methods.rs source code [crates/core/src/char/methods.rs]

1	//! impl char {}
2
3	use super::*;
4	use crate::panic::const_panic;
5	use crate::slice;
6	use crate::str::from_utf8_unchecked_mut;
7	use crate::ub_checks::assert_unsafe_precondition;
8	use crate::unicode::printable::is_printable;
9	use crate::unicode::{self, conversions};
10
11	impl char {
12	/// The lowest valid code point a `char` can have, `'\0'`.
13	///
14	/// Unlike integer types, `char` actually has a gap in the middle,
15	/// meaning that the range of possible `char`s is smaller than you
16	/// might expect. Ranges of `char` will automatically hop this gap
17	/// for you:
18	///
19	/// ```
20	/// let dist = u32::from(char::MAX) - u32::from(char::MIN);
21	/// let size = (char::MIN..=char::MAX).count() as u32;
22	/// assert!(size < dist);
23	/// ```
24	///
25	/// Despite this gap, the `MIN` and [`MAX`] values can be used as bounds for
26	/// all `char` values.
27	///
28	/// [`MAX`]: char::MAX
29	///
30	/// # Examples
31	///
32	/// ```
33	/// # fn something_which_returns_char() -> char { 'a' }
34	/// let c: char = something_which_returns_char();
35	/// assert!(char::MIN <= c);
36	///
37	/// let value_at_min = u32::from(char::MIN);
38	/// assert_eq!(char::from_u32(value_at_min), Some('`\0`'));
39	/// ```
40	#[stable(feature = "char_min", since = "1.83.0")]
41	pub const MIN: char = '`\0`';
42
43	/// The highest valid code point a `char` can have, `'\u{10FFFF}'`.
44	///
45	/// Unlike integer types, `char` actually has a gap in the middle,
46	/// meaning that the range of possible `char`s is smaller than you
47	/// might expect. Ranges of `char` will automatically hop this gap
48	/// for you:
49	///
50	/// ```
51	/// let dist = u32::from(char::MAX) - u32::from(char::MIN);
52	/// let size = (char::MIN..=char::MAX).count() as u32;
53	/// assert!(size < dist);
54	/// ```
55	///
56	/// Despite this gap, the [`MIN`] and `MAX` values can be used as bounds for
57	/// all `char` values.
58	///
59	/// [`MIN`]: char::MIN
60	///
61	/// # Examples
62	///
63	/// ```
64	/// # fn something_which_returns_char() -> char { 'a' }
65	/// let c: char = something_which_returns_char();
66	/// assert!(c <= char::MAX);
67	///
68	/// let value_at_max = u32::from(char::MAX);
69	/// assert_eq!(char::from_u32(value_at_max), Some('`\u{10FFFF}`'));
70	/// assert_eq!(char::from_u32(value_at_max + `1`), None);
71	/// ```
72	#[stable(feature = "assoc_char_consts", since = "1.52.0")]
73	pub const MAX: char = '`\u{10FFFF}`';
74
75	/// The maximum number of bytes required to [encode](char::encode_utf8) a `char` to
76	/// UTF-8 encoding.
77	#[unstable(feature = "char_max_len", issue = "121714")]
78	pub const MAX_LEN_UTF8: usize = `4`;
79
80	/// The maximum number of two-byte units required to [encode](char::encode_utf16) a `char`
81	/// to UTF-16 encoding.
82	#[unstable(feature = "char_max_len", issue = "121714")]
83	pub const MAX_LEN_UTF16: usize = `2`;
84
85	/// `U+FFFD REPLACEMENT CHARACTER` (�) is used in Unicode to represent a
86	/// decoding error.
87	///
88	/// It can occur, for example, when giving ill-formed UTF-8 bytes to
89	/// [`String::from_utf8_lossy`](../std/string/struct.String.html#method.from_utf8_lossy).
90	#[stable(feature = "assoc_char_consts", since = "1.52.0")]
91	pub const REPLACEMENT_CHARACTER: char = '`\u{FFFD}`';
92
93	/// The version of [Unicode](https://www.unicode.org/) that the Unicode parts of
94	/// `char` and `str` methods are based on.
95	///
96	/// New versions of Unicode are released regularly and subsequently all methods
97	/// in the standard library depending on Unicode are updated. Therefore the
98	/// behavior of some `char` and `str` methods and the value of this constant
99	/// changes over time. This is not* considered to be a breaking change.*
100	///
101	/// The version numbering scheme is explained in
102	/// [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).
103	#[stable(feature = "assoc_char_consts", since = "1.52.0")]
104	pub const UNICODE_VERSION: (u8, u8, u8) = crate::unicode::UNICODE_VERSION;
105
106	/// Creates an iterator over the native endian UTF-16 encoded code points in `iter`,
107	/// returning unpaired surrogates as `Err`s.
