M_has_value(__x._M_has_value)
465 {
466 if (_M_has_value)
467 std::construct_at(__builtin_addressof(_M_val),
468 std::move(__x)._M_val);
469 else
470 std::construct_at(__builtin_addressof(_M_unex),
471 std::move(__x)._M_unex);
472 }
473
474 template<typename _Up = remove_cv_t<_Tp>>
475 requires (!is_same_v<remove_cvref_t<_Up>, expected>)
476 && (!is_same_v<remove_cvref_t<_Up>, in_place_t>)
477 && (!is_same_v<remove_cvref_t<_Up>, unexpect_t>)
478 && is_constructible_v<_Tp, _Up>
479 && (!__expected::__is_unexpected<remove_cvref_t<_Up>>)
480 && __expected::__not_constructing_bool_from_expected<_Tp, _Up>
481 constexpr explicit(!is_convertible_v<_Up, _Tp>)
482 expected(_Up&& __v)
483 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
484 : _M_val(std::forward<_Up>(__v)), _M_has_value(true)
485 { }
486
487 template<typename _Gr = _Er>
488 requires is_constructible_v<_Er, const _Gr&>
489 constexpr explicit(!is_convertible_v<const _Gr&, _Er>)
490 expected(const unexpected<_Gr>& __u)
491 noexcept(is_nothrow_constructible_v<_Er, const _Gr&>)
492 : _M_unex(__u.error()), _M_has_value(false)
493 { }
494
495 template<typename _Gr = _Er>
496 requires is_constructible_v<_Er, _Gr>
497 constexpr explicit(!is_convertible_v<_Gr, _Er>)
498 expected(unexpected<_Gr>&& __u)
499 noexcept(is_nothrow_constructible_v<_Er, _Gr>)
500 : _M_unex(std::move(__u).error()), _M_has_value(false)
501 { }
502
503 template<typename... _Args>
504 requires is_constructible_v<_Tp, _Args...>
505 constexpr explicit
506 expected(in_place_t, _Args&&... __args)
507 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
508 : _M_val(std::forward<_Args>(__args)...), _M_has_value(true)
509 { }
510
511 template<typename _Up, typename... _Args>
512 requires is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
513 constexpr explicit
514 expected(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
515 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
516 _Args...>)
517 : _M_val(__il, std::forward<_Args>(__args)...), _M_has_value(true)
518 { }
519
520 template<typename... _Args>
521 requires is_constructible_v<_Er, _Args...>
522 constexpr explicit
523 expected(unexpect_t, _Args&&... __args)
524 noexcept(is_nothrow_constructible_v<_Er, _Args...>)
525 : _M_unex(std::forward<_Args>(__args)...), _M_has_value(false)
526 { }
527
528 template<typename _Up, typename... _Args>
529 requires is_constructible_v<_Er, initializer_list<_Up>&, _Args...>
530 constexpr explicit
531 expected(unexpect_t, initializer_list<_Up> __il, _Args&&... __args)
532 noexcept(is_nothrow_constructible_v<_Er, initializer_list<_Up>&,
533 _Args...>)
534 : _M_unex(__il, std::forward<_Args>(__args)...), _M_has_value(false)
535 { }
536
537 constexpr ~expected() = default;
538
539 constexpr ~expected()
540 requires (!is_trivially_destructible_v<_Tp>)
541 || (!is_trivially_destructible_v<_Er>)
542 {
543 if (_M_has_value)
544 std::destroy_at(__builtin_addressof(_M_val));
545 else
546 std::destroy_at(__builtin_addressof(_M_unex));
547 }
548
549 // assignment
550
551 expected& operator=(const expected&) = delete;
552
553 constexpr expected&
554 operator=(const expected& __x)
555 noexcept(__and_v<is_nothrow_copy_constructible<_Tp>,
556 is_nothrow_copy_constructible<_Er>,
557 is_nothrow_copy_assignable<_Tp>,
558 is_nothrow_copy_assignable<_Er>>)
559 requires is_copy_assignable_v<_Tp> && is_copy_constructible_v<_Tp>
560 && is_copy_assignable_v<_Er> && is_copy_constructible_v<_Er>
561 && (is_nothrow_move_constructible_v<_Tp>
562 || is_nothrow_move_constructible_v<_Er>)
563 {
564 if (__x._M_has_value)
565 this->_M_assign_val(__x._M_val);
566 else
567 this->_M_assign_unex(__x._M_unex);
568 return *this;
569 }
570
571 constexpr expected&
572 operator=(expected&& __x)
573 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
574 is_nothrow_move_constructible<_Er>,
575 is_nothrow_move_assignable<_Tp>,
576 is_nothrow_move_assignable<_Er>>)
577 requires is_move_assignable_v<_Tp> && is_move_constructible_v<_Tp>
578 && is_move_assignable_v<_Er> && is_move_constructible_v<_Er>
579 && (is_nothrow_move_constructible_v<_Tp>
580 || is_nothrow_move_constructible_v<_Er>)
581 {
582 if (__x._M_has_value)
583 _M_assign_val(std::move(__x._M_val));
584 else
585 _M_assign_unex(std::move(__x._M_unex));
586 return *this;
587 }
588
589 template<typename _Up = remove_cv_t<_Tp>>
590 requires (!is_same_v<expected, remove_cvref_t<_Up>>)
591 && (!__expected::__is_unexpected<remove_cvref_t<_Up>>)
592 && is_constructible_v<_Tp, _Up> && is_assignable_v<_Tp&, _Up>
593 && (is_nothrow_constructible_v<_Tp, _Up>
594 || is_nothrow_move_constructible_v<_Tp>
595 || is_nothrow_move_constructible_v<_Er>)
596 constexpr expected&
597 operator=(_Up&& __v)
598 {
599 _M_assign_val(std::forward<_Up>(__v));
600 return *this;
601 }
602
603 template<typename _Gr>
604 requires is_constructible_v<_Er, const _Gr&>
605 && is_assignable_v<_Er&, const _Gr&>
606 && (is_nothrow_constructible_v<_Er, const _Gr&>
607 || is_nothrow_move_constructible_v<_Tp>
608 || is_nothrow_move_constructible_v<_Er>)
609 constexpr expected&
610 operator=(const unexpected<_Gr>& __e)
611 {
612 _M_assign_unex(__e.error());
613 return *this;
614 }
615
616 template<typename _Gr>
617 requires is_constructible_v<_Er, _Gr>
618 && is_assignable_v<_Er&, _Gr>
619 && (is_nothrow_constructible_v<_Er, _Gr>
620 || is_nothrow_move_constructible_v<_Tp>
621 || is_nothrow_move_constructible_v<_Er>)
622 constexpr expected&
623 operator=(unexpected<_Gr>&& __e)
624 {
625 _M_assign_unex(std::move(__e).error());
626 return *this;
627 }
628
629 // modifiers
630
631 template<typename... _Args>
632 requires is_nothrow_constructible_v<_Tp, _Args...>
