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
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
//! impl char {}

use crate::slice;
use crate::str::from_utf8_unchecked_mut;
use crate::unicode::printable::is_printable;
use crate::unicode::{self, conversions};

use super::*;

#[lang = "char"]
impl char {
    /// The highest valid code point a `char` can have.
    ///
    /// A `char` is a [Unicode Scalar Value], which means that it is a [Code
    /// Point], but only ones within a certain range. `MAX` is the highest valid
    /// code point that's a valid [Unicode Scalar Value].
    ///
    /// [Unicode Scalar Value]: https://www.unicode.org/glossary/#unicode_scalar_value
    /// [Code Point]: https://www.unicode.org/glossary/#code_point
    #[stable(feature = "assoc_char_consts", since = "1.52.0")]
    pub const MAX: char = '\u{10ffff}';

    /// `U+FFFD REPLACEMENT CHARACTER` (�) is used in Unicode to represent a
    /// decoding error.
    ///
    /// It can occur, for example, when giving ill-formed UTF-8 bytes to
    /// [`String::from_utf8_lossy`](string/struct.String.html#method.from_utf8_lossy).
    #[stable(feature = "assoc_char_consts", since = "1.52.0")]
    pub const REPLACEMENT_CHARACTER: char = '\u{FFFD}';

    /// The version of [Unicode](https://www.unicode.org/) that the Unicode parts of
    /// `char` and `str` methods are based on.
    ///
    /// New versions of Unicode are released regularly and subsequently all methods
    /// in the standard library depending on Unicode are updated. Therefore the
    /// behavior of some `char` and `str` methods and the value of this constant
    /// changes over time. This is *not* considered to be a breaking change.
    ///
    /// The version numbering scheme is explained in
    /// [Unicode 11.0 or later, Section 3.1 Versions of the Unicode Standard](https://www.unicode.org/versions/Unicode11.0.0/ch03.pdf#page=4).
    #[stable(feature = "assoc_char_consts", since = "1.52.0")]
    pub const UNICODE_VERSION: (u8, u8, u8) = crate::unicode::UNICODE_VERSION;

    /// Creates an iterator over the UTF-16 encoded code points in `iter`,
    /// returning unpaired surrogates as `Err`s.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// use std::char::decode_utf16;
    ///
    /// // 𝄞mus<invalid>ic<invalid>
    /// let v = [
    ///     0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834,
    /// ];
    ///
    /// assert_eq!(
    ///     decode_utf16(v)
    ///         .map(|r| r.map_err(|e| e.unpaired_surrogate()))
    ///         .collect::<Vec<_>>(),
    ///     vec![
    ///         Ok('𝄞'),
    ///         Ok('m'), Ok('u'), Ok('s'),
    ///         Err(0xDD1E),
    ///         Ok('i'), Ok('c'),
    ///         Err(0xD834)
    ///     ]
    /// );
    /// ```
    ///
    /// A lossy decoder can be obtained by replacing `Err` results with the replacement character:
    ///
    /// ```
    /// use std::char::{decode_utf16, REPLACEMENT_CHARACTER};
    ///
    /// // 𝄞mus<invalid>ic<invalid>
    /// let v = [
    ///     0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834,
    /// ];
    ///
    /// assert_eq!(
    ///     decode_utf16(v)
    ///        .map(|r| r.unwrap_or(REPLACEMENT_CHARACTER))
    ///        .collect::<String>(),
    ///     "𝄞mus�ic�"
    /// );
    /// ```
    #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
    #[inline]
    pub fn decode_utf16<I: IntoIterator<Item = u16>>(iter: I) -> DecodeUtf16<I::IntoIter> {
        super::decode::decode_utf16(iter)
    }

    /// Converts a `u32` to a `char`.
    ///
    /// Note that all `char`s are valid [`u32`]s, and can be cast to one with
    /// `as`:
    ///
    /// ```
    /// let c = '💯';
    /// let i = c as u32;
    ///
    /// assert_eq!(128175, i);
    /// ```
    ///
    /// However, the reverse is not true: not all valid [`u32`]s are valid
    /// `char`s. `from_u32()` will return `None` if the input is not a valid value
    /// for a `char`.
    ///
    /// For an unsafe version of this function which ignores these checks, see
    /// [`from_u32_unchecked`].
    ///
    /// [`from_u32_unchecked`]: #method.from_u32_unchecked
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// use std::char;
    ///
    /// let c = char::from_u32(0x2764);
    ///
    /// assert_eq!(Some('❤'), c);
    /// ```
    ///
    /// Returning `None` when the input is not a valid `char`:
    ///
    /// ```
    /// use std::char;
    ///
    /// let c = char::from_u32(0x110000);
    ///
    /// assert_eq!(None, c);
    /// ```
    #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
    #[inline]
    pub fn from_u32(i: u32) -> Option<char> {
        super::convert::from_u32(i)
    }

    /// Converts a `u32` to a `char`, ignoring validity.
    ///
    /// Note that all `char`s are valid [`u32`]s, and can be cast to one with
    /// `as`:
    ///
    /// ```
    /// let c = '💯';
    /// let i = c as u32;
    ///
    /// assert_eq!(128175, i);
    /// ```
    ///
    /// However, the reverse is not true: not all valid [`u32`]s are valid
    /// `char`s. `from_u32_unchecked()` will ignore this, and blindly cast to
    /// `char`, possibly creating an invalid one.
    ///
    /// # Safety
    ///
    /// This function is unsafe, as it may construct invalid `char` values.
    ///
    /// For a safe version of this function, see the [`from_u32`] function.
    ///
    /// [`from_u32`]: #method.from_u32
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// use std::char;
    ///
    /// let c = unsafe { char::from_u32_unchecked(0x2764) };
    ///
    /// assert_eq!('❤', c);
    /// ```
    #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
    #[inline]
    pub unsafe fn from_u32_unchecked(i: u32) -> char {
        // SAFETY: the safety contract must be upheld by the caller.
        unsafe { super::convert::from_u32_unchecked(i) }
    }

