summaryrefslogtreecommitdiff
path: root/absl/container/inlined_vector.h
blob: 5f3f0095bca81d25d380109af3c5d7f8550edb09 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// -----------------------------------------------------------------------------
// File: inlined_vector.h
// -----------------------------------------------------------------------------
//
// This header file contains the declaration and definition of an "inlined
// vector" which behaves in an equivalent fashion to a `std::vector`, except
// that storage for small sequences of the vector are provided inline without
// requiring any heap allocation.
//
// An `absl::InlinedVector<T, N>` specifies the default capacity `N` as one of
// its template parameters. Instances where `size() <= N` hold contained
// elements in inline space. Typically `N` is very small so that sequences that
// are expected to be short do not require allocations.
//
// An `absl::InlinedVector` does not usually require a specific allocator. If
// the inlined vector grows beyond its initial constraints, it will need to
// allocate (as any normal `std::vector` would). This is usually performed with
// the default allocator (defined as `std::allocator<T>`). Optionally, a custom
// allocator type may be specified as `A` in `absl::InlinedVector<T, N, A>`.

#ifndef ABSL_CONTAINER_INLINED_VECTOR_H_
#define ABSL_CONTAINER_INLINED_VECTOR_H_

#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdlib>
#include <cstring>
#include <initializer_list>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

#include "absl/algorithm/algorithm.h"
#include "absl/base/internal/throw_delegate.h"
#include "absl/base/optimization.h"
#include "absl/base/port.h"
#include "absl/memory/memory.h"

namespace absl {

// -----------------------------------------------------------------------------
// InlinedVector
// -----------------------------------------------------------------------------
//
// An `absl::InlinedVector` is designed to be a drop-in replacement for
// `std::vector` for use cases where the vector's size is sufficiently small
// that it can be inlined. If the inlined vector does grow beyond its estimated
// capacity, it will trigger an initial allocation on the heap, and will behave
// as a `std:vector`. The API of the `absl::InlinedVector` within this file is
// designed to cover the same API footprint as covered by `std::vector`.
template <typename T, size_t N, typename A = std::allocator<T>>
class InlinedVector {
  static_assert(N > 0, "InlinedVector requires inline capacity greater than 0");
  constexpr static typename A::size_type inlined_capacity() {
    return static_cast<typename A::size_type>(N);
  }

  template <typename Iterator>
  using DisableIfIntegral =
      absl::enable_if_t<!std::is_integral<Iterator>::value>;

  template <typename Iterator>
  using EnableIfInputIterator = absl::enable_if_t<std::is_convertible<
      typename std::iterator_traits<Iterator>::iterator_category,
      std::input_iterator_tag>::value>;

  template <typename Iterator>
  using IteratorCategory =
      typename std::iterator_traits<Iterator>::iterator_category;

  using rvalue_reference = typename A::value_type&&;

 public:
  using allocator_type = A;
  using value_type = typename allocator_type::value_type;
  using pointer = typename allocator_type::pointer;
  using const_pointer = typename allocator_type::const_pointer;
  using reference = typename allocator_type::reference;
  using const_reference = typename allocator_type::const_reference;
  using size_type = typename allocator_type::size_type;
  using difference_type = typename allocator_type::difference_type;
  using iterator = pointer;
  using const_iterator = const_pointer;
  using reverse_iterator = std::reverse_iterator<iterator>;
  using const_reverse_iterator = std::reverse_iterator<const_iterator>;

  // ---------------------------------------------------------------------------
  // InlinedVector Constructors and Destructor
  // ---------------------------------------------------------------------------

  // Creates an empty inlined vector with a default initialized allocator.
  InlinedVector() noexcept(noexcept(allocator_type()))
      : allocator_and_tag_(allocator_type()) {}

  // Creates an empty inlined vector with a specified allocator.
  explicit InlinedVector(const allocator_type& alloc) noexcept
      : allocator_and_tag_(alloc) {}

  // Creates an inlined vector with `n` copies of `value_type()`.
  explicit InlinedVector(size_type n,
                         const allocator_type& alloc = allocator_type())
      : allocator_and_tag_(alloc) {
    InitAssign(n);
  }

  // Creates an inlined vector with `n` copies of `v`.
  InlinedVector(size_type n, const_reference v,
                const allocator_type& alloc = allocator_type())
      : allocator_and_tag_(alloc) {
    InitAssign(n, v);
  }

  // Creates an inlined vector of copies of the values in `init_list`.
  InlinedVector(std::initializer_list<value_type> init_list,
                const allocator_type& alloc = allocator_type())
      : allocator_and_tag_(alloc) {
    AppendRange(init_list.begin(), init_list.end(),
                IteratorCategory<decltype(init_list.begin())>{});
  }

  // Creates an inlined vector with elements constructed from the provided
  // Iterator range [`first`, `last`).
  //
  // NOTE: The `enable_if` prevents ambiguous interpretation between a call to
  // this constructor with two integral arguments and a call to the above
  // `InlinedVector(size_type, const_reference)` constructor.
  template <typename InputIterator, DisableIfIntegral<InputIterator>* = nullptr>
  InlinedVector(InputIterator first, InputIterator last,
                const allocator_type& alloc = allocator_type())
      : allocator_and_tag_(alloc) {
    AppendRange(first, last, IteratorCategory<InputIterator>{});
  }

  // Creates a copy of `other` using `other`'s allocator.
  InlinedVector(const InlinedVector& other);

  // Creates a copy of `other` but with a specified allocator.
  InlinedVector(const InlinedVector& other, const allocator_type& alloc);

  // Creates an inlined vector by moving in the contents of `other`.
  //
  // NOTE: This move constructor does not allocate and only moves the underlying
  // objects, so its `noexcept` specification depends on whether moving the
  // underlying objects can throw or not. We assume:
  //  a) move constructors should only throw due to allocation failure and
  //  b) if `value_type`'s move constructor allocates, it uses the same
  //     allocation function as the `InlinedVector`'s allocator, so the move
  //     constructor is non-throwing if the allocator is non-throwing or
  //     `value_type`'s move constructor is specified as `noexcept`.
  InlinedVector(InlinedVector&& v) noexcept(
      absl::allocator_is_nothrow<allocator_type>::value ||
      std::is_nothrow_move_constructible<value_type>::value);

