1 // <forward_list.h> -*- C++ -*-
2
3 // Copyright (C) 2008-2023 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 bits/forward_list.h
26 * This is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{forward_list}
28 */
29
30 #ifndef _FORWARD_LIST_H
31 #define _FORWARD_LIST_H 1
32
33 #pragma GCC system_header
34
35 #include <initializer_list>
36 #include <bits/stl_iterator_base_types.h>
37 #include <bits/stl_iterator.h>
38 #include <bits/stl_algobase.h>
39 #include <bits/stl_function.h>
40 #include <bits/allocator.h>
41 #include <ext/alloc_traits.h>
42 #include <ext/aligned_buffer.h>
43
44 namespace std _GLIBCXX_VISIBILITY(default)
45 {
46 _GLIBCXX_BEGIN_NAMESPACE_VERSION
47 _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
48
49 /**
50 * @brief A helper basic node class for %forward_list.
51 * This is just a linked list with nothing inside it.
52 * There are purely list shuffling utility methods here.
53 */
54 struct _Fwd_list_node_base
55 {
56 _Fwd_list_node_base() = default;
57 _Fwd_list_node_base(_Fwd_list_node_base&& __x) noexcept
58 : _M_next(__x._M_next)
59 { __x._M_next = nullptr; }
60
61 _Fwd_list_node_base(const _Fwd_list_node_base&) = delete;
62 _Fwd_list_node_base& operator=(const _Fwd_list_node_base&) = delete;
63
64 _Fwd_list_node_base&
65 operator=(_Fwd_list_node_base&& __x) noexcept
66 {
67 _M_next = __x._M_next;
68 __x._M_next = nullptr;
69 return *this;
70 }
71
72 _Fwd_list_node_base* _M_next = nullptr;
73
74 _Fwd_list_node_base*
75 _M_transfer_after(_Fwd_list_node_base* __begin,
76 _Fwd_list_node_base* __end) noexcept
77 {
78 _Fwd_list_node_base* __keep = __begin->_M_next;
79 if (__end)
80 {
81 __begin->_M_next = __end->_M_next;
82 __end->_M_next = _M_next;
83 }
84 else
85 __begin->_M_next = nullptr;
86 _M_next = __keep;
87 return __end;
88 }
89
90 void
91 _M_reverse_after() noexcept
92 {
93 _Fwd_list_node_base* __tail = _M_next;
94 if (!__tail)
95 return;
96 while (_Fwd_list_node_base* __temp = __tail->_M_next)
97 {
98 _Fwd_list_node_base* __keep = _M_next;
99 _M_next = __temp;
100 __tail->_M_next = __temp->_M_next;
101 _M_next->_M_next = __keep;
102 }
103 }
104 };
105
106 /**
107 * @brief A helper node class for %forward_list.
108 * This is just a linked list with uninitialized storage for a
109 * data value in each node.
110 * There is a sorting utility method.
111 */
112 template<typename _Tp>
113 struct _Fwd_list_node
114 : public _Fwd_list_node_base
115 {
116 _Fwd_list_node() = default;
117
118 __gnu_cxx::__aligned_buffer<_Tp> _M_storage;
119
120 _Tp*
121 _M_valptr() noexcept
122 { return _M_storage._M_ptr(); }
123
124 const _Tp*
125 _M_valptr() const noexcept
126 { return _M_storage._M_ptr(); }
127 };
128
129 /**
130 * @brief A forward_list::iterator.
131 *
132 * All the functions are op overloads.
133 */
134 template<typename _Tp>
135 struct _Fwd_list_iterator
136 {
137 typedef _Fwd_list_iterator<_Tp> _Self;
138 typedef _Fwd_list_node<_Tp> _Node;
139
140 typedef _Tp value_type;
141 typedef _Tp* pointer;
142 typedef _Tp& reference;
143 typedef ptrdiff_t difference_type;
144 typedef std::forward_iterator_tag iterator_category;
145
146 _Fwd_list_iterator() noexcept
147 : _M_node() { }
148
149 explicit
150 _Fwd_list_iterator(_Fwd_list_node_base* __n) noexcept
151 : _M_node(__n) { }
152
153 [[__nodiscard__]]
154 reference
155 operator*() const noexcept
156 { return *static_cast<_Node*>(this->_M_node)->_M_valptr(); }
157
158 [[__nodiscard__]]
159 pointer
160 operator->() const noexcept
161 { return static_cast<_Node*>(this->_M_node)->_M_valptr(); }
162
163 _Self&
164 operator++() noexcept
165 {
166 _M_node = _M_node->_M_next;
167 return *this;
168 }
169
170 _Self
171 operator++(int) noexcept
172 {
173 _Self __tmp(*this);
174 _M_node = _M_node->_M_next;
175 return __tmp;
176 }
177
178 /**
179 * @brief Forward list iterator equality comparison.
180 */
181 [[__nodiscard__]]
182 friend bool
183 operator==(const _Self& __x, const _Self& __y) noexcept
184 { return __x._M_node == __y._M_node; }
185
186 #if __cpp_impl_three_way_comparison < 201907L
187 /**
188 * @brief Forward list iterator inequality comparison.
189 */
190 [[__nodiscard__]]
191 friend bool
192 operator!=(const _Self& __x, const _Self& __y) noexcept
193 { return __x._M_node != __y._M_node; }
194 #endif
195
196 _Self
197 _M_next() const noexcept
198 {
199 if (_M_node)
200 return _Fwd_list_iterator(_M_node->_M_next);
201 else
202 return _Fwd_list_iterator(nullptr);
203 }
204
205 _Fwd_list_node_base* _M_node;
206 };
207
208 /**
209 * @brief A forward_list::const_iterator.
210 *
211 * All the functions are op overloads.
212 */
213 template<typename _Tp>
214 struct _Fwd_list_const_iterator
215 {
216 typedef _Fwd_list_const_iterator<_Tp> _Self;
217 typedef const _Fwd_list_node<_Tp> _Node;
218 typedef _Fwd_list_iterator<_Tp> iterator;
219
220 typedef _Tp value_type;
221 typedef const _Tp* pointer;
222 typedef const _Tp& reference;
223 typedef ptrdiff_t difference_type;
224 typedef std::forward_iterator_tag iterator_category;
225
226 _Fwd_list_const_iterator() noexcept
227 : _M_node() { }
228
229 explicit
230 _Fwd_list_const_iterator(const _Fwd_list_node_base* __n) noexcept
231 : _M_node(__n) { }
232
233 _Fwd_list_const_iterator(const iterator& __iter) noexcept
234 : _M_node(__iter._M_node) { }
235
236 [[__nodiscard__]]
237 reference
238 operator*() const noexcept
239 { return *static_cast<_Node*>(this->_M_node)->_M_valptr(); }
240
241 [[__nodiscard__]]
242 pointer
243 operator->() const noexcept
244 { return static_cast<_Node*>(this->_M_node)->_M_valptr(); }
245
246 _Self&
247 operator++() noexcept
248 {
249 _M_node = _M_node->_M_next;
250 return *this;
251 }
252
253 _Self
254 operator++(int) noexcept
255 {
256 _Self __tmp(*this);
257 _M_node = _M_node->_M_next;
258 return __tmp;
259 }
260
261 /**
262 * @brief Forward list const_iterator equality comparison.