    /// Converts a digit in the given radix to a `char`.
    ///
    /// A 'radix' here is sometimes also called a 'base'. A radix of two
    /// indicates a binary number, a radix of ten, decimal, and a radix of
    /// sixteen, hexadecimal, to give some common values. Arbitrary
    /// radices are supported.
    ///
    /// `from_digit()` will return `None` if the input is not a digit in
    /// the given radix.
    ///
    /// # Panics
    ///
    /// Panics if given a radix larger than 36.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// use std::char;
    ///
    /// let c = char::from_digit(4, 10);
    ///
    /// assert_eq!(Some('4'), c);
    ///
    /// // Decimal 11 is a single digit in base 16
    /// let c = char::from_digit(11, 16);
    ///
    /// assert_eq!(Some('b'), c);
    /// ```
    ///
    /// Returning `None` when the input is not a digit:
    ///
    /// ```
    /// use std::char;
    ///
    /// let c = char::from_digit(20, 10);
    ///
    /// assert_eq!(None, c);
    /// ```
    ///
    /// Passing a large radix, causing a panic:
    ///
    /// ```should_panic
    /// use std::char;
    ///
    /// // this panics
    /// char::from_digit(1, 37);
    /// ```
    #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
    #[inline]
    pub fn from_digit(num: u32, radix: u32) -> Option<char> {
        super::convert::from_digit(num, radix)
    }

    /// Checks if a `char` is a digit in the given radix.
    ///
    /// A 'radix' here is sometimes also called a 'base'. A radix of two
    /// indicates a binary number, a radix of ten, decimal, and a radix of
    /// sixteen, hexadecimal, to give some common values. Arbitrary
    /// radices are supported.
    ///
    /// Compared to [`is_numeric()`], this function only recognizes the characters
    /// `0-9`, `a-z` and `A-Z`.
    ///
    /// 'Digit' is defined to be only the following characters:
    ///
    /// * `0-9`
    /// * `a-z`
    /// * `A-Z`
    ///
    /// For a more comprehensive understanding of 'digit', see [`is_numeric()`].
    ///
    /// [`is_numeric()`]: #method.is_numeric
    ///
    /// # Panics
    ///
    /// Panics if given a radix larger than 36.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!('1'.is_digit(10));
    /// assert!('f'.is_digit(16));
    /// assert!(!'f'.is_digit(10));
    /// ```
    ///
    /// Passing a large radix, causing a panic:
    ///
    /// ```should_panic
    /// // this panics
    /// '1'.is_digit(37);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_digit(self, radix: u32) -> bool {
        self.to_digit(radix).is_some()
    }

    /// Converts a `char` to a digit in the given radix.
    ///
    /// A 'radix' here is sometimes also called a 'base'. A radix of two
    /// indicates a binary number, a radix of ten, decimal, and a radix of
    /// sixteen, hexadecimal, to give some common values. Arbitrary
    /// radices are supported.
    ///
    /// 'Digit' is defined to be only the following characters:
    ///
    /// * `0-9`
    /// * `a-z`
    /// * `A-Z`
    ///
    /// # Errors
    ///
    /// Returns `None` if the `char` does not refer to a digit in the given radix.
    ///
    /// # Panics
    ///
    /// Panics if given a radix larger than 36.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert_eq!('1'.to_digit(10), Some(1));
    /// assert_eq!('f'.to_digit(16), Some(15));
    /// ```
    ///
    /// Passing a non-digit results in failure:
    ///
    /// ```
    /// assert_eq!('f'.to_digit(10), None);
    /// assert_eq!('z'.to_digit(16), None);
    /// ```
    ///
    /// Passing a large radix, causing a panic:
    ///
    /// ```should_panic
    /// // this panics
    /// '1'.to_digit(37);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn to_digit(self, radix: u32) -> Option<u32> {
        assert!(radix <= 36, "to_digit: radix is too high (maximum 36)");
        // If not a digit, a number greater than radix will be created.
        let mut digit = (self as u32).wrapping_sub('0' as u32);
        if radix > 10 {
            if digit < 10 {
                return Some(digit);
            }
            // Force the 6th bit to be set to ensure ascii is lower case.
            digit = (self as u32 | 0b10_0000).wrapping_sub('a' as u32).saturating_add(10);
        }
        (digit < radix).then_some(digit)
    }

    /// Returns an iterator that yields the hexadecimal Unicode escape of a
    /// character as `char`s.
    ///
    /// This will escape characters with the Rust syntax of the form
    /// `\u{NNNNNN}` where `NNNNNN` is a hexadecimal representation.
    ///
    /// # Examples
    ///
    /// As an iterator:
    ///
    /// ```
    /// for c in '❤'.escape_unicode() {
    ///     print!("{}", c);
    /// }
    /// println!();
    /// ```
    ///
    /// Using `println!` directly:
    ///
    /// ```
    /// println!("{}", '❤'.escape_unicode());
    /// ```
    ///
    /// Both are equivalent to:
    ///
    /// ```
    /// println!("\\u{{2764}}");
    /// ```
    ///
    /// Using `to_string`:
    ///
    /// ```
    /// assert_eq!('❤'.escape_unicode().to_string(), "\\u{2764}");
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn escape_unicode(self) -> EscapeUnicode {
        let c = self as u32;

        // or-ing 1 ensures that for c==0 the code computes that one
        // digit should be printed and (which is the same) avoids the
        // (31 - 32) underflow
        let msb = 31 - (c | 1).leading_zeros();

        // the index of the most significant hex digit
        let ms_hex_digit = msb / 4;
        EscapeUnicode {
            c: self,
            state: EscapeUnicodeState::Backslash,
            hex_digit_idx: ms_hex_digit as usize,
        }
    }

    /// An extended version of `escape_debug` that optionally permits escaping
    /// Extended Grapheme codepoints, single quotes, and double quotes. This
    /// allows us to format characters like nonspacing marks better when they're
    /// at the start of a string, and allows escaping single quotes in
    /// characters, and double quotes in strings.
    #[inline]
    pub(crate) fn escape_debug_ext(self, args: EscapeDebugExtArgs) -> EscapeDebug {
        let init_state = match self {
            '\t' => EscapeDefaultState::Backslash('t'),
            '\r' => EscapeDefaultState::Backslash('r'),
            '\n' => EscapeDefaultState::Backslash('n'),
            '\\' => EscapeDefaultState::Backslash(self),
            '"' if args.escape_double_quote => EscapeDefaultState::Backslash(self),
            '\'' if args.escape_single_quote => EscapeDefaultState::Backslash(self),
            _ if args.escape_grapheme_extended && self.is_grapheme_extended() => {
                EscapeDefaultState::Unicode(self.escape_unicode())
            }
            _ if is_printable(self) => EscapeDefaultState::Char(self),
            _ => EscapeDefaultState::Unicode(self.escape_unicode()),
        };
        EscapeDebug(EscapeDefault { state: init_state })
    }