  // Creates an inlined vector by moving in the contents of `other`.
  //
  // NOTE: This move constructor allocates and subsequently moves the underlying
  // objects, so its `noexcept` specification depends on whether the allocation
  // can throw and whether moving the underlying objects can throw. Based on the
  // same assumptions as above, the `noexcept` specification is dominated by
  // whether the allocation can throw regardless of whether `value_type`'s move
  // constructor is specified as `noexcept`.
  InlinedVector(InlinedVector&& v, const allocator_type& alloc) noexcept(
      absl::allocator_is_nothrow<allocator_type>::value);

  ~InlinedVector() { clear(); }

  // ---------------------------------------------------------------------------
  // InlinedVector Member Accessors
  // ---------------------------------------------------------------------------

  // `InlinedVector::empty()`
  //
  // Checks if the inlined vector has no elements.
  bool empty() const noexcept { return !size(); }

  // `InlinedVector::size()`
  //
  // Returns the number of elements in the inlined vector.
  size_type size() const noexcept { return tag().size(); }

  // `InlinedVector::max_size()`
  //
  // Returns the maximum number of elements the vector can hold.
  size_type max_size() const noexcept {
    // One bit of the size storage is used to indicate whether the inlined
    // vector is allocated. As a result, the maximum size of the container that
    // we can express is half of the max for `size_type`.
    return (std::numeric_limits<size_type>::max)() / 2;
  }

  // `InlinedVector::capacity()`
  //
  // Returns the number of elements that can be stored in the inlined vector
  // without requiring a reallocation of underlying memory.
  //
  // NOTE: For most inlined vectors, `capacity()` should equal
  // `inlined_capacity()`. For inlined vectors which exceed this capacity, they
  // will no longer be inlined and `capacity()` will equal its capacity on the
  // allocated heap.
  size_type capacity() const noexcept {
    return allocated() ? allocation().capacity() : inlined_capacity();
  }

  // `InlinedVector::data()`
  //
  // Returns a `pointer` to elements of the inlined vector. This pointer can be
  // used to access and modify the contained elements.
  // Only results within the range [`0`, `size()`) are defined.
  pointer data() noexcept {
    return allocated() ? allocated_space() : inlined_space();
  }

  // Overload of `InlinedVector::data()` to return a `const_pointer` to elements
  // of the inlined vector. This pointer can be used to access (but not modify)
  // the contained elements.
  const_pointer data() const noexcept {
    return allocated() ? allocated_space() : inlined_space();
  }

  // `InlinedVector::operator[]()`
  //
  // Returns a `reference` to the `i`th element of the inlined vector using the
  // array operator.
  reference operator[](size_type i) {
    assert(i < size());
    return data()[i];
  }

  // Overload of `InlinedVector::operator[]()` to return a `const_reference` to
  // the `i`th element of the inlined vector.
  const_reference operator[](size_type i) const {
    assert(i < size());
    return data()[i];
  }

  // `InlinedVector::at()`
  //
  // Returns a `reference` to the `i`th element of the inlined vector.
  reference at(size_type i) {
    if (ABSL_PREDICT_FALSE(i >= size())) {
      base_internal::ThrowStdOutOfRange(
          "InlinedVector::at() failed bounds check");
    }
    return data()[i];
  }

  // Overload of `InlinedVector::at()` to return a `const_reference` to the
  // `i`th element of the inlined vector.
  const_reference at(size_type i) const {
    if (ABSL_PREDICT_FALSE(i >= size())) {
      base_internal::ThrowStdOutOfRange(
          "InlinedVector::at() failed bounds check");
    }
    return data()[i];
  }

  // `InlinedVector::front()`
  //
  // Returns a `reference` to the first element of the inlined vector.
  reference front() {
    assert(!empty());
    return at(0);
  }

  // Overload of `InlinedVector::front()` returns a `const_reference` to the
  // first element of the inlined vector.
  const_reference front() const {
    assert(!empty());
    return at(0);
  }

  // `InlinedVector::back()`
  //
  // Returns a `reference` to the last element of the inlined vector.
  reference back() {
    assert(!empty());
    return at(size() - 1);
  }

  // Overload of `InlinedVector::back()` to return a `const_reference` to the
  // last element of the inlined vector.
  const_reference back() const {
    assert(!empty());
    return at(size() - 1);
  }

  // `InlinedVector::begin()`
  //
  // Returns an `iterator` to the beginning of the inlined vector.
  iterator begin() noexcept { return data(); }

  // Overload of `InlinedVector::begin()` to return a `const_iterator` to
  // the beginning of the inlined vector.
  const_iterator begin() const noexcept { return data(); }

  // `InlinedVector::end()`
  //
  // Returns an `iterator` to the end of the inlined vector.
  iterator end() noexcept { return data() + size(); }

  // Overload of `InlinedVector::end()` to return a `const_iterator` to the
  // end of the inlined vector.
  const_iterator end() const noexcept { return data() + size(); }

  // `InlinedVector::cbegin()`
  //
  // Returns a `const_iterator` to the beginning of the inlined vector.
  const_iterator cbegin() const noexcept { return begin(); }

  // `InlinedVector::cend()`
  //
  // Returns a `const_iterator` to the end of the inlined vector.
  const_iterator cend() const noexcept { return end(); }

  // `InlinedVector::rbegin()`
  //
  // Returns a `reverse_iterator` from the end of the inlined vector.
  reverse_iterator rbegin() noexcept { return reverse_iterator(end()); }

  // Overload of `InlinedVector::rbegin()` to return a
  // `const_reverse_iterator` from the end of the inlined vector.
  const_reverse_iterator rbegin() const noexcept {
    return const_reverse_iterator(end());
  }

  // `InlinedVector::rend()`
  //
  // Returns a `reverse_iterator` from the beginning of the inlined vector.
  reverse_iterator rend() noexcept { return reverse_iterator(begin()); }

  // Overload of `InlinedVector::rend()` to return a `const_reverse_iterator`
  // from the beginning of the inlined vector.
  const_reverse_iterator rend() const noexcept {
    return const_reverse_iterator(begin());
  }

  // `InlinedVector::crbegin()`
  //
  // Returns a `const_reverse_iterator` from the end of the inlined vector.
  const_reverse_iterator crbegin() const noexcept { return rbegin(); }

