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
//! [`IndexMap`] is a hash table where the iteration order of the key-value
//! pairs is independent of the hash values of the keys.

mod core;
mod iter;
mod slice;

#[cfg(feature = "serde")]
#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
pub mod serde_seq;

#[cfg(test)]
mod tests;

pub use self::core::raw_entry_v1::{self, RawEntryApiV1};
pub use self::core::{Entry, IndexedEntry, OccupiedEntry, VacantEntry};
pub use self::iter::{
    Drain, IntoIter, IntoKeys, IntoValues, Iter, IterMut, Keys, Splice, Values, ValuesMut,
};
pub use self::slice::Slice;
pub use crate::mutable_keys::MutableKeys;

#[cfg(feature = "rayon")]
pub use crate::rayon::map as rayon;

use ::core::cmp::Ordering;
use ::core::fmt;
use ::core::hash::{BuildHasher, Hash, Hasher};
use ::core::mem;
use ::core::ops::{Index, IndexMut, RangeBounds};
use alloc::boxed::Box;
use alloc::vec::Vec;

#[cfg(feature = "std")]
use std::collections::hash_map::RandomState;

use self::core::IndexMapCore;
use crate::util::{third, try_simplify_range};
use crate::{Bucket, Entries, Equivalent, HashValue, TryReserveError};

/// A hash table where the iteration order of the key-value pairs is independent
/// of the hash values of the keys.
///
/// The interface is closely compatible with the standard
/// [`HashMap`][std::collections::HashMap],
/// but also has additional features.
///
/// # Order
///
/// The key-value pairs have a consistent order that is determined by
/// the sequence of insertion and removal calls on the map. The order does
/// not depend on the keys or the hash function at all.
///
/// All iterators traverse the map in *the order*.
///
/// The insertion order is preserved, with **notable exceptions** like the
/// [`.remove()`][Self::remove] or [`.swap_remove()`][Self::swap_remove] methods.
/// Methods such as [`.sort_by()`][Self::sort_by] of
/// course result in a new order, depending on the sorting order.
///
/// # Indices
///
/// The key-value pairs are indexed in a compact range without holes in the
/// range `0..self.len()`. For example, the method `.get_full` looks up the
/// index for a key, and the method `.get_index` looks up the key-value pair by
/// index.
///
/// # Examples
///
/// ```
/// use indexmap::IndexMap;
///
/// // count the frequency of each letter in a sentence.
/// let mut letters = IndexMap::new();
/// for ch in "a short treatise on fungi".chars() {
///     *letters.entry(ch).or_insert(0) += 1;
/// }
///
/// assert_eq!(letters[&'s'], 2);
/// assert_eq!(letters[&'t'], 3);
/// assert_eq!(letters[&'u'], 1);
/// assert_eq!(letters.get(&'y'), None);
/// ```
#[cfg(feature = "std")]
pub struct IndexMap<K, V, S = RandomState> {
    pub(crate) core: IndexMapCore<K, V>,
    hash_builder: S,
}
#[cfg(not(feature = "std"))]
pub struct IndexMap<K, V, S> {
    pub(crate) core: IndexMapCore<K, V>,
    hash_builder: S,
}

impl<K, V, S> Clone for IndexMap<K, V, S>
where
    K: Clone,
    V: Clone,
    S: Clone,
{
    fn clone(&self) -> Self {
        IndexMap {
            core: self.core.clone(),
            hash_builder: self.hash_builder.clone(),
        }
    }

    fn clone_from(&mut self, other: &Self) {
        self.core.clone_from(&other.core);
        self.hash_builder.clone_from(&other.hash_builder);
    }
}

impl<K, V, S> Entries for IndexMap<K, V, S> {
    type Entry = Bucket<K, V>;

    #[inline]
    fn into_entries(self) -> Vec<Self::Entry> {
        self.core.into_entries()
    }

    #[inline]
    fn as_entries(&self) -> &[Self::Entry] {
        self.core.as_entries()
    }

    #[inline]
    fn as_entries_mut(&mut self) -> &mut [Self::Entry] {
        self.core.as_entries_mut()
    }

    fn with_entries<F>(&mut self, f: F)
    where
        F: FnOnce(&mut [Self::Entry]),
    {
        self.core.with_entries(f);
    }
}

impl<K, V, S> fmt::Debug for IndexMap<K, V, S>
where
    K: fmt::Debug,
    V: fmt::Debug,
{
    #[cfg(not(feature = "test_debug"))]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_map().entries(self.iter()).finish()
    }

    #[cfg(feature = "test_debug")]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Let the inner `IndexMapCore` print all of its details
        f.debug_struct("IndexMap")
            .field("core", &self.core)
            .finish()
    }
}

#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
impl<K, V> IndexMap<K, V> {
    /// Create a new map. (Does not allocate.)
    #[inline]
    pub fn new() -> Self {
        Self::with_capacity(0)
    }

    /// Create a new map with capacity for `n` key-value pairs. (Does not
    /// allocate if `n` is zero.)
    ///
    /// Computes in **O(n)** time.
    #[inline]
    pub fn with_capacity(n: usize) -> Self {
        Self::with_capacity_and_hasher(n, <_>::default())
    }
}

impl<K, V, S> IndexMap<K, V, S> {
    /// Create a new map with capacity for `n` key-value pairs. (Does not
    /// allocate if `n` is zero.)
    ///
    /// Computes in **O(n)** time.
    #[inline]
    pub fn with_capacity_and_hasher(n: usize, hash_builder: S) -> Self {
        if n == 0 {
            Self::with_hasher(hash_builder)
        } else {
            IndexMap {
                core: IndexMapCore::with_capacity(n),
                hash_builder,
            }
        }
    }

    /// Create a new map with `hash_builder`.
    ///
    /// This function is `const`, so it
    /// can be called in `static` contexts.
    pub const fn with_hasher(hash_builder: S) -> Self {
        IndexMap {
            core: IndexMapCore::new(),
            hash_builder,
        }
    }