    /// Returns an iterator that yields the literal escape code of a character
    /// as `char`s.
    ///
    /// This will escape the characters similar to the `Debug` implementations
    /// of `str` or `char`.
    ///
    /// # Examples
    ///
    /// As an iterator:
    ///
    /// ```
    /// for c in '\n'.escape_debug() {
    ///     print!("{}", c);
    /// }
    /// println!();
    /// ```
    ///
    /// Using `println!` directly:
    ///
    /// ```
    /// println!("{}", '\n'.escape_debug());
    /// ```
    ///
    /// Both are equivalent to:
    ///
    /// ```
    /// println!("\\n");
    /// ```
    ///
    /// Using `to_string`:
    ///
    /// ```
    /// assert_eq!('\n'.escape_debug().to_string(), "\\n");
    /// ```
    #[stable(feature = "char_escape_debug", since = "1.20.0")]
    #[inline]
    pub fn escape_debug(self) -> EscapeDebug {
        self.escape_debug_ext(EscapeDebugExtArgs::ESCAPE_ALL)
    }

    /// Returns an iterator that yields the literal escape code of a character
    /// as `char`s.
    ///
    /// The default is chosen with a bias toward producing literals that are
    /// legal in a variety of languages, including C++11 and similar C-family
    /// languages. The exact rules are:
    ///
    /// * Tab is escaped as `\t`.
    /// * Carriage return is escaped as `\r`.
    /// * Line feed is escaped as `\n`.
    /// * Single quote is escaped as `\'`.
    /// * Double quote is escaped as `\"`.
    /// * Backslash is escaped as `\\`.
    /// * Any character in the 'printable ASCII' range `0x20` .. `0x7e`
    ///   inclusive is not escaped.
    /// * All other characters are given hexadecimal Unicode escapes; see
    ///   [`escape_unicode`].
    ///
    /// [`escape_unicode`]: #method.escape_unicode
    ///
    /// # Examples
    ///
    /// As an iterator:
    ///
    /// ```
    /// for c in '"'.escape_default() {
    ///     print!("{}", c);
    /// }
    /// println!();
    /// ```
    ///
    /// Using `println!` directly:
    ///
    /// ```
    /// println!("{}", '"'.escape_default());
    /// ```
    ///
    /// Both are equivalent to:
    ///
    /// ```
    /// println!("\\\"");
    /// ```
    ///
    /// Using `to_string`:
    ///
    /// ```
    /// assert_eq!('"'.escape_default().to_string(), "\\\"");
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn escape_default(self) -> EscapeDefault {
        let init_state = match self {
            '\t' => EscapeDefaultState::Backslash('t'),
            '\r' => EscapeDefaultState::Backslash('r'),
            '\n' => EscapeDefaultState::Backslash('n'),
            '\\' | '\'' | '"' => EscapeDefaultState::Backslash(self),
            '\x20'..='\x7e' => EscapeDefaultState::Char(self),
            _ => EscapeDefaultState::Unicode(self.escape_unicode()),
        };
        EscapeDefault { state: init_state }
    }

    /// Returns the number of bytes this `char` would need if encoded in UTF-8.
    ///
    /// That number of bytes is always between 1 and 4, inclusive.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let len = 'A'.len_utf8();
    /// assert_eq!(len, 1);
    ///
    /// let len = 'ß'.len_utf8();
    /// assert_eq!(len, 2);
    ///
    /// let len = 'ℝ'.len_utf8();
    /// assert_eq!(len, 3);
    ///
    /// let len = '💣'.len_utf8();
    /// assert_eq!(len, 4);
    /// ```
    ///
    /// The `&str` type guarantees that its contents are UTF-8, and so we can compare the length it
    /// would take if each code point was represented as a `char` vs in the `&str` itself:
    ///
    /// ```
    /// // as chars
    /// let eastern = '東';
    /// let capital = '京';
    ///
    /// // both can be represented as three bytes
    /// assert_eq!(3, eastern.len_utf8());
    /// assert_eq!(3, capital.len_utf8());
    ///
    /// // as a &str, these two are encoded in UTF-8
    /// let tokyo = "東京";
    ///
    /// let len = eastern.len_utf8() + capital.len_utf8();
    ///
    /// // we can see that they take six bytes total...
    /// assert_eq!(6, tokyo.len());
    ///
    /// // ... just like the &str
    /// assert_eq!(len, tokyo.len());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_stable(feature = "const_char_len_utf", since = "1.52.0")]
    #[inline]
    pub const fn len_utf8(self) -> usize {
        len_utf8(self as u32)
    }

    /// Returns the number of 16-bit code units this `char` would need if
    /// encoded in UTF-16.
    ///
    /// See the documentation for [`len_utf8()`] for more explanation of this
    /// concept. This function is a mirror, but for UTF-16 instead of UTF-8.
    ///
    /// [`len_utf8()`]: #method.len_utf8
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let n = 'ß'.len_utf16();
    /// assert_eq!(n, 1);
    ///
    /// let len = '💣'.len_utf16();
    /// assert_eq!(len, 2);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_stable(feature = "const_char_len_utf", since = "1.52.0")]
    #[inline]
    pub const fn len_utf16(self) -> usize {
        let ch = self as u32;
        if (ch & 0xFFFF) == ch { 1 } else { 2 }
    }

    /// Encodes this character as UTF-8 into the provided byte buffer,
    /// and then returns the subslice of the buffer that contains the encoded character.
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough.
    /// A buffer of length four is large enough to encode any `char`.
    ///
    /// # Examples
    ///
    /// In both of these examples, 'ß' takes two bytes to encode.
    ///
    /// ```
    /// let mut b = [0; 2];
    ///
    /// let result = 'ß'.encode_utf8(&mut b);
    ///
    /// assert_eq!(result, "ß");
    ///
    /// assert_eq!(result.len(), 2);
    /// ```
    ///
    /// A buffer that's too small:
    ///
    /// ```should_panic
    /// let mut b = [0; 1];
    ///
    /// // this panics
    /// 'ß'.encode_utf8(&mut b);
    /// ```
    #[stable(feature = "unicode_encode_char", since = "1.15.0")]
    #[inline]
    pub fn encode_utf8(self, dst: &mut [u8]) -> &mut str {
        // SAFETY: `char` is not a surrogate, so this is valid UTF-8.
        unsafe { from_utf8_unchecked_mut(encode_utf8_raw(self as u32, dst)) }
    }

