library/core/src/char/methods.rs

   1 //! impl char {}
   2
   3 use crate::slice;
   4 use crate::str::from_utf8_unchecked_mut;
   5 use crate::unicode::printable::is_printable;
   6 use crate::unicode::{self, conversions};
   7
   8 use super::*;
   9
  10 impl char {
  11     /// The highest valid code point a `char` can have, `'\u{10FFFF}'`.
  12     ///
  13     /// # Examples
  14     ///
  15     /// ```
  16     /// # fn something_which_returns_char() -> char { 'a' }
  17     /// let c: char = something_which_returns_char();
  18     /// assert!(c <= char::MAX);
  19     ///
  20     /// let value_at_max = char::MAX as u32;
  21     /// assert_eq!(char::from_u32(value_at_max), Some('\u{10FFFF}'));
  22     /// assert_eq!(char::from_u32(value_at_max + 1), None);
  23     /// ```
  24     #[stable(feature = "assoc_char_consts", since = "1.52.0")]
  25     pub const MAX: char = '\u{10ffff}';
  26
  27     /// `U+FFFD REPLACEMENT CHARACTER` (�) is used in Unicode to represent a
  28     /// decoding error.
  29     ///
  30     /// It can occur, for example, when giving ill-formed UTF-8 bytes to
  31     /// [`String::from_utf8_lossy`](../std/string/struct.String.html#method.from_utf8_lossy).
  32     #[stable(feature = "assoc_char_consts", since = "1.52.0")]
  33     pub const REPLACEMENT_CHARACTER: char = '\u{FFFD}';
  34
  35     /// The version of [Unicode](https://www.unicode.org/) that the Unicode parts of
  36     /// `char` and `str` methods are based on.
  37     ///
  38     /// New versions of Unicode are released regularly and subsequently all methods
  39     /// in the standard library depending on Unicode are updated. Therefore the
  40     /// behavior of some `char` and `str` methods and the value of this constant
  41     /// changes over time. This is *not* considered to be a breaking change.
  42     ///
  43     /// The version numbering scheme is explained in
  44     /// [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).
  45     #[stable(feature = "assoc_char_consts", since = "1.52.0")]
  46     pub const UNICODE_VERSION: (u8, u8, u8) = crate::unicode::UNICODE_VERSION;
  47
  48     /// Creates an iterator over the UTF-16 encoded code points in `iter`,
  49     /// returning unpaired surrogates as `Err`s.
  50     ///
  51     /// # Examples
  52     ///
  53     /// Basic usage:
  54     ///
  55     /// ```
  56     /// use std::char::decode_utf16;
  57     ///
  58     /// // 𝄞mus<invalid>ic<invalid>
  59     /// let v = [
  60     ///     0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834,
  61     /// ];
  62     ///
  63     /// assert_eq!(
  64     ///     decode_utf16(v)
  65     ///         .map(|r| r.map_err(|e| e.unpaired_surrogate()))
  66     ///         .collect::<Vec<_>>(),
  67     ///     vec![
  68     ///         Ok('𝄞'),
  69     ///         Ok('m'), Ok('u'), Ok('s'),
  70     ///         Err(0xDD1E),
  71     ///         Ok('i'), Ok('c'),
  72     ///         Err(0xD834)
  73     ///     ]
  74     /// );
  75     /// ```
  76     ///
  77     /// A lossy decoder can be obtained by replacing `Err` results with the replacement character:
  78     ///
  79     /// ```
  80     /// use std::char::{decode_utf16, REPLACEMENT_CHARACTER};
  81     ///
  82     /// // 𝄞mus<invalid>ic<invalid>
  83     /// let v = [
  84     ///     0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834,
  85     /// ];
  86     ///
  87     /// assert_eq!(
  88     ///     decode_utf16(v)
  89     ///        .map(|r| r.unwrap_or(REPLACEMENT_CHARACTER))
  90     ///        .collect::<String>(),
  91     ///     "𝄞mus�ic�"
  92     /// );
  93     /// ```
  94     #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
  95     #[inline]
  96     pub fn decode_utf16<I: IntoIterator<Item = u16>>(iter: I) -> DecodeUtf16<I::IntoIter> {
  97         super::decode::decode_utf16(iter)
  98     }
  99
 100     /// Converts a `u32` to a `char`.
 101     ///
 102     /// Note that all `char`s are valid [`u32`]s, and can be cast to one with
 103     /// [`as`](../std/keyword.as.html):
 104     ///
 105     /// ```
 106     /// let c = '💯';
 107     /// let i = c as u32;
 108     ///
 109     /// assert_eq!(128175, i);
 110     /// ```
 111     ///
 112     /// However, the reverse is not true: not all valid [`u32`]s are valid
 113     /// `char`s. `from_u32()` will return `None` if the input is not a valid value
 114     /// for a `char`.
 115     ///
 116     /// For an unsafe version of this function which ignores these checks, see
 117     /// [`from_u32_unchecked`].
 118     ///
 119     /// [`from_u32_unchecked`]: #method.from_u32_unchecked
 120     ///
 121     /// # Examples
 122     ///
 123     /// Basic usage:
 124     ///
 125     /// ```
 126     /// use std::char;
 127     ///
 128     /// let c = char::from_u32(0x2764);
 129     ///
 130     /// assert_eq!(Some('❤'), c);
 131     /// ```
 132     ///
 133     /// Returning `None` when the input is not a valid `char`:
 134     ///
 135     /// ```
 136     /// use std::char;
 137     ///
 138     /// let c = char::from_u32(0x110000);
 139     ///
 140     /// assert_eq!(None, c);
 141     /// ```
 142     #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
 143     #[rustc_const_unstable(feature = "const_char_convert", issue = "89259")]
 144     #[must_use]
 145     #[inline]
 146     pub const fn from_u32(i: u32) -> Option<char> {
 147         super::convert::from_u32(i)
 148     }
 149
 150     /// Converts a `u32` to a `char`, ignoring validity.
 151     ///
 152     /// Note that all `char`s are valid [`u32`]s, and can be cast to one with
 153     /// `as`:
 154     ///
 155     /// ```
 156     /// let c = '💯';
 157     /// let i = c as u32;
 158     ///
 159     /// assert_eq!(128175, i);
 160     /// ```
 161     ///
 162     /// However, the reverse is not true: not all valid [`u32`]s are valid
 163     /// `char`s. `from_u32_unchecked()` will ignore this, and blindly cast to
 164     /// `char`, possibly creating an invalid one.
 165     ///
 166     /// # Safety
 167     ///
 168     /// This function is unsafe, as it may construct invalid `char` values.
 169     ///
 170     /// For a safe version of this function, see the [`from_u32`] function.
 171     ///
 172     /// [`from_u32`]: #method.from_u32
 173     ///
 174     /// # Examples
 175     ///
 176     /// Basic usage:
 177     ///
 178     /// ```
 179     /// use std::char;
 180     ///
 181     /// let c = unsafe { char::from_u32_unchecked(0x2764) };
 182     ///
 183     /// assert_eq!('❤', c);
 184     /// ```
 185     #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
 186     #[rustc_const_unstable(feature = "const_char_convert", issue = "89259")]
 187     #[must_use]
 188     #[inline]
 189     pub const unsafe fn from_u32_unchecked(i: u32) -> char {
 190         // SAFETY: the safety contract must be upheld by the caller.
 191         unsafe { super::convert::from_u32_unchecked(i) }
 192     }
 193
 194     /// Converts a digit in the given radix to a `char`.
 195     ///
 196     /// A 'radix' here is sometimes also called a 'base'. A radix of two
 197     /// indicates a binary number, a radix of ten, decimal, and a radix of
 198     /// sixteen, hexadecimal, to give some common values. Arbitrary
 199     /// radices are supported.
 200     ///
 201     /// `from_digit()` will return `None` if the input is not a digit in
 202     /// the given radix.
 203     ///
 204     /// # Panics
 205     ///
 206     /// Panics if given a radix larger than 36.