  // `InlinedVector::crend()`
  //
  // Returns a `const_reverse_iterator` from the beginning of the inlined
  // vector.
  const_reverse_iterator crend() const noexcept { return rend(); }

  // `InlinedVector::get_allocator()`
  //
  // Returns a copy of the allocator of the inlined vector.
  allocator_type get_allocator() const { return allocator(); }

  // ---------------------------------------------------------------------------
  // InlinedVector Member Mutators
  // ---------------------------------------------------------------------------

  // `InlinedVector::operator=()`
  //
  // Replaces the contents of the inlined vector with copies of the elements in
  // the provided `std::initializer_list`.
  InlinedVector& operator=(std::initializer_list<value_type> init_list) {
    AssignRange(init_list.begin(), init_list.end(),
                IteratorCategory<decltype(init_list.begin())>{});
    return *this;
  }

  // Overload of `InlinedVector::operator=()` to replace the contents of the
  // inlined vector with the contents of `other`.
  InlinedVector& operator=(const InlinedVector& other) {
    if (ABSL_PREDICT_FALSE(this == &other)) return *this;

    // Optimized to avoid reallocation.
    // Prefer reassignment to copy construction for elements.
    if (size() < other.size()) {  // grow
      reserve(other.size());
      std::copy(other.begin(), other.begin() + size(), begin());
      std::copy(other.begin() + size(), other.end(), std::back_inserter(*this));
    } else {  // maybe shrink
      erase(begin() + other.size(), end());
      std::copy(other.begin(), other.end(), begin());
    }
    return *this;
  }

  // Overload of `InlinedVector::operator=()` to replace the contents of the
  // inlined vector with the contents of `other`.
  //
  // NOTE: As a result of calling this overload, `other` may be empty or it's
  // contents may be left in a moved-from state.
  InlinedVector& operator=(InlinedVector&& other) {
    if (ABSL_PREDICT_FALSE(this == &other)) return *this;

    if (other.allocated()) {
      clear();
      tag().set_allocated_size(other.size());
      init_allocation(other.allocation());
      other.tag() = Tag();
    } else {
      if (allocated()) clear();
      // Both are inlined now.
      if (size() < other.size()) {
        auto mid = std::make_move_iterator(other.begin() + size());
        std::copy(std::make_move_iterator(other.begin()), mid, begin());
        UninitializedCopy(mid, std::make_move_iterator(other.end()), end());
      } else {
        auto new_end = std::copy(std::make_move_iterator(other.begin()),
                                 std::make_move_iterator(other.end()), begin());
        Destroy(new_end, end());
      }
      tag().set_inline_size(other.size());
    }
    return *this;
  }

  // `InlinedVector::assign()`
  //
  // Replaces the contents of the inlined vector with `n` copies of `v`.
  void assign(size_type n, const_reference v) {
    if (n <= size()) {  // Possibly shrink
      std::fill_n(begin(), n, v);
      erase(begin() + n, end());
      return;
    }
    // Grow
    reserve(n);
    std::fill_n(begin(), size(), v);
    if (allocated()) {
      UninitializedFill(allocated_space() + size(), allocated_space() + n, v);
      tag().set_allocated_size(n);
    } else {
      UninitializedFill(inlined_space() + size(), inlined_space() + n, v);
      tag().set_inline_size(n);
    }
  }

  // Overload of `InlinedVector::assign()` to replace the contents of the
  // inlined vector with copies of the values in the provided
  // `std::initializer_list`.
  void assign(std::initializer_list<value_type> init_list) {
    AssignRange(init_list.begin(), init_list.end(),
                IteratorCategory<decltype(init_list.begin())>{});
  }

  // Overload of `InlinedVector::assign()` to replace the contents of the
  // inlined vector with values constructed from the range [`first`, `last`).
  template <typename InputIterator, DisableIfIntegral<InputIterator>* = nullptr>
  void assign(InputIterator first, InputIterator last) {
    AssignRange(first, last, IteratorCategory<InputIterator>{});
  }

  // `InlinedVector::resize()`
  //
  // Resizes the inlined vector to contain `n` elements. If `n` is smaller than
  // the inlined vector's current size, extra elements are destroyed. If `n` is
  // larger than the initial size, new elements are value-initialized.
  void resize(size_type n);

  // Overload of `InlinedVector::resize()` to resize the inlined vector to
  // contain `n` elements where, if `n` is larger than `size()`, the new values
  // will be copy-constructed from `v`.
  void resize(size_type n, const_reference v);

  // `InlinedVector::insert()`
  //
  // Copies `v` into `position`, returning an `iterator` pointing to the newly
  // inserted element.
  iterator insert(const_iterator position, const_reference v) {
    return emplace(position, v);
  }

  // Overload of `InlinedVector::insert()` for moving `v` into `position`,
  // returning an iterator pointing to the newly inserted element.
  iterator insert(const_iterator position, rvalue_reference v) {
    return emplace(position, std::move(v));
  }

  // Overload of `InlinedVector::insert()` for inserting `n` contiguous copies
  // of `v` starting at `position`. Returns an `iterator` pointing to the first
  // of the newly inserted elements.
  iterator insert(const_iterator position, size_type n, const_reference v) {
    return InsertWithCount(position, n, v);
  }

  // Overload of `InlinedVector::insert()` for copying the contents of the
  // `std::initializer_list` into the vector starting at `position`. Returns an
  // `iterator` pointing to the first of the newly inserted elements.
  iterator insert(const_iterator position,
                  std::initializer_list<value_type> init_list) {
    return insert(position, init_list.begin(), init_list.end());
  }

  // Overload of `InlinedVector::insert()` for inserting elements constructed
  // from the range [`first`, `last`). Returns an `iterator` pointing to the
  // first of the newly inserted elements.
  //
  // NOTE: The `enable_if` is intended to disambiguate the two three-argument
  // overloads of `insert()`.
  template <typename InputIterator,
            typename = EnableIfInputIterator<InputIterator>>
  iterator insert(const_iterator position, InputIterator first,
                  InputIterator last) {
    return InsertWithRange(position, first, last,
                           IteratorCategory<InputIterator>());
  }

  // `InlinedVector::emplace()`
  //
  // Constructs and inserts an object in the inlined vector at the given
  // `position`, returning an `iterator` pointing to the newly emplaced element.
  template <typename... Args>
  iterator emplace(const_iterator position, Args&&... args);