263 */
264 [[__nodiscard__]]
265 friend bool
266 operator==(const _Self& __x, const _Self& __y) noexcept
267 { return __x._M_node == __y._M_node; }
268
269 #if __cpp_impl_three_way_comparison < 201907L
270 /**
271 * @brief Forward list const_iterator inequality comparison.
272 */
273 [[__nodiscard__]]
274 friend bool
275 operator!=(const _Self& __x, const _Self& __y) noexcept
276 { return __x._M_node != __y._M_node; }
277 #endif
278
279 _Self
280 _M_next() const noexcept
281 {
282 if (this->_M_node)
283 return _Fwd_list_const_iterator(_M_node->_M_next);
284 else
285 return _Fwd_list_const_iterator(nullptr);
286 }
287
288 const _Fwd_list_node_base* _M_node;
289 };
290
291 /**
292 * @brief Base class for %forward_list.
293 */
294 template<typename _Tp, typename _Alloc>
295 struct _Fwd_list_base
296 {
297 protected:
298 typedef __alloc_rebind<_Alloc, _Fwd_list_node<_Tp>> _Node_alloc_type;
299 typedef __gnu_cxx::__alloc_traits<_Node_alloc_type> _Node_alloc_traits;
300
301 struct _Fwd_list_impl
302 : public _Node_alloc_type
303 {
304 _Fwd_list_node_base _M_head;
305
306 _Fwd_list_impl()
307 noexcept(is_nothrow_default_constructible<_Node_alloc_type>::value)
308 : _Node_alloc_type(), _M_head()
309 { }
310
311 _Fwd_list_impl(_Fwd_list_impl&&) = default;
312
313 _Fwd_list_impl(_Fwd_list_impl&& __fl, _Node_alloc_type&& __a)
314 : _Node_alloc_type(std::move(__a)), _M_head(std::move(__fl._M_head))
315 { }
316
317 _Fwd_list_impl(_Node_alloc_type&& __a)
318 : _Node_alloc_type(std::move(__a)), _M_head()
319 { }
320 };
321
322 _Fwd_list_impl _M_impl;
323
324 public:
325 typedef _Fwd_list_iterator<_Tp> iterator;
326 typedef _Fwd_list_const_iterator<_Tp> const_iterator;
327 typedef _Fwd_list_node<_Tp> _Node;
328
329 _Node_alloc_type&
330 _M_get_Node_allocator() noexcept
331 { return this->_M_impl; }
332
333 const _Node_alloc_type&
334 _M_get_Node_allocator() const noexcept
335 { return this->_M_impl; }
336
337 _Fwd_list_base() = default;
338
339 _Fwd_list_base(_Node_alloc_type&& __a)
340 : _M_impl(std::move(__a)) { }
341
342 // When allocators are always equal.
343 _Fwd_list_base(_Fwd_list_base&& __lst, _Node_alloc_type&& __a,
344 std::true_type)
345 : _M_impl(std::move(__lst._M_impl), std::move(__a))
346 { }
347
348 // When allocators are not always equal.
349 _Fwd_list_base(_Fwd_list_base&& __lst, _Node_alloc_type&& __a);
350
351 _Fwd_list_base(_Fwd_list_base&&) = default;
352
353 ~_Fwd_list_base()
354 { _M_erase_after(&_M_impl._M_head, nullptr); }
355
356 protected:
357 _Node*
358 _M_get_node()
359 {
360 auto __ptr = _Node_alloc_traits::allocate(_M_get_Node_allocator(), 1);
361 return std::__to_address(__ptr);
362 }
363
364 template<typename... _Args>
365 _Node*
366 _M_create_node(_Args&&... __args)
367 {
368 _Node* __node = this->_M_get_node();
369 __try
370 {
371 ::new ((void*)__node) _Node;
372 _Node_alloc_traits::construct(_M_get_Node_allocator(),
373 __node->_M_valptr(),
374 std::forward<_Args>(__args)...);
375 }
376 __catch(...)
377 {
378 this->_M_put_node(__node);
379 __throw_exception_again;
380 }
381 return __node;
382 }
383
384 template<typename... _Args>
385 _Fwd_list_node_base*
386 _M_insert_after(const_iterator __pos, _Args&&... __args);
387
388 void
389 _M_put_node(_Node* __p)
390 {
391 typedef typename _Node_alloc_traits::pointer _Ptr;
392 auto __ptr = std::pointer_traits<_Ptr>::pointer_to(*__p);
393 _Node_alloc_traits::deallocate(_M_get_Node_allocator(), __ptr, 1);
394 }
395
396 _Fwd_list_node_base*
397 _M_erase_after(_Fwd_list_node_base* __pos);
398
399 _Fwd_list_node_base*
400 _M_erase_after(_Fwd_list_node_base* __pos,
401 _Fwd_list_node_base* __last);
402 };
403
404 /**
405 * @brief A standard container with linear time access to elements,
406 * and fixed time insertion/deletion at any point in the sequence.
407 *
408 * @ingroup sequences
409 * @headerfile forward_list
410 * @since C++11
411 *
412 * @tparam _Tp Type of element.
413 * @tparam _Alloc Allocator type, defaults to allocator<_Tp>.
414 *
415 * Meets the requirements of a <a href="tables.html#65">container</a>, a
416 * <a href="tables.html#67">sequence</a>, including the
417 * <a href="tables.html#68">optional sequence requirements</a> with the
418 * %exception of @c at and @c operator[].
419 *
420 * This is a @e singly @e linked %list. Traversal up the
421 * %list requires linear time, but adding and removing elements (or
422 * @e nodes) is done in constant time, regardless of where the
423 * change takes place. Unlike std::vector and std::deque,
424 * random-access iterators are not provided, so subscripting ( @c
425 * [] ) access is not allowed. For algorithms which only need
426 * sequential access, this lack makes no difference.