    /// Return the number of elements the map can hold without reallocating.
    ///
    /// This number is a lower bound; the map might be able to hold more,
    /// but is guaranteed to be able to hold at least this many.
    ///
    /// Computes in **O(1)** time.
    pub fn capacity(&self) -> usize {
        self.core.capacity()
    }

    /// Return a reference to the map's `BuildHasher`.
    pub fn hasher(&self) -> &S {
        &self.hash_builder
    }

    /// Return the number of key-value pairs in the map.
    ///
    /// Computes in **O(1)** time.
    #[inline]
    pub fn len(&self) -> usize {
        self.core.len()
    }

    /// Returns true if the map contains no elements.
    ///
    /// Computes in **O(1)** time.
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Return an iterator over the key-value pairs of the map, in their order
    pub fn iter(&self) -> Iter<'_, K, V> {
        Iter::new(self.as_entries())
    }

    /// Return an iterator over the key-value pairs of the map, in their order
    pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
        IterMut::new(self.as_entries_mut())
    }

    /// Return an iterator over the keys of the map, in their order
    pub fn keys(&self) -> Keys<'_, K, V> {
        Keys::new(self.as_entries())
    }

    /// Return an owning iterator over the keys of the map, in their order
    pub fn into_keys(self) -> IntoKeys<K, V> {
        IntoKeys::new(self.into_entries())
    }

    /// Return an iterator over the values of the map, in their order
    pub fn values(&self) -> Values<'_, K, V> {
        Values::new(self.as_entries())
    }

    /// Return an iterator over mutable references to the values of the map,
    /// in their order
    pub fn values_mut(&mut self) -> ValuesMut<'_, K, V> {
        ValuesMut::new(self.as_entries_mut())
    }

    /// Return an owning iterator over the values of the map, in their order
    pub fn into_values(self) -> IntoValues<K, V> {
        IntoValues::new(self.into_entries())
    }

    /// Remove all key-value pairs in the map, while preserving its capacity.
    ///
    /// Computes in **O(n)** time.
    pub fn clear(&mut self) {
        self.core.clear();
    }

    /// Shortens the map, keeping the first `len` elements and dropping the rest.
    ///
    /// If `len` is greater than the map's current length, this has no effect.
    pub fn truncate(&mut self, len: usize) {
        self.core.truncate(len);
    }

    /// Clears the `IndexMap` in the given index range, returning those
    /// key-value pairs as a drain iterator.
    ///
    /// The range may be any type that implements [`RangeBounds<usize>`],
    /// including all of the `std::ops::Range*` types, or even a tuple pair of
    /// `Bound` start and end values. To drain the map entirely, use `RangeFull`
    /// like `map.drain(..)`.
    ///
    /// This shifts down all entries following the drained range to fill the
    /// gap, and keeps the allocated memory for reuse.
    ///
    /// ***Panics*** if the starting point is greater than the end point or if
    /// the end point is greater than the length of the map.
    pub fn drain<R>(&mut self, range: R) -> Drain<'_, K, V>
    where
        R: RangeBounds<usize>,
    {
        Drain::new(self.core.drain(range))
    }

    /// Splits the collection into two at the given index.
    ///
    /// Returns a newly allocated map containing the elements in the range
    /// `[at, len)`. After the call, the original map will be left containing
    /// the elements `[0, at)` with its previous capacity unchanged.
    ///
    /// ***Panics*** if `at > len`.
    pub fn split_off(&mut self, at: usize) -> Self
    where
        S: Clone,
    {
        Self {
            core: self.core.split_off(at),
            hash_builder: self.hash_builder.clone(),
        }
    }

    /// Reserve capacity for `additional` more key-value pairs.
    ///
    /// Computes in **O(n)** time.
    pub fn reserve(&mut self, additional: usize) {
        self.core.reserve(additional);
    }

    /// Reserve capacity for `additional` more key-value pairs, without over-allocating.
    ///
    /// Unlike `reserve`, this does not deliberately over-allocate the entry capacity to avoid
    /// frequent re-allocations. However, the underlying data structures may still have internal
    /// capacity requirements, and the allocator itself may give more space than requested, so this
    /// cannot be relied upon to be precisely minimal.
    ///
    /// Computes in **O(n)** time.
    pub fn reserve_exact(&mut self, additional: usize) {
        self.core.reserve_exact(additional);
    }

    /// Try to reserve capacity for `additional` more key-value pairs.
    ///
    /// Computes in **O(n)** time.
    pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
        self.core.try_reserve(additional)
    }

    /// Try to reserve capacity for `additional` more key-value pairs, without over-allocating.
    ///
    /// Unlike `try_reserve`, this does not deliberately over-allocate the entry capacity to avoid
    /// frequent re-allocations. However, the underlying data structures may still have internal
    /// capacity requirements, and the allocator itself may give more space than requested, so this
    /// cannot be relied upon to be precisely minimal.
    ///
    /// Computes in **O(n)** time.
    pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
        self.core.try_reserve_exact(additional)
    }

    /// Shrink the capacity of the map as much as possible.
    ///
    /// Computes in **O(n)** time.
    pub fn shrink_to_fit(&mut self) {
        self.core.shrink_to(0);
    }

    /// Shrink the capacity of the map with a lower limit.
    ///
    /// Computes in **O(n)** time.
    pub fn shrink_to(&mut self, min_capacity: usize) {
        self.core.shrink_to(min_capacity);
    }
}

impl<K, V, S> IndexMap<K, V, S>
where
    K: Hash + Eq,
    S: BuildHasher,
{
    /// Insert a key-value pair in the map.
    ///
    /// If an equivalent key already exists in the map: the key remains and
    /// retains in its place in the order, its corresponding value is updated
    /// with `value`, and the older value is returned inside `Some(_)`.
    ///
    /// If no equivalent key existed in the map: the new key-value pair is
    /// inserted, last in order, and `None` is returned.
    ///
    /// Computes in **O(1)** time (amortized average).
    ///
    /// See also [`entry`][Self::entry] if you want to insert *or* modify,
    /// or [`insert_full`][Self::insert_full] if you need to get the index of
    /// the corresponding key-value pair.
    pub fn insert(&mut self, key: K, value: V) -> Option<V> {
        self.insert_full(key, value).1
    }

