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
// `library/{std,core}/src/primitive_docs.rs` should have the same contents.
// These are different files so that relative links work properly without
// having to have `CARGO_PKG_NAME` set, but conceptually they should always be the same.
#[doc(primitive = "bool")]
#[doc(alias = "true")]
#[doc(alias = "false")]
/// The boolean type.
///
/// The `bool` represents a value, which could only be either [`true`] or [`false`]. If you cast
/// a `bool` into an integer, [`true`] will be 1 and [`false`] will be 0.
///
/// # Basic usage
///
/// `bool` implements various traits, such as [`BitAnd`], [`BitOr`], [`Not`], etc.,
/// which allow us to perform boolean operations using `&`, `|` and `!`.
///
/// [`if`] requires a `bool` value as its conditional. [`assert!`], which is an
/// important macro in testing, checks whether an expression is [`true`] and panics
/// if it isn't.
///
/// ```
/// let bool_val = true & false | false;
/// assert!(!bool_val);
/// ```
///
/// [`true`]: ../std/keyword.true.html
/// [`false`]: ../std/keyword.false.html
/// [`BitAnd`]: ops::BitAnd
/// [`BitOr`]: ops::BitOr
/// [`Not`]: ops::Not
/// [`if`]: ../std/keyword.if.html
///
/// # Examples
///
/// A trivial example of the usage of `bool`:
///
/// ```
/// let praise_the_borrow_checker = true;
///
/// // using the `if` conditional
/// if praise_the_borrow_checker {
///     println!("oh, yeah!");
/// } else {
///     println!("what?!!");
/// }
///
/// // ... or, a match pattern
/// match praise_the_borrow_checker {
///     true => println!("keep praising!"),
///     false => println!("you should praise!"),
/// }
/// ```
///
/// Also, since `bool` implements the [`Copy`] trait, we don't
/// have to worry about the move semantics (just like the integer and float primitives).
///
/// Now an example of `bool` cast to integer type:
///
/// ```
/// assert_eq!(true as i32, 1);
/// assert_eq!(false as i32, 0);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_bool {}

#[doc(primitive = "never")]
#[doc(alias = "!")]
//
/// The `!` type, also called "never".
///
/// `!` represents the type of computations which never resolve to any value at all. For example,
/// the [`exit`] function `fn exit(code: i32) -> !` exits the process without ever returning, and
/// so returns `!`.
///
/// `break`, `continue` and `return` expressions also have type `!`. For example we are allowed to
/// write:
///
/// ```
/// #![feature(never_type)]
/// # fn foo() -> u32 {
/// let x: ! = {
///     return 123
/// };
/// # }
/// ```
///
/// Although the `let` is pointless here, it illustrates the meaning of `!`. Since `x` is never
/// assigned a value (because `return` returns from the entire function), `x` can be given type
/// `!`. We could also replace `return 123` with a `panic!` or a never-ending `loop` and this code
/// would still be valid.
///
/// A more realistic usage of `!` is in this code:
///
/// ```
/// # fn get_a_number() -> Option<u32> { None }
/// # loop {
/// let num: u32 = match get_a_number() {
///     Some(num) => num,
///     None => break,
/// };
/// # }
/// ```
///
/// Both match arms must produce values of type [`u32`], but since `break` never produces a value
/// at all we know it can never produce a value which isn't a [`u32`]. This illustrates another
/// behaviour of the `!` type - expressions with type `!` will coerce into any other type.
///
/// [`u32`]: prim@u32
#[doc = concat!("[`exit`]: ", include_str!("../primitive_docs/process_exit.md"))]
///
/// # `!` and generics
///
/// ## Infallible errors
///
/// The main place you'll see `!` used explicitly is in generic code. Consider the [`FromStr`]
/// trait:
///
/// ```
/// trait FromStr: Sized {
///     type Err;
///     fn from_str(s: &str) -> Result<Self, Self::Err>;
/// }
/// ```
///
/// When implementing this trait for [`String`] we need to pick a type for [`Err`]. And since
/// converting a string into a string will never result in an error, the appropriate type is `!`.
/// (Currently the type actually used is an enum with no variants, though this is only because `!`
/// was added to Rust at a later date and it may change in the future.) With an [`Err`] type of
/// `!`, if we have to call [`String::from_str`] for some reason the result will be a
/// [`Result<String, !>`] which we can unpack like this:
///
/// ```
/// #![feature(exhaustive_patterns)]
/// use std::str::FromStr;
/// let Ok(s) = String::from_str("hello");
/// ```
///
/// Since the [`Err`] variant contains a `!`, it can never occur. If the `exhaustive_patterns`
/// feature is present this means we can exhaustively match on [`Result<T, !>`] by just taking the
/// [`Ok`] variant. This illustrates another behaviour of `!` - it can be used to "delete" certain
/// enum variants from generic types like `Result`.
///
/// ## Infinite loops
///
/// While [`Result<T, !>`] is very useful for removing errors, `!` can also be used to remove
/// successes as well. If we think of [`Result<T, !>`] as "if this function returns, it has not
/// errored," we get a very intuitive idea of [`Result<!, E>`] as well: if the function returns, it
/// *has* errored.
///
/// For example, consider the case of a simple web server, which can be simplified to:
///
/// ```ignore (hypothetical-example)
/// loop {
///     let (client, request) = get_request().expect("disconnected");
///     let response = request.process();
///     response.send(client);
/// }
/// ```
///
/// Currently, this isn't ideal, because we simply panic whenever we fail to get a new connection.
/// Instead, we'd like to keep track of this error, like this:
///
/// ```ignore (hypothetical-example)
/// loop {
///     match get_request() {
///         Err(err) => break err,
///         Ok((client, request)) => {
///             let response = request.process();
///             response.send(client);
///         },
///     }
/// }
/// ```
///
/// Now, when the server disconnects, we exit the loop with an error instead of panicking. While it
/// might be intuitive to simply return the error, we might want to wrap it in a [`Result<!, E>`]
/// instead:
///
/// ```ignore (hypothetical-example)
/// fn server_loop() -> Result<!, ConnectionError> {
///     loop {
///         let (client, request) = get_request()?;
///         let response = request.process();
///         response.send(client);
///     }
/// }
/// ```
///
/// Now, we can use `?` instead of `match`, and the return type makes a lot more sense: if the loop
/// ever stops, it means that an error occurred. We don't even have to wrap the loop in an `Ok`
/// because `!` coerces to `Result<!, ConnectionError>` automatically.
///
/// [`String::from_str`]: str::FromStr::from_str
#[doc = concat!("[`String`]: ", include_str!("../primitive_docs/string_string.md"))]
/// [`FromStr`]: str::FromStr
///
/// # `!` and traits
///
/// When writing your own traits, `!` should have an `impl` whenever there is an obvious `impl`
/// which doesn't `panic!`. The reason is that functions returning an `impl Trait` where `!`
/// does not have an `impl` of `Trait` cannot diverge as their only possible code path. In other
/// words, they can't return `!` from every code path. As an example, this code doesn't compile:
///
/// ```compile_fail
/// use std::ops::Add;
///
/// fn foo() -> impl Add<u32> {
///     unimplemented!()
/// }
/// ```
///
/// But this code does:
///
/// ```
/// use std::ops::Add;
///
/// fn foo() -> impl Add<u32> {
///     if true {
///         unimplemented!()
///     } else {
///         0
///     }
/// }
/// ```
///
/// The reason is that, in the first example, there are many possible types that `!` could coerce
/// to, because many types implement `Add<u32>`. However, in the second example,
/// the `else` branch returns a `0`, which the compiler infers from the return type to be of type
/// `u32`. Since `u32` is a concrete type, `!` can and will be coerced to it. See issue [#36375]
/// for more information on this quirk of `!`.
///
/// [#36375]: https://github.com/rust-lang/rust/issues/36375
///
/// As it turns out, though, most traits can have an `impl` for `!`. Take [`Debug`]
/// for example:
///
/// ```
/// #![feature(never_type)]
/// # use std::fmt;
/// # trait Debug {
/// #     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result;
/// # }
/// impl Debug for ! {
///     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
///         *self
///     }
/// }
/// ```
///
/// Once again we're using `!`'s ability to coerce into any other type, in this case
/// [`fmt::Result`]. Since this method takes a `&!` as an argument we know that it can never be
/// called (because there is no value of type `!` for it to be called with). Writing `*self`
/// essentially tells the compiler "We know that this code can never be run, so just treat the
/// entire function body as having type [`fmt::Result`]". This pattern can be used a lot when
/// implementing traits for `!`. Generally, any trait which only has methods which take a `self`
/// parameter should have such an impl.
///
/// On the other hand, one trait which would not be appropriate to implement is [`Default`]:
///
/// ```
/// trait Default {
///     fn default() -> Self;
/// }
/// ```
///
/// Since `!` has no values, it has no default value either. It's true that we could write an
/// `impl` for this which simply panics, but the same is true for any type (we could `impl
/// Default` for (eg.) [`File`] by just making [`default()`] panic.)
///
#[doc = concat!("[`File`]: ", include_str!("../primitive_docs/fs_file.md"))]
/// [`Debug`]: fmt::Debug
/// [`default()`]: Default::default
///
#[unstable(feature = "never_type", issue = "35121")]
mod prim_never {}