427 *
428 * Also unlike the other standard containers, std::forward_list provides
429 * specialized algorithms %unique to linked lists, such as
430 * splicing, sorting, and in-place reversal.
431 */
432 template<typename _Tp, typename _Alloc = allocator<_Tp>>
433 class forward_list : private _Fwd_list_base<_Tp, _Alloc>
434 {
435 static_assert(is_same<typename remove_cv<_Tp>::type, _Tp>::value,
436 "std::forward_list must have a non-const, non-volatile value_type");
437 #if __cplusplus > 201703L || defined __STRICT_ANSI__
438 static_assert(is_same<typename _Alloc::value_type, _Tp>::value,
439 "std::forward_list must have the same value_type as its allocator");
440 #endif
441
442 private:
443 typedef _Fwd_list_base<_Tp, _Alloc> _Base;
444 typedef _Fwd_list_node_base _Node_base;
445 typedef typename _Base::_Node _Node;
446 typedef typename _Base::_Node_alloc_type _Node_alloc_type;
447 typedef typename _Base::_Node_alloc_traits _Node_alloc_traits;
448 typedef allocator_traits<__alloc_rebind<_Alloc, _Tp>> _Alloc_traits;
449
450 public:
451 // types:
452 typedef _Tp value_type;
453 typedef typename _Alloc_traits::pointer pointer;
454 typedef typename _Alloc_traits::const_pointer const_pointer;
455 typedef value_type& reference;
456 typedef const value_type& const_reference;
457
458 typedef typename _Base::iterator iterator;
459 typedef typename _Base::const_iterator const_iterator;
460 typedef std::size_t size_type;
461 typedef std::ptrdiff_t difference_type;
462 typedef _Alloc allocator_type;
463
464 // 23.3.4.2 construct/copy/destroy:
465
466 /**
467 * @brief Creates a %forward_list with no elements.
468 */
469 forward_list() = default;
470
471 /**
472 * @brief Creates a %forward_list with no elements.
473 * @param __al An allocator object.
474 */
475 explicit
476 forward_list(const _Alloc& __al) noexcept
477 : _Base(_Node_alloc_type(__al))
478 { }
479
480 /**
481 * @brief Copy constructor with allocator argument.
482 * @param __list Input list to copy.
483 * @param __al An allocator object.
484 */
485 forward_list(const forward_list& __list,
486 const __type_identity_t<_Alloc>& __al)
487 : _Base(_Node_alloc_type(__al))
488 { _M_range_initialize(__list.begin(), __list.end()); }
489
490 private:
491 forward_list(forward_list&& __list, _Node_alloc_type&& __al,
492 false_type)
493 : _Base(std::move(__list), std::move(__al))
494 {
495 // If __list is not empty it means its allocator is not equal to __a,
496 // so we need to move from each element individually.
497 insert_after(cbefore_begin(),
498 std::__make_move_if_noexcept_iterator(__list.begin()),
499 std::__make_move_if_noexcept_iterator(__list.end()));
500 }
501
502 forward_list(forward_list&& __list, _Node_alloc_type&& __al,
503 true_type)
504 noexcept
505 : _Base(std::move(__list), _Node_alloc_type(__al), true_type{})
506 { }
507
508 public:
509 /**
510 * @brief Move constructor with allocator argument.
511 * @param __list Input list to move.
512 * @param __al An allocator object.
513 */
514 forward_list(forward_list&& __list,
515 const __type_identity_t<_Alloc>& __al)
516 noexcept(_Node_alloc_traits::_S_always_equal())
517 : forward_list(std::move(__list), _Node_alloc_type(__al),
518 typename _Node_alloc_traits::is_always_equal{})
519 { }
520
521 /**
522 * @brief Creates a %forward_list with default constructed elements.
523 * @param __n The number of elements to initially create.
524 * @param __al An allocator object.
525 *
526 * This constructor creates the %forward_list with @a __n default
527 * constructed elements.
528 */
529 explicit
530 forward_list(size_type __n, const _Alloc& __al = _Alloc())
531 : _Base(_Node_alloc_type(__al))
532 { _M_default_initialize(__n); }
533
534 /**
535 * @brief Creates a %forward_list with copies of an exemplar element.
536 * @param __n The number of elements to initially create.
537 * @param __value An element to copy.
538 * @param __al An allocator object.
539 *
540 * This constructor fills the %forward_list with @a __n copies of
541 * @a __value.
542 */
543 forward_list(size_type __n, const _Tp& __value,
544 const _Alloc& __al = _Alloc())
545 : _Base(_Node_alloc_type(__al))
546 { _M_fill_initialize(__n, __value); }
547
548 /**
549 * @brief Builds a %forward_list from a range.
550 * @param __first An input iterator.
551 * @param __last An input iterator.
552 * @param __al An allocator object.
553 *
554 * Create a %forward_list consisting of copies of the elements from
555 * [@a __first,@a __last). This is linear in N (where N is
556 * distance(@a __first,@a __last)).
557 */
558 template<typename _InputIterator,
559 typename = std::_RequireInputIter<_InputIterator>>
560 forward_list(_InputIterator __first, _InputIterator __last,
561 const _Alloc& __al = _Alloc())
562 : _Base(_Node_alloc_type(__al))
563 { _M_range_initialize(__first, __last); }
564
565 /**
566 * @brief The %forward_list copy constructor.
567 * @param __list A %forward_list of identical element and allocator
568 * types.
569 */
570 forward_list(const forward_list& __list)
571 : _Base(_Node_alloc_traits::_S_select_on_copy(
572 __list._M_get_Node_allocator()))
573 { _M_range_initialize(__list.begin(), __list.end()); }
574
575 /**
576 * @brief The %forward_list move constructor.
577 * @param __list A %forward_list of identical element and allocator
578 * types.
579 *
580 * The newly-created %forward_list contains the exact contents of the
581 * moved instance. The contents of the moved instance are a valid, but
582 * unspecified %forward_list.
583 */
584 forward_list(forward_list&&) = default;
585
586 /**
587 * @brief Builds a %forward_list from an initializer_list
588 * @param __il An initializer_list of value_type.
589 * @param __al An allocator object.
590 *
591 * Create a %forward_list consisting of copies of the elements
592 * in the initializer_list @a __il. This is linear in __il.size().
593 */
594 forward_list(std::initializer_list<_Tp> __il,
595 const _Alloc& __al = _Alloc())
596 : _Base(_Node_alloc_type(__al))
597 { _M_range_initialize(__il.begin(), __il.end()); }
598
599 /**
600 * @brief The forward_list dtor.