    /// Encodes this character as UTF-16 into the provided `u16` buffer,
    /// and then returns the subslice of the buffer that contains the encoded character.
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough.
    /// A buffer of length 2 is large enough to encode any `char`.
    ///
    /// # Examples
    ///
    /// In both of these examples, '𝕊' takes two `u16`s to encode.
    ///
    /// ```
    /// let mut b = [0; 2];
    ///
    /// let result = '𝕊'.encode_utf16(&mut b);
    ///
    /// assert_eq!(result.len(), 2);
    /// ```
    ///
    /// A buffer that's too small:
    ///
    /// ```should_panic
    /// let mut b = [0; 1];
    ///
    /// // this panics
    /// '𝕊'.encode_utf16(&mut b);
    /// ```
    #[stable(feature = "unicode_encode_char", since = "1.15.0")]
    #[inline]
    pub fn encode_utf16(self, dst: &mut [u16]) -> &mut [u16] {
        encode_utf16_raw(self as u32, dst)
    }

    /// Returns `true` if this `char` has the `Alphabetic` property.
    ///
    /// `Alphabetic` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
    /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!('a'.is_alphabetic());
    /// assert!('京'.is_alphabetic());
    ///
    /// let c = '💝';
    /// // love is many things, but it is not alphabetic
    /// assert!(!c.is_alphabetic());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_alphabetic(self) -> bool {
        match self {
            'a'..='z' | 'A'..='Z' => true,
            c => c > '\x7f' && unicode::Alphabetic(c),
        }
    }

    /// Returns `true` if this `char` has the `Lowercase` property.
    ///
    /// `Lowercase` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
    /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!('a'.is_lowercase());
    /// assert!('δ'.is_lowercase());
    /// assert!(!'A'.is_lowercase());
    /// assert!(!'Δ'.is_lowercase());
    ///
    /// // The various Chinese scripts and punctuation do not have case, and so:
    /// assert!(!'中'.is_lowercase());
    /// assert!(!' '.is_lowercase());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_lowercase(self) -> bool {
        match self {
            'a'..='z' => true,
            c => c > '\x7f' && unicode::Lowercase(c),
        }
    }

    /// Returns `true` if this `char` has the `Uppercase` property.
    ///
    /// `Uppercase` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
    /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!(!'a'.is_uppercase());
    /// assert!(!'δ'.is_uppercase());
    /// assert!('A'.is_uppercase());
    /// assert!('Δ'.is_uppercase());
    ///
    /// // The various Chinese scripts and punctuation do not have case, and so:
    /// assert!(!'中'.is_uppercase());
    /// assert!(!' '.is_uppercase());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_uppercase(self) -> bool {
        match self {
            'A'..='Z' => true,
            c => c > '\x7f' && unicode::Uppercase(c),
        }
    }

    /// Returns `true` if this `char` has the `White_Space` property.
    ///
    /// `White_Space` is specified in the [Unicode Character Database][ucd] [`PropList.txt`].
    ///
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`PropList.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/PropList.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!(' '.is_whitespace());
    ///
    /// // a non-breaking space
    /// assert!('\u{A0}'.is_whitespace());
    ///
    /// assert!(!'越'.is_whitespace());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_whitespace(self) -> bool {
        match self {
            ' ' | '\x09'..='\x0d' => true,
            c => c > '\x7f' && unicode::White_Space(c),
        }
    }

    /// Returns `true` if this `char` satisfies either [`is_alphabetic()`] or [`is_numeric()`].
    ///
    /// [`is_alphabetic()`]: #method.is_alphabetic
    /// [`is_numeric()`]: #method.is_numeric
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!('٣'.is_alphanumeric());
    /// assert!('7'.is_alphanumeric());
    /// assert!('৬'.is_alphanumeric());
    /// assert!('¾'.is_alphanumeric());
    /// assert!('①'.is_alphanumeric());
    /// assert!('K'.is_alphanumeric());
    /// assert!('و'.is_alphanumeric());
    /// assert!('藏'.is_alphanumeric());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_alphanumeric(self) -> bool {
        self.is_alphabetic() || self.is_numeric()
    }

    /// Returns `true` if this `char` has the general category for control codes.
    ///
    /// Control codes (code points with the general category of `Cc`) are described in Chapter 4
    /// (Character Properties) of the [Unicode Standard] and specified in the [Unicode Character
    /// Database][ucd] [`UnicodeData.txt`].
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// // U+009C, STRING TERMINATOR
    /// assert!('œ'.is_control());
    /// assert!(!'q'.is_control());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_control(self) -> bool {
        unicode::Cc(self)
    }

    /// Returns `true` if this `char` has the `Grapheme_Extend` property.
    ///
    /// `Grapheme_Extend` is described in [Unicode Standard Annex #29 (Unicode Text
    /// Segmentation)][uax29] and specified in the [Unicode Character Database][ucd]
    /// [`DerivedCoreProperties.txt`].
    ///
    /// [uax29]: https://www.unicode.org/reports/tr29/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
    #[inline]
    pub(crate) fn is_grapheme_extended(self) -> bool {
        unicode::Grapheme_Extend(self)
    }

    /// Returns `true` if this `char` has one of the general categories for numbers.
    ///
    /// The general categories for numbers (`Nd` for decimal digits, `Nl` for letter-like numeric
    /// characters, and `No` for other numeric characters) are specified in the [Unicode Character
    /// Database][ucd] [`UnicodeData.txt`].
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!('٣'.is_numeric());
    /// assert!('7'.is_numeric());
    /// assert!('৬'.is_numeric());
    /// assert!('¾'.is_numeric());
    /// assert!('①'.is_numeric());
    /// assert!(!'K'.is_numeric());
    /// assert!(!'و'.is_numeric());
    /// assert!(!'藏'.is_numeric());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_numeric(self) -> bool {
        match self {
            '0'..='9' => true,
            c => c > '\x7f' && unicode::N(c),
        }
    }

    /// Returns an iterator that yields the lowercase mapping of this `char` as one or more
    /// `char`s.
    ///
    /// If this `char` does not have a lowercase mapping, the iterator yields the same `char`.
    ///
    /// If this `char` has a one-to-one lowercase mapping given by the [Unicode Character
    /// Database][ucd] [`UnicodeData.txt`], the iterator yields that `char`.
    ///
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
    ///
    /// If this `char` requires special considerations (e.g. multiple `char`s) the iterator yields
    /// the `char`(s) given by [`SpecialCasing.txt`].
    ///
    /// [`SpecialCasing.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/SpecialCasing.txt
    ///
    /// This operation performs an unconditional mapping without tailoring. That is, the conversion
    /// is independent of context and language.
    ///
    /// In the [Unicode Standard], Chapter 4 (Character Properties) discusses case mapping in
    /// general and Chapter 3 (Conformance) discusses the default algorithm for case conversion.
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    ///
    /// # Examples
    ///
    /// As an iterator:
    ///
    /// ```
    /// for c in 'İ'.to_lowercase() {
    ///     print!("{}", c);
    /// }
    /// println!();
    /// ```
    ///
    /// Using `println!` directly:
    ///
    /// ```
    /// println!("{}", 'İ'.to_lowercase());
    /// ```
    ///
    /// Both are equivalent to:
    ///
    /// ```
    /// println!("i\u{307}");
    /// ```
    ///
    /// Using `to_string`:
    ///
    /// ```
    /// assert_eq!('C'.to_lowercase().to_string(), "c");
    ///
    /// // Sometimes the result is more than one character:
    /// assert_eq!('İ'.to_lowercase().to_string(), "i\u{307}");
    ///
    /// // Characters that do not have both uppercase and lowercase
    /// // convert into themselves.
    /// assert_eq!('山'.to_lowercase().to_string(), "山");
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn to_lowercase(self) -> ToLowercase {
        ToLowercase(CaseMappingIter::new(conversions::to_lower(self)))
    }