#[doc(primitive = "char")]
/// A character type.
///
/// The `char` type represents a single character. More specifically, since
/// 'character' isn't a well-defined concept in Unicode, `char` is a '[Unicode
/// scalar value]', which is similar to, but not the same as, a '[Unicode code
/// point]'.
///
/// [Unicode scalar value]: https://www.unicode.org/glossary/#unicode_scalar_value
/// [Unicode code point]: https://www.unicode.org/glossary/#code_point
///
/// This documentation describes a number of methods and trait implementations on the
/// `char` type. For technical reasons, there is additional, separate
/// documentation in [the `std::char` module](char/index.html) as well.
///
/// # Representation
///
/// `char` is always four bytes in size. This is a different representation than
/// a given character would have as part of a [`String`]. For example:
///
/// ```
/// let v = vec!['h', 'e', 'l', 'l', 'o'];
///
/// // five elements times four bytes for each element
/// assert_eq!(20, v.len() * std::mem::size_of::<char>());
///
/// let s = String::from("hello");
///
/// // five elements times one byte per element
/// assert_eq!(5, s.len() * std::mem::size_of::<u8>());
/// ```
///
#[doc = concat!("[`String`]: ", include_str!("../primitive_docs/string_string.md"))]
///
/// As always, remember that a human intuition for 'character' might not map to
/// Unicode's definitions. For example, despite looking similar, the 'é'
/// character is one Unicode code point while 'é' is two Unicode code points:
///
/// ```
/// let mut chars = "é".chars();
/// // U+00e9: 'latin small letter e with acute'
/// assert_eq!(Some('\u{00e9}'), chars.next());
/// assert_eq!(None, chars.next());
///
/// let mut chars = "é".chars();
/// // U+0065: 'latin small letter e'
/// assert_eq!(Some('\u{0065}'), chars.next());
/// // U+0301: 'combining acute accent'
/// assert_eq!(Some('\u{0301}'), chars.next());
/// assert_eq!(None, chars.next());
/// ```
///
/// This means that the contents of the first string above _will_ fit into a
/// `char` while the contents of the second string _will not_. Trying to create
/// a `char` literal with the contents of the second string gives an error:
///
/// ```text
/// error: character literal may only contain one codepoint: 'é'
/// let c = 'é';
///         ^^^
/// ```
///
/// Another implication of the 4-byte fixed size of a `char` is that
/// per-`char` processing can end up using a lot more memory:
///
/// ```
/// let s = String::from("love: ❤️");
/// let v: Vec<char> = s.chars().collect();
///
/// assert_eq!(12, std::mem::size_of_val(&s[..]));
/// assert_eq!(32, std::mem::size_of_val(&v[..]));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_char {}