  // `InlinedVector::emplace_back()`
  //
  // Constructs and appends a new element to the end of the inlined vector,
  // returning a `reference` to the emplaced element.
  template <typename... Args>
  reference emplace_back(Args&&... args) {
    size_type s = size();
    assert(s <= capacity());
    if (ABSL_PREDICT_FALSE(s == capacity())) {
      return GrowAndEmplaceBack(std::forward<Args>(args)...);
    }
    assert(s < capacity());

    pointer space;
    if (allocated()) {
      tag().set_allocated_size(s + 1);
      space = allocated_space();
    } else {
      tag().set_inline_size(s + 1);
      space = inlined_space();
    }
    return Construct(space + s, std::forward<Args>(args)...);
  }

  // `InlinedVector::push_back()`
  //
  // Appends a copy of `v` to the end of the inlined vector.
  void push_back(const_reference v) { static_cast<void>(emplace_back(v)); }

  // Overload of `InlinedVector::push_back()` for moving `v` into a newly
  // appended element.
  void push_back(rvalue_reference v) {
    static_cast<void>(emplace_back(std::move(v)));
  }

  // `InlinedVector::pop_back()`
  //
  // Destroys the element at the end of the inlined vector and shrinks the size
  // by `1` (unless the inlined vector is empty, in which case this is a no-op).
  void pop_back() noexcept {
    assert(!empty());
    size_type s = size();
    if (allocated()) {
      Destroy(allocated_space() + s - 1, allocated_space() + s);
      tag().set_allocated_size(s - 1);
    } else {
      Destroy(inlined_space() + s - 1, inlined_space() + s);
      tag().set_inline_size(s - 1);
    }
  }

  // `InlinedVector::erase()`
  //
  // Erases the element at `position` of the inlined vector, returning an
  // `iterator` pointing to the first element following the erased element.
  //
  // NOTE: May return the end iterator, which is not dereferencable.
  iterator erase(const_iterator position) {
    assert(position >= begin());
    assert(position < end());

    iterator pos = const_cast<iterator>(position);
    std::move(pos + 1, end(), pos);
    pop_back();
    return pos;
  }

  // Overload of `InlinedVector::erase()` for erasing all elements in the
  // range [`from`, `to`) in the inlined vector. Returns an `iterator` pointing
  // to the first element following the range erased or the end iterator if `to`
  // was the end iterator.
  iterator erase(const_iterator from, const_iterator to);

  // `InlinedVector::clear()`
  //
  // Destroys all elements in the inlined vector, sets the size of `0` and
  // deallocates the heap allocation if the inlined vector was allocated.
  void clear() noexcept {
    size_type s = size();
    if (allocated()) {
      Destroy(allocated_space(), allocated_space() + s);
      allocation().Dealloc(allocator());
    } else if (s != 0) {  // do nothing for empty vectors
      Destroy(inlined_space(), inlined_space() + s);
    }
    tag() = Tag();
  }

  // `InlinedVector::reserve()`
  //
  // Enlarges the underlying representation of the inlined vector so it can hold
  // at least `n` elements. This method does not change `size()` or the actual
  // contents of the vector.
  //
  // NOTE: If `n` does not exceed `capacity()`, `reserve()` will have no
  // effects. Otherwise, `reserve()` will reallocate, performing an n-time
  // element-wise move of everything contained.
  void reserve(size_type n) {
    if (n > capacity()) {
      // Make room for new elements
      EnlargeBy(n - size());
    }
  }

  // `InlinedVector::shrink_to_fit()`
  //
  // Reduces memory usage by freeing unused memory. After this call, calls to
  // `capacity()` will be equal to `(std::max)(inlined_capacity(), size())`.
  //
  // If `size() <= inlined_capacity()` and the elements are currently stored on
  // the heap, they will be moved to the inlined storage and the heap memory
  // will be deallocated.
  //
  // If `size() > inlined_capacity()` and `size() < capacity()` the elements
  // will be moved to a smaller heap allocation.
  void shrink_to_fit() {
    const auto s = size();
    if (ABSL_PREDICT_FALSE(!allocated() || s == capacity())) return;

    if (s <= inlined_capacity()) {
      // Move the elements to the inlined storage.
      // We have to do this using a temporary, because `inlined_storage` and
      // `allocation_storage` are in a union field.
      auto temp = std::move(*this);
      assign(std::make_move_iterator(temp.begin()),
             std::make_move_iterator(temp.end()));
      return;
    }

    // Reallocate storage and move elements.
    // We can't simply use the same approach as above, because `assign()` would
    // call into `reserve()` internally and reserve larger capacity than we need
    Allocation new_allocation(allocator(), s);
    UninitializedCopy(std::make_move_iterator(allocated_space()),
                      std::make_move_iterator(allocated_space() + s),
                      new_allocation.buffer());
    ResetAllocation(new_allocation, s);
  }

  // `InlinedVector::swap()`
  //
  // Swaps the contents of this inlined vector with the contents of `other`.
  void swap(InlinedVector& other);

  template <typename Hash>
  friend Hash AbslHashValue(Hash hash, const InlinedVector& inlined_vector) {
    const_pointer p = inlined_vector.data();
    size_type n = inlined_vector.size();
    return Hash::combine(Hash::combine_contiguous(std::move(hash), p, n), n);
  }

 private:
  // Holds whether the vector is allocated or not in the lowest bit and the size
  // in the high bits:
  //   `size_ = (size << 1) | is_allocated;`
  class Tag {
   public:
    Tag() : size_(0) {}
    size_type size() const { return size_ / 2; }
    void add_size(size_type n) { size_ += n * 2; }
    void set_inline_size(size_type n) { size_ = n * 2; }
    void set_allocated_size(size_type n) { size_ = (n * 2) + 1; }
    bool allocated() const { return size_ % 2; }

   private:
    size_type size_;
  };

  // Derives from `allocator_type` to use the empty base class optimization.
  // If the `allocator_type` is stateless, we can store our instance for free.
  class AllocatorAndTag : private allocator_type {
   public:
    explicit AllocatorAndTag(const allocator_type& a) : allocator_type(a) {}