633 constexpr _Tp&
634 emplace(_Args&&... __args) noexcept
635 {
636 if (_M_has_value)
637 std::destroy_at(__builtin_addressof(_M_val));
638 else
639 {
640 std::destroy_at(__builtin_addressof(_M_unex));
641 _M_has_value = true;
642 }
643 std::construct_at(__builtin_addressof(_M_val),
644 std::forward<_Args>(__args)...);
645 return _M_val;
646 }
647
648 template<typename _Up, typename... _Args>
649 requires is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
650 _Args...>
651 constexpr _Tp&
652 emplace(initializer_list<_Up> __il, _Args&&... __args) noexcept
653 {
654 if (_M_has_value)
655 std::destroy_at(__builtin_addressof(_M_val));
656 else
657 {
658 std::destroy_at(__builtin_addressof(_M_unex));
659 _M_has_value = true;
660 }
661 std::construct_at(__builtin_addressof(_M_val),
662 __il, std::forward<_Args>(__args)...);
663 return _M_val;
664 }
665
666 // swap
667 constexpr void
668 swap(expected& __x)
669 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
670 is_nothrow_move_constructible<_Er>,
671 is_nothrow_swappable<_Tp&>,
672 is_nothrow_swappable<_Er&>>)
673 requires is_swappable_v<_Tp> && is_swappable_v<_Er>
674 && is_move_constructible_v<_Tp>
675 && is_move_constructible_v<_Er>
676 && (is_nothrow_move_constructible_v<_Tp>
677 || is_nothrow_move_constructible_v<_Er>)
678 {
679 if (_M_has_value)
680 {
681 if (__x._M_has_value)
682 {
683 using std::swap;
684 swap(_M_val, __x._M_val);
685 }
686 else
687 this->_M_swap_val_unex(__x);
688 }
689 else
690 {
691 if (__x._M_has_value)
692 __x._M_swap_val_unex(*this);
693 else
694 {
695 using std::swap;
696 swap(_M_unex, __x._M_unex);
697 }
698 }
699 }
700
701 // observers
702
703 [[nodiscard]]
704 constexpr const _Tp*
705 operator->() const noexcept
706 {
707 __glibcxx_assert(_M_has_value);
708 return __builtin_addressof(_M_val);
709 }
710
711 [[nodiscard]]
712 constexpr _Tp*
713 operator->() noexcept
714 {
715 __glibcxx_assert(_M_has_value);
716 return __builtin_addressof(_M_val);
717 }
718
719 [[nodiscard]]
720 constexpr const _Tp&
721 operator*() const & noexcept
722 {
723 __glibcxx_assert(_M_has_value);
724 return _M_val;
725 }
726
727 [[nodiscard]]
728 constexpr _Tp&
729 operator*() & noexcept
730 {
731 __glibcxx_assert(_M_has_value);
732 return _M_val;
733 }
734
735 [[nodiscard]]
736 constexpr const _Tp&&
737 operator*() const && noexcept
738 {
739 __glibcxx_assert(_M_has_value);
740 return std::move(_M_val);
741 }
742
743 [[nodiscard]]
744 constexpr _Tp&&
745 operator*() && noexcept
746 {
747 __glibcxx_assert(_M_has_value);
748 return std::move(_M_val);
749 }
750
751 [[nodiscard]]
752 constexpr explicit
753 operator bool() const noexcept { return _M_has_value; }
754
755 [[nodiscard]]
756 constexpr bool has_value() const noexcept { return _M_has_value; }
757
758 constexpr const _Tp&
759 value() const &
760 {
761 static_assert( is_copy_constructible_v<_Er> );
762 if (_M_has_value) [[likely]]
763 return _M_val;
764 _GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(_M_unex));
765 }
766
767 constexpr _Tp&
768 value() &
769 {
770 static_assert( is_copy_constructible_v<_Er> );
771 if (_M_has_value) [[likely]]
772 return _M_val;
773 const auto& __unex = _M_unex;
774 _GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(__unex));
775 }
776
777 constexpr const _Tp&&
778 value() const &&
779 {
780 static_assert( is_copy_constructible_v<_Er> );
781 static_assert( is_constructible_v<_Er, const _Er&&> );
782 if (_M_has_value) [[likely]]
783 return std::move(_M_val);
784 _GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(std::move(_M_unex)));
785 }
786
787 constexpr _Tp&&
788 value() &&
789 {
790 static_assert( is_copy_constructible_v<_Er> );
791 static_assert( is_constructible_v<_Er, _Er&&> );
792 if (_M_has_value) [[likely]]
793 return std::move(_M_val);
794 _GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(std::move(_M_unex)));
795 }
796
797 constexpr const _Er&
798 error() const & noexcept
799 {
800 __glibcxx_assert(!_M_has_value);
801 return _M_unex;
802 }
803
804 constexpr _Er&
805 error() & noexcept
806 {
807 __glibcxx_assert(!_M_has_value);
808 return _M_unex;
809 }
810
811 constexpr const _Er&&
812 error() const && noexcept
813 {
814 __glibcxx_assert(!_M_has_value);
815 return std::move(_M_unex);
816 }
817
818 constexpr _Er&&
819 error() && noexcept
820 {
821 __glibcxx_assert(!_M_has_value);
822 return std::move(_M_unex);
823 }
824
825 template<typename _Up = remove_cv_t<_Tp>>
826 constexpr _Tp
827 value_or(_Up&& __v) const &
828 noexcept(__and_v<is_nothrow_copy_constructible<_Tp>,
829 is_nothrow_convertible<_Up, _Tp>>)
830 {
831 static_assert( is_copy_constructible_v<_Tp> );
832 static_assert( is_convertible_v<_Up, _Tp> );
833
834 if (_M_has_value)
835 return _M_val;
836 return static_cast<_Tp>(std::forward<_Up>(__v));
837 }
838
839 template<typename _Up = remove_cv_t<_Tp>>
840 constexpr _Tp
841 value_or(_Up&& __v) &&
842 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
843 is_nothrow_convertible<_Up, _Tp>>)
844 {
845 static_assert( is_move_constructible_v<_Tp> );
846 static_assert( is_convertible_v<_Up, _Tp> );
847
848 if (_M_has_value)
849 return std::move(_M_val);
850 return static_cast<_Tp>(std::forward<_Up>(__v));
851 }
852
853 template<typename _Gr = _Er>
854 constexpr _Er
855 error_or(_Gr&& __e) const&
856 {
857 static_assert( is_copy_constructible_v<_Er> );
858 static_assert( is_convertible_v<_Gr, _Er> );
859
860 if (_M_has_value)
861 return std::forward<_Gr>(__e);
862 return _M_unex;
863 }
864
865 template<typename _Gr = _Er>
866 constexpr _Er
867 error_or(_Gr&& __e) &&
868 {
869 static_assert( is_move_constructible_v<_Er> );