 207     ///
 208     /// # Examples
 209     ///
 210     /// Basic usage:
 211     ///
 212     /// ```
 213     /// use std::char;
 214     ///
 215     /// let c = char::from_digit(4, 10);
 216     ///
 217     /// assert_eq!(Some('4'), c);
 218     ///
 219     /// // Decimal 11 is a single digit in base 16
 220     /// let c = char::from_digit(11, 16);
 221     ///
 222     /// assert_eq!(Some('b'), c);
 223     /// ```
 224     ///
 225     /// Returning `None` when the input is not a digit:
 226     ///
 227     /// ```
 228     /// use std::char;
 229     ///
 230     /// let c = char::from_digit(20, 10);
 231     ///
 232     /// assert_eq!(None, c);
 233     /// ```
 234     ///
 235     /// Passing a large radix, causing a panic:
 236     ///
 237     /// ```should_panic
 238     /// use std::char;
 239     ///
 240     /// // this panics
 241     /// let _c = char::from_digit(1, 37);
 242     /// ```
 243     #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
 244     #[rustc_const_unstable(feature = "const_char_convert", issue = "89259")]
 245     #[must_use]
 246     #[inline]
 247     pub const fn from_digit(num: u32, radix: u32) -> Option<char> {
 248         super::convert::from_digit(num, radix)
 249     }
 250
 251     /// Checks if a `char` is a digit in the given radix.
 252     ///
 253     /// A 'radix' here is sometimes also called a 'base'. A radix of two
 254     /// indicates a binary number, a radix of ten, decimal, and a radix of
 255     /// sixteen, hexadecimal, to give some common values. Arbitrary
 256     /// radices are supported.
 257     ///
 258     /// Compared to [`is_numeric()`], this function only recognizes the characters
 259     /// `0-9`, `a-z` and `A-Z`.
 260     ///
 261     /// 'Digit' is defined to be only the following characters:
 262     ///
 263     /// * `0-9`
 264     /// * `a-z`
 265     /// * `A-Z`
 266     ///
 267     /// For a more comprehensive understanding of 'digit', see [`is_numeric()`].
 268     ///
 269     /// [`is_numeric()`]: #method.is_numeric
 270     ///
 271     /// # Panics
 272     ///
 273     /// Panics if given a radix larger than 36.
 274     ///
 275     /// # Examples
 276     ///
 277     /// Basic usage:
 278     ///
 279     /// ```
 280     /// assert!('1'.is_digit(10));
 281     /// assert!('f'.is_digit(16));
 282     /// assert!(!'f'.is_digit(10));
 283     /// ```
 284     ///
 285     /// Passing a large radix, causing a panic:
 286     ///
 287     /// ```should_panic
 288     /// // this panics
 289     /// '1'.is_digit(37);
 290     /// ```
 291     #[stable(feature = "rust1", since = "1.0.0")]
 292     #[inline]
 293     pub fn is_digit(self, radix: u32) -> bool {
 294         self.to_digit(radix).is_some()
 295     }
 296
 297     /// Converts a `char` to a digit in the given radix.
 298     ///
 299     /// A 'radix' here is sometimes also called a 'base'. A radix of two
 300     /// indicates a binary number, a radix of ten, decimal, and a radix of
 301     /// sixteen, hexadecimal, to give some common values. Arbitrary
 302     /// radices are supported.
 303     ///
 304     /// 'Digit' is defined to be only the following characters:
 305     ///
 306     /// * `0-9`
 307     /// * `a-z`
 308     /// * `A-Z`
 309     ///
 310     /// # Errors
 311     ///
 312     /// Returns `None` if the `char` does not refer to a digit in the given radix.
 313     ///
 314     /// # Panics
 315     ///
 316     /// Panics if given a radix larger than 36.
 317     ///
 318     /// # Examples
 319     ///
 320     /// Basic usage:
 321     ///
 322     /// ```
 323     /// assert_eq!('1'.to_digit(10), Some(1));
 324     /// assert_eq!('f'.to_digit(16), Some(15));
 325     /// ```
 326     ///
 327     /// Passing a non-digit results in failure:
 328     ///
 329     /// ```
 330     /// assert_eq!('f'.to_digit(10), None);
 331     /// assert_eq!('z'.to_digit(16), None);
 332     /// ```
 333     ///
 334     /// Passing a large radix, causing a panic:
 335     ///
 336     /// ```should_panic
 337     /// // this panics
 338     /// let _ = '1'.to_digit(37);
 339     /// ```
 340     #[stable(feature = "rust1", since = "1.0.0")]
 341     #[rustc_const_unstable(feature = "const_char_convert", issue = "89259")]
 342     #[must_use = "this returns the result of the operation, \
 343                   without modifying the original"]
 344     #[inline]
 345     pub const fn to_digit(self, radix: u32) -> Option<u32> {
 346         // If not a digit, a number greater than radix will be created.
 347         let mut digit = (self as u32).wrapping_sub('0' as u32);
 348         if radix > 10 {
 349             assert!(radix <= 36, "to_digit: radix is too high (maximum 36)");
 350             if digit < 10 {
 351                 return Some(digit);
 352             }
 353             // Force the 6th bit to be set to ensure ascii is lower case.
 354             digit = (self as u32 | 0b10_0000).wrapping_sub('a' as u32).saturating_add(10);
 355         }
 356         // FIXME: once then_some is const fn, use it here
 357         if digit < radix { Some(digit) } else { None }
 358     }
 359
 360     /// Returns an iterator that yields the hexadecimal Unicode escape of a
 361     /// character as `char`s.
 362     ///
 363     /// This will escape characters with the Rust syntax of the form
 364     /// `\u{NNNNNN}` where `NNNNNN` is a hexadecimal representation.
 365     ///
 366     /// # Examples
 367     ///
 368     /// As an iterator:
 369     ///
 370     /// ```
 371     /// for c in '❤'.escape_unicode() {
 372     ///     print!("{c}");
 373     /// }
 374     /// println!();
 375     /// ```
 376     ///
 377     /// Using `println!` directly:
 378     ///
 379     /// ```
 380     /// println!("{}", '❤'.escape_unicode());
 381     /// ```
 382     ///
 383     /// Both are equivalent to:
 384     ///
 385     /// ```
 386     /// println!("\\u{{2764}}");
 387     /// ```
 388     ///
 389     /// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
 390     ///
 391     /// ```
 392     /// assert_eq!('❤'.escape_unicode().to_string(), "\\u{2764}");
 393     /// ```
 394     #[must_use = "this returns the escaped char as an iterator, \
 395                   without modifying the original"]
 396     #[stable(feature = "rust1", since = "1.0.0")]
 397     #[inline]
 398     pub fn escape_unicode(self) -> EscapeUnicode {
 399         let c = self as u32;
 400
 401         // or-ing 1 ensures that for c==0 the code computes that one
 402         // digit should be printed and (which is the same) avoids the
 403         // (31 - 32) underflow
 404         let msb = 31 - (c | 1).leading_zeros();
 405
 406         // the index of the most significant hex digit
 407         let ms_hex_digit = msb / 4;
 408         EscapeUnicode {
 409             c: self,
 410             state: EscapeUnicodeState::Backslash,
 411             hex_digit_idx: ms_hex_digit as usize,
 412         }
 413     }
 414
 415     /// An extended version of `escape_debug` that optionally permits escaping
 416     /// Extended Grapheme codepoints, single quotes, and double quotes. This
 417     /// allows us to format characters like nonspacing marks better when they're
 418     /// at the start of a string, and allows escaping single quotes in
 419     /// characters, and double quotes in strings.
 420     #[inline]
 421     pub(crate) fn escape_debug_ext(self, args: EscapeDebugExtArgs) -> EscapeDebug {
 422         let init_state = match self {
 423             '\0' => EscapeDefaultState::Backslash('0'),
 424             '\t' => EscapeDefaultState::Backslash('t'),
 425             '\r' => EscapeDefaultState::Backslash('r'),
 426             '\n' => EscapeDefaultState::Backslash('n'),
 427             '\\' => EscapeDefaultState::Backslash(self),
 428             '"' if args.escape_double_quote => EscapeDefaultState::Backslash(self),
 429             '\'' if args.escape_single_quote => EscapeDefaultState::Backslash(self),
 430             _ if args.escape_grapheme_extended && self.is_grapheme_extended() => {
 431                 EscapeDefaultState::Unicode(self.escape_unicode())
 432             }
 433             _ if is_printable(self) => EscapeDefaultState::Char(self),
 434             _ => EscapeDefaultState::Unicode(self.escape_unicode()),
 435         };
 436         EscapeDebug(EscapeDefault { state: init_state })
 437     }
 438
 439     /// Returns an iterator that yields the literal escape code of a character
 440     /// as `char`s.
 441     ///
 442     /// This will escape the characters similar to the [`Debug`](core::fmt::Debug) implementations
 443     /// of `str` or `char`.