    Tag& tag() { return tag_; }
    const Tag& tag() const { return tag_; }

    allocator_type& allocator() { return *this; }
    const allocator_type& allocator() const { return *this; }

   private:
    Tag tag_;
  };

  class Allocation {
   public:
    Allocation(allocator_type& a, size_type capacity)
        : capacity_(capacity), buffer_(Create(a, capacity)) {}

    void Dealloc(allocator_type& a) {
      std::allocator_traits<allocator_type>::deallocate(a, buffer_, capacity_);
    }

    size_type capacity() const { return capacity_; }

    const_pointer buffer() const { return buffer_; }

    pointer buffer() { return buffer_; }

   private:
    static pointer Create(allocator_type& a, size_type n) {
      return std::allocator_traits<allocator_type>::allocate(a, n);
    }

    size_type capacity_;
    pointer buffer_;
  };

  const Tag& tag() const { return allocator_and_tag_.tag(); }

  Tag& tag() { return allocator_and_tag_.tag(); }

  Allocation& allocation() {
    return reinterpret_cast<Allocation&>(rep_.allocation_storage.allocation);
  }

  const Allocation& allocation() const {
    return reinterpret_cast<const Allocation&>(
        rep_.allocation_storage.allocation);
  }

  void init_allocation(const Allocation& allocation) {
    new (&rep_.allocation_storage.allocation) Allocation(allocation);
  }

  // TODO(absl-team): investigate whether the reinterpret_cast is appropriate.
  pointer inlined_space() {
    return reinterpret_cast<pointer>(
        std::addressof(rep_.inlined_storage.inlined[0]));
  }

  const_pointer inlined_space() const {
    return reinterpret_cast<const_pointer>(
        std::addressof(rep_.inlined_storage.inlined[0]));
  }

  pointer allocated_space() { return allocation().buffer(); }

  const_pointer allocated_space() const { return allocation().buffer(); }

  const allocator_type& allocator() const {
    return allocator_and_tag_.allocator();
  }

  allocator_type& allocator() { return allocator_and_tag_.allocator(); }

  bool allocated() const { return tag().allocated(); }

  // Enlarge the underlying representation so we can store `size_ + delta` elems
  // in allocated space. The size is not changed, and any newly added memory is
  // not initialized.
  void EnlargeBy(size_type delta);

  // Shift all elements from `position` to `end()` by `n` places to the right.
  // If the vector needs to be enlarged, memory will be allocated.
  // Returns `iterator`s pointing to the start of the previously-initialized
  // portion and the start of the uninitialized portion of the created gap.
  // The number of initialized spots is `pair.second - pair.first`. The number
  // of raw spots is `n - (pair.second - pair.first)`.
  //
  // Updates the size of the InlinedVector internally.
  std::pair<iterator, iterator> ShiftRight(const_iterator position,
                                           size_type n);

  void ResetAllocation(Allocation new_allocation, size_type new_size) {
    if (allocated()) {
      Destroy(allocated_space(), allocated_space() + size());
      assert(begin() == allocated_space());
      allocation().Dealloc(allocator());
      allocation() = new_allocation;
    } else {
      Destroy(inlined_space(), inlined_space() + size());
      init_allocation(new_allocation);  // bug: only init once
    }
    tag().set_allocated_size(new_size);
  }

  template <typename... Args>
  reference GrowAndEmplaceBack(Args&&... args) {
    assert(size() == capacity());
    const size_type s = size();

    Allocation new_allocation(allocator(), 2 * capacity());

    reference new_element =
        Construct(new_allocation.buffer() + s, std::forward<Args>(args)...);
    UninitializedCopy(std::make_move_iterator(data()),
                      std::make_move_iterator(data() + s),
                      new_allocation.buffer());

    ResetAllocation(new_allocation, s + 1);

    return new_element;
  }

  void InitAssign(size_type n);

  void InitAssign(size_type n, const_reference v);

  template <typename... Args>
  reference Construct(pointer p, Args&&... args) {
    std::allocator_traits<allocator_type>::construct(
        allocator(), p, std::forward<Args>(args)...);
    return *p;
  }

  template <typename Iterator>
  void UninitializedCopy(Iterator src, Iterator src_last, pointer dst) {
    for (; src != src_last; ++dst, ++src) Construct(dst, *src);
  }

  template <typename... Args>
  void UninitializedFill(pointer dst, pointer dst_last, const Args&... args) {
    for (; dst != dst_last; ++dst) Construct(dst, args...);
  }

  // Destroy [`from`, `to`) in place.
  void Destroy(pointer from, pointer to);

  template <typename Iterator>
  void AppendRange(Iterator first, Iterator last, std::forward_iterator_tag);

  template <typename Iterator>
  void AppendRange(Iterator first, Iterator last, std::input_iterator_tag);

  template <typename Iterator>
  void AssignRange(Iterator first, Iterator last, std::forward_iterator_tag);

  template <typename Iterator>
  void AssignRange(Iterator first, Iterator last, std::input_iterator_tag);

  iterator InsertWithCount(const_iterator position, size_type n,
                           const_reference v);

  template <typename ForwardIterator>
  iterator InsertWithRange(const_iterator position, ForwardIterator first,
                           ForwardIterator last, std::forward_iterator_tag);

  template <typename InputIterator>
  iterator InsertWithRange(const_iterator position, InputIterator first,
                           InputIterator last, std::input_iterator_tag);

  // Stores either the inlined or allocated representation
  union Rep {
    using ValueTypeBuffer =
        absl::aligned_storage_t<sizeof(value_type), alignof(value_type)>;
    using AllocationBuffer =
        absl::aligned_storage_t<sizeof(Allocation), alignof(Allocation)>;

    // Structs wrap the buffers to perform indirection that solves a bizarre
    // compilation error on Visual Studio (all known versions).
    struct InlinedRep {
      ValueTypeBuffer inlined[N];
    };
    struct AllocatedRep {
      AllocationBuffer allocation;
    };

    InlinedRep inlined_storage;
    AllocatedRep allocation_storage;
  };

  AllocatorAndTag allocator_and_tag_;
  Rep rep_;
};

// -----------------------------------------------------------------------------
// InlinedVector Non-Member Functions
// -----------------------------------------------------------------------------