870 static_assert( is_convertible_v<_Gr, _Er> );
871
872 if (_M_has_value)
873 return std::forward<_Gr>(__e);
874 return std::move(_M_unex);
875 }
876
877 // monadic operations
878
879 template<typename _Fn> requires is_constructible_v<_Er, _Er&>
880 constexpr auto
881 and_then(_Fn&& __f) &
882 {
883 using _Up = __expected::__result<_Fn, _Tp&>;
884 static_assert(__expected::__is_expected<_Up>,
885 "the function passed to std::expected<T, E>::and_then "
886 "must return a std::expected");
887 static_assert(is_same_v<typename _Up::error_type, _Er>,
888 "the function passed to std::expected<T, E>::and_then "
889 "must return a std::expected with the same error_type");
890
891 if (has_value())
892 return std::__invoke(std::forward<_Fn>(__f), _M_val);
893 else
894 return _Up(unexpect, _M_unex);
895 }
896
897 template<typename _Fn> requires is_constructible_v<_Er, const _Er&>
898 constexpr auto
899 and_then(_Fn&& __f) const &
900 {
901 using _Up = __expected::__result<_Fn, const _Tp&>;
902 static_assert(__expected::__is_expected<_Up>,
903 "the function passed to std::expected<T, E>::and_then "
904 "must return a std::expected");
905 static_assert(is_same_v<typename _Up::error_type, _Er>,
906 "the function passed to std::expected<T, E>::and_then "
907 "must return a std::expected with the same error_type");
908
909 if (has_value())
910 return std::__invoke(std::forward<_Fn>(__f), _M_val);
911 else
912 return _Up(unexpect, _M_unex);
913 }
914
915 template<typename _Fn> requires is_constructible_v<_Er, _Er>
916 constexpr auto
917 and_then(_Fn&& __f) &&
918 {
919 using _Up = __expected::__result<_Fn, _Tp&&>;
920 static_assert(__expected::__is_expected<_Up>,
921 "the function passed to std::expected<T, E>::and_then "
922 "must return a std::expected");
923 static_assert(is_same_v<typename _Up::error_type, _Er>,
924 "the function passed to std::expected<T, E>::and_then "
925 "must return a std::expected with the same error_type");
926
927 if (has_value())
928 return std::__invoke(std::forward<_Fn>(__f), std::move(_M_val));
929 else
930 return _Up(unexpect, std::move(_M_unex));
931 }
932
933
934 template<typename _Fn> requires is_constructible_v<_Er, const _Er>
935 constexpr auto
936 and_then(_Fn&& __f) const &&
937 {
938 using _Up = __expected::__result<_Fn, const _Tp&&>;
939 static_assert(__expected::__is_expected<_Up>,
940 "the function passed to std::expected<T, E>::and_then "
941 "must return a std::expected");
942 static_assert(is_same_v<typename _Up::error_type, _Er>,
943 "the function passed to std::expected<T, E>::and_then "
944 "must return a std::expected with the same error_type");
945
946 if (has_value())
947 return std::__invoke(std::forward<_Fn>(__f), std::move(_M_val));
948 else
949 return _Up(unexpect, std::move(_M_unex));
950 }
951
952 template<typename _Fn> requires is_constructible_v<_Tp, _Tp&>
953 constexpr auto
954 or_else(_Fn&& __f) &
955 {
956 using _Gr = __expected::__result<_Fn, _Er&>;
957 static_assert(__expected::__is_expected<_Gr>,
958 "the function passed to std::expected<T, E>::or_else "
959 "must return a std::expected");
960 static_assert(is_same_v<typename _Gr::value_type, _Tp>,
961 "the function passed to std::expected<T, E>::or_else "
962 "must return a std::expected with the same value_type");
963
964 if (has_value())
965 return _Gr(in_place, _M_val);
966 else
967 return std::__invoke(std::forward<_Fn>(__f), _M_unex);
968 }
969
970 template<typename _Fn> requires is_constructible_v<_Tp, const _Tp&>
971 constexpr auto
972 or_else(_Fn&& __f) const &
973 {
974 using _Gr = __expected::__result<_Fn, const _Er&>;
975 static_assert(__expected::__is_expected<_Gr>,
976 "the function passed to std::expected<T, E>::or_else "
977 "must return a std::expected");
978 static_assert(is_same_v<typename _Gr::value_type, _Tp>,
979 "the function passed to std::expected<T, E>::or_else "
980 "must return a std::expected with the same value_type");
981
982 if (has_value())
983 return _Gr(in_place, _M_val);
984 else
985 return std::__invoke(std::forward<_Fn>(__f), _M_unex);
986 }
987
988
989 template<typename _Fn> requires is_constructible_v<_Tp, _Tp>
990 constexpr auto
991 or_else(_Fn&& __f) &&
992 {
993 using _Gr = __expected::__result<_Fn, _Er&&>;
994 static_assert(__expected::__is_expected<_Gr>,
995 "the function passed to std::expected<T, E>::or_else "
996 "must return a std::expected");
997 static_assert(is_same_v<typename _Gr::value_type, _Tp>,
998 "the function passed to std::expected<T, E>::or_else "
999 "must return a std::expected with the same value_type");
1000
1001 if (has_value())
1002 return _Gr(in_place, std::move(_M_val));
1003 else
1004 return std::__invoke(std::forward<_Fn>(__f), std::move(_M_unex));
1005 }
1006
1007 template<typename _Fn> requires is_constructible_v<_Tp, const _Tp>
1008 constexpr auto
1009 or_else(_Fn&& __f) const &&
1010 {
1011 using _Gr = __expected::__result<_Fn, const _Er&&>;
1012 static_assert(__expected::__is_expected<_Gr>,
1013 "the function passed to std::expected<T, E>::or_else "
1014 "must return a std::expected");
1015 static_assert(is_same_v<typename _Gr::value_type, _Tp>,
1016 "the function passed to std::expected<T, E>::or_else "
1017 "must return a std::expected with the same value_type");
1018
1019 if (has_value())
1020 return _Gr(in_place, std::move(_M_val));
1021 else
1022 return std::__invoke(std::forward<_Fn>(__f), std::move(_M_unex));
1023 }
1024
1025 template<typename _Fn> requires is_constructible_v<_Er, _Er&>
1026 constexpr auto
1027 transform(_Fn&& __f) &
1028 {
1029 using _Up = __expected::__result_xform<_Fn, _Tp&>;
1030 using _Res = expected<_Up, _Er>;
1031
1032 if (has_value())
1033 return _Res(__in_place_inv{}, [&]() {