    /// Insert a key-value pair in the map, and get their index.
    ///
    /// If an equivalent key already exists in the map: the key remains and
    /// retains in its place in the order, its corresponding value is updated
    /// with `value`, and the older value is returned inside `(index, Some(_))`.
    ///
    /// If no equivalent key existed in the map: the new key-value pair is
    /// inserted, last in order, and `(index, None)` is returned.
    ///
    /// Computes in **O(1)** time (amortized average).
    ///
    /// See also [`entry`][Self::entry] if you want to insert *or* modify.
    pub fn insert_full(&mut self, key: K, value: V) -> (usize, Option<V>) {
        let hash = self.hash(&key);
        self.core.insert_full(hash, key, value)
    }

    /// Insert a key-value pair in the map at its ordered position among sorted keys.
    ///
    /// This is equivalent to finding the position with
    /// [`binary_search_keys`][Self::binary_search_keys], then either updating
    /// it or calling [`shift_insert`][Self::shift_insert] for a new key.
    ///
    /// If the sorted key is found in the map, its corresponding value is
    /// updated with `value`, and the older value is returned inside
    /// `(index, Some(_))`. Otherwise, the new key-value pair is inserted at
    /// the sorted position, and `(index, None)` is returned.
    ///
    /// If the existing keys are **not** already sorted, then the insertion
    /// index is unspecified (like [`slice::binary_search`]), but the key-value
    /// pair is moved to or inserted at that position regardless.
    ///
    /// Computes in **O(n)** time (average). Instead of repeating calls to
    /// `insert_sorted`, it may be faster to call batched [`insert`][Self::insert]
    /// or [`extend`][Self::extend] and only call [`sort_keys`][Self::sort_keys]
    /// or [`sort_unstable_keys`][Self::sort_unstable_keys] once.
    pub fn insert_sorted(&mut self, key: K, value: V) -> (usize, Option<V>)
    where
        K: Ord,
    {
        match self.binary_search_keys(&key) {
            Ok(i) => (i, Some(mem::replace(&mut self[i], value))),
            Err(i) => (i, self.shift_insert(i, key, value)),
        }
    }

    /// Insert a key-value pair in the map at the given index.
    ///
    /// If an equivalent key already exists in the map: the key remains and
    /// is moved to the new position in the map, its corresponding value is updated
    /// with `value`, and the older value is returned inside `Some(_)`.
    ///
    /// If no equivalent key existed in the map: the new key-value pair is
    /// inserted at the given index, and `None` is returned.
    ///
    /// ***Panics*** if `index` is out of bounds.
    ///
    /// Computes in **O(n)** time (average).
    ///
    /// See also [`entry`][Self::entry] if you want to insert *or* modify,
    /// perhaps only using the index for new entries with [`VacantEntry::shift_insert`].
    pub fn shift_insert(&mut self, index: usize, key: K, value: V) -> Option<V> {
        match self.entry(key) {
            Entry::Occupied(mut entry) => {
                let old = mem::replace(entry.get_mut(), value);
                entry.move_index(index);
                Some(old)
            }
            Entry::Vacant(entry) => {
                entry.shift_insert(index, value);
                None
            }
        }
    }

    /// Get the given key’s corresponding entry in the map for insertion and/or
    /// in-place manipulation.
    ///
    /// Computes in **O(1)** time (amortized average).
    pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
        let hash = self.hash(&key);
        self.core.entry(hash, key)
    }

    /// Creates a splicing iterator that replaces the specified range in the map
    /// with the given `replace_with` key-value iterator and yields the removed
    /// items. `replace_with` does not need to be the same length as `range`.
    ///
    /// The `range` is removed even if the iterator is not consumed until the
    /// end. It is unspecified how many elements are removed from the map if the
    /// `Splice` value is leaked.
    ///
    /// The input iterator `replace_with` is only consumed when the `Splice`
    /// value is dropped. If a key from the iterator matches an existing entry
    /// in the map (outside of `range`), then the value will be updated in that
    /// position. Otherwise, the new key-value pair will be inserted in the
    /// replaced `range`.
    ///
    /// ***Panics*** if the starting point is greater than the end point or if
    /// the end point is greater than the length of the map.
    ///
    /// # Examples
    ///
    /// ```
    /// use indexmap::IndexMap;
    ///
    /// let mut map = IndexMap::from([(0, '_'), (1, 'a'), (2, 'b'), (3, 'c'), (4, 'd')]);
    /// let new = [(5, 'E'), (4, 'D'), (3, 'C'), (2, 'B'), (1, 'A')];
    /// let removed: Vec<_> = map.splice(2..4, new).collect();
    ///
    /// // 1 and 4 got new values, while 5, 3, and 2 were newly inserted.
    /// assert!(map.into_iter().eq([(0, '_'), (1, 'A'), (5, 'E'), (3, 'C'), (2, 'B'), (4, 'D')]));
    /// assert_eq!(removed, &[(2, 'b'), (3, 'c')]);
    /// ```
    pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, K, V, S>
    where
        R: RangeBounds<usize>,
        I: IntoIterator<Item = (K, V)>,
    {
        Splice::new(self, range, replace_with.into_iter())
    }
}

impl<K, V, S> IndexMap<K, V, S>
where
    S: BuildHasher,
{
    pub(crate) fn hash<Q: ?Sized + Hash>(&self, key: &Q) -> HashValue {
        let mut h = self.hash_builder.build_hasher();
        key.hash(&mut h);
        HashValue(h.finish() as usize)
    }