// `swap()`
//
// Swaps the contents of two inlined vectors. This convenience function
// simply calls `InlinedVector::swap()`.
template <typename T, size_t N, typename A>
void swap(InlinedVector<T, N, A>& a,
          InlinedVector<T, N, A>& b) noexcept(noexcept(a.swap(b))) {
  a.swap(b);
}

// `operator==()`
//
// Tests the equivalency of the contents of two inlined vectors.
template <typename T, size_t N, typename A>
bool operator==(const InlinedVector<T, N, A>& a,
                const InlinedVector<T, N, A>& b) {
  return absl::equal(a.begin(), a.end(), b.begin(), b.end());
}

// `operator!=()`
//
// Tests the inequality of the contents of two inlined vectors.
template <typename T, size_t N, typename A>
bool operator!=(const InlinedVector<T, N, A>& a,
                const InlinedVector<T, N, A>& b) {
  return !(a == b);
}

// `operator<()`
//
// Tests whether the contents of one inlined vector are less than the contents
// of another through a lexicographical comparison operation.
template <typename T, size_t N, typename A>
bool operator<(const InlinedVector<T, N, A>& a,
               const InlinedVector<T, N, A>& b) {
  return std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end());
}

// `operator>()`
//
// Tests whether the contents of one inlined vector are greater than the
// contents of another through a lexicographical comparison operation.
template <typename T, size_t N, typename A>
bool operator>(const InlinedVector<T, N, A>& a,
               const InlinedVector<T, N, A>& b) {
  return b < a;
}

// `operator<=()`
//
// Tests whether the contents of one inlined vector are less than or equal to
// the contents of another through a lexicographical comparison operation.
template <typename T, size_t N, typename A>
bool operator<=(const InlinedVector<T, N, A>& a,
                const InlinedVector<T, N, A>& b) {
  return !(b < a);
}

// `operator>=()`
//
// Tests whether the contents of one inlined vector are greater than or equal to
// the contents of another through a lexicographical comparison operation.
template <typename T, size_t N, typename A>
bool operator>=(const InlinedVector<T, N, A>& a,
                const InlinedVector<T, N, A>& b) {
  return !(a < b);
}

// -----------------------------------------------------------------------------
// Implementation of InlinedVector
//
// Do not depend on any below implementation details!
// -----------------------------------------------------------------------------

template <typename T, size_t N, typename A>
InlinedVector<T, N, A>::InlinedVector(const InlinedVector& other)
    : allocator_and_tag_(other.allocator()) {
  reserve(other.size());
  if (allocated()) {
    UninitializedCopy(other.begin(), other.end(), allocated_space());
    tag().set_allocated_size(other.size());
  } else {
    UninitializedCopy(other.begin(), other.end(), inlined_space());
    tag().set_inline_size(other.size());
  }
}

template <typename T, size_t N, typename A>
InlinedVector<T, N, A>::InlinedVector(const InlinedVector& other,
                                      const allocator_type& alloc)
    : allocator_and_tag_(alloc) {
  reserve(other.size());
  if (allocated()) {
    UninitializedCopy(other.begin(), other.end(), allocated_space());
    tag().set_allocated_size(other.size());
  } else {
    UninitializedCopy(other.begin(), other.end(), inlined_space());
    tag().set_inline_size(other.size());
  }
}

template <typename T, size_t N, typename A>
InlinedVector<T, N, A>::InlinedVector(InlinedVector&& other) noexcept(
    absl::allocator_is_nothrow<allocator_type>::value ||
    std::is_nothrow_move_constructible<value_type>::value)
    : allocator_and_tag_(other.allocator_and_tag_) {
  if (other.allocated()) {
    // We can just steal the underlying buffer from the source.
    // That leaves the source empty, so we clear its size.
    init_allocation(other.allocation());
    other.tag() = Tag();
  } else {
    UninitializedCopy(
        std::make_move_iterator(other.inlined_space()),
        std::make_move_iterator(other.inlined_space() + other.size()),
        inlined_space());
  }
}

template <typename T, size_t N, typename A>
InlinedVector<T, N, A>::InlinedVector(InlinedVector&& other,
                                      const allocator_type& alloc) noexcept(  //
    absl::allocator_is_nothrow<allocator_type>::value)
    : allocator_and_tag_(alloc) {
  if (other.allocated()) {
    if (alloc == other.allocator()) {
      // We can just steal the allocation from the source.
      tag() = other.tag();
      init_allocation(other.allocation());
      other.tag() = Tag();
    } else {
      // We need to use our own allocator
      reserve(other.size());
      UninitializedCopy(std::make_move_iterator(other.begin()),
                        std::make_move_iterator(other.end()),
                        allocated_space());
      tag().set_allocated_size(other.size());
    }
  } else {
    UninitializedCopy(
        std::make_move_iterator(other.inlined_space()),
        std::make_move_iterator(other.inlined_space() + other.size()),
        inlined_space());
    tag().set_inline_size(other.size());
  }
}

template <typename T, size_t N, typename A>
void InlinedVector<T, N, A>::InitAssign(size_type n, const_reference v) {
  if (n > inlined_capacity()) {
    Allocation new_allocation(allocator(), n);
    init_allocation(new_allocation);
    UninitializedFill(allocated_space(), allocated_space() + n, v);
    tag().set_allocated_size(n);
  } else {
    UninitializedFill(inlined_space(), inlined_space() + n, v);
    tag().set_inline_size(n);
  }
}

template <typename T, size_t N, typename A>
void InlinedVector<T, N, A>::InitAssign(size_type n) {
  if (n > inlined_capacity()) {
    Allocation new_allocation(allocator(), n);
    init_allocation(new_allocation);
    UninitializedFill(allocated_space(), allocated_space() + n);
    tag().set_allocated_size(n);
  } else {
    UninitializedFill(inlined_space(), inlined_space() + n);
    tag().set_inline_size(n);
  }
}

template <typename T, size_t N, typename A>
void InlinedVector<T, N, A>::resize(size_type n) {
  size_type s = size();
  if (n < s) {
    erase(begin() + n, end());
    return;
  }
  reserve(n);
  assert(capacity() >= n);