1034 return std::__invoke(std::forward<_Fn>(__f),
1035 _M_val);
1036 });
1037 else
1038 return _Res(unexpect, _M_unex);
1039 }
1040
1041 template<typename _Fn> requires is_constructible_v<_Er, const _Er&>
1042 constexpr auto
1043 transform(_Fn&& __f) const &
1044 {
1045 using _Up = __expected::__result_xform<_Fn, const _Tp&>;
1046 using _Res = expected<_Up, _Er>;
1047
1048 if (has_value())
1049 return _Res(__in_place_inv{}, [&]() {
1050 return std::__invoke(std::forward<_Fn>(__f),
1051 _M_val);
1052 });
1053 else
1054 return _Res(unexpect, _M_unex);
1055 }
1056
1057 template<typename _Fn> requires is_constructible_v<_Er, _Er>
1058 constexpr auto
1059 transform(_Fn&& __f) &&
1060 {
1061 using _Up = __expected::__result_xform<_Fn, _Tp>;
1062 using _Res = expected<_Up, _Er>;
1063
1064 if (has_value())
1065 return _Res(__in_place_inv{}, [&]() {
1066 return std::__invoke(std::forward<_Fn>(__f),
1067 std::move(_M_val));
1068 });
1069 else
1070 return _Res(unexpect, std::move(_M_unex));
1071 }
1072
1073 template<typename _Fn> requires is_constructible_v<_Er, const _Er>
1074 constexpr auto
1075 transform(_Fn&& __f) const &&
1076 {
1077 using _Up = __expected::__result_xform<_Fn, const _Tp>;
1078 using _Res = expected<_Up, _Er>;
1079
1080 if (has_value())
1081 return _Res(__in_place_inv{}, [&]() {
1082 return std::__invoke(std::forward<_Fn>(__f),
1083 std::move(_M_val));
1084 });
1085 else
1086 return _Res(unexpect, std::move(_M_unex));
1087 }
1088
1089 template<typename _Fn> requires is_constructible_v<_Tp, _Tp&>
1090 constexpr auto
1091 transform_error(_Fn&& __f) &
1092 {
1093 using _Gr = __expected::__result_xform<_Fn, _Er&>;
1094 using _Res = expected<_Tp, _Gr>;
1095
1096 if (has_value())
1097 return _Res(in_place, _M_val);
1098 else
1099 return _Res(__unexpect_inv{}, [&]() {
1100 return std::__invoke(std::forward<_Fn>(__f),
1101 _M_unex);
1102 });
1103 }
1104
1105 template<typename _Fn> requires is_constructible_v<_Tp, const _Tp&>
1106 constexpr auto
1107 transform_error(_Fn&& __f) const &
1108 {
1109 using _Gr = __expected::__result_xform<_Fn, const _Er&>;
1110 using _Res = expected<_Tp, _Gr>;
1111
1112 if (has_value())
1113 return _Res(in_place, _M_val);
1114 else
1115 return _Res(__unexpect_inv{}, [&]() {
1116 return std::__invoke(std::forward<_Fn>(__f),
1117 _M_unex);
1118 });
1119 }
1120
1121 template<typename _Fn> requires is_constructible_v<_Tp, _Tp>
1122 constexpr auto
1123 transform_error(_Fn&& __f) &&
1124 {
1125 using _Gr = __expected::__result_xform<_Fn, _Er&&>;
1126 using _Res = expected<_Tp, _Gr>;
1127
1128 if (has_value())
1129 return _Res(in_place, std::move(_M_val));
1130 else
1131 return _Res(__unexpect_inv{}, [&]() {
1132 return std::__invoke(std::forward<_Fn>(__f),
1133 std::move(_M_unex));
1134 });
1135 }
1136
1137 template<typename _Fn> requires is_constructible_v<_Tp, const _Tp>
1138 constexpr auto
1139 transform_error(_Fn&& __f) const &&
1140 {
1141 using _Gr = __expected::__result_xform<_Fn, const _Er&&>;
1142 using _Res = expected<_Tp, _Gr>;
1143
1144 if (has_value())
1145 return _Res(in_place, std::move(_M_val));
1146 else
1147 return _Res(__unexpect_inv{}, [&]() {
1148 return std::__invoke(std::forward<_Fn>(__f),
1149 std::move(_M_unex));
1150 });
1151 }
1152
1153 // equality operators
1154
1155 template<typename _Up, typename _Er2>
1156 requires (!is_void_v<_Up>)
1157 && requires (const _Tp& __t, const _Up& __u,
1158 const _Er& __e, const _Er2& __e2) {
1159 { __t == __u } -> convertible_to<bool>;
1160 { __e == __e2 } -> convertible_to<bool>;
1161 }
1162 friend constexpr bool
1163 operator==(const expected& __x, const expected<_Up, _Er2>& __y)
1164 noexcept(noexcept(bool(*__x == *__y))
1165 && noexcept(bool(__x.error() == __y.error())))
1166 {
1167 if (__x.has_value())
1168 return __y.has_value() && bool(*__x == *__y);
1169 else
1170 return !__y.has_value() && bool(__x.error() == __y.error());
1171 }
1172
1173 template<typename _Up, same_as<_Tp> _Vp>
1174 requires (!__expected::__is_expected<_Up>)
1175 && requires (const _Tp& __t, const _Up& __u) {
1176 { __t == __u } -> convertible_to<bool>;
1177 }
1178 friend constexpr bool
1179 operator==(const expected<_Vp, _Er>& __x, const _Up& __v)
1180 noexcept(noexcept(bool(*__x == __v)))
1181 { return __x.has_value() && bool(*__x == __v); }
1182
1183 template<typename _Er2>
1184 requires requires (const _Er& __e, const _Er2& __e2) {
1185 { __e == __e2 } -> convertible_to<bool>;
1186 }
1187 friend constexpr bool
1188 operator==(const expected& __x, const unexpected<_Er2>& __e)
1189 noexcept(noexcept(bool(__x.error() == __e.error())))
1190 { return !__x.has_value() && bool(__x.error() == __e.error()); }
1191
1192 friend constexpr void
1193 swap(expected& __x, expected& __y)
1194 noexcept(noexcept(__x.swap(__y)))
1195 requires requires {__x.swap(__y);}
1196 { __x.swap(__y); }
1197
1198 private:
1199 template<typename, typename> friend class expected;
1200
1201 template<typename _Vp>
1202 constexpr void
1203 _M_assign_val(_Vp&& __v)
1204 {
1205 if (_M_has_value)
1206 _M_val = std::forward<_Vp>(__v);
1207 else
1208 {
1209 __expected::__reinit(__builtin_addressof(_M_val),
1210 __builtin_addressof(_M_unex),
1211 std::forward<_Vp>(__v));
1212 _M_has_value = true;
1213 }
1214 }
1215
1216 template<typename _Vp>
1217 constexpr void
1218 _M_assign_unex(_Vp&& __v)
1219 {
1220 if (_M_has_value)
1221 {
1222 __expected::__reinit(__builtin_addressof(_M_unex),
1223 __builtin_addressof(_M_val),
1224 std::forward<_Vp>(__v));
1225 _M_has_value = false;
1226 }
1227 else
1228 _M_unex = std::forward<_Vp>(__v);
1229 }
1230
1231 // Swap two expected objects when only one has a value.