#[doc(primitive = "unit")]
#[doc(alias = "(")]
#[doc(alias = ")")]
#[doc(alias = "()")]
//
/// The `()` type, also called "unit".
///
/// The `()` type has exactly one value `()`, and is used when there
/// is no other meaningful value that could be returned. `()` is most
/// commonly seen implicitly: functions without a `-> ...` implicitly
/// have return type `()`, that is, these are equivalent:
///
/// ```rust
/// fn long() -> () {}
///
/// fn short() {}
/// ```
///
/// The semicolon `;` can be used to discard the result of an
/// expression at the end of a block, making the expression (and thus
/// the block) evaluate to `()`. For example,
///
/// ```rust
/// fn returns_i64() -> i64 {
///     1i64
/// }
/// fn returns_unit() {
///     1i64;
/// }
///
/// let is_i64 = {
///     returns_i64()
/// };
/// let is_unit = {
///     returns_i64();
/// };
/// ```
///
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_unit {}

#[doc(primitive = "pointer")]
#[doc(alias = "ptr")]
#[doc(alias = "*")]
#[doc(alias = "*const")]
#[doc(alias = "*mut")]
//
/// Raw, unsafe pointers, `*const T`, and `*mut T`.
///
/// *[See also the `std::ptr` module](ptr).*
///
/// Working with raw pointers in Rust is uncommon, typically limited to a few patterns.
/// Raw pointers can be unaligned or [`null`]. However, when a raw pointer is
/// dereferenced (using the `*` operator), it must be non-null and aligned.
///
/// Storing through a raw pointer using `*ptr = data` calls `drop` on the old value, so
/// [`write`] must be used if the type has drop glue and memory is not already
/// initialized - otherwise `drop` would be called on the uninitialized memory.
///
/// Use the [`null`] and [`null_mut`] functions to create null pointers, and the
/// [`is_null`] method of the `*const T` and `*mut T` types to check for null.
/// The `*const T` and `*mut T` types also define the [`offset`] method, for
/// pointer math.
///
/// # Common ways to create raw pointers
///
/// ## 1. Coerce a reference (`&T`) or mutable reference (`&mut T`).
///
/// ```
/// let my_num: i32 = 10;
/// let my_num_ptr: *const i32 = &my_num;
/// let mut my_speed: i32 = 88;
/// let my_speed_ptr: *mut i32 = &mut my_speed;
/// ```
///
/// To get a pointer to a boxed value, dereference the box:
///
/// ```
/// let my_num: Box<i32> = Box::new(10);
/// let my_num_ptr: *const i32 = &*my_num;
/// let mut my_speed: Box<i32> = Box::new(88);
/// let my_speed_ptr: *mut i32 = &mut *my_speed;
/// ```
///
/// This does not take ownership of the original allocation
/// and requires no resource management later,
/// but you must not use the pointer after its lifetime.
///
/// ## 2. Consume a box (`Box<T>`).
///
/// The [`into_raw`] function consumes a box and returns
/// the raw pointer. It doesn't destroy `T` or deallocate any memory.
///
/// ```
/// let my_speed: Box<i32> = Box::new(88);
/// let my_speed: *mut i32 = Box::into_raw(my_speed);
///
/// // By taking ownership of the original `Box<T>` though
/// // we are obligated to put it together later to be destroyed.
/// unsafe {
///     drop(Box::from_raw(my_speed));
/// }
/// ```
///
/// Note that here the call to [`drop`] is for clarity - it indicates
/// that we are done with the given value and it should be destroyed.
///
/// ## 3. Create it using `ptr::addr_of!`
///
/// Instead of coercing a reference to a raw pointer, you can use the macros
/// [`ptr::addr_of!`] (for `*const T`) and [`ptr::addr_of_mut!`] (for `*mut T`).
/// These macros allow you to create raw pointers to fields to which you cannot
/// create a reference (without causing undefined behaviour), such as an
/// unaligned field. This might be necessary if packed structs or uninitialized
/// memory is involved.
///
/// ```
/// #[derive(Debug, Default, Copy, Clone)]
/// #[repr(C, packed)]
/// struct S {
///     aligned: u8,
///     unaligned: u32,
/// }
/// let s = S::default();
/// let p = std::ptr::addr_of!(s.unaligned); // not allowed with coercion
/// ```
///
/// ## 4. Get it from C.
///
/// ```
/// # #![feature(rustc_private)]
/// extern crate libc;
///
/// use std::mem;
///
/// unsafe {
///     let my_num: *mut i32 = libc::malloc(mem::size_of::<i32>()) as *mut i32;
///     if my_num.is_null() {
///         panic!("failed to allocate memory");
///     }
///     libc::free(my_num as *mut libc::c_void);
/// }
/// ```
///
/// Usually you wouldn't literally use `malloc` and `free` from Rust,
/// but C APIs hand out a lot of pointers generally, so are a common source
/// of raw pointers in Rust.
///
/// [`null`]: ptr::null
/// [`null_mut`]: ptr::null_mut
/// [`is_null`]: pointer::is_null
/// [`offset`]: pointer::offset
#[doc = concat!("[`into_raw`]: ", include_str!("../primitive_docs/box_into_raw.md"))]
/// [`drop`]: mem::drop
/// [`write`]: ptr::write
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_pointer {}