  // Fill new space with elements constructed in-place.
  if (allocated()) {
    UninitializedFill(allocated_space() + s, allocated_space() + n);
    tag().set_allocated_size(n);
  } else {
    UninitializedFill(inlined_space() + s, inlined_space() + n);
    tag().set_inline_size(n);
  }
}

template <typename T, size_t N, typename A>
void InlinedVector<T, N, A>::resize(size_type n, const_reference v) {
  size_type s = size();
  if (n < s) {
    erase(begin() + n, end());
    return;
  }
  reserve(n);
  assert(capacity() >= n);

  // Fill new space with copies of 'v'.
  if (allocated()) {
    UninitializedFill(allocated_space() + s, allocated_space() + n, v);
    tag().set_allocated_size(n);
  } else {
    UninitializedFill(inlined_space() + s, inlined_space() + n, v);
    tag().set_inline_size(n);
  }
}

template <typename T, size_t N, typename A>
template <typename... Args>
auto InlinedVector<T, N, A>::emplace(const_iterator position, Args&&... args)
    -> iterator {
  assert(position >= begin());
  assert(position <= end());
  if (ABSL_PREDICT_FALSE(position == end())) {
    emplace_back(std::forward<Args>(args)...);
    return end() - 1;
  }

  T new_t = T(std::forward<Args>(args)...);

  auto range = ShiftRight(position, 1);
  if (range.first == range.second) {
    // constructing into uninitialized memory
    Construct(range.first, std::move(new_t));
  } else {
    // assigning into moved-from object
    *range.first = T(std::move(new_t));
  }

  return range.first;
}

template <typename T, size_t N, typename A>
auto InlinedVector<T, N, A>::erase(const_iterator from, const_iterator to)
    -> iterator {
  assert(begin() <= from);
  assert(from <= to);
  assert(to <= end());

  iterator range_start = const_cast<iterator>(from);
  iterator range_end = const_cast<iterator>(to);

  size_type s = size();
  ptrdiff_t erase_gap = std::distance(range_start, range_end);
  if (erase_gap > 0) {
    pointer space;
    if (allocated()) {
      space = allocated_space();
      tag().set_allocated_size(s - erase_gap);
    } else {
      space = inlined_space();
      tag().set_inline_size(s - erase_gap);
    }
    std::move(range_end, space + s, range_start);
    Destroy(space + s - erase_gap, space + s);
  }
  return range_start;
}

template <typename T, size_t N, typename A>
void InlinedVector<T, N, A>::swap(InlinedVector& other) {
  using std::swap;  // Augment ADL with `std::swap`.
  if (ABSL_PREDICT_FALSE(this == &other)) return;

  if (allocated() && other.allocated()) {
    // Both out of line, so just swap the tag, allocation, and allocator.
    swap(tag(), other.tag());
    swap(allocation(), other.allocation());
    swap(allocator(), other.allocator());
    return;
  }
  if (!allocated() && !other.allocated()) {
    // Both inlined: swap up to smaller size, then move remaining elements.
    InlinedVector* a = this;
    InlinedVector* b = &other;
    if (size() < other.size()) {
      swap(a, b);
    }

    const size_type a_size = a->size();
    const size_type b_size = b->size();
    assert(a_size >= b_size);
    // `a` is larger. Swap the elements up to the smaller array size.
    std::swap_ranges(a->inlined_space(), a->inlined_space() + b_size,
                     b->inlined_space());

    // Move the remaining elements:
    //   [`b_size`, `a_size`) from `a` -> [`b_size`, `a_size`) from `b`
    b->UninitializedCopy(a->inlined_space() + b_size,
                         a->inlined_space() + a_size,
                         b->inlined_space() + b_size);
    a->Destroy(a->inlined_space() + b_size, a->inlined_space() + a_size);

    swap(a->tag(), b->tag());
    swap(a->allocator(), b->allocator());
    assert(b->size() == a_size);
    assert(a->size() == b_size);
    return;
  }

  // One is out of line, one is inline.
  // We first move the elements from the inlined vector into the
  // inlined space in the other vector.  We then put the other vector's
  // pointer/capacity into the originally inlined vector and swap
  // the tags.
  InlinedVector* a = this;
  InlinedVector* b = &other;
  if (a->allocated()) {
    swap(a, b);
  }
  assert(!a->allocated());
  assert(b->allocated());
  const size_type a_size = a->size();
  const size_type b_size = b->size();
  // In an optimized build, `b_size` would be unused.
  static_cast<void>(b_size);

  // Made Local copies of `size()`, don't need `tag()` accurate anymore
  swap(a->tag(), b->tag());

  // Copy `b_allocation` out before `b`'s union gets clobbered by `inline_space`
  Allocation b_allocation = b->allocation();

  b->UninitializedCopy(a->inlined_space(), a->inlined_space() + a_size,
                       b->inlined_space());
  a->Destroy(a->inlined_space(), a->inlined_space() + a_size);

  a->allocation() = b_allocation;

  if (a->allocator() != b->allocator()) {
    swap(a->allocator(), b->allocator());
  }

  assert(b->size() == a_size);
  assert(a->size() == b_size);
}

template <typename T, size_t N, typename A>
void InlinedVector<T, N, A>::EnlargeBy(size_type delta) {
  const size_type s = size();
  assert(s <= capacity());

  size_type target = std::max(inlined_capacity(), s + delta);

  // Compute new capacity by repeatedly doubling current capacity
  // TODO(psrc): Check and avoid overflow?
  size_type new_capacity = capacity();
  while (new_capacity < target) {
    new_capacity <<= 1;
  }

  Allocation new_allocation(allocator(), new_capacity);

  UninitializedCopy(std::make_move_iterator(data()),
                    std::make_move_iterator(data() + s),
                    new_allocation.buffer());

  ResetAllocation(new_allocation, s);
}

template <typename T, size_t N, typename A>
auto InlinedVector<T, N, A>::ShiftRight(const_iterator position, size_type n)
    -> std::pair<iterator, iterator> {
  iterator start_used = const_cast<iterator>(position);
  iterator start_raw = const_cast<iterator>(position);
  size_type s = size();
  size_type required_size = s + n;

  if (required_size > capacity()) {
    // Compute new capacity by repeatedly doubling current capacity
    size_type new_capacity = capacity();
    while (new_capacity < required_size) {
      new_capacity <<= 1;
    }
    // Move everyone into the new allocation, leaving a gap of `n` for the
    // requested shift.
    Allocation new_allocation(allocator(), new_capacity);
    size_type index = position - begin();
    UninitializedCopy(std::make_move_iterator(data()),
                      std::make_move_iterator(data() + index),
                      new_allocation.buffer());
    UninitializedCopy(std::make_move_iterator(data() + index),
                      std::make_move_iterator(data() + s),
                      new_allocation.buffer() + index + n);
    ResetAllocation(new_allocation, s);