    /// Return `true` if an equivalent to `key` exists in the map.
    ///
    /// Computes in **O(1)** time (average).
    pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool
    where
        Q: Hash + Equivalent<K>,
    {
        self.get_index_of(key).is_some()
    }

    /// Return a reference to the value stored for `key`, if it is present,
    /// else `None`.
    ///
    /// Computes in **O(1)** time (average).
    pub fn get<Q: ?Sized>(&self, key: &Q) -> Option<&V>
    where
        Q: Hash + Equivalent<K>,
    {
        if let Some(i) = self.get_index_of(key) {
            let entry = &self.as_entries()[i];
            Some(&entry.value)
        } else {
            None
        }
    }

    /// Return references to the key-value pair stored for `key`,
    /// if it is present, else `None`.
    ///
    /// Computes in **O(1)** time (average).
    pub fn get_key_value<Q: ?Sized>(&self, key: &Q) -> Option<(&K, &V)>
    where
        Q: Hash + Equivalent<K>,
    {
        if let Some(i) = self.get_index_of(key) {
            let entry = &self.as_entries()[i];
            Some((&entry.key, &entry.value))
        } else {
            None
        }
    }

    /// Return item index, key and value
    pub fn get_full<Q: ?Sized>(&self, key: &Q) -> Option<(usize, &K, &V)>
    where
        Q: Hash + Equivalent<K>,
    {
        if let Some(i) = self.get_index_of(key) {
            let entry = &self.as_entries()[i];
            Some((i, &entry.key, &entry.value))
        } else {
            None
        }
    }

    /// Return item index, if it exists in the map
    ///
    /// Computes in **O(1)** time (average).
    pub fn get_index_of<Q: ?Sized>(&self, key: &Q) -> Option<usize>
    where
        Q: Hash + Equivalent<K>,
    {
        match self.as_entries() {
            [] => None,
            [x] => key.equivalent(&x.key).then_some(0),
            _ => {
                let hash = self.hash(key);
                self.core.get_index_of(hash, key)
            }
        }
    }

    pub fn get_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<&mut V>
    where
        Q: Hash + Equivalent<K>,
    {
        if let Some(i) = self.get_index_of(key) {
            let entry = &mut self.as_entries_mut()[i];
            Some(&mut entry.value)
        } else {
            None
        }
    }

    pub fn get_full_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, &K, &mut V)>
    where
        Q: Hash + Equivalent<K>,
    {
        if let Some(i) = self.get_index_of(key) {
            let entry = &mut self.as_entries_mut()[i];
            Some((i, &entry.key, &mut entry.value))
        } else {
            None
        }
    }

    /// Remove the key-value pair equivalent to `key` and return
    /// its value.
    ///
    /// **NOTE:** This is equivalent to [`.swap_remove(key)`][Self::swap_remove], replacing this
    /// entry's position with the last element, and it is deprecated in favor of calling that
    /// explicitly. If you need to preserve the relative order of the keys in the map, use
    /// [`.shift_remove(key)`][Self::shift_remove] instead.
    #[deprecated(note = "`remove` disrupts the map order -- \
        use `swap_remove` or `shift_remove` for explicit behavior.")]
    pub fn remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
    where
        Q: Hash + Equivalent<K>,
    {
        self.swap_remove(key)
    }

    /// Remove and return the key-value pair equivalent to `key`.
    ///
    /// **NOTE:** This is equivalent to [`.swap_remove_entry(key)`][Self::swap_remove_entry],
    /// replacing this entry's position with the last element, and it is deprecated in favor of
    /// calling that explicitly. If you need to preserve the relative order of the keys in the map,
    /// use [`.shift_remove_entry(key)`][Self::shift_remove_entry] instead.
    #[deprecated(note = "`remove_entry` disrupts the map order -- \
        use `swap_remove_entry` or `shift_remove_entry` for explicit behavior.")]
    pub fn remove_entry<Q: ?Sized>(&mut self, key: &Q) -> Option<(K, V)>
    where
        Q: Hash + Equivalent<K>,
    {
        self.swap_remove_entry(key)
    }

    /// Remove the key-value pair equivalent to `key` and return
    /// its value.
    ///
    /// Like [`Vec::swap_remove`], the pair is removed by swapping it with the
    /// last element of the map and popping it off. **This perturbs
    /// the position of what used to be the last element!**
    ///
    /// Return `None` if `key` is not in map.
    ///
    /// Computes in **O(1)** time (average).
    pub fn swap_remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
    where
        Q: Hash + Equivalent<K>,
    {
        self.swap_remove_full(key).map(third)
    }

    /// Remove and return the key-value pair equivalent to `key`.
    ///
    /// Like [`Vec::swap_remove`], the pair is removed by swapping it with the
    /// last element of the map and popping it off. **This perturbs
    /// the position of what used to be the last element!**
    ///
    /// Return `None` if `key` is not in map.
    ///
    /// Computes in **O(1)** time (average).
    pub fn swap_remove_entry<Q: ?Sized>(&mut self, key: &Q) -> Option<(K, V)>
    where
        Q: Hash + Equivalent<K>,
    {
        match self.swap_remove_full(key) {
            Some((_, key, value)) => Some((key, value)),
            None => None,
        }
    }

    /// Remove the key-value pair equivalent to `key` and return it and
    /// the index it had.
    ///
    /// Like [`Vec::swap_remove`], the pair is removed by swapping it with the
    /// last element of the map and popping it off. **This perturbs
    /// the position of what used to be the last element!**
    ///
    /// Return `None` if `key` is not in map.
    ///
    /// Computes in **O(1)** time (average).
    pub fn swap_remove_full<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, K, V)>
    where
        Q: Hash + Equivalent<K>,
    {
        match self.as_entries() {
            [x] if key.equivalent(&x.key) => {
                let (k, v) = self.core.pop()?;
                Some((0, k, v))
            }
            [_] | [] => None,
            _ => {
                let hash = self.hash(key);
                self.core.swap_remove_full(hash, key)
            }
        }
    }