1232 // Precondition: this->_M_has_value && !__rhs._M_has_value
1233 constexpr void
1234 _M_swap_val_unex(expected& __rhs)
1235 noexcept(__and_v<is_nothrow_move_constructible<_Er>,
1236 is_nothrow_move_constructible<_Tp>>)
1237 {
1238 if constexpr (is_nothrow_move_constructible_v<_Er>)
1239 {
1240 __expected::_Guard<_Er> __guard(__rhs._M_unex);
1241 std::construct_at(__builtin_addressof(__rhs._M_val),
1242 std::move(_M_val)); // might throw
1243 __rhs._M_has_value = true;
1244 std::destroy_at(__builtin_addressof(_M_val));
1245 std::construct_at(__builtin_addressof(_M_unex),
1246 __guard.release());
1247 _M_has_value = false;
1248 }
1249 else
1250 {
1251 __expected::_Guard<_Tp> __guard(_M_val);
1252 std::construct_at(__builtin_addressof(_M_unex),
1253 std::move(__rhs._M_unex)); // might throw
1254 _M_has_value = false;
1255 std::destroy_at(__builtin_addressof(__rhs._M_unex));
1256 std::construct_at(__builtin_addressof(__rhs._M_val),
1257 __guard.release());
1258 __rhs._M_has_value = true;
1259 }
1260 }
1261
1262 using __in_place_inv = __expected::__in_place_inv;
1263 using __unexpect_inv = __expected::__unexpect_inv;
1264
1265 template<typename _Fn>
1266 explicit constexpr
1267 expected(__in_place_inv, _Fn&& __fn)
1268 : _M_val(std::forward<_Fn>(__fn)()), _M_has_value(true)
1269 { }
1270
1271 template<typename _Fn>
1272 explicit constexpr
1273 expected(__unexpect_inv, _Fn&& __fn)
1274 : _M_unex(std::forward<_Fn>(__fn)()), _M_has_value(false)
1275 { }
1276
1277 union {
1278 remove_cv_t<_Tp> _M_val;
1279 _Er _M_unex;
1280 };
1281
1282 bool _M_has_value;
1283 };
1284
1285 // Partial specialization for std::expected<cv void, E>
1286 template<typename _Tp, typename _Er> requires is_void_v<_Tp>
1287 class expected<_Tp, _Er>
1288 {
1289 static_assert( __expected::__can_be_unexpected<_Er> );
1290
1291 template<typename _Up, typename _Err, typename _Unex = unexpected<_Er>>
1292 static constexpr bool __cons_from_expected
1293 = __or_v<is_constructible<_Unex, expected<_Up, _Err>&>,
1294 is_constructible<_Unex, expected<_Up, _Err>>,
1295 is_constructible<_Unex, const expected<_Up, _Err>&>,
1296 is_constructible<_Unex, const expected<_Up, _Err>>
1297 >;
1298
1299 template<typename _Up>
1300 static constexpr bool __same_val
1301 = is_same_v<typename _Up::value_type, _Tp>;
1302
1303 template<typename _Up>
1304 static constexpr bool __same_err
1305 = is_same_v<typename _Up::error_type, _Er>;
1306
1307 public:
1308 using value_type = _Tp;
1309 using error_type = _Er;
1310 using unexpected_type = unexpected<_Er>;
1311
1312 template<typename _Up>
1313 using rebind = expected<_Up, error_type>;
1314
1315 constexpr
1316 expected() noexcept
1317 : _M_void(), _M_has_value(true)
1318 { }
1319
1320 expected(const expected&) = default;
1321
1322 constexpr
1323 expected(const expected& __x)
1324 noexcept(is_nothrow_copy_constructible_v<_Er>)
1325 requires is_copy_constructible_v<_Er>
1326 && (!is_trivially_copy_constructible_v<_Er>)
1327 : _M_void(), _M_has_value(__x._M_has_value)
1328 {
1329 if (!_M_has_value)
1330 std::construct_at(__builtin_addressof(_M_unex), __x._M_unex);
1331 }
1332
1333 expected(expected&&) = default;
1334
1335 constexpr
1336 expected(expected&& __x)
1337 noexcept(is_nothrow_move_constructible_v<_Er>)
1338 requires is_move_constructible_v<_Er>
1339 && (!is_trivially_move_constructible_v<_Er>)
1340 : _M_void(), _M_has_value(__x._M_has_value)
1341 {
1342 if (!_M_has_value)
1343 std::construct_at(__builtin_addressof(_M_unex),
1344 std::move(__x)._M_unex);
1345 }
1346
1347 template<typename _Up, typename _Gr>
1348 requires is_void_v<_Up>
1349 && is_constructible_v<_Er, const _Gr&>
1350 && (!__cons_from_expected<_Up, _Gr>)
1351 constexpr explicit(!is_convertible_v<const _Gr&, _Er>)
1352 expected(const expected<_Up, _Gr>& __x)
1353 noexcept(is_nothrow_constructible_v<_Er, const _Gr&>)
1354 : _M_void(), _M_has_value(__x._M_has_value)
1355 {
1356 if (!_M_has_value)
1357 std::construct_at(__builtin_addressof(_M_unex), __x._M_unex);
1358 }
1359
1360 template<typename _Up, typename _Gr>
1361 requires is_void_v<_Up>
1362 && is_constructible_v<_Er, _Gr>
1363 && (!__cons_from_expected<_Up, _Gr>)
1364 constexpr explicit(!is_convertible_v<_Gr, _Er>)
1365 expected(expected<_Up, _Gr>&& __x)
1366 noexcept(is_nothrow_constructible_v<_Er, _Gr>)
1367 : _M_void(), _M_has_value(__x._M_has_value)
1368 {
1369 if (!_M_has_value)
1370 std::construct_at(__builtin_addressof(_M_unex),
1371 std::move(__x)._M_unex);
1372 }
1373
1374 template<typename _Gr = _Er>
1375 requires is_constructible_v<_Er, const _Gr&>
1376 constexpr explicit(!is_convertible_v<const _Gr&, _Er>)
1377 expected(const unexpected<_Gr>& __u)
1378 noexcept(is_nothrow_constructible_v<_Er, const _Gr&>)
1379 : _M_unex(__u.error()), _M_has_value(false)
1380 { }
1381
1382 template<typename _Gr = _Er>