    // New allocation means our iterator is invalid, so we'll recalculate.
    // Since the entire gap is in new space, there's no used space to reuse.
    start_raw = begin() + index;
    start_used = start_raw;
  } else {
    // If we had enough space, it's a two-part move. Elements going into
    // previously-unoccupied space need an `UninitializedCopy()`. Elements
    // going into a previously-occupied space are just a `std::move()`.
    iterator pos = const_cast<iterator>(position);
    iterator raw_space = end();
    size_type slots_in_used_space = raw_space - pos;
    size_type new_elements_in_used_space = std::min(n, slots_in_used_space);
    size_type new_elements_in_raw_space = n - new_elements_in_used_space;
    size_type old_elements_in_used_space =
        slots_in_used_space - new_elements_in_used_space;

    UninitializedCopy(std::make_move_iterator(pos + old_elements_in_used_space),
                      std::make_move_iterator(raw_space),
                      raw_space + new_elements_in_raw_space);
    std::move_backward(pos, pos + old_elements_in_used_space, raw_space);

    // If the gap is entirely in raw space, the used space starts where the raw
    // space starts, leaving no elements in used space. If the gap is entirely
    // in used space, the raw space starts at the end of the gap, leaving all
    // elements accounted for within the used space.
    start_used = pos;
    start_raw = pos + new_elements_in_used_space;
  }
  tag().add_size(n);
  return std::make_pair(start_used, start_raw);
}

template <typename T, size_t N, typename A>
void InlinedVector<T, N, A>::Destroy(pointer from, pointer to) {
  for (pointer cur = from; cur != to; ++cur) {
    std::allocator_traits<allocator_type>::destroy(allocator(), cur);
  }
#ifndef NDEBUG
  // Overwrite unused memory with `0xab` so we can catch uninitialized usage.
  // Cast to `void*` to tell the compiler that we don't care that we might be
  // scribbling on a vtable pointer.
  if (from != to) {
    auto len = sizeof(value_type) * std::distance(from, to);
    std::memset(reinterpret_cast<void*>(from), 0xab, len);
  }
#endif
}

template <typename T, size_t N, typename A>
template <typename Iterator>
void InlinedVector<T, N, A>::AppendRange(Iterator first, Iterator last,
                                         std::forward_iterator_tag) {
  auto length = std::distance(first, last);
  reserve(size() + length);
  if (allocated()) {
    UninitializedCopy(first, last, allocated_space() + size());
    tag().set_allocated_size(size() + length);
  } else {
    UninitializedCopy(first, last, inlined_space() + size());
    tag().set_inline_size(size() + length);
  }
}

template <typename T, size_t N, typename A>
template <typename Iterator>
void InlinedVector<T, N, A>::AppendRange(Iterator first, Iterator last,
                                         std::input_iterator_tag) {
  std::copy(first, last, std::back_inserter(*this));
}

template <typename T, size_t N, typename A>
template <typename Iterator>
void InlinedVector<T, N, A>::AssignRange(Iterator first, Iterator last,
                                         std::forward_iterator_tag) {
  auto length = std::distance(first, last);
  // Prefer reassignment to copy construction for elements.
  if (static_cast<size_type>(length) <= size()) {
    erase(std::copy(first, last, begin()), end());
    return;
  }
  reserve(length);
  iterator out = begin();
  for (; out != end(); ++first, ++out) *out = *first;
  if (allocated()) {
    UninitializedCopy(first, last, out);
    tag().set_allocated_size(length);
  } else {
    UninitializedCopy(first, last, out);
    tag().set_inline_size(length);
  }
}

template <typename T, size_t N, typename A>
template <typename Iterator>
void InlinedVector<T, N, A>::AssignRange(Iterator first, Iterator last,
                                         std::input_iterator_tag) {
  // Optimized to avoid reallocation.
  // Prefer reassignment to copy construction for elements.
  iterator out = begin();
  for (; first != last && out != end(); ++first, ++out) {
    *out = *first;
  }
  erase(out, end());
  std::copy(first, last, std::back_inserter(*this));
}

template <typename T, size_t N, typename A>
auto InlinedVector<T, N, A>::InsertWithCount(const_iterator position,
                                             size_type n, const_reference v)
    -> iterator {
  assert(position >= begin() && position <= end());
  if (ABSL_PREDICT_FALSE(n == 0)) return const_cast<iterator>(position);

  value_type copy = v;
  std::pair<iterator, iterator> it_pair = ShiftRight(position, n);
  std::fill(it_pair.first, it_pair.second, copy);
  UninitializedFill(it_pair.second, it_pair.first + n, copy);

  return it_pair.first;
}

template <typename T, size_t N, typename A>
template <typename ForwardIterator>
auto InlinedVector<T, N, A>::InsertWithRange(const_iterator position,
                                             ForwardIterator first,
                                             ForwardIterator last,
                                             std::forward_iterator_tag)
    -> iterator {
  assert(position >= begin() && position <= end());
  if (ABSL_PREDICT_FALSE(first == last)) return const_cast<iterator>(position);

  auto n = std::distance(first, last);
  std::pair<iterator, iterator> it_pair = ShiftRight(position, n);
  size_type used_spots = it_pair.second - it_pair.first;
  ForwardIterator open_spot = std::next(first, used_spots);
  std::copy(first, open_spot, it_pair.first);
  UninitializedCopy(open_spot, last, it_pair.second);
  return it_pair.first;
}

template <typename T, size_t N, typename A>
template <typename InputIterator>
auto InlinedVector<T, N, A>::InsertWithRange(const_iterator position,
                                             InputIterator first,
                                             InputIterator last,
                                             std::input_iterator_tag)
    -> iterator {
  assert(position >= begin() && position <= end());
  size_type index = position - cbegin();
  size_type i = index;
  while (first != last) insert(begin() + i++, *first++);
  return begin() + index;
}

}  // namespace absl

#endif  // ABSL_CONTAINER_INLINED_VECTOR_H_