108	///
109	/// # Examples
110	///
111	/// Basic usage:
112	///
113	/// ```
114	/// // 𝄞mus<invalid>ic<invalid>
115	/// let v = [
116	/// `0xD834`, `0xDD1E`, `0x006d`, `0x0075`, `0x0073`, `0xDD1E`, `0x0069`, `0x0063`, `0xD834`,
117	/// ];
118	///
119	/// assert_eq!(
120	/// char::decode_utf16(v)
121	/// .map(\|r\| r.map_err(\|e\| e.unpaired_surrogate()))
122	/// .collect::<Vec<_>>(),
123	/// vec![
124	/// Ok('𝄞'),
125	/// Ok('m'), Ok('u'), Ok('s'),
126	/// Err(`0xDD1E`),
127	/// Ok('i'), Ok('c'),
128	/// Err(`0xD834`)
129	/// ]
130	/// );
131	/// ```
132	///
133	/// A lossy decoder can be obtained by replacing `Err` results with the replacement character:
134	///
135	/// ```
136	/// // 𝄞mus<invalid>ic<invalid>
137	/// let v = [
138	/// `0xD834`, `0xDD1E`, `0x006d`, `0x0075`, `0x0073`, `0xDD1E`, `0x0069`, `0x0063`, `0xD834`,
139	/// ];
140	///
141	/// assert_eq!(
142	/// char::decode_utf16(v)
143	/// .map(\|r\| r.unwrap_or(char::REPLACEMENT_CHARACTER))
144	/// .collect::<String>(),
145	/// "𝄞mus�ic�"
146	/// );
147	/// ```
148	#[stable(feature = "assoc_char_funcs", since = "1.52.0")]
149	#[inline]
150	pub fn decode_utf16<I: IntoIterator<Item = u16>>(iter: I) -> DecodeUtf16<I::IntoIter> {
151	super::decode::decode_utf16(iter)
152	}
153
154	/// Converts a `u32` to a `char`.
155	///
156	/// Note that all `char`s are valid [`u32`]s, and can be cast to one with
157	/// [`as`](../std/keyword.as.html):
158	///
159	/// ```
160	/// let c = '💯';
161	/// let i = c as u32;
162	///
163	/// assert_eq!(`128175`, i);
164	/// ```
165	///
166	/// However, the reverse is not true: not all valid [`u32`]s are valid
167	/// `char`s. `from_u32()` will return `None` if the input is not a valid value
168	/// for a `char`.
169	///
170	/// For an unsafe version of this function which ignores these checks, see
171	/// [`from_u32_unchecked`].
172	///
173	/// [`from_u32_unchecked`]: #method.from_u32_unchecked
174	///
175	/// # Examples
176	///
177	/// Basic usage:
178	///
179	/// ```
180	/// let c = char::from_u32(`0x2764`);
181	///
182	/// assert_eq!(Some('❤'), c);
183	/// ```
184	///
185	/// Returning `None` when the input is not a valid `char`:
186	///
187	/// ```
188	/// let c = char::from_u32(`0x110000`);
189	///
190	/// assert_eq!(None, c);
191	/// ```
192	#[stable(feature = "assoc_char_funcs", since = "1.52.0")]
193	#[rustc_const_stable(feature = "const_char_convert", since = "1.67.0")]
194	#[must_use]
195	#[inline]
196	pub const fn from_u32(i: u32) -> Option<char> {
197	super::convert::from_u32(i)
198	}
199
200	/// Converts a `u32` to a `char`, ignoring validity.
201	///
202	/// Note that all `char`s are valid [`u32`]s, and can be cast to one with
203	/// `as`:
204	///
205	/// ```
206	/// let c = '💯';
207	/// let i = c as u32;
208	///
209	/// assert_eq!(`128175`, i);
210	/// ```
211	///
212	/// However, the reverse is not true: not all valid [`u32`]s are valid
213	/// `char`s. `from_u32_unchecked()` will ignore this, and blindly cast to
214	/// `char`, possibly creating an invalid one.
215	///
216	/// # Safety
217	///
218	/// This function is unsafe, as it may construct invalid `char` values.
219	///
220	/// For a safe version of this function, see the [`from_u32`] function.
221	///
222	/// [`from_u32`]: #method.from_u32
223	///
224	/// # Examples
225	///
226	/// Basic usage:
227	///
228	/// ```
229	/// let c = unsafe { char::from_u32_unchecked(`0x2764`) };
230	///
231	/// assert_eq!('❤', c);
232	/// ```
233	#[stable(feature = "assoc_char_funcs", since = "1.52.0")]
234	#[rustc_const_stable(feature = "const_char_from_u32_unchecked", since = "1.81.0")]
235	#[must_use]
236	#[inline]
237	pub const unsafe fn from_u32_unchecked(i: u32) -> char {
238	// SAFETY: the safety contract must be upheld by the caller.