    /// Returns an iterator that yields the uppercase mapping of this `char` as one or more
    /// `char`s.
    ///
    /// If this `char` does not have an uppercase mapping, the iterator yields the same `char`.
    ///
    /// If this `char` has a one-to-one uppercase mapping given by the [Unicode Character
    /// Database][ucd] [`UnicodeData.txt`], the iterator yields that `char`.
    ///
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
    ///
    /// If this `char` requires special considerations (e.g. multiple `char`s) the iterator yields
    /// the `char`(s) given by [`SpecialCasing.txt`].
    ///
    /// [`SpecialCasing.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/SpecialCasing.txt
    ///
    /// This operation performs an unconditional mapping without tailoring. That is, the conversion
    /// is independent of context and language.
    ///
    /// In the [Unicode Standard], Chapter 4 (Character Properties) discusses case mapping in
    /// general and Chapter 3 (Conformance) discusses the default algorithm for case conversion.
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    ///
    /// # Examples
    ///
    /// As an iterator:
    ///
    /// ```
    /// for c in 'ß'.to_uppercase() {
    ///     print!("{}", c);
    /// }
    /// println!();
    /// ```
    ///
    /// Using `println!` directly:
    ///
    /// ```
    /// println!("{}", 'ß'.to_uppercase());
    /// ```
    ///
    /// Both are equivalent to:
    ///
    /// ```
    /// println!("SS");
    /// ```
    ///
    /// Using `to_string`:
    ///
    /// ```
    /// assert_eq!('c'.to_uppercase().to_string(), "C");
    ///
    /// // Sometimes the result is more than one character:
    /// assert_eq!('ß'.to_uppercase().to_string(), "SS");
    ///
    /// // Characters that do not have both uppercase and lowercase
    /// // convert into themselves.
    /// assert_eq!('山'.to_uppercase().to_string(), "山");
    /// ```
    ///
    /// # Note on locale
    ///
    /// In Turkish, the equivalent of 'i' in Latin has five forms instead of two:
    ///
    /// * 'Dotless': I / ı, sometimes written ï
    /// * 'Dotted': İ / i
    ///
    /// Note that the lowercase dotted 'i' is the same as the Latin. Therefore:
    ///
    /// ```
    /// let upper_i = 'i'.to_uppercase().to_string();
    /// ```
    ///
    /// The value of `upper_i` here relies on the language of the text: if we're
    /// in `en-US`, it should be `"I"`, but if we're in `tr_TR`, it should
    /// be `"İ"`. `to_uppercase()` does not take this into account, and so:
    ///
    /// ```
    /// let upper_i = 'i'.to_uppercase().to_string();
    ///
    /// assert_eq!(upper_i, "I");
    /// ```
    ///
    /// holds across languages.
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn to_uppercase(self) -> ToUppercase {
        ToUppercase(CaseMappingIter::new(conversions::to_upper(self)))
    }

    /// Checks if the value is within the ASCII range.
    ///
    /// # Examples
    ///
    /// ```
    /// let ascii = 'a';
    /// let non_ascii = '❤';
    ///
    /// assert!(ascii.is_ascii());
    /// assert!(!non_ascii.is_ascii());
    /// ```
    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
    #[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.32.0")]
    #[inline]
    pub const fn is_ascii(&self) -> bool {
        *self as u32 <= 0x7F
    }

    /// Makes a copy of the value in its ASCII upper case equivalent.
    ///
    /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
    /// but non-ASCII letters are unchanged.
    ///
    /// To uppercase the value in-place, use [`make_ascii_uppercase()`].
    ///
    /// To uppercase ASCII characters in addition to non-ASCII characters, use
    /// [`to_uppercase()`].
    ///
    /// # Examples
    ///
    /// ```
    /// let ascii = 'a';
    /// let non_ascii = '❤';
    ///
    /// assert_eq!('A', ascii.to_ascii_uppercase());
    /// assert_eq!('❤', non_ascii.to_ascii_uppercase());
    /// ```
    ///
    /// [`make_ascii_uppercase()`]: #method.make_ascii_uppercase
    /// [`to_uppercase()`]: #method.to_uppercase
    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
    #[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.52.0")]
    #[inline]
    pub const fn to_ascii_uppercase(&self) -> char {
        if self.is_ascii_lowercase() {
            (*self as u8).ascii_change_case_unchecked() as char
        } else {
            *self
        }
    }

    /// Makes a copy of the value in its ASCII lower case equivalent.
    ///
    /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
    /// but non-ASCII letters are unchanged.
    ///
    /// To lowercase the value in-place, use [`make_ascii_lowercase()`].
    ///
    /// To lowercase ASCII characters in addition to non-ASCII characters, use
    /// [`to_lowercase()`].
    ///
    /// # Examples
    ///
    /// ```
    /// let ascii = 'A';
    /// let non_ascii = '❤';
    ///
    /// assert_eq!('a', ascii.to_ascii_lowercase());
    /// assert_eq!('❤', non_ascii.to_ascii_lowercase());
    /// ```
    ///
    /// [`make_ascii_lowercase()`]: #method.make_ascii_lowercase
    /// [`to_lowercase()`]: #method.to_lowercase
    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
    #[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.52.0")]
    #[inline]
    pub const fn to_ascii_lowercase(&self) -> char {
        if self.is_ascii_uppercase() {
            (*self as u8).ascii_change_case_unchecked() as char
        } else {
            *self
        }
    }