1383 requires is_constructible_v<_Er, _Gr>
1384 constexpr explicit(!is_convertible_v<_Gr, _Er>)
1385 expected(unexpected<_Gr>&& __u)
1386 noexcept(is_nothrow_constructible_v<_Er, _Gr>)
1387 : _M_unex(std::move(__u).error()), _M_has_value(false)
1388 { }
1389
1390 constexpr explicit
1391 expected(in_place_t) noexcept
1392 : expected()
1393 { }
1394
1395 template<typename... _Args>
1396 requires is_constructible_v<_Er, _Args...>
1397 constexpr explicit
1398 expected(unexpect_t, _Args&&... __args)
1399 noexcept(is_nothrow_constructible_v<_Er, _Args...>)
1400 : _M_unex(std::forward<_Args>(__args)...), _M_has_value(false)
1401 { }
1402
1403 template<typename _Up, typename... _Args>
1404 requires is_constructible_v<_Er, initializer_list<_Up>&, _Args...>
1405 constexpr explicit
1406 expected(unexpect_t, initializer_list<_Up> __il, _Args&&... __args)
1407 noexcept(is_nothrow_constructible_v<_Er, initializer_list<_Up>&,
1408 _Args...>)
1409 : _M_unex(__il, std::forward<_Args>(__args)...), _M_has_value(false)
1410 { }
1411
1412 constexpr ~expected() = default;
1413
1414 constexpr ~expected() requires (!is_trivially_destructible_v<_Er>)
1415 {
1416 if (!_M_has_value)
1417 std::destroy_at(__builtin_addressof(_M_unex));
1418 }
1419
1420 // assignment
1421
1422 expected& operator=(const expected&) = delete;
1423
1424 constexpr expected&
1425 operator=(const expected& __x)
1426 noexcept(__and_v<is_nothrow_copy_constructible<_Er>,
1427 is_nothrow_copy_assignable<_Er>>)
1428 requires is_copy_constructible_v<_Er>
1429 && is_copy_assignable_v<_Er>
1430 {
1431 if (__x._M_has_value)
1432 emplace();
1433 else
1434 _M_assign_unex(__x._M_unex);
1435 return *this;
1436 }
1437
1438 constexpr expected&
1439 operator=(expected&& __x)
1440 noexcept(__and_v<is_nothrow_move_constructible<_Er>,
1441 is_nothrow_move_assignable<_Er>>)
1442 requires is_move_constructible_v<_Er>
1443 && is_move_assignable_v<_Er>
1444 {
1445 if (__x._M_has_value)
1446 emplace();
1447 else
1448 _M_assign_unex(std::move(__x._M_unex));
1449 return *this;
1450 }
1451
1452 template<typename _Gr>
1453 requires is_constructible_v<_Er, const _Gr&>
1454 && is_assignable_v<_Er&, const _Gr&>
1455 constexpr expected&
1456 operator=(const unexpected<_Gr>& __e)
1457 {
1458 _M_assign_unex(__e.error());
1459 return *this;
1460 }
1461
1462 template<typename _Gr>
1463 requires is_constructible_v<_Er, _Gr>
1464 && is_assignable_v<_Er&, _Gr>
1465 constexpr expected&
1466 operator=(unexpected<_Gr>&& __e)
1467 {
1468 _M_assign_unex(std::move(__e.error()));
1469 return *this;
1470 }
1471
1472 // modifiers
1473
1474 constexpr void
1475 emplace() noexcept
1476 {
1477 if (!_M_has_value)
1478 {
1479 std::destroy_at(__builtin_addressof(_M_unex));
1480 _M_has_value = true;
1481 }
1482 }
1483
1484 // swap
1485 constexpr void
1486 swap(expected& __x)
1487 noexcept(__and_v<is_nothrow_swappable<_Er&>,
1488 is_nothrow_move_constructible<_Er>>)
1489 requires is_swappable_v<_Er> && is_move_constructible_v<_Er>
1490 {
1491 if (_M_has_value)
1492 {
1493 if (!__x._M_has_value)
1494 {
1495 std::construct_at(__builtin_addressof(_M_unex),
1496 std::move(__x._M_unex)); // might throw
1497 std::destroy_at(__builtin_addressof(__x._M_unex));
1498 _M_has_value = false;
1499 __x._M_has_value = true;
1500 }
1501 }
1502 else
1503 {
1504 if (__x._M_has_value)
1505 {
1506 std::construct_at(__builtin_addressof(__x._M_unex),
1507 std::move(_M_unex)); // might throw
1508 std::destroy_at(__builtin_addressof(_M_unex));
1509 _M_has_value = true;
1510 __x._M_has_value = false;
1511 }
1512 else
1513 {
1514 using std::swap;
1515 swap(_M_unex, __x._M_unex);
1516 }
1517 }
1518 }
1519
1520 // observers
1521
1522 [[nodiscard]]
1523 constexpr explicit
1524 operator bool() const noexcept { return _M_has_value; }
1525
1526 [[nodiscard]]
1527 constexpr bool has_value() const noexcept { return _M_has_value; }
1528
1529 constexpr void
1530 operator*() const noexcept { __glibcxx_assert(_M_has_value); }
1531
1532 constexpr void
1533 value() const&
1534 {
1535 static_assert( is_copy_constructible_v<_Er> );
1536 if (_M_has_value) [[likely]]
1537 return;
1538 _GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(_M_unex));
1539 }
1540
1541 constexpr void
1542 value() &&
1543 {
1544 static_assert( is_copy_constructible_v<_Er> );
1545 static_assert( is_move_constructible_v<_Er> );
1546 if (_M_has_value) [[likely]]
1547 return;
1548 _GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(std::move(_M_unex)));
1549 }
1550
1551 constexpr const _Er&
1552 error() const & noexcept
1553 {
1554 __glibcxx_assert(!_M_has_value);
1555 return _M_unex;
1556 }
1557
1558 constexpr _Er&
1559 error() & noexcept
1560 {
1561 __glibcxx_assert(!_M_has_value);
1562 return _M_unex;
1563 }
1564
1565 constexpr const _Er&&
1566 error() const && noexcept
1567 {
1568 __glibcxx_assert(!_M_has_value);