601 */
602 ~forward_list() noexcept
603 { }
604
605 /**
606 * @brief The %forward_list assignment operator.
607 * @param __list A %forward_list of identical element and allocator
608 * types.
609 *
610 * All the elements of @a __list are copied.
611 *
612 * Whether the allocator is copied depends on the allocator traits.
613 */
614 forward_list&
615 operator=(const forward_list& __list);
616
617 /**
618 * @brief The %forward_list move assignment operator.
619 * @param __list A %forward_list of identical element and allocator
620 * types.
621 *
622 * The contents of @a __list are moved into this %forward_list
623 * (without copying, if the allocators permit it).
624 *
625 * Afterwards @a __list is a valid, but unspecified %forward_list
626 *
627 * Whether the allocator is moved depends on the allocator traits.
628 */
629 forward_list&
630 operator=(forward_list&& __list)
631 noexcept(_Node_alloc_traits::_S_nothrow_move())
632 {
633 constexpr bool __move_storage =
634 _Node_alloc_traits::_S_propagate_on_move_assign()
635 || _Node_alloc_traits::_S_always_equal();
636 _M_move_assign(std::move(__list), __bool_constant<__move_storage>());
637 return *this;
638 }
639
640 /**
641 * @brief The %forward_list initializer list assignment operator.
642 * @param __il An initializer_list of value_type.
643 *
644 * Replace the contents of the %forward_list with copies of the
645 * elements in the initializer_list @a __il. This is linear in
646 * __il.size().
647 */
648 forward_list&
649 operator=(std::initializer_list<_Tp> __il)
650 {
651 assign(__il);
652 return *this;
653 }
654
655 /**
656 * @brief Assigns a range to a %forward_list.
657 * @param __first An input iterator.
658 * @param __last An input iterator.
659 *
660 * This function fills a %forward_list with copies of the elements
661 * in the range [@a __first,@a __last).
662 *
663 * Note that the assignment completely changes the %forward_list and
664 * that the number of elements of the resulting %forward_list is the
665 * same as the number of elements assigned.
666 */
667 template<typename _InputIterator,
668 typename = std::_RequireInputIter<_InputIterator>>
669 void
670 assign(_InputIterator __first, _InputIterator __last)
671 {
672 typedef is_assignable<_Tp, decltype(*__first)> __assignable;
673 _M_assign(__first, __last, __assignable());
674 }
675
676 /**
677 * @brief Assigns a given value to a %forward_list.
678 * @param __n Number of elements to be assigned.
679 * @param __val Value to be assigned.
680 *
681 * This function fills a %forward_list with @a __n copies of the
682 * given value. Note that the assignment completely changes the
683 * %forward_list, and that the resulting %forward_list has __n
684 * elements.
685 */
686 void
687 assign(size_type __n, const _Tp& __val)
688 { _M_assign_n(__n, __val, is_copy_assignable<_Tp>()); }
689
690 /**
691 * @brief Assigns an initializer_list to a %forward_list.
692 * @param __il An initializer_list of value_type.
693 *
694 * Replace the contents of the %forward_list with copies of the
695 * elements in the initializer_list @a __il. This is linear in
696 * il.size().
697 */
698 void
699 assign(std::initializer_list<_Tp> __il)
700 { assign(__il.begin(), __il.end()); }
701
702 /// Get a copy of the memory allocation object.
703 allocator_type
704 get_allocator() const noexcept
705 { return allocator_type(this->_M_get_Node_allocator()); }
706
707 // 23.3.4.3 iterators:
708
709 /**
710 * Returns a read/write iterator that points before the first element
711 * in the %forward_list. Iteration is done in ordinary element order.
712 */
713 [[__nodiscard__]]
714 iterator
715 before_begin() noexcept
716 { return iterator(&this->_M_impl._M_head); }
717
718 /**
719 * Returns a read-only (constant) iterator that points before the
720 * first element in the %forward_list. Iteration is done in ordinary
721 * element order.
722 */
723 [[__nodiscard__]]
724 const_iterator
725 before_begin() const noexcept
726 { return const_iterator(&this->_M_impl._M_head); }
727
728 /**
729 * Returns a read/write iterator that points to the first element
730 * in the %forward_list. Iteration is done in ordinary element order.
731 */
732 [[__nodiscard__]]
733 iterator
734 begin() noexcept
735 { return iterator(this->_M_impl._M_head._M_next); }
736
737 /**
738 * Returns a read-only (constant) iterator that points to the first
739 * element in the %forward_list. Iteration is done in ordinary
740 * element order.
741 */
742 [[__nodiscard__]]
743 const_iterator
744 begin() const noexcept
745 { return const_iterator(this->_M_impl._M_head._M_next); }
746
747 /**
748 * Returns a read/write iterator that points one past the last
749 * element in the %forward_list. Iteration is done in ordinary
750 * element order.
751 */
752 [[__nodiscard__]]
753 iterator
754 end() noexcept
755 { return iterator(nullptr); }
756
757 /**
758 * Returns a read-only iterator that points one past the last
759 * element in the %forward_list. Iteration is done in ordinary
760 * element order.
761 */
762 [[__nodiscard__]]
763 const_iterator
764 end() const noexcept
765 { return const_iterator(nullptr); }
766
767 /**
768 * Returns a read-only (constant) iterator that points to the
769 * first element in the %forward_list. Iteration is done in ordinary
770 * element order.
771 */
772 [[__nodiscard__]]
773 const_iterator
774 cbegin() const noexcept
775 { return const_iterator(this->_M_impl._M_head._M_next); }
776
777 /**
778 * Returns a read-only (constant) iterator that points before the
779 * first element in the %forward_list. Iteration is done in ordinary
780 * element order.
781 */
782 [[__nodiscard__]]
783 const_iterator
784 cbefore_begin() const noexcept
785 { return const_iterator(&this->_M_impl._M_head); }
786
787 /**
788 * Returns a read-only (constant) iterator that points one past
789 * the last element in the %forward_list. Iteration is done in
790 * ordinary element order.
791 */
792 [[__nodiscard__]]
793 const_iterator
794 cend() const noexcept
795 { return const_iterator(nullptr); }
796
797 /**
798 * Returns true if the %forward_list is empty. (Thus begin() would
799 * equal end().)
800 */
801 [[__nodiscard__]]
802 bool
803 empty() const noexcept
804 { return this->_M_impl._M_head._M_next == nullptr; }
805
806 /**
807 * Returns the largest possible number of elements of %forward_list.
808 */
809 [[__nodiscard__]]
810 size_type
811 max_size() const noexcept
812 { return _Node_alloc_traits::max_size(this->_M_get_Node_allocator()); }
813
814 // 23.3.4.4 element access:
815
816 /**
817 * Returns a read/write reference to the data at the first
818 * element of the %forward_list.