#[doc(primitive = "array")]
#[doc(alias = "[]")]
#[doc(alias = "[T;N]")] // unfortunately, rustdoc doesn't have fuzzy search for aliases
#[doc(alias = "[T; N]")]
/// A fixed-size array, denoted `[T; N]`, for the element type, `T`, and the
/// non-negative compile-time constant size, `N`.
///
/// There are two syntactic forms for creating an array:
///
/// * A list with each element, i.e., `[x, y, z]`.
/// * A repeat expression `[x; N]`, which produces an array with `N` copies of `x`.
///   The type of `x` must be [`Copy`].
///
/// Note that `[expr; 0]` is allowed, and produces an empty array.
/// This will still evaluate `expr`, however, and immediately drop the resulting value, so
/// be mindful of side effects.
///
/// Arrays of *any* size implement the following traits if the element type allows it:
///
/// - [`Copy`]
/// - [`Clone`]
/// - [`Debug`]
/// - [`IntoIterator`] (implemented for `[T; N]`, `&[T; N]` and `&mut [T; N]`)
/// - [`PartialEq`], [`PartialOrd`], [`Eq`], [`Ord`]
/// - [`Hash`]
/// - [`AsRef`], [`AsMut`]
/// - [`Borrow`], [`BorrowMut`]
///
/// Arrays of sizes from 0 to 32 (inclusive) implement the [`Default`] trait
/// if the element type allows it. As a stopgap, trait implementations are
/// statically generated up to size 32.
///
/// Arrays coerce to [slices (`[T]`)][slice], so a slice method may be called on
/// an array. Indeed, this provides most of the API for working with arrays.
/// Slices have a dynamic size and do not coerce to arrays.
///
/// You can move elements out of an array with a [slice pattern]. If you want
/// one element, see [`mem::replace`].
///
/// # Examples
///
/// ```
/// let mut array: [i32; 3] = [0; 3];
///
/// array[1] = 1;
/// array[2] = 2;
///
/// assert_eq!([1, 2], &array[1..]);
///
/// // This loop prints: 0 1 2
/// for x in array {
///     print!("{} ", x);
/// }
/// ```
///
/// You can also iterate over reference to the array's elements:
///
/// ```
/// let array: [i32; 3] = [0; 3];
///
/// for x in &array { }
/// ```
///
/// You can use a [slice pattern] to move elements out of an array:
///
/// ```
/// fn move_away(_: String) { /* Do interesting things. */ }
///
/// let [john, roa] = ["John".to_string(), "Roa".to_string()];
/// move_away(john);
/// move_away(roa);
/// ```
///
/// # Editions
///
/// Prior to Rust 1.53, arrays did not implement [`IntoIterator`] by value, so the method call
/// `array.into_iter()` auto-referenced into a [slice iterator](slice::iter). Right now, the old
/// behavior is preserved in the 2015 and 2018 editions of Rust for compatibility, ignoring
/// [`IntoIterator`] by value. In the future, the behavior on the 2015 and 2018 edition
/// might be made consistent to the behavior of later editions.
///
/// ```rust,edition2018
/// // Rust 2015 and 2018:
///
/// # #![allow(array_into_iter)] // override our `deny(warnings)`
/// let array: [i32; 3] = [0; 3];
///
/// // This creates a slice iterator, producing references to each value.
/// for item in array.into_iter().enumerate() {
///     let (i, x): (usize, &i32) = item;
///     println!("array[{}] = {}", i, x);
/// }
///
/// // The `array_into_iter` lint suggests this change for future compatibility:
/// for item in array.iter().enumerate() {
///     let (i, x): (usize, &i32) = item;
///     println!("array[{}] = {}", i, x);
/// }
///
/// // You can explicitly iterate an array by value using
/// // `IntoIterator::into_iter` or `std::array::IntoIter::new`:
/// for item in IntoIterator::into_iter(array).enumerate() {
///     let (i, x): (usize, i32) = item;
///     println!("array[{}] = {}", i, x);
/// }
/// ```
///
/// Starting in the 2021 edition, `array.into_iter()` uses `IntoIterator` normally to iterate
/// by value, and `iter()` should be used to iterate by reference like previous editions.
///
/// ```rust,edition2021
/// // Rust 2021:
///
/// let array: [i32; 3] = [0; 3];
///
/// // This iterates by reference:
/// for item in array.iter().enumerate() {
///     let (i, x): (usize, &i32) = item;
///     println!("array[{}] = {}", i, x);
/// }
///
/// // This iterates by value:
/// for item in array.into_iter().enumerate() {
///     let (i, x): (usize, i32) = item;
///     println!("array[{}] = {}", i, x);
/// }
/// ```
///
/// Future language versions might start treating the `array.into_iter()`
/// syntax on editions 2015 and 2018 the same as on edition 2021. So code using
/// those older editions should still be written with this change in mind, to
/// prevent breakage in the future. The safest way to accomplish this is to
/// avoid the `into_iter` syntax on those editions. If an edition update is not
/// viable/desired, there are multiple alternatives:
/// * use `iter`, equivalent to the old behavior, creating references
/// * use [`IntoIterator::into_iter`], equivalent to the post-2021 behavior (Rust 1.53+)
/// * replace `for ... in array.into_iter() {` with `for ... in array {`,
///   equivalent to the post-2021 behavior (Rust 1.53+)
///
/// ```rust,edition2018
/// // Rust 2015 and 2018:
///
/// let array: [i32; 3] = [0; 3];
///
/// // This iterates by reference:
/// for item in array.iter() {
///     let x: &i32 = item;
///     println!("{}", x);
/// }
///
/// // This iterates by value:
/// for item in IntoIterator::into_iter(array) {
///     let x: i32 = item;
///     println!("{}", x);
/// }
///
/// // This iterates by value:
/// for item in array {
///     let x: i32 = item;
///     println!("{}", x);
/// }
///
/// // IntoIter can also start a chain.
/// // This iterates by value:
/// for item in IntoIterator::into_iter(array).enumerate() {
///     let (i, x): (usize, i32) = item;
///     println!("array[{}] = {}", i, x);
/// }
/// ```
///
/// [slice]: prim@slice
/// [`Debug`]: fmt::Debug
/// [`Hash`]: hash::Hash
/// [`Borrow`]: borrow::Borrow
/// [`BorrowMut`]: borrow::BorrowMut
/// [slice pattern]: ../reference/patterns.html#slice-patterns
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_array {}