239	unsafe { super::convert::from_u32_unchecked(i) }
240	}
241
242	/// Converts a digit in the given radix to a `char`.
243	///
244	/// A 'radix' here is sometimes also called a 'base'. A radix of two
245	/// indicates a binary number, a radix of ten, decimal, and a radix of
246	/// sixteen, hexadecimal, to give some common values. Arbitrary
247	/// radices are supported.
248	///
249	/// `from_digit()` will return `None` if the input is not a digit in
250	/// the given radix.
251	///
252	/// # Panics
253	///
254	/// Panics if given a radix larger than 36.
255	///
256	/// # Examples
257	///
258	/// Basic usage:
259	///
260	/// ```
261	/// let c = char::from_digit(`4`, `10`);
262	///
263	/// assert_eq!(Some('4'), c);
264	///
265	/// // Decimal 11 is a single digit in base 16
266	/// let c = char::from_digit(`11`, `16`);
267	///
268	/// assert_eq!(Some('b'), c);
269	/// ```
270	///
271	/// Returning `None` when the input is not a digit:
272	///
273	/// ```
274	/// let c = char::from_digit(`20`, `10`);
275	///
276	/// assert_eq!(None, c);
277	/// ```
278	///
279	/// Passing a large radix, causing a panic:
280	///
281	/// ```should_panic
282	/// // this panics
283	/// let _c = char::from_digit(`1`, `37`);
284	/// ```
285	#[stable(feature = "assoc_char_funcs", since = "1.52.0")]
286	#[rustc_const_stable(feature = "const_char_convert", since = "1.67.0")]
287	#[must_use]
288	#[inline]
289	pub const fn from_digit(num: u32, radix: u32) -> Option<char> {
290	super::convert::from_digit(num, radix)
291	}
292
293	/// Checks if a `char` is a digit in the given radix.
294	///
295	/// A 'radix' here is sometimes also called a 'base'. A radix of two
296	/// indicates a binary number, a radix of ten, decimal, and a radix of
297	/// sixteen, hexadecimal, to give some common values. Arbitrary
298	/// radices are supported.
299	///
300	/// Compared to [`is_numeric()`], this function only recognizes the characters
301	/// `0-9`, `a-z` and `A-Z`.
302	///
303	/// 'Digit' is defined to be only the following characters:
304	///
305	/// `0-9`*
306	/// `a-z`*
307	/// `A-Z`*
308	///
309	/// For a more comprehensive understanding of 'digit', see [`is_numeric()`].
310	///
311	/// [`is_numeric()`]: #method.is_numeric
312	///
313	/// # Panics
314	///
315	/// Panics if given a radix smaller than 2 or larger than 36.
316	///
317	/// # Examples
318	///
319	/// Basic usage:
320	///
321	/// ```
322	/// assert!('1'.is_digit(`10`));
323	/// assert!('f'.is_digit(`16`));
324	/// assert!(!'f'.is_digit(`10`));
325	/// ```
326	///
327	/// Passing a large radix, causing a panic:
328	///
329	/// ```should_panic
330	/// // this panics
331	/// '1'.is_digit(`37`);
332	/// ```
333	///
334	/// Passing a small radix, causing a panic:
335	///
336	/// ```should_panic
337	/// // this panics
338	/// '1'.is_digit(`1`);
339	/// ```
340	#[stable(feature = "rust1", since = "1.0.0")]
341	#[rustc_const_stable(feature = "const_char_classify", since = "1.87.0")]
342	#[inline]
343	pub const fn is_digit(self, radix: u32) -> bool {
344	self.to_digit(radix).is_some()
345	}
346
347	/// Converts a `char` to a digit in the given radix.
348	///
349	/// A 'radix' here is sometimes also called a 'base'. A radix of two
350	/// indicates a binary number, a radix of ten, decimal, and a radix of
351	/// sixteen, hexadecimal, to give some common values. Arbitrary
352	/// radices are supported.
353	///
354	/// 'Digit' is defined to be only the following characters:
355	///
356	/// `0-9`*
357	/// `a-z`*
358	/// `A-Z`*
359	///
360	/// # Errors
361	///
362	/// Returns `None` if the `char` does not refer to a digit in the given radix.
363	///
364	/// # Panics
365	///
366	/// Panics if given a radix smaller than 2 or larger than 36.