819 */
820 [[__nodiscard__]]
821 reference
822 front()
823 {
824 _Node* __front = static_cast<_Node*>(this->_M_impl._M_head._M_next);
825 return *__front->_M_valptr();
826 }
827
828 /**
829 * Returns a read-only (constant) reference to the data at the first
830 * element of the %forward_list.
831 */
832 [[__nodiscard__]]
833 const_reference
834 front() const
835 {
836 _Node* __front = static_cast<_Node*>(this->_M_impl._M_head._M_next);
837 return *__front->_M_valptr();
838 }
839
840 // 23.3.4.5 modifiers:
841
842 /**
843 * @brief Constructs object in %forward_list at the front of the
844 * list.
845 * @param __args Arguments.
846 *
847 * This function will insert an object of type Tp constructed
848 * with Tp(std::forward<Args>(args)...) at the front of the list
849 * Due to the nature of a %forward_list this operation can
850 * be done in constant time, and does not invalidate iterators
851 * and references.
852 */
853 template<typename... _Args>
854 #if __cplusplus > 201402L
855 reference
856 #else
857 void
858 #endif
859 emplace_front(_Args&&... __args)
860 {
861 this->_M_insert_after(cbefore_begin(),
862 std::forward<_Args>(__args)...);
863 #if __cplusplus > 201402L
864 return front();
865 #endif
866 }
867
868 /**
869 * @brief Add data to the front of the %forward_list.
870 * @param __val Data to be added.
871 *
872 * This is a typical stack operation. The function creates an
873 * element at the front of the %forward_list and assigns the given
874 * data to it. Due to the nature of a %forward_list this operation
875 * can be done in constant time, and does not invalidate iterators
876 * and references.
877 */
878 void
879 push_front(const _Tp& __val)
880 { this->_M_insert_after(cbefore_begin(), __val); }
881
882 /**
883 *
884 */
885 void
886 push_front(_Tp&& __val)
887 { this->_M_insert_after(cbefore_begin(), std::move(__val)); }
888
889 /**
890 * @brief Removes first element.
891 *
892 * This is a typical stack operation. It shrinks the %forward_list
893 * by one. Due to the nature of a %forward_list this operation can
894 * be done in constant time, and only invalidates iterators/references
895 * to the element being removed.
896 *
897 * Note that no data is returned, and if the first element's data
898 * is needed, it should be retrieved before pop_front() is
899 * called.
900 */
901 void
902 pop_front()
903 { this->_M_erase_after(&this->_M_impl._M_head); }
904
905 /**
906 * @brief Constructs object in %forward_list after the specified
907 * iterator.
908 * @param __pos A const_iterator into the %forward_list.
909 * @param __args Arguments.
910 * @return An iterator that points to the inserted data.
911 *
912 * This function will insert an object of type T constructed
913 * with T(std::forward<Args>(args)...) after the specified
914 * location. Due to the nature of a %forward_list this operation can
915 * be done in constant time, and does not invalidate iterators
916 * and references.
917 */
918 template<typename... _Args>
919 iterator
920 emplace_after(const_iterator __pos, _Args&&... __args)
921 { return iterator(this->_M_insert_after(__pos,
922 std::forward<_Args>(__args)...)); }
923
924 /**
925 * @brief Inserts given value into %forward_list after specified
926 * iterator.
927 * @param __pos An iterator into the %forward_list.
928 * @param __val Data to be inserted.
929 * @return An iterator that points to the inserted data.
930 *
931 * This function will insert a copy of the given value after
932 * the specified location. Due to the nature of a %forward_list this
933 * operation can be done in constant time, and does not
934 * invalidate iterators and references.
935 */
936 iterator
937 insert_after(const_iterator __pos, const _Tp& __val)
938 { return iterator(this->_M_insert_after(__pos, __val)); }
939
940 /**
941 *
942 */
943 iterator
944 insert_after(const_iterator __pos, _Tp&& __val)
945 { return iterator(this->_M_insert_after(__pos, std::move(__val))); }
946
947 /**
948 * @brief Inserts a number of copies of given data into the
949 * %forward_list.
950 * @param __pos An iterator into the %forward_list.
951 * @param __n Number of elements to be inserted.
952 * @param __val Data to be inserted.
953 * @return An iterator pointing to the last inserted copy of
954 * @a val or @a pos if @a n == 0.
955 *
956 * This function will insert a specified number of copies of the
957 * given data after the location specified by @a pos.
958 *
959 * This operation is linear in the number of elements inserted and
960 * does not invalidate iterators and references.
961 */
962 iterator
963 insert_after(const_iterator __pos, size_type __n, const _Tp& __val);
964
965 /**
966 * @brief Inserts a range into the %forward_list.
967 * @param __pos An iterator into the %forward_list.
968 * @param __first An input iterator.
969 * @param __last An input iterator.
970 * @return An iterator pointing to the last inserted element or
971 * @a __pos if @a __first == @a __last.
972 *
973 * This function will insert copies of the data in the range
974 * [@a __first,@a __last) into the %forward_list after the
975 * location specified by @a __pos.
976 *
977 * This operation is linear in the number of elements inserted and
978 * does not invalidate iterators and references.
979 */
980 template<typename _InputIterator,
981 typename = std::_RequireInputIter<_InputIterator>>
982 iterator
983 insert_after(const_iterator __pos,
984 _InputIterator __first, _InputIterator __last);
985
986 /**
987 * @brief Inserts the contents of an initializer_list into
988 * %forward_list after the specified iterator.
989 * @param __pos An iterator into the %forward_list.
990 * @param __il An initializer_list of value_type.
991 * @return An iterator pointing to the last inserted element
992 * or @a __pos if @a __il is empty.
993 *
994 * This function will insert copies of the data in the
995 * initializer_list @a __il into the %forward_list before the location
996 * specified by @a __pos.
997 *
998 * This operation is linear in the number of elements inserted and
999 * does not invalidate iterators and references.
1000 */
1001 iterator
1002 insert_after(const_iterator __pos, std::initializer_list<_Tp> __il)
1003 { return insert_after(__pos, __il.begin(), __il.end()); }
1004
1005 /**
1006 * @brief Removes the element pointed to by the iterator following
1007 * @c pos.
1008 * @param __pos Iterator pointing before element to be erased.
1009 * @return An iterator pointing to the element following the one
1010 * that was erased, or end() if no such element exists.
1011 *
1012 * This function will erase the element at the given position and
1013 * thus shorten the %forward_list by one.