    /// Checks that two values are an ASCII case-insensitive match.
    ///
    /// Equivalent to `to_ascii_lowercase(a) == to_ascii_lowercase(b)`.
    ///
    /// # Examples
    ///
    /// ```
    /// let upper_a = 'A';
    /// let lower_a = 'a';
    /// let lower_z = 'z';
    ///
    /// assert!(upper_a.eq_ignore_ascii_case(&lower_a));
    /// assert!(upper_a.eq_ignore_ascii_case(&upper_a));
    /// assert!(!upper_a.eq_ignore_ascii_case(&lower_z));
    /// ```
    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
    #[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.52.0")]
    #[inline]
    pub const fn eq_ignore_ascii_case(&self, other: &char) -> bool {
        self.to_ascii_lowercase() == other.to_ascii_lowercase()
    }

    /// Converts this type to its ASCII upper case equivalent in-place.
    ///
    /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
    /// but non-ASCII letters are unchanged.
    ///
    /// To return a new uppercased value without modifying the existing one, use
    /// [`to_ascii_uppercase()`].
    ///
    /// # Examples
    ///
    /// ```
    /// let mut ascii = 'a';
    ///
    /// ascii.make_ascii_uppercase();
    ///
    /// assert_eq!('A', ascii);
    /// ```
    ///
    /// [`to_ascii_uppercase()`]: #method.to_ascii_uppercase
    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
    #[inline]
    pub fn make_ascii_uppercase(&mut self) {
        *self = self.to_ascii_uppercase();
    }

    /// Converts this type to its ASCII lower case equivalent in-place.
    ///
    /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
    /// but non-ASCII letters are unchanged.
    ///
    /// To return a new lowercased value without modifying the existing one, use
    /// [`to_ascii_lowercase()`].
    ///
    /// # Examples
    ///
    /// ```
    /// let mut ascii = 'A';
    ///
    /// ascii.make_ascii_lowercase();
    ///
    /// assert_eq!('a', ascii);
    /// ```
    ///
    /// [`to_ascii_lowercase()`]: #method.to_ascii_lowercase
    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
    #[inline]
    pub fn make_ascii_lowercase(&mut self) {
        *self = self.to_ascii_lowercase();
    }

    /// Checks if the value is an ASCII alphabetic character:
    ///
    /// - U+0041 'A' ..= U+005A 'Z', or
    /// - U+0061 'a' ..= U+007A 'z'.
    ///
    /// # Examples
    ///
    /// ```
    /// let uppercase_a = 'A';
    /// let uppercase_g = 'G';
    /// let a = 'a';
    /// let g = 'g';
    /// let zero = '0';
    /// let percent = '%';
    /// let space = ' ';
    /// let lf = '\n';
    /// let esc: char = 0x1b_u8.into();
    ///
    /// assert!(uppercase_a.is_ascii_alphabetic());
    /// assert!(uppercase_g.is_ascii_alphabetic());
    /// assert!(a.is_ascii_alphabetic());
    /// assert!(g.is_ascii_alphabetic());
    /// assert!(!zero.is_ascii_alphabetic());
    /// assert!(!percent.is_ascii_alphabetic());
    /// assert!(!space.is_ascii_alphabetic());
    /// assert!(!lf.is_ascii_alphabetic());
    /// assert!(!esc.is_ascii_alphabetic());
    /// ```
    #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
    #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
    #[inline]
    pub const fn is_ascii_alphabetic(&self) -> bool {
        matches!(*self, 'A'..='Z' | 'a'..='z')
    }

    /// Checks if the value is an ASCII uppercase character:
    /// U+0041 'A' ..= U+005A 'Z'.
    ///
    /// # Examples
    ///
    /// ```
    /// let uppercase_a = 'A';
    /// let uppercase_g = 'G';
    /// let a = 'a';
    /// let g = 'g';
    /// let zero = '0';
    /// let percent = '%';
    /// let space = ' ';
    /// let lf = '\n';
    /// let esc: char = 0x1b_u8.into();
    ///
    /// assert!(uppercase_a.is_ascii_uppercase());
    /// assert!(uppercase_g.is_ascii_uppercase());
    /// assert!(!a.is_ascii_uppercase());
    /// assert!(!g.is_ascii_uppercase());
    /// assert!(!zero.is_ascii_uppercase());
    /// assert!(!percent.is_ascii_uppercase());
    /// assert!(!space.is_ascii_uppercase());
    /// assert!(!lf.is_ascii_uppercase());
    /// assert!(!esc.is_ascii_uppercase());
    /// ```
    #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
    #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
    #[inline]
    pub const fn is_ascii_uppercase(&self) -> bool {
        matches!(*self, 'A'..='Z')
    }

    /// Checks if the value is an ASCII lowercase character:
    /// U+0061 'a' ..= U+007A 'z'.
    ///
    /// # Examples
    ///
    /// ```
    /// let uppercase_a = 'A';
    /// let uppercase_g = 'G';
    /// let a = 'a';
    /// let g = 'g';
    /// let zero = '0';
    /// let percent = '%';
    /// let space = ' ';
    /// let lf = '\n';
    /// let esc: char = 0x1b_u8.into();
    ///
    /// assert!(!uppercase_a.is_ascii_lowercase());
    /// assert!(!uppercase_g.is_ascii_lowercase());
    /// assert!(a.is_ascii_lowercase());
    /// assert!(g.is_ascii_lowercase());
    /// assert!(!zero.is_ascii_lowercase());
    /// assert!(!percent.is_ascii_lowercase());
    /// assert!(!space.is_ascii_lowercase());
    /// assert!(!lf.is_ascii_lowercase());
    /// assert!(!esc.is_ascii_lowercase());
    /// ```
    #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
    #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
    #[inline]
    pub const fn is_ascii_lowercase(&self) -> bool {
        matches!(*self, 'a'..='z')
    }

    /// Checks if the value is an ASCII alphanumeric character:
    ///
    /// - U+0041 'A' ..= U+005A 'Z', or
    /// - U+0061 'a' ..= U+007A 'z', or
    /// - U+0030 '0' ..= U+0039 '9'.
    ///
    /// # Examples
    ///
    /// ```
    /// let uppercase_a = 'A';
    /// let uppercase_g = 'G';
    /// let a = 'a';
    /// let g = 'g';
    /// let zero = '0';
    /// let percent = '%';
    /// let space = ' ';
    /// let lf = '\n';
    /// let esc: char = 0x1b_u8.into();
    ///
    /// assert!(uppercase_a.is_ascii_alphanumeric());
    /// assert!(uppercase_g.is_ascii_alphanumeric());
    /// assert!(a.is_ascii_alphanumeric());
    /// assert!(g.is_ascii_alphanumeric());
    /// assert!(zero.is_ascii_alphanumeric());
    /// assert!(!percent.is_ascii_alphanumeric());
    /// assert!(!space.is_ascii_alphanumeric());
    /// assert!(!lf.is_ascii_alphanumeric());
    /// assert!(!esc.is_ascii_alphanumeric());
    /// ```
    #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
    #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
    #[inline]
    pub const fn is_ascii_alphanumeric(&self) -> bool {
        matches!(*self, '0'..='9' | 'A'..='Z' | 'a'..='z')
    }