    /// Remove the key-value pair equivalent to `key` and return
    /// its value.
    ///
    /// Like [`Vec::remove`], the pair is removed by shifting all of the
    /// elements that follow it, preserving their relative order.
    /// **This perturbs the index of all of those elements!**
    ///
    /// Return `None` if `key` is not in map.
    ///
    /// Computes in **O(n)** time (average).
    pub fn shift_remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
    where
        Q: Hash + Equivalent<K>,
    {
        self.shift_remove_full(key).map(third)
    }

    /// Remove and return the key-value pair equivalent to `key`.
    ///
    /// Like [`Vec::remove`], the pair is removed by shifting all of the
    /// elements that follow it, preserving their relative order.
    /// **This perturbs the index of all of those elements!**
    ///
    /// Return `None` if `key` is not in map.
    ///
    /// Computes in **O(n)** time (average).
    pub fn shift_remove_entry<Q: ?Sized>(&mut self, key: &Q) -> Option<(K, V)>
    where
        Q: Hash + Equivalent<K>,
    {
        match self.shift_remove_full(key) {
            Some((_, key, value)) => Some((key, value)),
            None => None,
        }
    }

    /// Remove the key-value pair equivalent to `key` and return it and
    /// the index it had.
    ///
    /// Like [`Vec::remove`], the pair is removed by shifting all of the
    /// elements that follow it, preserving their relative order.
    /// **This perturbs the index of all of those elements!**
    ///
    /// Return `None` if `key` is not in map.
    ///
    /// Computes in **O(n)** time (average).
    pub fn shift_remove_full<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, K, V)>
    where
        Q: Hash + Equivalent<K>,
    {
        match self.as_entries() {
            [x] if key.equivalent(&x.key) => {
                let (k, v) = self.core.pop()?;
                Some((0, k, v))
            }
            [_] | [] => None,
            _ => {
                let hash = self.hash(key);
                self.core.shift_remove_full(hash, key)
            }
        }
    }
}

impl<K, V, S> IndexMap<K, V, S> {
    /// Remove the last key-value pair
    ///
    /// This preserves the order of the remaining elements.
    ///
    /// Computes in **O(1)** time (average).
    pub fn pop(&mut self) -> Option<(K, V)> {
        self.core.pop()
    }

    /// Scan through each key-value pair in the map and keep those where the
    /// closure `keep` returns `true`.
    ///
    /// The elements are visited in order, and remaining elements keep their
    /// order.
    ///
    /// Computes in **O(n)** time (average).
    pub fn retain<F>(&mut self, mut keep: F)
    where
        F: FnMut(&K, &mut V) -> bool,
    {
        self.core.retain_in_order(move |k, v| keep(k, v));
    }

    pub(crate) fn retain_mut<F>(&mut self, keep: F)
    where
        F: FnMut(&mut K, &mut V) -> bool,
    {
        self.core.retain_in_order(keep);
    }

    /// Sort the map’s key-value pairs by the default ordering of the keys.
    ///
    /// This is a stable sort -- but equivalent keys should not normally coexist in
    /// a map at all, so [`sort_unstable_keys`][Self::sort_unstable_keys] is preferred
    /// because it is generally faster and doesn't allocate auxiliary memory.
    ///
    /// See [`sort_by`](Self::sort_by) for details.
    pub fn sort_keys(&mut self)
    where
        K: Ord,
    {
        self.with_entries(move |entries| {
            entries.sort_by(move |a, b| K::cmp(&a.key, &b.key));
        });
    }

    /// Sort the map’s key-value pairs in place using the comparison
    /// function `cmp`.
    ///
    /// The comparison function receives two key and value pairs to compare (you
    /// can sort by keys or values or their combination as needed).
    ///
    /// Computes in **O(n log n + c)** time and **O(n)** space where *n* is
    /// the length of the map and *c* the capacity. The sort is stable.
    pub fn sort_by<F>(&mut self, mut cmp: F)
    where
        F: FnMut(&K, &V, &K, &V) -> Ordering,
    {
        self.with_entries(move |entries| {
            entries.sort_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
        });
    }

    /// Sort the key-value pairs of the map and return a by-value iterator of
    /// the key-value pairs with the result.
    ///
    /// The sort is stable.
    pub fn sorted_by<F>(self, mut cmp: F) -> IntoIter<K, V>
    where
        F: FnMut(&K, &V, &K, &V) -> Ordering,
    {
        let mut entries = self.into_entries();
        entries.sort_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
        IntoIter::new(entries)
    }

    /// Sort the map's key-value pairs by the default ordering of the keys, but
    /// may not preserve the order of equal elements.
    ///
    /// See [`sort_unstable_by`](Self::sort_unstable_by) for details.
    pub fn sort_unstable_keys(&mut self)
    where
        K: Ord,
    {
        self.with_entries(move |entries| {
            entries.sort_unstable_by(move |a, b| K::cmp(&a.key, &b.key));
        });
    }

    /// Sort the map's key-value pairs in place using the comparison function `cmp`, but
    /// may not preserve the order of equal elements.
    ///
    /// The comparison function receives two key and value pairs to compare (you
    /// can sort by keys or values or their combination as needed).
    ///
    /// Computes in **O(n log n + c)** time where *n* is
    /// the length of the map and *c* is the capacity. The sort is unstable.
    pub fn sort_unstable_by<F>(&mut self, mut cmp: F)
    where
        F: FnMut(&K, &V, &K, &V) -> Ordering,
    {
        self.with_entries(move |entries| {
            entries.sort_unstable_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
        });
    }