1014 *
1015 * Due to the nature of a %forward_list this operation can be done
1016 * in constant time, and only invalidates iterators/references to
1017 * the element being removed. The user is also cautioned that
1018 * this function only erases the element, and that if the element
1019 * is itself a pointer, the pointed-to memory is not touched in
1020 * any way. Managing the pointer is the user's responsibility.
1021 */
1022 iterator
1023 erase_after(const_iterator __pos)
1024 { return iterator(this->_M_erase_after(const_cast<_Node_base*>
1025 (__pos._M_node))); }
1026
1027 /**
1028 * @brief Remove a range of elements.
1029 * @param __pos Iterator pointing before the first element to be
1030 * erased.
1031 * @param __last Iterator pointing to one past the last element to be
1032 * erased.
1033 * @return @ __last.
1034 *
1035 * This function will erase the elements in the range
1036 * @a (__pos,__last) and shorten the %forward_list accordingly.
1037 *
1038 * This operation is linear time in the size of the range and only
1039 * invalidates iterators/references to the element being removed.
1040 * The user is also cautioned that this function only erases the
1041 * elements, and that if the elements themselves are pointers, the
1042 * pointed-to memory is not touched in any way. Managing the pointer
1043 * is the user's responsibility.
1044 */
1045 iterator
1046 erase_after(const_iterator __pos, const_iterator __last)
1047 { return iterator(this->_M_erase_after(const_cast<_Node_base*>
1048 (__pos._M_node),
1049 const_cast<_Node_base*>
1050 (__last._M_node))); }
1051
1052 /**
1053 * @brief Swaps data with another %forward_list.
1054 * @param __list A %forward_list of the same element and allocator
1055 * types.
1056 *
1057 * This exchanges the elements between two lists in constant
1058 * time. Note that the global std::swap() function is
1059 * specialized such that std::swap(l1,l2) will feed to this
1060 * function.
1061 *
1062 * Whether the allocators are swapped depends on the allocator traits.
1063 */
1064 void
1065 swap(forward_list& __list) noexcept
1066 {
1067 std::swap(this->_M_impl._M_head._M_next,
1068 __list._M_impl._M_head._M_next);
1069 _Node_alloc_traits::_S_on_swap(this->_M_get_Node_allocator(),
1070 __list._M_get_Node_allocator());
1071 }
1072
1073 /**
1074 * @brief Resizes the %forward_list to the specified number of
1075 * elements.
1076 * @param __sz Number of elements the %forward_list should contain.
1077 *
1078 * This function will %resize the %forward_list to the specified
1079 * number of elements. If the number is smaller than the
1080 * %forward_list's current number of elements the %forward_list
1081 * is truncated, otherwise the %forward_list is extended and the
1082 * new elements are default constructed.
1083 */
1084 void
1085 resize(size_type __sz);
1086
1087 /**
1088 * @brief Resizes the %forward_list to the specified number of
1089 * elements.
1090 * @param __sz Number of elements the %forward_list should contain.
1091 * @param __val Data with which new elements should be populated.
1092 *
1093 * This function will %resize the %forward_list to the specified
1094 * number of elements. If the number is smaller than the
1095 * %forward_list's current number of elements the %forward_list
1096 * is truncated, otherwise the %forward_list is extended and new
1097 * elements are populated with given data.
1098 */
1099 void
1100 resize(size_type __sz, const value_type& __val);
1101
1102 /**
1103 * @brief Erases all the elements.
1104 *
1105 * Note that this function only erases
1106 * the elements, and that if the elements themselves are
1107 * pointers, the pointed-to memory is not touched in any way.
1108 * Managing the pointer is the user's responsibility.
1109 */
1110 void
1111 clear() noexcept
1112 { this->_M_erase_after(&this->_M_impl._M_head, nullptr); }
1113
1114 // 23.3.4.6 forward_list operations:
1115
1116 /**
1117 * @brief Insert contents of another %forward_list.
1118 * @param __pos Iterator referencing the element to insert after.
1119 * @param __list Source list.
1120 *
1121 * The elements of @a list are inserted in constant time after
1122 * the element referenced by @a pos. @a list becomes an empty
1123 * list.
1124 *
1125 * Requires this != @a x.
1126 */
1127 void
1128 splice_after(const_iterator __pos, forward_list&& __list) noexcept
1129 {
1130 if (!__list.empty())
1131 _M_splice_after(__pos, __list.before_begin(), __list.end());
1132 }
1133
1134 void
1135 splice_after(const_iterator __pos, forward_list& __list) noexcept
1136 { splice_after(__pos, std::move(__list)); }
1137
1138 /**
1139 * @brief Insert element from another %forward_list.
1140 * @param __pos Iterator referencing the element to insert after.
1141 * @param __list Source list.
1142 * @param __i Iterator referencing the element before the element
1143 * to move.
1144 *
1145 * Removes the element in list @a list referenced by @a i and
1146 * inserts it into the current list after @a pos.
1147 */
1148 void
1149 splice_after(const_iterator __pos, forward_list&& __list,
1150 const_iterator __i) noexcept;
1151
1152 void
1153 splice_after(const_iterator __pos, forward_list& __list,
1154 const_iterator __i) noexcept
1155 { splice_after(__pos, std::move(__list), __i); }
1156
1157 /**
1158 * @brief Insert range from another %forward_list.
1159 * @param __pos Iterator referencing the element to insert after.
1160 * @param __list Source list.
1161 * @param __before Iterator referencing before the start of range
1162 * in list.
1163 * @param __last Iterator referencing the end of range in list.
1164 *
1165 * Removes elements in the range (__before,__last) and inserts them
1166 * after @a __pos in constant time.
1167 *
1168 * Undefined if @a __pos is in (__before,__last).
1169 * @{
1170 */
1171 void
1172 splice_after(const_iterator __pos, forward_list&&,
1173 const_iterator __before, const_iterator __last) noexcept
1174 { _M_splice_after(__pos, __before, __last); }
1175
1176 void
1177 splice_after(const_iterator __pos, forward_list&,
1178 const_iterator __before, const_iterator __last) noexcept
1179 { _M_splice_after(__pos, __before, __last); }
1180 /// @}
1181
1182 private:
1183 #if __cplusplus > 201703L
1184 # define __cpp_lib_list_remove_return_type 201806L
1185 using __remove_return_type = size_type;
1186 # define _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG \
1187 __attribute__((__abi_tag__("__cxx20")))
1188 #else
1189 using __remove_return_type = void;
1190 # define _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
1191 #endif
1192 public:
1193
1194 /**
1195 * @brief Remove all elements equal to value.