 444     ///
 445     /// # Examples
 446     ///
 447     /// As an iterator:
 448     ///
 449     /// ```
 450     /// for c in '\n'.escape_debug() {
 451     ///     print!("{c}");
 452     /// }
 453     /// println!();
 454     /// ```
 455     ///
 456     /// Using `println!` directly:
 457     ///
 458     /// ```
 459     /// println!("{}", '\n'.escape_debug());
 460     /// ```
 461     ///
 462     /// Both are equivalent to:
 463     ///
 464     /// ```
 465     /// println!("\\n");
 466     /// ```
 467     ///
 468     /// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
 469     ///
 470     /// ```
 471     /// assert_eq!('\n'.escape_debug().to_string(), "\\n");
 472     /// ```
 473     #[must_use = "this returns the escaped char as an iterator, \
 474                   without modifying the original"]
 475     #[stable(feature = "char_escape_debug", since = "1.20.0")]
 476     #[inline]
 477     pub fn escape_debug(self) -> EscapeDebug {
 478         self.escape_debug_ext(EscapeDebugExtArgs::ESCAPE_ALL)
 479     }
 480
 481     /// Returns an iterator that yields the literal escape code of a character
 482     /// as `char`s.
 483     ///
 484     /// The default is chosen with a bias toward producing literals that are
 485     /// legal in a variety of languages, including C++11 and similar C-family
 486     /// languages. The exact rules are:
 487     ///
 488     /// * Tab is escaped as `\t`.
 489     /// * Carriage return is escaped as `\r`.
 490     /// * Line feed is escaped as `\n`.
 491     /// * Single quote is escaped as `\'`.
 492     /// * Double quote is escaped as `\"`.
 493     /// * Backslash is escaped as `\\`.
 494     /// * Any character in the 'printable ASCII' range `0x20` .. `0x7e`
 495     ///   inclusive is not escaped.
 496     /// * All other characters are given hexadecimal Unicode escapes; see
 497     ///   [`escape_unicode`].
 498     ///
 499     /// [`escape_unicode`]: #method.escape_unicode
 500     ///
 501     /// # Examples
 502     ///
 503     /// As an iterator:
 504     ///
 505     /// ```
 506     /// for c in '"'.escape_default() {
 507     ///     print!("{c}");
 508     /// }
 509     /// println!();
 510     /// ```
 511     ///
 512     /// Using `println!` directly:
 513     ///
 514     /// ```
 515     /// println!("{}", '"'.escape_default());
 516     /// ```
 517     ///
 518     /// Both are equivalent to:
 519     ///
 520     /// ```
 521     /// println!("\\\"");
 522     /// ```
 523     ///
 524     /// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
 525     ///
 526     /// ```
 527     /// assert_eq!('"'.escape_default().to_string(), "\\\"");
 528     /// ```
 529     #[must_use = "this returns the escaped char as an iterator, \
 530                   without modifying the original"]
 531     #[stable(feature = "rust1", since = "1.0.0")]
 532     #[inline]
 533     pub fn escape_default(self) -> EscapeDefault {
 534         let init_state = match self {
 535             '\t' => EscapeDefaultState::Backslash('t'),
 536             '\r' => EscapeDefaultState::Backslash('r'),
 537             '\n' => EscapeDefaultState::Backslash('n'),
 538             '\\' | '\'' | '"' => EscapeDefaultState::Backslash(self),
 539             '\x20'..='\x7e' => EscapeDefaultState::Char(self),
 540             _ => EscapeDefaultState::Unicode(self.escape_unicode()),
 541         };
 542         EscapeDefault { state: init_state }
 543     }
 544
 545     /// Returns the number of bytes this `char` would need if encoded in UTF-8.
 546     ///
 547     /// That number of bytes is always between 1 and 4, inclusive.
 548     ///
 549     /// # Examples
 550     ///
 551     /// Basic usage:
 552     ///
 553     /// ```
 554     /// let len = 'A'.len_utf8();
 555     /// assert_eq!(len, 1);
 556     ///
 557     /// let len = 'ß'.len_utf8();
 558     /// assert_eq!(len, 2);
 559     ///
 560     /// let len = 'ℝ'.len_utf8();
 561     /// assert_eq!(len, 3);
 562     ///
 563     /// let len = '💣'.len_utf8();
 564     /// assert_eq!(len, 4);
 565     /// ```
 566     ///
 567     /// The `&str` type guarantees that its contents are UTF-8, and so we can compare the length it
 568     /// would take if each code point was represented as a `char` vs in the `&str` itself:
 569     ///
 570     /// ```
 571     /// // as chars
 572     /// let eastern = '東';
 573     /// let capital = '京';
 574     ///
 575     /// // both can be represented as three bytes
 576     /// assert_eq!(3, eastern.len_utf8());
 577     /// assert_eq!(3, capital.len_utf8());
 578     ///
 579     /// // as a &str, these two are encoded in UTF-8
 580     /// let tokyo = "東京";
 581     ///
 582     /// let len = eastern.len_utf8() + capital.len_utf8();
 583     ///
 584     /// // we can see that they take six bytes total...
 585     /// assert_eq!(6, tokyo.len());
 586     ///
 587     /// // ... just like the &str
 588     /// assert_eq!(len, tokyo.len());
 589     /// ```
 590     #[stable(feature = "rust1", since = "1.0.0")]
 591     #[rustc_const_stable(feature = "const_char_len_utf", since = "1.52.0")]
 592     #[inline]
 593     pub const fn len_utf8(self) -> usize {
 594         len_utf8(self as u32)
 595     }
 596
 597     /// Returns the number of 16-bit code units this `char` would need if
 598     /// encoded in UTF-16.
 599     ///
 600     /// See the documentation for [`len_utf8()`] for more explanation of this
 601     /// concept. This function is a mirror, but for UTF-16 instead of UTF-8.
 602     ///
 603     /// [`len_utf8()`]: #method.len_utf8
 604     ///
 605     /// # Examples
 606     ///
 607     /// Basic usage:
 608     ///
 609     /// ```
 610     /// let n = 'ß'.len_utf16();
 611     /// assert_eq!(n, 1);
 612     ///
 613     /// let len = '💣'.len_utf16();
 614     /// assert_eq!(len, 2);
 615     /// ```
 616     #[stable(feature = "rust1", since = "1.0.0")]
 617     #[rustc_const_stable(feature = "const_char_len_utf", since = "1.52.0")]
 618     #[inline]
 619     pub const fn len_utf16(self) -> usize {
 620         let ch = self as u32;
 621         if (ch & 0xFFFF) == ch { 1 } else { 2 }
 622     }
 623
 624     /// Encodes this character as UTF-8 into the provided byte buffer,
 625     /// and then returns the subslice of the buffer that contains the encoded character.
 626     ///
 627     /// # Panics
 628     ///
 629     /// Panics if the buffer is not large enough.
 630     /// A buffer of length four is large enough to encode any `char`.
 631     ///
 632     /// # Examples
 633     ///
 634     /// In both of these examples, 'ß' takes two bytes to encode.
 635     ///
 636     /// ```
 637     /// let mut b = [0; 2];
 638     ///
 639     /// let result = 'ß'.encode_utf8(&mut b);
 640     ///
 641     /// assert_eq!(result, "ß");
 642     ///
 643     /// assert_eq!(result.len(), 2);
 644     /// ```
 645     ///
 646     /// A buffer that's too small:
 647     ///
 648     /// ```should_panic
 649     /// let mut b = [0; 1];
 650     ///
 651     /// // this panics
 652     /// 'ß'.encode_utf8(&mut b);
 653     /// ```
 654     #[stable(feature = "unicode_encode_char", since = "1.15.0")]
 655     #[inline]
 656     pub fn encode_utf8(self, dst: &mut [u8]) -> &mut str {
 657         // SAFETY: `char` is not a surrogate, so this is valid UTF-8.
 658         unsafe { from_utf8_unchecked_mut(encode_utf8_raw(self as u32, dst)) }
 659     }
 660
 661     /// Encodes this character as UTF-16 into the provided `u16` buffer,
 662     /// and then returns the subslice of the buffer that contains the encoded character.
 663     ///
 664     /// # Panics
 665     ///
 666     /// Panics if the buffer is not large enough.
 667     /// A buffer of length 2 is large enough to encode any `char`.
 668     ///
 669     /// # Examples
 670     ///
 671     /// In both of these examples, '𝕊' takes two `u16`s to encode.