    /// Checks if the value is an ASCII decimal digit:
    /// U+0030 '0' ..= U+0039 '9'.
    ///
    /// # Examples
    ///
    /// ```
    /// let uppercase_a = 'A';
    /// let uppercase_g = 'G';
    /// let a = 'a';
    /// let g = 'g';
    /// let zero = '0';
    /// let percent = '%';
    /// let space = ' ';
    /// let lf = '\n';
    /// let esc: char = 0x1b_u8.into();
    ///
    /// assert!(!uppercase_a.is_ascii_digit());
    /// assert!(!uppercase_g.is_ascii_digit());
    /// assert!(!a.is_ascii_digit());
    /// assert!(!g.is_ascii_digit());
    /// assert!(zero.is_ascii_digit());
    /// assert!(!percent.is_ascii_digit());
    /// assert!(!space.is_ascii_digit());
    /// assert!(!lf.is_ascii_digit());
    /// assert!(!esc.is_ascii_digit());
    /// ```
    #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
    #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
    #[inline]
    pub const fn is_ascii_digit(&self) -> bool {
        matches!(*self, '0'..='9')
    }

    /// Checks if the value is an ASCII hexadecimal digit:
    ///
    /// - U+0030 '0' ..= U+0039 '9', or
    /// - U+0041 'A' ..= U+0046 'F', or
    /// - U+0061 'a' ..= U+0066 'f'.
    ///
    /// # Examples
    ///
    /// ```
    /// let uppercase_a = 'A';
    /// let uppercase_g = 'G';
    /// let a = 'a';
    /// let g = 'g';
    /// let zero = '0';
    /// let percent = '%';
    /// let space = ' ';
    /// let lf = '\n';
    /// let esc: char = 0x1b_u8.into();
    ///
    /// assert!(uppercase_a.is_ascii_hexdigit());
    /// assert!(!uppercase_g.is_ascii_hexdigit());
    /// assert!(a.is_ascii_hexdigit());
    /// assert!(!g.is_ascii_hexdigit());
    /// assert!(zero.is_ascii_hexdigit());
    /// assert!(!percent.is_ascii_hexdigit());
    /// assert!(!space.is_ascii_hexdigit());
    /// assert!(!lf.is_ascii_hexdigit());
    /// assert!(!esc.is_ascii_hexdigit());
    /// ```
    #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
    #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
    #[inline]
    pub const fn is_ascii_hexdigit(&self) -> bool {
        matches!(*self, '0'..='9' | 'A'..='F' | 'a'..='f')
    }

    /// Checks if the value is an ASCII punctuation character:
    ///
    /// - U+0021 ..= U+002F `! " # $ % & ' ( ) * + , - . /`, or
    /// - U+003A ..= U+0040 `: ; < = > ? @`, or
    /// - U+005B ..= U+0060 ``[ \ ] ^ _ ` ``, or
    /// - U+007B ..= U+007E `{ | } ~`
    ///
    /// # Examples
    ///
    /// ```
    /// let uppercase_a = 'A';
    /// let uppercase_g = 'G';
    /// let a = 'a';
    /// let g = 'g';
    /// let zero = '0';
    /// let percent = '%';
    /// let space = ' ';
    /// let lf = '\n';
    /// let esc: char = 0x1b_u8.into();
    ///
    /// assert!(!uppercase_a.is_ascii_punctuation());
    /// assert!(!uppercase_g.is_ascii_punctuation());
    /// assert!(!a.is_ascii_punctuation());
    /// assert!(!g.is_ascii_punctuation());
    /// assert!(!zero.is_ascii_punctuation());
    /// assert!(percent.is_ascii_punctuation());
    /// assert!(!space.is_ascii_punctuation());
    /// assert!(!lf.is_ascii_punctuation());
    /// assert!(!esc.is_ascii_punctuation());
    /// ```
    #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
    #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
    #[inline]
    pub const fn is_ascii_punctuation(&self) -> bool {
        matches!(*self, '!'..='/' | ':'..='@' | '['..='`' | '{'..='~')
    }

    /// Checks if the value is an ASCII graphic character:
    /// U+0021 '!' ..= U+007E '~'.
    ///
    /// # Examples
    ///
    /// ```
    /// let uppercase_a = 'A';
    /// let uppercase_g = 'G';
    /// let a = 'a';
    /// let g = 'g';
    /// let zero = '0';
    /// let percent = '%';
    /// let space = ' ';
    /// let lf = '\n';
    /// let esc: char = 0x1b_u8.into();
    ///
    /// assert!(uppercase_a.is_ascii_graphic());
    /// assert!(uppercase_g.is_ascii_graphic());
    /// assert!(a.is_ascii_graphic());
    /// assert!(g.is_ascii_graphic());
    /// assert!(zero.is_ascii_graphic());
    /// assert!(percent.is_ascii_graphic());
    /// assert!(!space.is_ascii_graphic());
    /// assert!(!lf.is_ascii_graphic());
    /// assert!(!esc.is_ascii_graphic());
    /// ```
    #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
    #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
    #[inline]
    pub const fn is_ascii_graphic(&self) -> bool {
        matches!(*self, '!'..='~')
    }

    /// Checks if the value is an ASCII whitespace character:
    /// U+0020 SPACE, U+0009 HORIZONTAL TAB, U+000A LINE FEED,
    /// U+000C FORM FEED, or U+000D CARRIAGE RETURN.
    ///
    /// Rust uses the WhatWG Infra Standard's [definition of ASCII
    /// whitespace][infra-aw]. There are several other definitions in
    /// wide use. For instance, [the POSIX locale][pct] includes
    /// U+000B VERTICAL TAB as well as all the above characters,
    /// but—from the very same specification—[the default rule for
    /// "field splitting" in the Bourne shell][bfs] considers *only*
    /// SPACE, HORIZONTAL TAB, and LINE FEED as whitespace.
    ///
    /// If you are writing a program that will process an existing
    /// file format, check what that format's definition of whitespace is
    /// before using this function.
    ///
    /// [infra-aw]: https://infra.spec.whatwg.org/#ascii-whitespace
    /// [pct]: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap07.html#tag_07_03_01
    /// [bfs]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_05
    ///
    /// # Examples
    ///
    /// ```
    /// let uppercase_a = 'A';
    /// let uppercase_g = 'G';
    /// let a = 'a';
    /// let g = 'g';
    /// let zero = '0';
    /// let percent = '%';
    /// let space = ' ';
    /// let lf = '\n';
    /// let esc: char = 0x1b_u8.into();
    ///
    /// assert!(!uppercase_a.is_ascii_whitespace());
    /// assert!(!uppercase_g.is_ascii_whitespace());
    /// assert!(!a.is_ascii_whitespace());
    /// assert!(!g.is_ascii_whitespace());
    /// assert!(!zero.is_ascii_whitespace());
    /// assert!(!percent.is_ascii_whitespace());
    /// assert!(space.is_ascii_whitespace());
    /// assert!(lf.is_ascii_whitespace());
    /// assert!(!esc.is_ascii_whitespace());
    /// ```
    #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
    #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
    #[inline]
    pub const fn is_ascii_whitespace(&self) -> bool {
        matches!(*self, '\t' | '\n' | '\x0C' | '\r' | ' ')
    }