#[doc(primitive = "slice")]
#[doc(alias = "[")]
#[doc(alias = "]")]
#[doc(alias = "[]")]
/// A dynamically-sized view into a contiguous sequence, `[T]`. Contiguous here
/// means that elements are laid out so that every element is the same
/// distance from its neighbors.
///
/// *[See also the `std::slice` module](crate::slice).*
///
/// Slices are a view into a block of memory represented as a pointer and a
/// length.
///
/// ```
/// // slicing a Vec
/// let vec = vec![1, 2, 3];
/// let int_slice = &vec[..];
/// // coercing an array to a slice
/// let str_slice: &[&str] = &["one", "two", "three"];
/// ```
///
/// Slices are either mutable or shared. The shared slice type is `&[T]`,
/// while the mutable slice type is `&mut [T]`, where `T` represents the element
/// type. For example, you can mutate the block of memory that a mutable slice
/// points to:
///
/// ```
/// let mut x = [1, 2, 3];
/// let x = &mut x[..]; // Take a full slice of `x`.
/// x[1] = 7;
/// assert_eq!(x, &[1, 7, 3]);
/// ```
///
/// As slices store the length of the sequence they refer to, they have twice
/// the size of pointers to [`Sized`](marker/trait.Sized.html) types.
/// Also see the reference on
/// [dynamically sized types](../reference/dynamically-sized-types.html).
///
/// ```
/// # use std::rc::Rc;
/// let pointer_size = std::mem::size_of::<&u8>();
/// assert_eq!(2 * pointer_size, std::mem::size_of::<&[u8]>());
/// assert_eq!(2 * pointer_size, std::mem::size_of::<*const [u8]>());
/// assert_eq!(2 * pointer_size, std::mem::size_of::<Box<[u8]>>());
/// assert_eq!(2 * pointer_size, std::mem::size_of::<Rc<[u8]>>());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_slice {}

#[doc(primitive = "str")]
//
/// String slices.
///
/// *[See also the `std::str` module](crate::str).*
///
/// The `str` type, also called a 'string slice', is the most primitive string
/// type. It is usually seen in its borrowed form, `&str`. It is also the type
/// of string literals, `&'static str`.
///
/// String slices are always valid UTF-8.
///
/// # Examples
///
/// String literals are string slices:
///
/// ```
/// let hello = "Hello, world!";
///
/// // with an explicit type annotation
/// let hello: &'static str = "Hello, world!";
/// ```
///
/// They are `'static` because they're stored directly in the final binary, and
/// so will be valid for the `'static` duration.
///
/// # Representation
///
/// A `&str` is made up of two components: a pointer to some bytes, and a
/// length. You can look at these with the [`as_ptr`] and [`len`] methods:
///
/// ```
/// use std::slice;
/// use std::str;
///
/// let story = "Once upon a time...";
///
/// let ptr = story.as_ptr();
/// let len = story.len();
///
/// // story has nineteen bytes
/// assert_eq!(19, len);
///
/// // We can re-build a str out of ptr and len. This is all unsafe because
/// // we are responsible for making sure the two components are valid:
/// let s = unsafe {
///     // First, we build a &[u8]...
///     let slice = slice::from_raw_parts(ptr, len);
///
///     // ... and then convert that slice into a string slice
///     str::from_utf8(slice)
/// };
///
/// assert_eq!(s, Ok(story));
/// ```
///
/// [`as_ptr`]: str::as_ptr
/// [`len`]: str::len
///
/// Note: This example shows the internals of `&str`. `unsafe` should not be
/// used to get a string slice under normal circumstances. Use `as_str`
/// instead.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_str {}