 672     ///
 673     /// ```
 674     /// let mut b = [0; 2];
 675     ///
 676     /// let result = '𝕊'.encode_utf16(&mut b);
 677     ///
 678     /// assert_eq!(result.len(), 2);
 679     /// ```
 680     ///
 681     /// A buffer that's too small:
 682     ///
 683     /// ```should_panic
 684     /// let mut b = [0; 1];
 685     ///
 686     /// // this panics
 687     /// '𝕊'.encode_utf16(&mut b);
 688     /// ```
 689     #[stable(feature = "unicode_encode_char", since = "1.15.0")]
 690     #[inline]
 691     pub fn encode_utf16(self, dst: &mut [u16]) -> &mut [u16] {
 692         encode_utf16_raw(self as u32, dst)
 693     }
 694
 695     /// Returns `true` if this `char` has the `Alphabetic` property.
 696     ///
 697     /// `Alphabetic` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
 698     /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
 699     ///
 700     /// [Unicode Standard]: https://www.unicode.org/versions/latest/
 701     /// [ucd]: https://www.unicode.org/reports/tr44/
 702     /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
 703     ///
 704     /// # Examples
 705     ///
 706     /// Basic usage:
 707     ///
 708     /// ```
 709     /// assert!('a'.is_alphabetic());
 710     /// assert!('京'.is_alphabetic());
 711     ///
 712     /// let c = '💝';
 713     /// // love is many things, but it is not alphabetic
 714     /// assert!(!c.is_alphabetic());
 715     /// ```
 716     #[must_use]
 717     #[stable(feature = "rust1", since = "1.0.0")]
 718     #[inline]
 719     pub fn is_alphabetic(self) -> bool {
 720         match self {
 721             'a'..='z' | 'A'..='Z' => true,
 722             c => c > '\x7f' && unicode::Alphabetic(c),
 723         }
 724     }
 725
 726     /// Returns `true` if this `char` has the `Lowercase` property.
 727     ///
 728     /// `Lowercase` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
 729     /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
 730     ///
 731     /// [Unicode Standard]: https://www.unicode.org/versions/latest/
 732     /// [ucd]: https://www.unicode.org/reports/tr44/
 733     /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
 734     ///
 735     /// # Examples
 736     ///
 737     /// Basic usage:
 738     ///
 739     /// ```
 740     /// assert!('a'.is_lowercase());
 741     /// assert!('δ'.is_lowercase());
 742     /// assert!(!'A'.is_lowercase());
 743     /// assert!(!'Δ'.is_lowercase());
 744     ///
 745     /// // The various Chinese scripts and punctuation do not have case, and so:
 746     /// assert!(!'中'.is_lowercase());
 747     /// assert!(!' '.is_lowercase());
 748     /// ```
 749     #[must_use]
 750     #[stable(feature = "rust1", since = "1.0.0")]
 751     #[inline]
 752     pub fn is_lowercase(self) -> bool {
 753         match self {
 754             'a'..='z' => true,
 755             c => c > '\x7f' && unicode::Lowercase(c),
 756         }
 757     }
 758
 759     /// Returns `true` if this `char` has the `Uppercase` property.
 760     ///
 761     /// `Uppercase` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
 762     /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
 763     ///
 764     /// [Unicode Standard]: https://www.unicode.org/versions/latest/
 765     /// [ucd]: https://www.unicode.org/reports/tr44/
 766     /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
 767     ///
 768     /// # Examples
 769     ///
 770     /// Basic usage:
 771     ///
 772     /// ```
 773     /// assert!(!'a'.is_uppercase());
 774     /// assert!(!'δ'.is_uppercase());
 775     /// assert!('A'.is_uppercase());
 776     /// assert!('Δ'.is_uppercase());
 777     ///
 778     /// // The various Chinese scripts and punctuation do not have case, and so:
 779     /// assert!(!'中'.is_uppercase());
 780     /// assert!(!' '.is_uppercase());
 781     /// ```
 782     #[must_use]
 783     #[stable(feature = "rust1", since = "1.0.0")]
 784     #[inline]
 785     pub fn is_uppercase(self) -> bool {
 786         match self {
 787             'A'..='Z' => true,
 788             c => c > '\x7f' && unicode::Uppercase(c),
 789         }
 790     }
 791
 792     /// Returns `true` if this `char` has the `White_Space` property.
 793     ///
 794     /// `White_Space` is specified in the [Unicode Character Database][ucd] [`PropList.txt`].
 795     ///
 796     /// [ucd]: https://www.unicode.org/reports/tr44/
 797     /// [`PropList.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/PropList.txt
 798     ///
 799     /// # Examples
 800     ///
 801     /// Basic usage:
 802     ///
 803     /// ```
 804     /// assert!(' '.is_whitespace());
 805     ///
 806     /// // line break
 807     /// assert!('\n'.is_whitespace());
 808     ///
 809     /// // a non-breaking space
 810     /// assert!('\u{A0}'.is_whitespace());
 811     ///
 812     /// assert!(!'越'.is_whitespace());
 813     /// ```
 814     #[must_use]
 815     #[stable(feature = "rust1", since = "1.0.0")]
 816     #[inline]
 817     pub fn is_whitespace(self) -> bool {
 818         match self {
 819             ' ' | '\x09'..='\x0d' => true,
 820             c => c > '\x7f' && unicode::White_Space(c),
 821         }
 822     }
 823
 824     /// Returns `true` if this `char` satisfies either [`is_alphabetic()`] or [`is_numeric()`].
 825     ///
 826     /// [`is_alphabetic()`]: #method.is_alphabetic
 827     /// [`is_numeric()`]: #method.is_numeric
 828     ///
 829     /// # Examples
 830     ///
 831     /// Basic usage:
 832     ///
 833     /// ```
 834     /// assert!('٣'.is_alphanumeric());
 835     /// assert!('7'.is_alphanumeric());
 836     /// assert!('৬'.is_alphanumeric());
 837     /// assert!('¾'.is_alphanumeric());
 838     /// assert!('①'.is_alphanumeric());
 839     /// assert!('K'.is_alphanumeric());
 840     /// assert!('و'.is_alphanumeric());
 841     /// assert!('藏'.is_alphanumeric());
 842     /// ```
 843     #[must_use]
 844     #[stable(feature = "rust1", since = "1.0.0")]
 845     #[inline]
 846     pub fn is_alphanumeric(self) -> bool {
 847         self.is_alphabetic() || self.is_numeric()
 848     }
 849
 850     /// Returns `true` if this `char` has the general category for control codes.
 851     ///
 852     /// Control codes (code points with the general category of `Cc`) are described in Chapter 4
 853     /// (Character Properties) of the [Unicode Standard] and specified in the [Unicode Character
 854     /// Database][ucd] [`UnicodeData.txt`].
 855     ///
 856     /// [Unicode Standard]: https://www.unicode.org/versions/latest/
 857     /// [ucd]: https://www.unicode.org/reports/tr44/
 858     /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
 859     ///
 860     /// # Examples
 861     ///
 862     /// Basic usage:
 863     ///
 864     /// ```
 865     /// // U+009C, STRING TERMINATOR
 866     /// assert!('\9c'.is_control());
 867     /// assert!(!'q'.is_control());
 868     /// ```
 869     #[must_use]
 870     #[stable(feature = "rust1", since = "1.0.0")]
 871     #[inline]
 872     pub fn is_control(self) -> bool {
 873         unicode::Cc(self)
 874     }
 875
 876     /// Returns `true` if this `char` has the `Grapheme_Extend` property.
 877     ///
 878     /// `Grapheme_Extend` is described in [Unicode Standard Annex #29 (Unicode Text
 879     /// Segmentation)][uax29] and specified in the [Unicode Character Database][ucd]
 880     /// [`DerivedCoreProperties.txt`].
 881     ///
 882     /// [uax29]: https://www.unicode.org/reports/tr29/
 883     /// [ucd]: https://www.unicode.org/reports/tr44/
 884     /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
 885     #[must_use]
 886     #[inline]
 887     pub(crate) fn is_grapheme_extended(self) -> bool {
 888         unicode::Grapheme_Extend(self)
 889     }
 890
 891     /// Returns `true` if this `char` has one of the general categories for numbers.
 892     ///
 893     /// The general categories for numbers (`Nd` for decimal digits, `Nl` for letter-like numeric
 894     /// characters, and `No` for other numeric characters) are specified in the [Unicode Character
 895     /// Database][ucd] [`UnicodeData.txt`]. Note that this means ideographic numbers like '三'
 896     /// are considered alphabetic, not numeric. Please consider to use `is_ascii_digit` or `is_digit`.