    /// Sort the key-value pairs of the map and return a by-value iterator of
    /// the key-value pairs with the result.
    ///
    /// The sort is unstable.
    #[inline]
    pub fn sorted_unstable_by<F>(self, mut cmp: F) -> IntoIter<K, V>
    where
        F: FnMut(&K, &V, &K, &V) -> Ordering,
    {
        let mut entries = self.into_entries();
        entries.sort_unstable_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
        IntoIter::new(entries)
    }

    /// Sort the map’s key-value pairs in place using a sort-key extraction function.
    ///
    /// During sorting, the function is called at most once per entry, by using temporary storage
    /// to remember the results of its evaluation. The order of calls to the function is
    /// unspecified and may change between versions of `indexmap` or the standard library.
    ///
    /// Computes in **O(m n + n log n + c)** time () and **O(n)** space, where the function is
    /// **O(m)**, *n* is the length of the map, and *c* the capacity. The sort is stable.
    pub fn sort_by_cached_key<T, F>(&mut self, mut sort_key: F)
    where
        T: Ord,
        F: FnMut(&K, &V) -> T,
    {
        self.with_entries(move |entries| {
            entries.sort_by_cached_key(move |a| sort_key(&a.key, &a.value));
        });
    }

    /// Search over a sorted map for a key.
    ///
    /// Returns the position where that key is present, or the position where it can be inserted to
    /// maintain the sort. See [`slice::binary_search`] for more details.
    ///
    /// Computes in **O(log(n))** time, which is notably less scalable than looking the key up
    /// using [`get_index_of`][IndexMap::get_index_of], but this can also position missing keys.
    pub fn binary_search_keys(&self, x: &K) -> Result<usize, usize>
    where
        K: Ord,
    {
        self.as_slice().binary_search_keys(x)
    }

    /// Search over a sorted map with a comparator function.
    ///
    /// Returns the position where that value is present, or the position where it can be inserted
    /// to maintain the sort. See [`slice::binary_search_by`] for more details.
    ///
    /// Computes in **O(log(n))** time.
    #[inline]
    pub fn binary_search_by<'a, F>(&'a self, f: F) -> Result<usize, usize>
    where
        F: FnMut(&'a K, &'a V) -> Ordering,
    {
        self.as_slice().binary_search_by(f)
    }

    /// Search over a sorted map with an extraction function.
    ///
    /// Returns the position where that value is present, or the position where it can be inserted
    /// to maintain the sort. See [`slice::binary_search_by_key`] for more details.
    ///
    /// Computes in **O(log(n))** time.
    #[inline]
    pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, f: F) -> Result<usize, usize>
    where
        F: FnMut(&'a K, &'a V) -> B,
        B: Ord,
    {
        self.as_slice().binary_search_by_key(b, f)
    }

    /// Returns the index of the partition point of a sorted map according to the given predicate
    /// (the index of the first element of the second partition).
    ///
    /// See [`slice::partition_point`] for more details.
    ///
    /// Computes in **O(log(n))** time.
    #[must_use]
    pub fn partition_point<P>(&self, pred: P) -> usize
    where
        P: FnMut(&K, &V) -> bool,
    {
        self.as_slice().partition_point(pred)
    }

    /// Reverses the order of the map’s key-value pairs in place.
    ///
    /// Computes in **O(n)** time and **O(1)** space.
    pub fn reverse(&mut self) {
        self.core.reverse()
    }

    /// Returns a slice of all the key-value pairs in the map.
    ///
    /// Computes in **O(1)** time.
    pub fn as_slice(&self) -> &Slice<K, V> {
        Slice::from_slice(self.as_entries())
    }

    /// Returns a mutable slice of all the key-value pairs in the map.
    ///
    /// Computes in **O(1)** time.
    pub fn as_mut_slice(&mut self) -> &mut Slice<K, V> {
        Slice::from_mut_slice(self.as_entries_mut())
    }

    /// Converts into a boxed slice of all the key-value pairs in the map.
    ///
    /// Note that this will drop the inner hash table and any excess capacity.
    pub fn into_boxed_slice(self) -> Box<Slice<K, V>> {
        Slice::from_boxed(self.into_entries().into_boxed_slice())
    }

    /// Get a key-value pair by index
    ///
    /// Valid indices are *0 <= index < self.len()*
    ///
    /// Computes in **O(1)** time.
    pub fn get_index(&self, index: usize) -> Option<(&K, &V)> {
        self.as_entries().get(index).map(Bucket::refs)
    }

    /// Get a key-value pair by index
    ///
    /// Valid indices are *0 <= index < self.len()*
    ///
    /// Computes in **O(1)** time.
    pub fn get_index_mut(&mut self, index: usize) -> Option<(&K, &mut V)> {
        self.as_entries_mut().get_mut(index).map(Bucket::ref_mut)
    }

    /// Get an entry in the map by index for in-place manipulation.
    ///
    /// Valid indices are *0 <= index < self.len()*
    ///
    /// Computes in **O(1)** time.
    pub fn get_index_entry(&mut self, index: usize) -> Option<IndexedEntry<'_, K, V>> {
        if index >= self.len() {
            return None;
        }
        Some(IndexedEntry::new(&mut self.core, index))
    }

    /// Returns a slice of key-value pairs in the given range of indices.
    ///
    /// Valid indices are *0 <= index < self.len()*
    ///
    /// Computes in **O(1)** time.
    pub fn get_range<R: RangeBounds<usize>>(&self, range: R) -> Option<&Slice<K, V>> {
        let entries = self.as_entries();
        let range = try_simplify_range(range, entries.len())?;
        entries.get(range).map(Slice::from_slice)
    }