1196 * @param __val The value to remove.
1197 *
1198 * Removes every element in the list equal to @a __val.
1199 * Remaining elements stay in list order. Note that this
1200 * function only erases the elements, and that if the elements
1201 * themselves are pointers, the pointed-to memory is not
1202 * touched in any way. Managing the pointer is the user's
1203 * responsibility.
1204 */
1205 _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
1206 __remove_return_type
1207 remove(const _Tp& __val);
1208
1209 /**
1210 * @brief Remove all elements satisfying a predicate.
1211 * @param __pred Unary predicate function or object.
1212 *
1213 * Removes every element in the list for which the predicate
1214 * returns true. Remaining elements stay in list order. Note
1215 * that this function only erases the elements, and that if the
1216 * elements themselves are pointers, the pointed-to memory is
1217 * not touched in any way. Managing the pointer is the user's
1218 * responsibility.
1219 */
1220 template<typename _Pred>
1221 __remove_return_type
1222 remove_if(_Pred __pred);
1223
1224 /**
1225 * @brief Remove consecutive duplicate elements.
1226 *
1227 * For each consecutive set of elements with the same value,
1228 * remove all but the first one. Remaining elements stay in
1229 * list order. Note that this function only erases the
1230 * elements, and that if the elements themselves are pointers,
1231 * the pointed-to memory is not touched in any way. Managing
1232 * the pointer is the user's responsibility.
1233 */
1234 _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
1235 __remove_return_type
1236 unique()
1237 { return unique(std::equal_to<_Tp>()); }
1238
1239 #undef _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
1240
1241 /**
1242 * @brief Remove consecutive elements satisfying a predicate.
1243 * @param __binary_pred Binary predicate function or object.
1244 *
1245 * For each consecutive set of elements [first,last) that
1246 * satisfy predicate(first,i) where i is an iterator in
1247 * [first,last), remove all but the first one. Remaining
1248 * elements stay in list order. Note that this function only
1249 * erases the elements, and that if the elements themselves are
1250 * pointers, the pointed-to memory is not touched in any way.
1251 * Managing the pointer is the user's responsibility.
1252 */
1253 template<typename _BinPred>
1254 __remove_return_type
1255 unique(_BinPred __binary_pred);
1256
1257 /**
1258 * @brief Merge sorted lists.
1259 * @param __list Sorted list to merge.
1260 *
1261 * Assumes that both @a list and this list are sorted according to
1262 * operator<(). Merges elements of @a __list into this list in
1263 * sorted order, leaving @a __list empty when complete. Elements in
1264 * this list precede elements in @a __list that are equal.
1265 */
1266 void
1267 merge(forward_list&& __list)
1268 { merge(std::move(__list), std::less<_Tp>()); }
1269
1270 void
1271 merge(forward_list& __list)
1272 { merge(std::move(__list)); }
1273
1274 /**
1275 * @brief Merge sorted lists according to comparison function.
1276 * @param __list Sorted list to merge.
1277 * @param __comp Comparison function defining sort order.
1278 *
1279 * Assumes that both @a __list and this list are sorted according to
1280 * comp. Merges elements of @a __list into this list
1281 * in sorted order, leaving @a __list empty when complete. Elements
1282 * in this list precede elements in @a __list that are equivalent
1283 * according to comp().
1284 */
1285 template<typename _Comp>
1286 void
1287 merge(forward_list&& __list, _Comp __comp);
1288
1289 template<typename _Comp>
1290 void
1291 merge(forward_list& __list, _Comp __comp)
1292 { merge(std::move(__list), __comp); }
1293
1294 /**
1295 * @brief Sort the elements of the list.
1296 *
1297 * Sorts the elements of this list in NlogN time. Equivalent
1298 * elements remain in list order.
1299 */
1300 void
1301 sort()
1302 { sort(std::less<_Tp>()); }
1303
1304 /**
1305 * @brief Sort the forward_list using a comparison function.
1306 *
1307 * Sorts the elements of this list in NlogN time. Equivalent
1308 * elements remain in list order.
1309 */
1310 template<typename _Comp>
1311 void
1312 sort(_Comp __comp);
1313
1314 /**
1315 * @brief Reverse the elements in list.
1316 *
1317 * Reverse the order of elements in the list in linear time.
1318 */
1319 void
1320 reverse() noexcept
1321 { this->_M_impl._M_head._M_reverse_after(); }
1322
1323 private:
1324 // Called by the range constructor to implement [23.3.4.2]/9
1325 template<typename _InputIterator>
1326 void
1327 _M_range_initialize(_InputIterator __first, _InputIterator __last);
1328
1329 // Called by forward_list(n,v,a), and the range constructor when it
1330 // turns out to be the same thing.
1331 void
1332 _M_fill_initialize(size_type __n, const value_type& __value);
1333
1334 // Called by splice_after and insert_after.
1335 iterator
1336 _M_splice_after(const_iterator __pos, const_iterator __before,
1337 const_iterator __last);
1338
1339 // Called by forward_list(n).
1340 void
1341 _M_default_initialize(size_type __n);
1342
1343 // Called by resize(sz).
1344 void
1345 _M_default_insert_after(const_iterator __pos, size_type __n);
1346
1347 // Called by operator=(forward_list&&)
1348 void
1349 _M_move_assign(forward_list&& __list, true_type) noexcept
1350 {
1351 clear();
1352 this->_M_impl._M_head._M_next = __list._M_impl._M_head._M_next;
1353 __list._M_impl._M_head._M_next = nullptr;
1354 std::__alloc_on_move(this->_M_get_Node_allocator(),
1355 __list._M_get_Node_allocator());
1356 }
1357
1358 // Called by operator=(forward_list&&)
1359 void
1360 _M_move_assign(forward_list&& __list, false_type)
1361 {
1362 if (__list._M_get_Node_allocator() == this->_M_get_Node_allocator())
1363 _M_move_assign(std::move(__list), true_type());
1364 else
1365 // The rvalue's allocator cannot be moved, or is not equal,
1366 // so we need to individually move each element.
1367 this->assign(std::make_move_iterator(__list.begin()),
1368 std::make_move_iterator(__list.end()));
1369 }
1370
1371 // Called by assign(_InputIterator, _InputIterator) if _Tp is
1372 // CopyAssignable.