 897     ///
 898     /// This method doesn't cover everything that could be considered a number, e.g. ideographic numbers like '三'.
 899     /// If you want everything including characters with overlapping purposes then you might want to use
 900     /// a unicode or language-processing library that exposes the appropriate character properties instead
 901     /// of looking at the unicode categories.
 902     ///
 903     /// If you want to parse ASCII decimal digits (0-9) or ASCII base-N, use
 904     /// `is_ascii_digit` or `is_digit` instead.
 905     ///
 906     /// [Unicode Standard]: https://www.unicode.org/versions/latest/
 907     /// [ucd]: https://www.unicode.org/reports/tr44/
 908     /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
 909     ///
 910     /// # Examples
 911     ///
 912     /// Basic usage:
 913     ///
 914     /// ```
 915     /// assert!('٣'.is_numeric());
 916     /// assert!('7'.is_numeric());
 917     /// assert!('৬'.is_numeric());
 918     /// assert!('¾'.is_numeric());
 919     /// assert!('①'.is_numeric());
 920     /// assert!(!'K'.is_numeric());
 921     /// assert!(!'و'.is_numeric());
 922     /// assert!(!'藏'.is_numeric());
 923     /// assert!(!'三'.is_numeric());
 924     /// ```
 925     #[must_use]
 926     #[stable(feature = "rust1", since = "1.0.0")]
 927     #[inline]
 928     pub fn is_numeric(self) -> bool {
 929         match self {
 930             '0'..='9' => true,
 931             c => c > '\x7f' && unicode::N(c),
 932         }
 933     }
 934
 935     /// Returns an iterator that yields the lowercase mapping of this `char` as one or more
 936     /// `char`s.
 937     ///
 938     /// If this `char` does not have a lowercase mapping, the iterator yields the same `char`.
 939     ///
 940     /// If this `char` has a one-to-one lowercase mapping given by the [Unicode Character
 941     /// Database][ucd] [`UnicodeData.txt`], the iterator yields that `char`.
 942     ///
 943     /// [ucd]: https://www.unicode.org/reports/tr44/
 944     /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
 945     ///
 946     /// If this `char` requires special considerations (e.g. multiple `char`s) the iterator yields
 947     /// the `char`(s) given by [`SpecialCasing.txt`].
 948     ///
 949     /// [`SpecialCasing.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/SpecialCasing.txt
 950     ///
 951     /// This operation performs an unconditional mapping without tailoring. That is, the conversion
 952     /// is independent of context and language.
 953     ///
 954     /// In the [Unicode Standard], Chapter 4 (Character Properties) discusses case mapping in
 955     /// general and Chapter 3 (Conformance) discusses the default algorithm for case conversion.
 956     ///
 957     /// [Unicode Standard]: https://www.unicode.org/versions/latest/
 958     ///
 959     /// # Examples
 960     ///
 961     /// As an iterator:
 962     ///
 963     /// ```
 964     /// for c in 'İ'.to_lowercase() {
 965     ///     print!("{c}");
 966     /// }
 967     /// println!();
 968     /// ```
 969     ///
 970     /// Using `println!` directly:
 971     ///
 972     /// ```
 973     /// println!("{}", 'İ'.to_lowercase());
 974     /// ```
 975     ///
 976     /// Both are equivalent to:
 977     ///
 978     /// ```
 979     /// println!("i\u{307}");
 980     /// ```
 981     ///
 982     /// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
 983     ///
 984     /// ```
 985     /// assert_eq!('C'.to_lowercase().to_string(), "c");
 986     ///
 987     /// // Sometimes the result is more than one character:
 988     /// assert_eq!('İ'.to_lowercase().to_string(), "i\u{307}");
 989     ///
 990     /// // Characters that do not have both uppercase and lowercase
 991     /// // convert into themselves.
 992     /// assert_eq!('山'.to_lowercase().to_string(), "山");
 993     /// ```
 994     #[must_use = "this returns the lowercase character as a new iterator, \
 995                   without modifying the original"]
 996     #[stable(feature = "rust1", since = "1.0.0")]
 997     #[inline]
 998     pub fn to_lowercase(self) -> ToLowercase {
 999         ToLowercase(CaseMappingIter::new(conversions::to_lower(self)))
1000     }
1001
1002     /// Returns an iterator that yields the uppercase mapping of this `char` as one or more
1003     /// `char`s.
1004     ///
1005     /// If this `char` does not have an uppercase mapping, the iterator yields the same `char`.
1006     ///
1007     /// If this `char` has a one-to-one uppercase mapping given by the [Unicode Character
1008     /// Database][ucd] [`UnicodeData.txt`], the iterator yields that `char`.
1009     ///
1010     /// [ucd]: https://www.unicode.org/reports/tr44/
1011     /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
1012     ///
1013     /// If this `char` requires special considerations (e.g. multiple `char`s) the iterator yields
1014     /// the `char`(s) given by [`SpecialCasing.txt`].
1015     ///
1016     /// [`SpecialCasing.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/SpecialCasing.txt
1017     ///
1018     /// This operation performs an unconditional mapping without tailoring. That is, the conversion
1019     /// is independent of context and language.
1020     ///
1021     /// In the [Unicode Standard], Chapter 4 (Character Properties) discusses case mapping in
1022     /// general and Chapter 3 (Conformance) discusses the default algorithm for case conversion.
1023     ///
1024     /// [Unicode Standard]: https://www.unicode.org/versions/latest/
1025     ///
1026     /// # Examples
1027     ///
1028     /// As an iterator:
1029     ///
1030     /// ```
1031     /// for c in 'ß'.to_uppercase() {
1032     ///     print!("{c}");
1033     /// }
1034     /// println!();
1035     /// ```
1036     ///
1037     /// Using `println!` directly:
1038     ///
1039     /// ```
1040     /// println!("{}", 'ß'.to_uppercase());
1041     /// ```
1042     ///
1043     /// Both are equivalent to:
1044     ///
1045     /// ```
1046     /// println!("SS");
1047     /// ```
1048     ///
1049     /// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
1050     ///
1051     /// ```
1052     /// assert_eq!('c'.to_uppercase().to_string(), "C");
1053     ///
1054     /// // Sometimes the result is more than one character:
1055     /// assert_eq!('ß'.to_uppercase().to_string(), "SS");
1056     ///
1057     /// // Characters that do not have both uppercase and lowercase
1058     /// // convert into themselves.
1059     /// assert_eq!('山'.to_uppercase().to_string(), "山");
1060     /// ```
1061     ///
1062     /// # Note on locale
1063     ///
1064     /// In Turkish, the equivalent of 'i' in Latin has five forms instead of two:
1065     ///
1066     /// * 'Dotless': I / ı, sometimes written ï
1067     /// * 'Dotted': İ / i
1068     ///
1069     /// Note that the lowercase dotted 'i' is the same as the Latin. Therefore:
1070     ///
1071     /// ```
1072     /// let upper_i = 'i'.to_uppercase().to_string();
1073     /// ```
1074     ///
1075     /// The value of `upper_i` here relies on the language of the text: if we're
1076     /// in `en-US`, it should be `"I"`, but if we're in `tr_TR`, it should
1077     /// be `"İ"`. `to_uppercase()` does not take this into account, and so:
1078     ///
1079     /// ```
1080     /// let upper_i = 'i'.to_uppercase().to_string();
1081     ///
1082     /// assert_eq!(upper_i, "I");
1083     /// ```
1084     ///
1085     /// holds across languages.
1086     #[must_use = "this returns the uppercase character as a new iterator, \
1087                   without modifying the original"]
1088     #[stable(feature = "rust1", since = "1.0.0")]
1089     #[inline]
1090     pub fn to_uppercase(self) -> ToUppercase {
1091         ToUppercase(CaseMappingIter::new(conversions::to_upper(self)))
1092     }
1093
1094     /// Checks if the value is within the ASCII range.
1095     ///
1096     /// # Examples
1097     ///
1098     /// ```
1099     /// let ascii = 'a';
1100     /// let non_ascii = '❤';
1101     ///
1102     /// assert!(ascii.is_ascii());
1103     /// assert!(!non_ascii.is_ascii());
1104     /// ```
1105     #[must_use]
1106     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1107     #[rustc_const_stable(feature = "const_char_is_ascii", since = "1.32.0")]
1108     #[inline]
1109     pub const fn is_ascii(&self) -> bool {
1110         *self as u32 <= 0x7F
1111     }
1112
1113     /// Makes a copy of the value in its ASCII upper case equivalent.
1114     ///
1115     /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
1116     /// but non-ASCII letters are unchanged.