#[doc(primitive = "tuple")]
#[doc(alias = "(")]
#[doc(alias = ")")]
#[doc(alias = "()")]
//
/// A finite heterogeneous sequence, `(T, U, ..)`.
///
/// Let's cover each of those in turn:
///
/// Tuples are *finite*. In other words, a tuple has a length. Here's a tuple
/// of length `3`:
///
/// ```
/// ("hello", 5, 'c');
/// ```
///
/// 'Length' is also sometimes called 'arity' here; each tuple of a different
/// length is a different, distinct type.
///
/// Tuples are *heterogeneous*. This means that each element of the tuple can
/// have a different type. In that tuple above, it has the type:
///
/// ```
/// # let _:
/// (&'static str, i32, char)
/// # = ("hello", 5, 'c');
/// ```
///
/// Tuples are a *sequence*. This means that they can be accessed by position;
/// this is called 'tuple indexing', and it looks like this:
///
/// ```rust
/// let tuple = ("hello", 5, 'c');
///
/// assert_eq!(tuple.0, "hello");
/// assert_eq!(tuple.1, 5);
/// assert_eq!(tuple.2, 'c');
/// ```
///
/// The sequential nature of the tuple applies to its implementations of various
/// traits. For example, in [`PartialOrd`] and [`Ord`], the elements are compared
/// sequentially until the first non-equal set is found.
///
/// For more about tuples, see [the book](../book/ch03-02-data-types.html#the-tuple-type).
///
/// # Trait implementations
///
/// If every type inside a tuple implements one of the following traits, then a
/// tuple itself also implements it.
///
/// * [`Clone`]
/// * [`Copy`]
/// * [`PartialEq`]
/// * [`Eq`]
/// * [`PartialOrd`]
/// * [`Ord`]
/// * [`Debug`]
/// * [`Default`]
/// * [`Hash`]
///
/// [`Debug`]: fmt::Debug
/// [`Hash`]: hash::Hash
///
/// Due to a temporary restriction in Rust's type system, these traits are only
/// implemented on tuples of arity 12 or less. In the future, this may change.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let tuple = ("hello", 5, 'c');
///
/// assert_eq!(tuple.0, "hello");
/// ```
///
/// Tuples are often used as a return type when you want to return more than
/// one value:
///
/// ```
/// fn calculate_point() -> (i32, i32) {
///     // Don't do a calculation, that's not the point of the example
///     (4, 5)
/// }
///
/// let point = calculate_point();
///
/// assert_eq!(point.0, 4);
/// assert_eq!(point.1, 5);
///
/// // Combining this with patterns can be nicer.
///
/// let (x, y) = calculate_point();
///
/// assert_eq!(x, 4);
/// assert_eq!(y, 5);
/// ```
///
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_tuple {}

#[doc(primitive = "f32")]
/// A 32-bit floating point type (specifically, the "binary32" type defined in IEEE 754-2008).
///
/// This type can represent a wide range of decimal numbers, like `3.5`, `27`,
/// `-113.75`, `0.0078125`, `34359738368`, `0`, `-1`. So unlike integer types
/// (such as `i32`), floating point types can represent non-integer numbers,
/// too.
///
/// However, being able to represent this wide range of numbers comes at the
/// cost of precision: floats can only represent some of the real numbers and
/// calculation with floats round to a nearby representable number. For example,
/// `5.0` and `1.0` can be exactly represented as `f32`, but `1.0 / 5.0` results
/// in `0.20000000298023223876953125` since `0.2` cannot be exactly represented
/// as `f32`. Note, however, that printing floats with `println` and friends will
/// often discard insignificant digits: `println!("{}", 1.0f32 / 5.0f32)` will
/// print `0.2`.
///
/// Additionally, `f32` can represent some special values:
///
/// - −0.0: IEEE 754 floating point numbers have a bit that indicates their sign, so −0.0 is a
///   possible value. For comparison −0.0 = +0.0, but floating point operations can carry
///   the sign bit through arithmetic operations. This means −0.0 × +0.0 produces −0.0 and
///   a negative number rounded to a value smaller than a float can represent also produces −0.0.
/// - [∞](#associatedconstant.INFINITY) and
///   [−∞](#associatedconstant.NEG_INFINITY): these result from calculations
///   like `1.0 / 0.0`.
/// - [NaN (not a number)](#associatedconstant.NAN): this value results from
///   calculations like `(-1.0).sqrt()`. NaN has some potentially unexpected
///   behavior: it is unequal to any float, including itself! It is also neither
///   smaller nor greater than any float, making it impossible to sort. Lastly,
///   it is considered infectious as almost all calculations where one of the
///   operands is NaN will also result in NaN.
///
/// For more information on floating point numbers, see [Wikipedia][wikipedia].
///
/// *[See also the `std::f32::consts` module](crate::f32::consts).*
///
/// [wikipedia]: https://en.wikipedia.org/wiki/Single-precision_floating-point_format
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_f32 {}

#[doc(primitive = "f64")]
/// A 64-bit floating point type (specifically, the "binary64" type defined in IEEE 754-2008).
///
/// This type is very similar to [`f32`], but has increased
/// precision by using twice as many bits. Please see [the documentation for
/// `f32`][`f32`] or [Wikipedia on double precision
/// values][wikipedia] for more information.
///
/// *[See also the `std::f64::consts` module](crate::f64::consts).*
///
/// [`f32`]: prim@f32
/// [wikipedia]: https://en.wikipedia.org/wiki/Double-precision_floating-point_format
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_f64 {}

#[doc(primitive = "i8")]
//
/// The 8-bit signed integer type.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_i8 {}

#[doc(primitive = "i16")]
//
/// The 16-bit signed integer type.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_i16 {}

#[doc(primitive = "i32")]
//
/// The 32-bit signed integer type.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_i32 {}

#[doc(primitive = "i64")]
//
/// The 64-bit signed integer type.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_i64 {}

#[doc(primitive = "i128")]
//
/// The 128-bit signed integer type.
#[stable(feature = "i128", since = "1.26.0")]
mod prim_i128 {}

#[doc(primitive = "u8")]
//
/// The 8-bit unsigned integer type.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_u8 {}

#[doc(primitive = "u16")]
//
/// The 16-bit unsigned integer type.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_u16 {}

#[doc(primitive = "u32")]
//
/// The 32-bit unsigned integer type.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_u32 {}

#[doc(primitive = "u64")]
//
/// The 64-bit unsigned integer type.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_u64 {}

#[doc(primitive = "u128")]
//
/// The 128-bit unsigned integer type.
#[stable(feature = "i128", since = "1.26.0")]
mod prim_u128 {}

#[doc(primitive = "isize")]
//
/// The pointer-sized signed integer type.
///
/// The size of this primitive is how many bytes it takes to reference any
/// location in memory. For example, on a 32 bit target, this is 4 bytes
/// and on a 64 bit target, this is 8 bytes.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_isize {}