    /// Checks if the value is an ASCII control character:
    /// U+0000 NUL ..= U+001F UNIT SEPARATOR, or U+007F DELETE.
    /// Note that most ASCII whitespace characters are control
    /// characters, but SPACE is not.
    ///
    /// # Examples
    ///
    /// ```
    /// let uppercase_a = 'A';
    /// let uppercase_g = 'G';
    /// let a = 'a';
    /// let g = 'g';
    /// let zero = '0';
    /// let percent = '%';
    /// let space = ' ';
    /// let lf = '\n';
    /// let esc: char = 0x1b_u8.into();
    ///
    /// assert!(!uppercase_a.is_ascii_control());
    /// assert!(!uppercase_g.is_ascii_control());
    /// assert!(!a.is_ascii_control());
    /// assert!(!g.is_ascii_control());
    /// assert!(!zero.is_ascii_control());
    /// assert!(!percent.is_ascii_control());
    /// assert!(!space.is_ascii_control());
    /// assert!(lf.is_ascii_control());
    /// assert!(esc.is_ascii_control());
    /// ```
    #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
    #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
    #[inline]
    pub const fn is_ascii_control(&self) -> bool {
        matches!(*self, '\0'..='\x1F' | '\x7F')
    }
}

pub(crate) struct EscapeDebugExtArgs {
    /// Escape Extended Grapheme codepoints?
    pub(crate) escape_grapheme_extended: bool,

    /// Escape single quotes?
    pub(crate) escape_single_quote: bool,

    /// Escape double quotes?
    pub(crate) escape_double_quote: bool,
}

impl EscapeDebugExtArgs {
    pub(crate) const ESCAPE_ALL: Self = Self {
        escape_grapheme_extended: true,
        escape_single_quote: true,
        escape_double_quote: true,
    };
}

#[inline]
const fn len_utf8(code: u32) -> usize {
    if code < MAX_ONE_B {
        1
    } else if code < MAX_TWO_B {
        2
    } else if code < MAX_THREE_B {
        3
    } else {
        4
    }
}

/// Encodes a raw u32 value as UTF-8 into the provided byte buffer,
/// and then returns the subslice of the buffer that contains the encoded character.
///
/// Unlike `char::encode_utf8`, this method also handles codepoints in the surrogate range.
/// (Creating a `char` in the surrogate range is UB.)
/// The result is valid [generalized UTF-8] but not valid UTF-8.
///
/// [generalized UTF-8]: https://simonsapin.github.io/wtf-8/#generalized-utf8
///
/// # Panics
///
/// Panics if the buffer is not large enough.
/// A buffer of length four is large enough to encode any `char`.
#[unstable(feature = "char_internals", reason = "exposed only for libstd", issue = "none")]
#[doc(hidden)]
#[inline]
pub fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> &mut [u8] {
    let len = len_utf8(code);
    match (len, &mut dst[..]) {
        (1, [a, ..]) => {
            *a = code as u8;
        }
        (2, [a, b, ..]) => {
            *a = (code >> 6 & 0x1F) as u8 | TAG_TWO_B;
            *b = (code & 0x3F) as u8 | TAG_CONT;
        }
        (3, [a, b, c, ..]) => {
            *a = (code >> 12 & 0x0F) as u8 | TAG_THREE_B;
            *b = (code >> 6 & 0x3F) as u8 | TAG_CONT;
            *c = (code & 0x3F) as u8 | TAG_CONT;
        }
        (4, [a, b, c, d, ..]) => {
            *a = (code >> 18 & 0x07) as u8 | TAG_FOUR_B;
            *b = (code >> 12 & 0x3F) as u8 | TAG_CONT;
            *c = (code >> 6 & 0x3F) as u8 | TAG_CONT;
            *d = (code & 0x3F) as u8 | TAG_CONT;
        }
        _ => panic!(
            "encode_utf8: need {} bytes to encode U+{:X}, but the buffer has {}",
            len,
            code,
            dst.len(),
        ),
    };
    &mut dst[..len]
}

/// Encodes a raw u32 value as UTF-16 into the provided `u16` buffer,
/// and then returns the subslice of the buffer that contains the encoded character.
///
/// Unlike `char::encode_utf16`, this method also handles codepoints in the surrogate range.
/// (Creating a `char` in the surrogate range is UB.)
///
/// # Panics
///
/// Panics if the buffer is not large enough.
/// A buffer of length 2 is large enough to encode any `char`.
#[unstable(feature = "char_internals", reason = "exposed only for libstd", issue = "none")]
#[doc(hidden)]
#[inline]
pub fn encode_utf16_raw(mut code: u32, dst: &mut [u16]) -> &mut [u16] {
    // SAFETY: each arm checks whether there are enough bits to write into
    unsafe {
        if (code & 0xFFFF) == code && !dst.is_empty() {
            // The BMP falls through
            *dst.get_unchecked_mut(0) = code as u16;
            slice::from_raw_parts_mut(dst.as_mut_ptr(), 1)
        } else if dst.len() >= 2 {
            // Supplementary planes break into surrogates.
            code -= 0x1_0000;
            *dst.get_unchecked_mut(0) = 0xD800 | ((code >> 10) as u16);
            *dst.get_unchecked_mut(1) = 0xDC00 | ((code as u16) & 0x3FF);
            slice::from_raw_parts_mut(dst.as_mut_ptr(), 2)
        } else {
            panic!(
                "encode_utf16: need {} units to encode U+{:X}, but the buffer has {}",
                from_u32_unchecked(code).len_utf16(),
                code,
                dst.len(),
            )
        }
    }
}