1117     ///
1118     /// To uppercase the value in-place, use [`make_ascii_uppercase()`].
1119     ///
1120     /// To uppercase ASCII characters in addition to non-ASCII characters, use
1121     /// [`to_uppercase()`].
1122     ///
1123     /// # Examples
1124     ///
1125     /// ```
1126     /// let ascii = 'a';
1127     /// let non_ascii = '❤';
1128     ///
1129     /// assert_eq!('A', ascii.to_ascii_uppercase());
1130     /// assert_eq!('❤', non_ascii.to_ascii_uppercase());
1131     /// ```
1132     ///
1133     /// [`make_ascii_uppercase()`]: #method.make_ascii_uppercase
1134     /// [`to_uppercase()`]: #method.to_uppercase
1135     #[must_use = "to uppercase the value in-place, use `make_ascii_uppercase()`"]
1136     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1137     #[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.52.0")]
1138     #[inline]
1139     pub const fn to_ascii_uppercase(&self) -> char {
1140         if self.is_ascii_lowercase() {
1141             (*self as u8).ascii_change_case_unchecked() as char
1142         } else {
1143             *self
1144         }
1145     }
1146
1147     /// Makes a copy of the value in its ASCII lower case equivalent.
1148     ///
1149     /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
1150     /// but non-ASCII letters are unchanged.
1151     ///
1152     /// To lowercase the value in-place, use [`make_ascii_lowercase()`].
1153     ///
1154     /// To lowercase ASCII characters in addition to non-ASCII characters, use
1155     /// [`to_lowercase()`].
1156     ///
1157     /// # Examples
1158     ///
1159     /// ```
1160     /// let ascii = 'A';
1161     /// let non_ascii = '❤';
1162     ///
1163     /// assert_eq!('a', ascii.to_ascii_lowercase());
1164     /// assert_eq!('❤', non_ascii.to_ascii_lowercase());
1165     /// ```
1166     ///
1167     /// [`make_ascii_lowercase()`]: #method.make_ascii_lowercase
1168     /// [`to_lowercase()`]: #method.to_lowercase
1169     #[must_use = "to lowercase the value in-place, use `make_ascii_lowercase()`"]
1170     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1171     #[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.52.0")]
1172     #[inline]
1173     pub const fn to_ascii_lowercase(&self) -> char {
1174         if self.is_ascii_uppercase() {
1175             (*self as u8).ascii_change_case_unchecked() as char
1176         } else {
1177             *self
1178         }
1179     }
1180
1181     /// Checks that two values are an ASCII case-insensitive match.
1182     ///
1183     /// Equivalent to <code>[to_ascii_lowercase]\(a) == [to_ascii_lowercase]\(b)</code>.
1184     ///
1185     /// # Examples
1186     ///
1187     /// ```
1188     /// let upper_a = 'A';
1189     /// let lower_a = 'a';
1190     /// let lower_z = 'z';
1191     ///
1192     /// assert!(upper_a.eq_ignore_ascii_case(&lower_a));
1193     /// assert!(upper_a.eq_ignore_ascii_case(&upper_a));
1194     /// assert!(!upper_a.eq_ignore_ascii_case(&lower_z));
1195     /// ```
1196     ///
1197     /// [to_ascii_lowercase]: #method.to_ascii_lowercase
1198     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1199     #[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.52.0")]
1200     #[inline]
1201     pub const fn eq_ignore_ascii_case(&self, other: &char) -> bool {
1202         self.to_ascii_lowercase() == other.to_ascii_lowercase()
1203     }
1204
1205     /// Converts this type to its ASCII upper case equivalent in-place.
1206     ///
1207     /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
1208     /// but non-ASCII letters are unchanged.
1209     ///
1210     /// To return a new uppercased value without modifying the existing one, use
1211     /// [`to_ascii_uppercase()`].
1212     ///
1213     /// # Examples
1214     ///
1215     /// ```
1216     /// let mut ascii = 'a';
1217     ///
1218     /// ascii.make_ascii_uppercase();
1219     ///
1220     /// assert_eq!('A', ascii);
1221     /// ```
1222     ///
1223     /// [`to_ascii_uppercase()`]: #method.to_ascii_uppercase
1224     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1225     #[inline]
1226     pub fn make_ascii_uppercase(&mut self) {
1227         *self = self.to_ascii_uppercase();
1228     }
1229
1230     /// Converts this type to its ASCII lower case equivalent in-place.
1231     ///
1232     /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
1233     /// but non-ASCII letters are unchanged.
1234     ///
1235     /// To return a new lowercased value without modifying the existing one, use
1236     /// [`to_ascii_lowercase()`].
1237     ///
1238     /// # Examples
1239     ///
1240     /// ```
1241     /// let mut ascii = 'A';
1242     ///
1243     /// ascii.make_ascii_lowercase();
1244     ///
1245     /// assert_eq!('a', ascii);
1246     /// ```
1247     ///
1248     /// [`to_ascii_lowercase()`]: #method.to_ascii_lowercase
1249     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1250     #[inline]
1251     pub fn make_ascii_lowercase(&mut self) {
1252         *self = self.to_ascii_lowercase();
1253     }
1254
1255     /// Checks if the value is an ASCII alphabetic character:
1256     ///
1257     /// - U+0041 'A' ..= U+005A 'Z', or
1258     /// - U+0061 'a' ..= U+007A 'z'.
1259     ///
1260     /// # Examples
1261     ///
1262     /// ```
1263     /// let uppercase_a = 'A';
1264     /// let uppercase_g = 'G';
1265     /// let a = 'a';
1266     /// let g = 'g';
1267     /// let zero = '0';
1268     /// let percent = '%';
1269     /// let space = ' ';
1270     /// let lf = '\n';
1271     /// let esc = '\x1b';
1272     ///
1273     /// assert!(uppercase_a.is_ascii_alphabetic());
1274     /// assert!(uppercase_g.is_ascii_alphabetic());
1275     /// assert!(a.is_ascii_alphabetic());
1276     /// assert!(g.is_ascii_alphabetic());
1277     /// assert!(!zero.is_ascii_alphabetic());
1278     /// assert!(!percent.is_ascii_alphabetic());
1279     /// assert!(!space.is_ascii_alphabetic());
1280     /// assert!(!lf.is_ascii_alphabetic());
1281     /// assert!(!esc.is_ascii_alphabetic());
1282     /// ```
1283     #[must_use]
1284     #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1285     #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1286     #[inline]
1287     pub const fn is_ascii_alphabetic(&self) -> bool {
1288         matches!(*self, 'A'..='Z' | 'a'..='z')
1289     }
1290
1291     /// Checks if the value is an ASCII uppercase character:
1292     /// U+0041 'A' ..= U+005A 'Z'.
1293     ///
1294     /// # Examples
1295     ///
1296     /// ```
1297     /// let uppercase_a = 'A';
1298     /// let uppercase_g = 'G';
1299     /// let a = 'a';
1300     /// let g = 'g';
1301     /// let zero = '0';
1302     /// let percent = '%';
1303     /// let space = ' ';
1304     /// let lf = '\n';
1305     /// let esc = '\x1b';
1306     ///
1307     /// assert!(uppercase_a.is_ascii_uppercase());
1308     /// assert!(uppercase_g.is_ascii_uppercase());
1309     /// assert!(!a.is_ascii_uppercase());
1310     /// assert!(!g.is_ascii_uppercase());
1311     /// assert!(!zero.is_ascii_uppercase());
1312     /// assert!(!percent.is_ascii_uppercase());
1313     /// assert!(!space.is_ascii_uppercase());
1314     /// assert!(!lf.is_ascii_uppercase());
1315     /// assert!(!esc.is_ascii_uppercase());
1316     /// ```
1317     #[must_use]
1318     #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1319     #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1320     #[inline]
1321     pub const fn is_ascii_uppercase(&self) -> bool {
1322         matches!(*self, 'A'..='Z')
1323     }
1324
1325     /// Checks if the value is an ASCII lowercase character:
1326     /// U+0061 'a' ..= U+007A 'z'.