1569 return std::move(_M_unex);
1570 }
1571
1572 constexpr _Er&&
1573 error() && noexcept
1574 {
1575 __glibcxx_assert(!_M_has_value);
1576 return std::move(_M_unex);
1577 }
1578
1579 template<typename _Gr = _Er>
1580 constexpr _Er
1581 error_or(_Gr&& __e) const&
1582 {
1583 static_assert( is_copy_constructible_v<_Er> );
1584 static_assert( is_convertible_v<_Gr, _Er> );
1585
1586 if (_M_has_value)
1587 return std::forward<_Gr>(__e);
1588 return _M_unex;
1589 }
1590
1591 template<typename _Gr = _Er>
1592 constexpr _Er
1593 error_or(_Gr&& __e) &&
1594 {
1595 static_assert( is_move_constructible_v<_Er> );
1596 static_assert( is_convertible_v<_Gr, _Er> );
1597
1598 if (_M_has_value)
1599 return std::forward<_Gr>(__e);
1600 return std::move(_M_unex);
1601 }
1602
1603 // monadic operations
1604
1605 template<typename _Fn> requires is_constructible_v<_Er, _Er&>
1606 constexpr auto
1607 and_then(_Fn&& __f) &
1608 {
1609 using _Up = __expected::__result0<_Fn>;
1610 static_assert(__expected::__is_expected<_Up>);
1611 static_assert(is_same_v<typename _Up::error_type, _Er>);
1612
1613 if (has_value())
1614 return std::__invoke(std::forward<_Fn>(__f));
1615 else
1616 return _Up(unexpect, _M_unex);
1617 }
1618
1619 template<typename _Fn> requires is_constructible_v<_Er, const _Er&>
1620 constexpr auto
1621 and_then(_Fn&& __f) const &
1622 {
1623 using _Up = __expected::__result0<_Fn>;
1624 static_assert(__expected::__is_expected<_Up>);
1625 static_assert(is_same_v<typename _Up::error_type, _Er>);
1626
1627 if (has_value())
1628 return std::__invoke(std::forward<_Fn>(__f));
1629 else
1630 return _Up(unexpect, _M_unex);
1631 }
1632
1633 template<typename _Fn> requires is_constructible_v<_Er, _Er>
1634 constexpr auto
1635 and_then(_Fn&& __f) &&
1636 {
1637 using _Up = __expected::__result0<_Fn>;
1638 static_assert(__expected::__is_expected<_Up>);
1639 static_assert(is_same_v<typename _Up::error_type, _Er>);
1640
1641 if (has_value())
1642 return std::__invoke(std::forward<_Fn>(__f));
1643 else
1644 return _Up(unexpect, std::move(_M_unex));
1645 }
1646
1647 template<typename _Fn> requires is_constructible_v<_Er, const _Er>
1648 constexpr auto
1649 and_then(_Fn&& __f) const &&
1650 {
1651 using _Up = __expected::__result0<_Fn>;
1652 static_assert(__expected::__is_expected<_Up>);
1653 static_assert(is_same_v<typename _Up::error_type, _Er>);
1654
1655 if (has_value())
1656 return std::__invoke(std::forward<_Fn>(__f));
1657 else
1658 return _Up(unexpect, std::move(_M_unex));
1659 }
1660
1661 template<typename _Fn>
1662 constexpr auto
1663 or_else(_Fn&& __f) &
1664 {
1665 using _Gr = __expected::__result<_Fn, _Er&>;
1666 static_assert(__expected::__is_expected<_Gr>);
1667 static_assert(is_same_v<typename _Gr::value_type, _Tp>);
1668
1669 if (has_value())
1670 return _Gr();
1671 else
1672 return std::__invoke(std::forward<_Fn>(__f), _M_unex);
1673 }
1674
1675 template<typename _Fn>
1676 constexpr auto
1677 or_else(_Fn&& __f) const &
1678 {
1679 using _Gr = __expected::__result<_Fn, const _Er&>;
1680 static_assert(__expected::__is_expected<_Gr>);
1681 static_assert(is_same_v<typename _Gr::value_type, _Tp>);
1682
1683 if (has_value())
1684 return _Gr();
1685 else
1686 return std::__invoke(std::forward<_Fn>(__f), _M_unex);
1687 }
1688
1689 template<typename _Fn>
1690 constexpr auto
1691 or_else(_Fn&& __f) &&
1692 {
1693 using _Gr = __expected::__result<_Fn, _Er&&>;
1694 static_assert(__expected::__is_expected<_Gr>);
1695 static_assert(is_same_v<typename _Gr::value_type, _Tp>);
1696
1697 if (has_value())
1698 return _Gr();
1699 else
1700 return std::__invoke(std::forward<_Fn>(__f), std::move(_M_unex));
1701 }
1702
1703 template<typename _Fn>
1704 constexpr auto
1705 or_else(_Fn&& __f) const &&
1706 {
1707 using _Gr = __expected::__result<_Fn, const _Er&&>;
1708 static_assert(__expected::__is_expected<_Gr>);
1709 static_assert(is_same_v<typename _Gr::value_type, _Tp>);
1710
1711 if (has_value())
1712 return _Gr();
1713 else
1714 return std::__invoke(std::forward<_Fn>(__f), std::move(_M_unex));
1715 }
1716
1717 template<typename _Fn> requires is_constructible_v<_Er, _Er&>
1718 constexpr auto
1719 transform(_Fn&& __f) &
1720 {
1721 using _Up = __expected::__result0_xform<_Fn>;
1722 using _Res = expected<_Up, _Er>;
1723
1724 if (has_value())
1725 return _Res(__in_place_inv{}, std::forward<_Fn>(__f));
1726 else
1727 return _Res(unexpect, _M_unex);
1728 }
1729
1730 template<typename _Fn> requires is_constructible_v<_Er, const _Er&>
1731 constexpr auto
1732 transform(_Fn&& __f) const &
1733 {
1734 using _Up = __expected::__result0_xform<_Fn>;
1735 using _Res = expected<_Up, _Er>;
1736
1737 if (has_value())
1738 return _Res(__in_place_inv{}, std::forward<_Fn>(__f));
1739 else
1740 return _Res(unexpect, _M_unex);
1741 }
1742