#[doc(primitive = "usize")]
//
/// The pointer-sized unsigned integer type.
///
/// The size of this primitive is how many bytes it takes to reference any
/// location in memory. For example, on a 32 bit target, this is 4 bytes
/// and on a 64 bit target, this is 8 bytes.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_usize {}

#[doc(primitive = "reference")]
#[doc(alias = "&")]
#[doc(alias = "&mut")]
//
/// References, both shared and mutable.
///
/// A reference represents a borrow of some owned value. You can get one by using the `&` or `&mut`
/// operators on a value, or by using a [`ref`](../std/keyword.ref.html) or
/// <code>[ref](../std/keyword.ref.html) [mut](../std/keyword.mut.html)</code> pattern.
///
/// For those familiar with pointers, a reference is just a pointer that is assumed to be
/// aligned, not null, and pointing to memory containing a valid value of `T` - for example,
/// <code>&[bool]</code> can only point to an allocation containing the integer values `1`
/// ([`true`](../std/keyword.true.html)) or `0` ([`false`](../std/keyword.false.html)), but
/// creating a <code>&[bool]</code> that points to an allocation containing
/// the value `3` causes undefined behaviour.
/// In fact, <code>[Option]\<&T></code> has the same memory representation as a
/// nullable but aligned pointer, and can be passed across FFI boundaries as such.
///
/// In most cases, references can be used much like the original value. Field access, method
/// calling, and indexing work the same (save for mutability rules, of course). In addition, the
/// comparison operators transparently defer to the referent's implementation, allowing references
/// to be compared the same as owned values.
///
/// References have a lifetime attached to them, which represents the scope for which the borrow is
/// valid. A lifetime is said to "outlive" another one if its representative scope is as long or
/// longer than the other. The `'static` lifetime is the longest lifetime, which represents the
/// total life of the program. For example, string literals have a `'static` lifetime because the
/// text data is embedded into the binary of the program, rather than in an allocation that needs
/// to be dynamically managed.
///
/// `&mut T` references can be freely coerced into `&T` references with the same referent type, and
/// references with longer lifetimes can be freely coerced into references with shorter ones.
///
/// Reference equality by address, instead of comparing the values pointed to, is accomplished via
/// implicit reference-pointer coercion and raw pointer equality via [`ptr::eq`], while
/// [`PartialEq`] compares values.
///
/// ```
/// use std::ptr;
///
/// let five = 5;
/// let other_five = 5;
/// let five_ref = &five;
/// let same_five_ref = &five;
/// let other_five_ref = &other_five;
///
/// assert!(five_ref == same_five_ref);
/// assert!(five_ref == other_five_ref);
///
/// assert!(ptr::eq(five_ref, same_five_ref));
/// assert!(!ptr::eq(five_ref, other_five_ref));
/// ```
///
/// For more information on how to use references, see [the book's section on "References and
/// Borrowing"][book-refs].
///
/// [book-refs]: ../book/ch04-02-references-and-borrowing.html
///
/// # Trait implementations
///
/// The following traits are implemented for all `&T`, regardless of the type of its referent:
///
/// * [`Copy`]
/// * [`Clone`] \(Note that this will not defer to `T`'s `Clone` implementation if it exists!)
/// * [`Deref`]
/// * [`Borrow`]
/// * [`Pointer`]
///
/// [`Deref`]: ops::Deref
/// [`Borrow`]: borrow::Borrow
/// [`Pointer`]: fmt::Pointer
///
/// `&mut T` references get all of the above except `Copy` and `Clone` (to prevent creating
/// multiple simultaneous mutable borrows), plus the following, regardless of the type of its
/// referent:
///
/// * [`DerefMut`]
/// * [`BorrowMut`]
///
/// [`DerefMut`]: ops::DerefMut
/// [`BorrowMut`]: borrow::BorrowMut
/// [bool]: prim@bool
///
/// The following traits are implemented on `&T` references if the underlying `T` also implements
/// that trait:
///
/// * All the traits in [`std::fmt`] except [`Pointer`] and [`fmt::Write`]
/// * [`PartialOrd`]
/// * [`Ord`]
/// * [`PartialEq`]
/// * [`Eq`]
/// * [`AsRef`]
/// * [`Fn`] \(in addition, `&T` references get [`FnMut`] and [`FnOnce`] if `T: Fn`)
/// * [`Hash`]
/// * [`ToSocketAddrs`]
///
/// [`std::fmt`]: fmt
/// ['Pointer`]: fmt::Pointer
/// [`Hash`]: hash::Hash
#[doc = concat!("[`ToSocketAddrs`]: ", include_str!("../primitive_docs/net_tosocketaddrs.md"))]
///
/// `&mut T` references get all of the above except `ToSocketAddrs`, plus the following, if `T`
/// implements that trait:
///
/// * [`AsMut`]
/// * [`FnMut`] \(in addition, `&mut T` references get [`FnOnce`] if `T: FnMut`)
/// * [`fmt::Write`]
/// * [`Iterator`]
/// * [`DoubleEndedIterator`]
/// * [`ExactSizeIterator`]
/// * [`FusedIterator`]
/// * [`TrustedLen`]
/// * [`Send`] \(note that `&T` references only get `Send` if <code>T: [Sync]</code>)
/// * [`io::Write`]
/// * [`Read`]
/// * [`Seek`]
/// * [`BufRead`]
///
/// [`FusedIterator`]: iter::FusedIterator
/// [`TrustedLen`]: iter::TrustedLen
#[doc = concat!("[`Seek`]: ", include_str!("../primitive_docs/io_seek.md"))]
#[doc = concat!("[`BufRead`]: ", include_str!("../primitive_docs/io_bufread.md"))]
#[doc = concat!("[`Read`]: ", include_str!("../primitive_docs/io_read.md"))]
#[doc = concat!("[`io::Write`]: ", include_str!("../primitive_docs/io_write.md"))]
///
/// Note that due to method call deref coercion, simply calling a trait method will act like they
/// work on references as well as they do on owned values! The implementations described here are
/// meant for generic contexts, where the final type `T` is a type parameter or otherwise not
/// locally known.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_ref {}