    /// Returns a mutable slice of key-value pairs in the given range of indices.
    ///
    /// Valid indices are *0 <= index < self.len()*
    ///
    /// Computes in **O(1)** time.
    pub fn get_range_mut<R: RangeBounds<usize>>(&mut self, range: R) -> Option<&mut Slice<K, V>> {
        let entries = self.as_entries_mut();
        let range = try_simplify_range(range, entries.len())?;
        entries.get_mut(range).map(Slice::from_mut_slice)
    }

    /// Get the first key-value pair
    ///
    /// Computes in **O(1)** time.
    pub fn first(&self) -> Option<(&K, &V)> {
        self.as_entries().first().map(Bucket::refs)
    }

    /// Get the first key-value pair, with mutable access to the value
    ///
    /// Computes in **O(1)** time.
    pub fn first_mut(&mut self) -> Option<(&K, &mut V)> {
        self.as_entries_mut().first_mut().map(Bucket::ref_mut)
    }

    /// Get the last key-value pair
    ///
    /// Computes in **O(1)** time.
    pub fn last(&self) -> Option<(&K, &V)> {
        self.as_entries().last().map(Bucket::refs)
    }

    /// Get the last key-value pair, with mutable access to the value
    ///
    /// Computes in **O(1)** time.
    pub fn last_mut(&mut self) -> Option<(&K, &mut V)> {
        self.as_entries_mut().last_mut().map(Bucket::ref_mut)
    }

    /// Remove the key-value pair by index
    ///
    /// Valid indices are *0 <= index < self.len()*
    ///
    /// Like [`Vec::swap_remove`], the pair is removed by swapping it with the
    /// last element of the map and popping it off. **This perturbs
    /// the position of what used to be the last element!**
    ///
    /// Computes in **O(1)** time (average).
    pub fn swap_remove_index(&mut self, index: usize) -> Option<(K, V)> {
        self.core.swap_remove_index(index)
    }

    /// Remove the key-value pair by index
    ///
    /// Valid indices are *0 <= index < self.len()*
    ///
    /// Like [`Vec::remove`], the pair is removed by shifting all of the
    /// elements that follow it, preserving their relative order.
    /// **This perturbs the index of all of those elements!**
    ///
    /// Computes in **O(n)** time (average).
    pub fn shift_remove_index(&mut self, index: usize) -> Option<(K, V)> {
        self.core.shift_remove_index(index)
    }

    /// Moves the position of a key-value pair from one index to another
    /// by shifting all other pairs in-between.
    ///
    /// * If `from < to`, the other pairs will shift down while the targeted pair moves up.
    /// * If `from > to`, the other pairs will shift up while the targeted pair moves down.
    ///
    /// ***Panics*** if `from` or `to` are out of bounds.
    ///
    /// Computes in **O(n)** time (average).
    pub fn move_index(&mut self, from: usize, to: usize) {
        self.core.move_index(from, to)
    }

    /// Swaps the position of two key-value pairs in the map.
    ///
    /// ***Panics*** if `a` or `b` are out of bounds.
    ///
    /// Computes in **O(1)** time (average).
    pub fn swap_indices(&mut self, a: usize, b: usize) {
        self.core.swap_indices(a, b)
    }
}

/// Access [`IndexMap`] values corresponding to a key.
///
/// # Examples
///
/// ```
/// use indexmap::IndexMap;
///
/// let mut map = IndexMap::new();
/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
///     map.insert(word.to_lowercase(), word.to_uppercase());
/// }
/// assert_eq!(map["lorem"], "LOREM");
/// assert_eq!(map["ipsum"], "IPSUM");
/// ```
///
/// ```should_panic
/// use indexmap::IndexMap;
///
/// let mut map = IndexMap::new();
/// map.insert("foo", 1);
/// println!("{:?}", map["bar"]); // panics!
/// ```
impl<K, V, Q: ?Sized, S> Index<&Q> for IndexMap<K, V, S>
where
    Q: Hash + Equivalent<K>,
    S: BuildHasher,
{
    type Output = V;

    /// Returns a reference to the value corresponding to the supplied `key`.
    ///
    /// ***Panics*** if `key` is not present in the map.
    fn index(&self, key: &Q) -> &V {
        self.get(key).expect("IndexMap: key not found")
    }
}

/// Access [`IndexMap`] values corresponding to a key.
///
/// Mutable indexing allows changing / updating values of key-value
/// pairs that are already present.
///
/// You can **not** insert new pairs with index syntax, use `.insert()`.
///
/// # Examples
///
/// ```
/// use indexmap::IndexMap;
///
/// let mut map = IndexMap::new();
/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
///     map.insert(word.to_lowercase(), word.to_string());
/// }
/// let lorem = &mut map["lorem"];
/// assert_eq!(lorem, "Lorem");
/// lorem.retain(char::is_lowercase);
/// assert_eq!(map["lorem"], "orem");
/// ```
///
/// ```should_panic
/// use indexmap::IndexMap;
///
/// let mut map = IndexMap::new();
/// map.insert("foo", 1);
/// map["bar"] = 1; // panics!
/// ```
impl<K, V, Q: ?Sized, S> IndexMut<&Q> for IndexMap<K, V, S>
where
    Q: Hash + Equivalent<K>,
    S: BuildHasher,
{
    /// Returns a mutable reference to the value corresponding to the supplied `key`.
    ///
    /// ***Panics*** if `key` is not present in the map.
    fn index_mut(&mut self, key: &Q) -> &mut V {
        self.get_mut(key).expect("IndexMap: key not found")
    }
}