1743 template<typename _Fn> requires is_constructible_v<_Er, _Er>
1744 constexpr auto
1745 transform(_Fn&& __f) &&
1746 {
1747 using _Up = __expected::__result0_xform<_Fn>;
1748 using _Res = expected<_Up, _Er>;
1749
1750 if (has_value())
1751 return _Res(__in_place_inv{}, std::forward<_Fn>(__f));
1752 else
1753 return _Res(unexpect, std::move(_M_unex));
1754 }
1755
1756 template<typename _Fn> requires is_constructible_v<_Er, const _Er>
1757 constexpr auto
1758 transform(_Fn&& __f) const &&
1759 {
1760 using _Up = __expected::__result0_xform<_Fn>;
1761 using _Res = expected<_Up, _Er>;
1762
1763 if (has_value())
1764 return _Res(__in_place_inv{}, std::forward<_Fn>(__f));
1765 else
1766 return _Res(unexpect, std::move(_M_unex));
1767 }
1768
1769 template<typename _Fn>
1770 constexpr auto
1771 transform_error(_Fn&& __f) &
1772 {
1773 using _Gr = __expected::__result_xform<_Fn, _Er&>;
1774 using _Res = expected<_Tp, _Gr>;
1775
1776 if (has_value())
1777 return _Res();
1778 else
1779 return _Res(__unexpect_inv{}, [&]() {
1780 return std::__invoke(std::forward<_Fn>(__f),
1781 _M_unex);
1782 });
1783 }
1784
1785 template<typename _Fn>
1786 constexpr auto
1787 transform_error(_Fn&& __f) const &
1788 {
1789 using _Gr = __expected::__result_xform<_Fn, const _Er&>;
1790 using _Res = expected<_Tp, _Gr>;
1791
1792 if (has_value())
1793 return _Res();
1794 else
1795 return _Res(__unexpect_inv{}, [&]() {
1796 return std::__invoke(std::forward<_Fn>(__f),
1797 _M_unex);
1798 });
1799 }
1800
1801 template<typename _Fn>
1802 constexpr auto
1803 transform_error(_Fn&& __f) &&
1804 {
1805 using _Gr = __expected::__result_xform<_Fn, _Er&&>;
1806 using _Res = expected<_Tp, _Gr>;
1807
1808 if (has_value())
1809 return _Res();
1810 else
1811 return _Res(__unexpect_inv{}, [&]() {
1812 return std::__invoke(std::forward<_Fn>(__f),
1813 std::move(_M_unex));
1814 });
1815 }
1816
1817 template<typename _Fn>
1818 constexpr auto
1819 transform_error(_Fn&& __f) const &&
1820 {
1821 using _Gr = __expected::__result_xform<_Fn, const _Er&&>;
1822 using _Res = expected<_Tp, _Gr>;
1823
1824 if (has_value())
1825 return _Res();
1826 else
1827 return _Res(__unexpect_inv{}, [&]() {
1828 return std::__invoke(std::forward<_Fn>(__f),
1829 std::move(_M_unex));
1830 });
1831 }
1832
1833 // equality operators
1834
1835 template<typename _Up, typename _Er2>
1836 requires is_void_v<_Up>
1837 && requires (const _Er& __e, const _Er2& __e2) {
1838 { __e == __e2 } -> convertible_to<bool>;
1839 }
1840 friend constexpr bool
1841 operator==(const expected& __x, const expected<_Up, _Er2>& __y)
1842 noexcept(noexcept(bool(__x.error() == __y.error())))
1843 {
1844 if (__x.has_value())
1845 return __y.has_value();
1846 else
1847 return !__y.has_value() && bool(__x.error() == __y.error());
1848 }
1849
1850 template<typename _Er2>
1851 requires requires (const _Er& __e, const _Er2& __e2) {
1852 { __e == __e2 } -> convertible_to<bool>;
1853 }
1854 friend constexpr bool
1855 operator==(const expected& __x, const unexpected<_Er2>& __e)
1856 noexcept(noexcept(bool(__x.error() == __e.error())))
1857 { return !__x.has_value() && bool(__x.error() == __e.error()); }
1858
1859 friend constexpr void
1860 swap(expected& __x, expected& __y)
1861 noexcept(noexcept(__x.swap(__y)))
1862 requires requires { __x.swap(__y); }
1863 { __x.swap(__y); }
1864
1865 private:
1866 template<typename, typename> friend class expected;
1867
1868 template<typename _Vp>
1869 constexpr void
1870 _M_assign_unex(_Vp&& __v)
1871 {
1872 if (_M_has_value)
1873 {
1874 std::construct_at(__builtin_addressof(_M_unex),
1875 std::forward<_Vp>(__v));
1876 _M_has_value = false;
1877 }
1878 else
1879 _M_unex = std::forward<_Vp>(__v);
1880 }
1881
1882 using __in_place_inv = __expected::__in_place_inv;
1883 using __unexpect_inv = __expected::__unexpect_inv;
1884
1885 template<typename _Fn>
1886 explicit constexpr
1887 expected(__in_place_inv, _Fn&& __fn)
1888 : _M_void(), _M_has_value(true)
1889 { std::forward<_Fn>(__fn)(); }
1890
1891 template<typename _Fn>
1892 explicit constexpr
1893 expected(__unexpect_inv, _Fn&& __fn)
1894 : _M_unex(std::forward<_Fn>(__fn)()), _M_has_value(false)
1895 { }
1896
1897 union {
1898 struct { } _M_void;
1899 _Er _M_unex;
1900 };
1901
1902 bool _M_has_value;
1903 };
1904 /// @}
1905
1906_GLIBCXX_END_NAMESPACE_VERSION
1907} // namespace std
1908
1909#endif // __cpp_lib_expected
1910#endif // _GLIBCXX_EXPECTED
std::operator*
constexpr complex< _Tp > operator*(const complex< _Tp > &__x, const complex< _Tp > &__y)
Return new complex value x times y.
Definition complex:434
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:138
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::unexpected
void unexpected()
std
ISO C++ entities toplevel namespace is std.
std::exception
Base class for all library exceptions.
Definition exception.h:62