#[doc(primitive = "fn")]
//
/// Function pointers, like `fn(usize) -> bool`.
///
/// *See also the traits [`Fn`], [`FnMut`], and [`FnOnce`].*
///
/// [`Fn`]: ops::Fn
/// [`FnMut`]: ops::FnMut
/// [`FnOnce`]: ops::FnOnce
///
/// Function pointers are pointers that point to *code*, not data. They can be called
/// just like functions. Like references, function pointers are, among other things, assumed to
/// not be null, so if you want to pass a function pointer over FFI and be able to accommodate null
/// pointers, make your type [`Option<fn()>`](core::option#options-and-pointers-nullable-pointers)
/// with your required signature.
///
/// ### Safety
///
/// Plain function pointers are obtained by casting either plain functions, or closures that don't
/// capture an environment:
///
/// ```
/// fn add_one(x: usize) -> usize {
///     x + 1
/// }
///
/// let ptr: fn(usize) -> usize = add_one;
/// assert_eq!(ptr(5), 6);
///
/// let clos: fn(usize) -> usize = |x| x + 5;
/// assert_eq!(clos(5), 10);
/// ```
///
/// In addition to varying based on their signature, function pointers come in two flavors: safe
/// and unsafe. Plain `fn()` function pointers can only point to safe functions,
/// while `unsafe fn()` function pointers can point to safe or unsafe functions.
///
/// ```
/// fn add_one(x: usize) -> usize {
///     x + 1
/// }
///
/// unsafe fn add_one_unsafely(x: usize) -> usize {
///     x + 1
/// }
///
/// let safe_ptr: fn(usize) -> usize = add_one;
///
/// //ERROR: mismatched types: expected normal fn, found unsafe fn
/// //let bad_ptr: fn(usize) -> usize = add_one_unsafely;
///
/// let unsafe_ptr: unsafe fn(usize) -> usize = add_one_unsafely;
/// let really_safe_ptr: unsafe fn(usize) -> usize = add_one;
/// ```
///
/// ### ABI
///
/// On top of that, function pointers can vary based on what ABI they use. This
/// is achieved by adding the `extern` keyword before the type, followed by the
/// ABI in question. The default ABI is "Rust", i.e., `fn()` is the exact same
/// type as `extern "Rust" fn()`. A pointer to a function with C ABI would have
/// type `extern "C" fn()`.
///
/// `extern "ABI" { ... }` blocks declare functions with ABI "ABI". The default
/// here is "C", i.e., functions declared in an `extern {...}` block have "C"
/// ABI.
///
/// For more information and a list of supported ABIs, see [the nomicon's
/// section on foreign calling conventions][nomicon-abi].
///
/// [nomicon-abi]: ../nomicon/ffi.html#foreign-calling-conventions
///
/// ### Variadic functions
///
/// Extern function declarations with the "C" or "cdecl" ABIs can also be *variadic*, allowing them
/// to be called with a variable number of arguments. Normal Rust functions, even those with an
/// `extern "ABI"`, cannot be variadic. For more information, see [the nomicon's section on
/// variadic functions][nomicon-variadic].
///
/// [nomicon-variadic]: ../nomicon/ffi.html#variadic-functions
///
/// ### Creating function pointers
///
/// When `bar` is the name of a function, then the expression `bar` is *not* a
/// function pointer. Rather, it denotes a value of an unnameable type that
/// uniquely identifies the function `bar`. The value is zero-sized because the
/// type already identifies the function. This has the advantage that "calling"
/// the value (it implements the `Fn*` traits) does not require dynamic
/// dispatch.
///
/// This zero-sized type *coerces* to a regular function pointer. For example:
///
/// ```rust
/// use std::mem;
///
/// fn bar(x: i32) {}
///
/// let not_bar_ptr = bar; // `not_bar_ptr` is zero-sized, uniquely identifying `bar`
/// assert_eq!(mem::size_of_val(&not_bar_ptr), 0);
///
/// let bar_ptr: fn(i32) = not_bar_ptr; // force coercion to function pointer
/// assert_eq!(mem::size_of_val(&bar_ptr), mem::size_of::<usize>());
///
/// let footgun = &bar; // this is a shared reference to the zero-sized type identifying `bar`
/// ```
///
/// The last line shows that `&bar` is not a function pointer either. Rather, it
/// is a reference to the function-specific ZST. `&bar` is basically never what you
/// want when `bar` is a function.
///
/// ### Traits
///
/// Function pointers implement the following traits:
///
/// * [`Clone`]
/// * [`PartialEq`]
/// * [`Eq`]
/// * [`PartialOrd`]
/// * [`Ord`]
/// * [`Hash`]
/// * [`Pointer`]
/// * [`Debug`]
///
/// [`Hash`]: hash::Hash
/// [`Pointer`]: fmt::Pointer
///
/// Due to a temporary restriction in Rust's type system, these traits are only implemented on
/// functions that take 12 arguments or less, with the `"Rust"` and `"C"` ABIs. In the future, this
/// may change.
///
/// In addition, function pointers of *any* signature, ABI, or safety are [`Copy`], and all *safe*
/// function pointers implement [`Fn`], [`FnMut`], and [`FnOnce`]. This works because these traits
/// are specially known to the compiler.
#[stable(feature = "rust1", since = "1.0.0")]
mod prim_fn {}