1327     ///
1328     /// # Examples
1329     ///
1330     /// ```
1331     /// let uppercase_a = 'A';
1332     /// let uppercase_g = 'G';
1333     /// let a = 'a';
1334     /// let g = 'g';
1335     /// let zero = '0';
1336     /// let percent = '%';
1337     /// let space = ' ';
1338     /// let lf = '\n';
1339     /// let esc = '\x1b';
1340     ///
1341     /// assert!(!uppercase_a.is_ascii_lowercase());
1342     /// assert!(!uppercase_g.is_ascii_lowercase());
1343     /// assert!(a.is_ascii_lowercase());
1344     /// assert!(g.is_ascii_lowercase());
1345     /// assert!(!zero.is_ascii_lowercase());
1346     /// assert!(!percent.is_ascii_lowercase());
1347     /// assert!(!space.is_ascii_lowercase());
1348     /// assert!(!lf.is_ascii_lowercase());
1349     /// assert!(!esc.is_ascii_lowercase());
1350     /// ```
1351     #[must_use]
1352     #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1353     #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1354     #[inline]
1355     pub const fn is_ascii_lowercase(&self) -> bool {
1356         matches!(*self, 'a'..='z')
1357     }
1358
1359     /// Checks if the value is an ASCII alphanumeric character:
1360     ///
1361     /// - U+0041 'A' ..= U+005A 'Z', or
1362     /// - U+0061 'a' ..= U+007A 'z', or
1363     /// - U+0030 '0' ..= U+0039 '9'.
1364     ///
1365     /// # Examples
1366     ///
1367     /// ```
1368     /// let uppercase_a = 'A';
1369     /// let uppercase_g = 'G';
1370     /// let a = 'a';
1371     /// let g = 'g';
1372     /// let zero = '0';
1373     /// let percent = '%';
1374     /// let space = ' ';
1375     /// let lf = '\n';
1376     /// let esc = '\x1b';
1377     ///
1378     /// assert!(uppercase_a.is_ascii_alphanumeric());
1379     /// assert!(uppercase_g.is_ascii_alphanumeric());
1380     /// assert!(a.is_ascii_alphanumeric());
1381     /// assert!(g.is_ascii_alphanumeric());
1382     /// assert!(zero.is_ascii_alphanumeric());
1383     /// assert!(!percent.is_ascii_alphanumeric());
1384     /// assert!(!space.is_ascii_alphanumeric());
1385     /// assert!(!lf.is_ascii_alphanumeric());
1386     /// assert!(!esc.is_ascii_alphanumeric());
1387     /// ```
1388     #[must_use]
1389     #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1390     #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1391     #[inline]
1392     pub const fn is_ascii_alphanumeric(&self) -> bool {
1393         matches!(*self, '0'..='9' | 'A'..='Z' | 'a'..='z')
1394     }
1395
1396     /// Checks if the value is an ASCII decimal digit:
1397     /// U+0030 '0' ..= U+0039 '9'.
1398     ///
1399     /// # Examples
1400     ///
1401     /// ```
1402     /// let uppercase_a = 'A';
1403     /// let uppercase_g = 'G';
1404     /// let a = 'a';
1405     /// let g = 'g';
1406     /// let zero = '0';
1407     /// let percent = '%';
1408     /// let space = ' ';
1409     /// let lf = '\n';
1410     /// let esc = '\x1b';
1411     ///
1412     /// assert!(!uppercase_a.is_ascii_digit());
1413     /// assert!(!uppercase_g.is_ascii_digit());
1414     /// assert!(!a.is_ascii_digit());
1415     /// assert!(!g.is_ascii_digit());
1416     /// assert!(zero.is_ascii_digit());
1417     /// assert!(!percent.is_ascii_digit());
1418     /// assert!(!space.is_ascii_digit());
1419     /// assert!(!lf.is_ascii_digit());
1420     /// assert!(!esc.is_ascii_digit());
1421     /// ```
1422     #[must_use]
1423     #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1424     #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1425     #[inline]
1426     pub const fn is_ascii_digit(&self) -> bool {
1427         matches!(*self, '0'..='9')
1428     }
1429
1430     /// Checks if the value is an ASCII hexadecimal digit:
1431     ///
1432     /// - U+0030 '0' ..= U+0039 '9', or
1433     /// - U+0041 'A' ..= U+0046 'F', or
1434     /// - U+0061 'a' ..= U+0066 'f'.
1435     ///
1436     /// # Examples
1437     ///
1438     /// ```
1439     /// let uppercase_a = 'A';
1440     /// let uppercase_g = 'G';
1441     /// let a = 'a';
1442     /// let g = 'g';
1443     /// let zero = '0';
1444     /// let percent = '%';
1445     /// let space = ' ';
1446     /// let lf = '\n';
1447     /// let esc = '\x1b';
1448     ///
1449     /// assert!(uppercase_a.is_ascii_hexdigit());
1450     /// assert!(!uppercase_g.is_ascii_hexdigit());
1451     /// assert!(a.is_ascii_hexdigit());
1452     /// assert!(!g.is_ascii_hexdigit());
1453     /// assert!(zero.is_ascii_hexdigit());
1454     /// assert!(!percent.is_ascii_hexdigit());
1455     /// assert!(!space.is_ascii_hexdigit());
1456     /// assert!(!lf.is_ascii_hexdigit());
1457     /// assert!(!esc.is_ascii_hexdigit());
1458     /// ```
1459     #[must_use]
1460     #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1461     #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1462     #[inline]
1463     pub const fn is_ascii_hexdigit(&self) -> bool {
1464         matches!(*self, '0'..='9' | 'A'..='F' | 'a'..='f')
1465     }
1466
1467     /// Checks if the value is an ASCII punctuation character:
1468     ///
1469     /// - U+0021 ..= U+002F `! " # $ % & ' ( ) * + , - . /`, or
1470     /// - U+003A ..= U+0040 `: ; < = > ? @`, or
1471     /// - U+005B ..= U+0060 ``[ \ ] ^ _ ` ``, or
1472     /// - U+007B ..= U+007E `{ | } ~`
1473     ///
1474     /// # Examples
1475     ///
1476     /// ```
1477     /// let uppercase_a = 'A';
1478     /// let uppercase_g = 'G';
1479     /// let a = 'a';
1480     /// let g = 'g';
1481     /// let zero = '0';
1482     /// let percent = '%';
1483     /// let space = ' ';
1484     /// let lf = '\n';
1485     /// let esc = '\x1b';
1486     ///
1487     /// assert!(!uppercase_a.is_ascii_punctuation());
1488     /// assert!(!uppercase_g.is_ascii_punctuation());
1489     /// assert!(!a.is_ascii_punctuation());
1490     /// assert!(!g.is_ascii_punctuation());
1491     /// assert!(!zero.is_ascii_punctuation());
1492     /// assert!(percent.is_ascii_punctuation());
1493     /// assert!(!space.is_ascii_punctuation());
1494     /// assert!(!lf.is_ascii_punctuation());
1495     /// assert!(!esc.is_ascii_punctuation());
1496     /// ```
1497     #[must_use]
1498     #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1499     #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1500     #[inline]
1501     pub const fn is_ascii_punctuation(&self) -> bool {
1502         matches!(*self, '!'..='/' | ':'..='@' | '['..='`' | '{'..='~')
1503     }
1504
1505     /// Checks if the value is an ASCII graphic character:
1506     /// U+0021 '!' ..= U+007E '~'.
1507     ///
1508     /// # Examples
1509     ///
1510     /// ```
1511     /// let uppercase_a = 'A';
1512     /// let uppercase_g = 'G';
1513     /// let a = 'a';
1514     /// let g = 'g';
1515     /// let zero = '0';
1516     /// let percent = '%';
1517     /// let space = ' ';
1518     /// let lf = '\n';
1519     /// let esc = '\x1b';
1520     ///
1521     /// assert!(uppercase_a.is_ascii_graphic());
1522     /// assert!(uppercase_g.is_ascii_graphic());
1523     /// assert!(a.is_ascii_graphic());
1524     /// assert!(g.is_ascii_graphic());
1525     /// assert!(zero.is_ascii_graphic());
1526     /// assert!(percent.is_ascii_graphic());
1527     /// assert!(!space.is_ascii_graphic());
1528     /// assert!(!lf.is_ascii_graphic());
1529     /// assert!(!esc.is_ascii_graphic());
1530     /// ```
1531     #[must_use]
1532     #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1533     #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1534     #[inline]
1535     pub const fn is_ascii_graphic(&self) -> bool {
1536         matches!(*self, '!'..='~')
1537     }
1538
1539     /// Checks if the value is an ASCII whitespace character:
1540     /// U+0020 SPACE, U+0009 HORIZONTAL TAB, U+000A LINE FEED,
1541     /// U+000C FORM FEED, or U+000D CARRIAGE RETURN.