1373 template<typename _InputIterator>
1374 void
1375 _M_assign(_InputIterator __first, _InputIterator __last, true_type)
1376 {
1377 auto __prev = before_begin();
1378 auto __curr = begin();
1379 auto __end = end();
1380 while (__curr != __end && __first != __last)
1381 {
1382 *__curr = *__first;
1383 ++__prev;
1384 ++__curr;
1385 ++__first;
1386 }
1387 if (__first != __last)
1388 insert_after(__prev, __first, __last);
1389 else if (__curr != __end)
1390 erase_after(__prev, __end);
1391 }
1392
1393 // Called by assign(_InputIterator, _InputIterator) if _Tp is not
1394 // CopyAssignable.
1395 template<typename _InputIterator>
1396 void
1397 _M_assign(_InputIterator __first, _InputIterator __last, false_type)
1398 {
1399 clear();
1400 insert_after(cbefore_begin(), __first, __last);
1401 }
1402
1403 // Called by assign(size_type, const _Tp&) if Tp is CopyAssignable
1404 void
1405 _M_assign_n(size_type __n, const _Tp& __val, true_type)
1406 {
1407 auto __prev = before_begin();
1408 auto __curr = begin();
1409 auto __end = end();
1410 while (__curr != __end && __n > 0)
1411 {
1412 *__curr = __val;
1413 ++__prev;
1414 ++__curr;
1415 --__n;
1416 }
1417 if (__n > 0)
1418 insert_after(__prev, __n, __val);
1419 else if (__curr != __end)
1420 erase_after(__prev, __end);
1421 }
1422
1423 // Called by assign(size_type, const _Tp&) if Tp is non-CopyAssignable
1424 void
1425 _M_assign_n(size_type __n, const _Tp& __val, false_type)
1426 {
1427 clear();
1428 insert_after(cbefore_begin(), __n, __val);
1429 }
1430 };
1431
1432 #if __cpp_deduction_guides >= 201606
1433 template<typename _InputIterator, typename _ValT
1434 = typename iterator_traits<_InputIterator>::value_type,
1435 typename _Allocator = allocator<_ValT>,
1436 typename = _RequireInputIter<_InputIterator>,
1437 typename = _RequireAllocator<_Allocator>>
1438 forward_list(_InputIterator, _InputIterator, _Allocator = _Allocator())
1439 -> forward_list<_ValT, _Allocator>;
1440 #endif
1441
1442 /**
1443 * @brief Forward list equality comparison.
1444 * @param __lx A %forward_list
1445 * @param __ly A %forward_list of the same type as @a __lx.
1446 * @return True iff the elements of the forward lists are equal.
1447 *
1448 * This is an equivalence relation. It is linear in the number of
1449 * elements of the forward lists. Deques are considered equivalent
1450 * if corresponding elements compare equal.
1451 */
1452 template<typename _Tp, typename _Alloc>
1453 [[__nodiscard__]]
1454 bool
1455 operator==(const forward_list<_Tp, _Alloc>& __lx,
1456 const forward_list<_Tp, _Alloc>& __ly);
1457
1458 #if __cpp_lib_three_way_comparison
1459 /**
1460 * @brief Forward list ordering relation.
1461 * @param __x A `forward_list`.
1462 * @param __y A `forward_list` of the same type as `__x`.
1463 * @return A value indicating whether `__x` is less than, equal to,
1464 * greater than, or incomparable with `__y`.
1465 *
1466 * See `std::lexicographical_compare_three_way()` for how the determination
1467 * is made. This operator is used to synthesize relational operators like
1468 * `<` and `>=` etc.
1469 */
1470 template<typename _Tp, typename _Alloc>
1471 [[nodiscard]]
1472 inline __detail::__synth3way_t<_Tp>
1473 operator<=>(const forward_list<_Tp, _Alloc>& __x,
1474 const forward_list<_Tp, _Alloc>& __y)
1475 {
1476 return std::lexicographical_compare_three_way(__x.begin(), __x.end(),
1477 __y.begin(), __y.end(),
1478 __detail::__synth3way);
1479 }
1480 #else
1481 /**
1482 * @brief Forward list ordering relation.
1483 * @param __lx A %forward_list.
1484 * @param __ly A %forward_list of the same type as @a __lx.
1485 * @return True iff @a __lx is lexicographically less than @a __ly.
1486 *
1487 * This is a total ordering relation. It is linear in the number of
1488 * elements of the forward lists. The elements must be comparable
1489 * with @c <.
1490 *
1491 * See std::lexicographical_compare() for how the determination is made.
1492 */
1493 template<typename _Tp, typename _Alloc>
1494 [[__nodiscard__]]
1495 inline bool
1496 operator<(const forward_list<_Tp, _Alloc>& __lx,
1497 const forward_list<_Tp, _Alloc>& __ly)
1498 { return std::lexicographical_compare(__lx.cbegin(), __lx.cend(),
1499 __ly.cbegin(), __ly.cend()); }
1500
1501 /// Based on operator==
1502 template<typename _Tp, typename _Alloc>
1503 [[__nodiscard__]]
1504 inline bool
1505 operator!=(const forward_list<_Tp, _Alloc>& __lx,
1506 const forward_list<_Tp, _Alloc>& __ly)
1507 { return !(__lx == __ly); }
1508
1509 /// Based on operator<
1510 template<typename _Tp, typename _Alloc>
1511 [[__nodiscard__]]
1512 inline bool
1513 operator>(const forward_list<_Tp, _Alloc>& __lx,
1514 const forward_list<_Tp, _Alloc>& __ly)
1515 { return (__ly < __lx); }
1516
1517 /// Based on operator<
1518 template<typename _Tp, typename _Alloc>
1519 [[__nodiscard__]]
1520 inline bool
1521 operator>=(const forward_list<_Tp, _Alloc>& __lx,
1522 const forward_list<_Tp, _Alloc>& __ly)
1523 { return !(__lx < __ly); }
1524
1525 /// Based on operator<
1526 template<typename _Tp, typename _Alloc>
1527 [[__nodiscard__]]
1528 inline bool
1529 operator<=(const forward_list<_Tp, _Alloc>& __lx,
1530 const forward_list<_Tp, _Alloc>& __ly)
1531 { return !(__ly < __lx); }
1532 #endif // three-way comparison
1533
1534 /// See std::forward_list::swap().
1535 template<typename _Tp, typename _Alloc>
1536 inline void
1537 swap(forward_list<_Tp, _Alloc>& __lx,
1538 forward_list<_Tp, _Alloc>& __ly)
1539 noexcept(noexcept(__lx.swap(__ly)))
1540 { __lx.swap(__ly); }
1541
1542 _GLIBCXX_END_NAMESPACE_CONTAINER
1543 _GLIBCXX_END_NAMESPACE_VERSION
1544 } // namespace std
1545
1546 #endif // _FORWARD_LIST_H