/// Access [`IndexMap`] values at indexed positions.
///
/// See [`Index<usize> for Keys`][keys] to access a map's keys instead.
///
/// [keys]: Keys#impl-Index<usize>-for-Keys<'a,+K,+V>
///
/// # Examples
///
/// ```
/// use indexmap::IndexMap;
///
/// let mut map = IndexMap::new();
/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
///     map.insert(word.to_lowercase(), word.to_uppercase());
/// }
/// assert_eq!(map[0], "LOREM");
/// assert_eq!(map[1], "IPSUM");
/// map.reverse();
/// assert_eq!(map[0], "AMET");
/// assert_eq!(map[1], "SIT");
/// map.sort_keys();
/// assert_eq!(map[0], "AMET");
/// assert_eq!(map[1], "DOLOR");
/// ```
///
/// ```should_panic
/// use indexmap::IndexMap;
///
/// let mut map = IndexMap::new();
/// map.insert("foo", 1);
/// println!("{:?}", map[10]); // panics!
/// ```
impl<K, V, S> Index<usize> for IndexMap<K, V, S> {
    type Output = V;

    /// Returns a reference to the value at the supplied `index`.
    ///
    /// ***Panics*** if `index` is out of bounds.
    fn index(&self, index: usize) -> &V {
        self.get_index(index)
            .expect("IndexMap: index out of bounds")
            .1
    }
}

/// Access [`IndexMap`] values at indexed positions.
///
/// Mutable indexing allows changing / updating indexed values
/// that are already present.
///
/// You can **not** insert new values with index syntax -- use [`.insert()`][IndexMap::insert].
///
/// # Examples
///
/// ```
/// use indexmap::IndexMap;
///
/// let mut map = IndexMap::new();
/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
///     map.insert(word.to_lowercase(), word.to_string());
/// }
/// let lorem = &mut map[0];
/// assert_eq!(lorem, "Lorem");
/// lorem.retain(char::is_lowercase);
/// assert_eq!(map["lorem"], "orem");
/// ```
///
/// ```should_panic
/// use indexmap::IndexMap;
///
/// let mut map = IndexMap::new();
/// map.insert("foo", 1);
/// map[10] = 1; // panics!
/// ```
impl<K, V, S> IndexMut<usize> for IndexMap<K, V, S> {
    /// Returns a mutable reference to the value at the supplied `index`.
    ///
    /// ***Panics*** if `index` is out of bounds.
    fn index_mut(&mut self, index: usize) -> &mut V {
        self.get_index_mut(index)
            .expect("IndexMap: index out of bounds")
            .1
    }
}

impl<K, V, S> FromIterator<(K, V)> for IndexMap<K, V, S>
where
    K: Hash + Eq,
    S: BuildHasher + Default,
{
    /// Create an `IndexMap` from the sequence of key-value pairs in the
    /// iterable.
    ///
    /// `from_iter` uses the same logic as `extend`. See
    /// [`extend`][IndexMap::extend] for more details.
    fn from_iter<I: IntoIterator<Item = (K, V)>>(iterable: I) -> Self {
        let iter = iterable.into_iter();
        let (low, _) = iter.size_hint();
        let mut map = Self::with_capacity_and_hasher(low, <_>::default());
        map.extend(iter);
        map
    }
}

#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
impl<K, V, const N: usize> From<[(K, V); N]> for IndexMap<K, V, RandomState>
where
    K: Hash + Eq,
{
    /// # Examples
    ///
    /// ```
    /// use indexmap::IndexMap;
    ///
    /// let map1 = IndexMap::from([(1, 2), (3, 4)]);
    /// let map2: IndexMap<_, _> = [(1, 2), (3, 4)].into();
    /// assert_eq!(map1, map2);
    /// ```
    fn from(arr: [(K, V); N]) -> Self {
        Self::from_iter(arr)
    }
}

impl<K, V, S> Extend<(K, V)> for IndexMap<K, V, S>
where
    K: Hash + Eq,
    S: BuildHasher,
{
    /// Extend the map with all key-value pairs in the iterable.
    ///
    /// This is equivalent to calling [`insert`][IndexMap::insert] for each of
    /// them in order, which means that for keys that already existed
    /// in the map, their value is updated but it keeps the existing order.
    ///
    /// New keys are inserted in the order they appear in the sequence. If
    /// equivalents of a key occur more than once, the last corresponding value
    /// prevails.
    fn extend<I: IntoIterator<Item = (K, V)>>(&mut self, iterable: I) {
        // (Note: this is a copy of `std`/`hashbrown`'s reservation logic.)
        // Keys may be already present or show multiple times in the iterator.
        // Reserve the entire hint lower bound if the map is empty.
        // Otherwise reserve half the hint (rounded up), so the map
        // will only resize twice in the worst case.
        let iter = iterable.into_iter();
        let reserve = if self.is_empty() {
            iter.size_hint().0
        } else {
            (iter.size_hint().0 + 1) / 2
        };
        self.reserve(reserve);
        iter.for_each(move |(k, v)| {
            self.insert(k, v);
        });
    }
}

impl<'a, K, V, S> Extend<(&'a K, &'a V)> for IndexMap<K, V, S>
where
    K: Hash + Eq + Copy,
    V: Copy,
    S: BuildHasher,
{
    /// Extend the map with all key-value pairs in the iterable.
    ///
    /// See the first extend method for more details.
    fn extend<I: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iterable: I) {
        self.extend(iterable.into_iter().map(|(&key, &value)| (key, value)));
    }
}

impl<K, V, S> Default for IndexMap<K, V, S>
where
    S: Default,
{
    /// Return an empty [`IndexMap`]
    fn default() -> Self {
        Self::with_capacity_and_hasher(0, S::default())
    }
}

impl<K, V1, S1, V2, S2> PartialEq<IndexMap<K, V2, S2>> for IndexMap<K, V1, S1>
where
    K: Hash + Eq,
    V1: PartialEq<V2>,
    S1: BuildHasher,
    S2: BuildHasher,
{
    fn eq(&self, other: &IndexMap<K, V2, S2>) -> bool {
        if self.len() != other.len() {
            return false;
        }

        self.iter()
            .all(|(key, value)| other.get(key).map_or(false, |v| *value == *v))
    }
}

impl<K, V, S> Eq for IndexMap<K, V, S>
where
    K: Eq + Hash,
    V: Eq,
    S: BuildHasher,
{
}