1542     ///
1543     /// Rust uses the WhatWG Infra Standard's [definition of ASCII
1544     /// whitespace][infra-aw]. There are several other definitions in
1545     /// wide use. For instance, [the POSIX locale][pct] includes
1546     /// U+000B VERTICAL TAB as well as all the above characters,
1547     /// but—from the very same specification—[the default rule for
1548     /// "field splitting" in the Bourne shell][bfs] considers *only*
1549     /// SPACE, HORIZONTAL TAB, and LINE FEED as whitespace.
1550     ///
1551     /// If you are writing a program that will process an existing
1552     /// file format, check what that format's definition of whitespace is
1553     /// before using this function.
1554     ///
1555     /// [infra-aw]: https://infra.spec.whatwg.org/#ascii-whitespace
1556     /// [pct]: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap07.html#tag_07_03_01
1557     /// [bfs]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_05
1558     ///
1559     /// # Examples
1560     ///
1561     /// ```
1562     /// let uppercase_a = 'A';
1563     /// let uppercase_g = 'G';
1564     /// let a = 'a';
1565     /// let g = 'g';
1566     /// let zero = '0';
1567     /// let percent = '%';
1568     /// let space = ' ';
1569     /// let lf = '\n';
1570     /// let esc = '\x1b';
1571     ///
1572     /// assert!(!uppercase_a.is_ascii_whitespace());
1573     /// assert!(!uppercase_g.is_ascii_whitespace());
1574     /// assert!(!a.is_ascii_whitespace());
1575     /// assert!(!g.is_ascii_whitespace());
1576     /// assert!(!zero.is_ascii_whitespace());
1577     /// assert!(!percent.is_ascii_whitespace());
1578     /// assert!(space.is_ascii_whitespace());
1579     /// assert!(lf.is_ascii_whitespace());
1580     /// assert!(!esc.is_ascii_whitespace());
1581     /// ```
1582     #[must_use]
1583     #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1584     #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1585     #[inline]
1586     pub const fn is_ascii_whitespace(&self) -> bool {
1587         matches!(*self, '\t' | '\n' | '\x0C' | '\r' | ' ')
1588     }
1589
1590     /// Checks if the value is an ASCII control character:
1591     /// U+0000 NUL ..= U+001F UNIT SEPARATOR, or U+007F DELETE.
1592     /// Note that most ASCII whitespace characters are control
1593     /// characters, but SPACE is not.
1594     ///
1595     /// # Examples
1596     ///
1597     /// ```
1598     /// let uppercase_a = 'A';
1599     /// let uppercase_g = 'G';
1600     /// let a = 'a';
1601     /// let g = 'g';
1602     /// let zero = '0';
1603     /// let percent = '%';
1604     /// let space = ' ';
1605     /// let lf = '\n';
1606     /// let esc = '\x1b';
1607     ///
1608     /// assert!(!uppercase_a.is_ascii_control());
1609     /// assert!(!uppercase_g.is_ascii_control());
1610     /// assert!(!a.is_ascii_control());
1611     /// assert!(!g.is_ascii_control());
1612     /// assert!(!zero.is_ascii_control());
1613     /// assert!(!percent.is_ascii_control());
1614     /// assert!(!space.is_ascii_control());
1615     /// assert!(lf.is_ascii_control());
1616     /// assert!(esc.is_ascii_control());
1617     /// ```
1618     #[must_use]
1619     #[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1620     #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1621     #[inline]
1622     pub const fn is_ascii_control(&self) -> bool {
1623         matches!(*self, '\0'..='\x1F' | '\x7F')
1624     }
1625 }
1626
1627 pub(crate) struct EscapeDebugExtArgs {
1628     /// Escape Extended Grapheme codepoints?
1629     pub(crate) escape_grapheme_extended: bool,
1630
1631     /// Escape single quotes?
1632     pub(crate) escape_single_quote: bool,
1633
1634     /// Escape double quotes?
1635     pub(crate) escape_double_quote: bool,
1636 }
1637
1638 impl EscapeDebugExtArgs {
1639     pub(crate) const ESCAPE_ALL: Self = Self {
1640         escape_grapheme_extended: true,
1641         escape_single_quote: true,
1642         escape_double_quote: true,
1643     };
1644 }
1645
1646 #[inline]
1647 const fn len_utf8(code: u32) -> usize {
1648     if code < MAX_ONE_B {
1649         1
1650     } else if code < MAX_TWO_B {
1651         2
1652     } else if code < MAX_THREE_B {
1653         3
1654     } else {
1655         4
1656     }
1657 }
1658
1659 /// Encodes a raw u32 value as UTF-8 into the provided byte buffer,
1660 /// and then returns the subslice of the buffer that contains the encoded character.
1661 ///
1662 /// Unlike `char::encode_utf8`, this method also handles codepoints in the surrogate range.
1663 /// (Creating a `char` in the surrogate range is UB.)
1664 /// The result is valid [generalized UTF-8] but not valid UTF-8.
1665 ///
1666 /// [generalized UTF-8]: https://simonsapin.github.io/wtf-8/#generalized-utf8
1667 ///
1668 /// # Panics
1669 ///
1670 /// Panics if the buffer is not large enough.
1671 /// A buffer of length four is large enough to encode any `char`.
1672 #[unstable(feature = "char_internals", reason = "exposed only for libstd", issue = "none")]
1673 #[doc(hidden)]
1674 #[inline]
1675 pub fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> &mut [u8] {
1676     let len = len_utf8(code);
1677     match (len, &mut dst[..]) {
1678         (1, [a, ..]) => {
1679             *a = code as u8;
1680         }
1681         (2, [a, b, ..]) => {
1682             *a = (code >> 6 & 0x1F) as u8 | TAG_TWO_B;
1683             *b = (code & 0x3F) as u8 | TAG_CONT;
1684         }
1685         (3, [a, b, c, ..]) => {
1686             *a = (code >> 12 & 0x0F) as u8 | TAG_THREE_B;
1687             *b = (code >> 6 & 0x3F) as u8 | TAG_CONT;
1688             *c = (code & 0x3F) as u8 | TAG_CONT;
1689         }
1690         (4, [a, b, c, d, ..]) => {
1691             *a = (code >> 18 & 0x07) as u8 | TAG_FOUR_B;
1692             *b = (code >> 12 & 0x3F) as u8 | TAG_CONT;
1693             *c = (code >> 6 & 0x3F) as u8 | TAG_CONT;
1694             *d = (code & 0x3F) as u8 | TAG_CONT;
1695         }
1696         _ => panic!(
1697             "encode_utf8: need {} bytes to encode U+{:X}, but the buffer has {}",
1698             len,
1699             code,
1700             dst.len(),
1701         ),
1702     };
1703     &mut dst[..len]
1704 }
1705
1706 /// Encodes a raw u32 value as UTF-16 into the provided `u16` buffer,
1707 /// and then returns the subslice of the buffer that contains the encoded character.
1708 ///
1709 /// Unlike `char::encode_utf16`, this method also handles codepoints in the surrogate range.
1710 /// (Creating a `char` in the surrogate range is UB.)
1711 ///
1712 /// # Panics
1713 ///
1714 /// Panics if the buffer is not large enough.
1715 /// A buffer of length 2 is large enough to encode any `char`.
1716 #[unstable(feature = "char_internals", reason = "exposed only for libstd", issue = "none")]
1717 #[doc(hidden)]
1718 #[inline]
1719 pub fn encode_utf16_raw(mut code: u32, dst: &mut [u16]) -> &mut [u16] {
1720     // SAFETY: each arm checks whether there are enough bits to write into
1721     unsafe {
1722         if (code & 0xFFFF) == code && !dst.is_empty() {
1723             // The BMP falls through
1724             *dst.get_unchecked_mut(0) = code as u16;
1725             slice::from_raw_parts_mut(dst.as_mut_ptr(), 1)
1726         } else if dst.len() >= 2 {
1727             // Supplementary planes break into surrogates.
1728             code -= 0x1_0000;
1729             *dst.get_unchecked_mut(0) = 0xD800 | ((code >> 10) as u16);
1730             *dst.get_unchecked_mut(1) = 0xDC00 | ((code as u16) & 0x3FF);
1731             slice::from_raw_parts_mut(dst.as_mut_ptr(), 2)
1732         } else {
1733             panic!(
1734                 "encode_utf16: need {} units to encode U+{:X}, but the buffer has {}",
1735                 from_u32_unchecked(code).len_utf16(),
1736                 code,
1737                 dst.len(),
1738             )
1739         }
1740     }
1741 }