367	///
368	/// # Examples
369	///
370	/// Basic usage:
371	///
372	/// ```
373	/// assert_eq!('1'.to_digit(`10`), Some(`1`));
374	/// assert_eq!('f'.to_digit(`16`), Some(`15`));
375	/// ```
376	///
377	/// Passing a non-digit results in failure:
378	///
379	/// ```
380	/// assert_eq!('f'.to_digit(`10`), None);
381	/// assert_eq!('z'.to_digit(`16`), None);
382	/// ```
383	///
384	/// Passing a large radix, causing a panic:
385	///
386	/// ```should_panic
387	/// // this panics
388	/// let _ = '1'.to_digit(`37`);
389	/// ```
390	/// Passing a small radix, causing a panic:
391	///
392	/// ```should_panic
393	/// // this panics
394	/// let _ = '1'.to_digit(`1`);
395	/// ```
396	#[stable(feature = "rust1", since = "1.0.0")]
397	#[rustc_const_stable(feature = "const_char_convert", since = "1.67.0")]
398	#[must_use = "this returns the result of the operation, \
399	without modifying the original"]
400	#[inline]
401	pub const fn to_digit(self, radix: u32) -> Option<u32> {
402	assert!(
403	radix >= `2` && radix <= `36`,
404	"to_digit: invalid radix -- radix must be in the range 2 to 36 inclusive"
405	);
406	// check radix to remove letter handling code when radix is a known constant
407	let value = if self > '9' && radix > `10` {
408	// mask to convert ASCII letters to uppercase
409	const TO_UPPERCASE_MASK: u32 = !`0b0010_0000`;
410	// Converts an ASCII letter to its corresponding integer value:
411	// A-Z => 10-35, a-z => 10-35. Other characters produce values >= 36.
412	//
413	// Add Overflow Safety:
414	// By applying the mask after the subtraction, the first addendum is
415	// constrained such that it never exceeds u32::MAX - 0x20.
416	((self as u32).wrapping_sub('A' as u32) & TO_UPPERCASE_MASK) + `10`
417	} else {
418	// convert digit to value, non-digits wrap to values > 36
419	(self as u32).wrapping_sub('0' as u32)
420	};
421	// FIXME(const-hack): once then_some is const fn, use it here
422	if value < radix { Some(value) } else { None }
423	}
424
425	/// Returns an iterator that yields the hexadecimal Unicode escape of a
426	/// character as `char`s.
427	///
428	/// This will escape characters with the Rust syntax of the form
429	/// `\u{NNNNNN}` where `NNNNNN` is a hexadecimal representation.
430	///
431	/// # Examples
432	///
433	/// As an iterator:
434	///
435	/// ```
436	/// for c in '❤'.escape_unicode() {
437	/// print!("{c}");
438	/// }
439	/// println!();
440	/// ```
441	///
442	/// Using `println!` directly:
443	///
444	/// ```
445	/// println!("{}", '❤'.escape_unicode());
446	/// ```
447	///
448	/// Both are equivalent to:
449	///
450	/// ```
451	/// println!("`\\`u{{2764}}");
452	/// ```
453	///
454	/// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
455	///
456	/// ```
457	/// assert_eq!('❤'.escape_unicode().to_string(), "`\\`u{2764}");
458	/// ```
459	#[must_use = "this returns the escaped char as an iterator, \
460	without modifying the original"]
461	#[stable(feature = "rust1", since = "1.0.0")]
462	#[inline]
463	pub fn escape_unicode(self) -> EscapeUnicode {
464	EscapeUnicode::new(self)
465	}
466
467	/// An extended version of `escape_debug` that optionally permits escaping
468	/// Extended Grapheme codepoints, single quotes, and double quotes. This
469	/// allows us to format characters like nonspacing marks better when they're
470	/// at the start of a string, and allows escaping single quotes in
471	/// characters, and double quotes in strings.
472	#[inline]
473	pub(crate) fn escape_debug_ext(self, args: EscapeDebugExtArgs) -> EscapeDebug {
474	match self {
475	'`\0`' => EscapeDebug::backslash(ascii::Char::Digit0),
476	'`\t`' => EscapeDebug::backslash(ascii::Char::SmallT),
477	'`\r`' => EscapeDebug::backslash(ascii::Char::SmallR),
478	'`\n`' => EscapeDebug::backslash(ascii::Char::SmallN),
479	'`\\`' => EscapeDebug::backslash(ascii::Char::ReverseSolidus),
480	'`\"`' if args.escape_double_quote => EscapeDebug::backslash(ascii::Char::QuotationMark),
481	'`\'`' if args.escape_single_quote => EscapeDebug::backslash(ascii::Char::Apostrophe),
482	_ if args.escape_grapheme_extended && self.is_grapheme_extended() => {
483	EscapeDebug::unicode(self)
484	}
485	_ if is_printable(self) => EscapeDebug::printable(self),
486	_ => EscapeDebug::unicode(self),
487	}
488	}
489
490	/// Returns an iterator that yields the literal escape code of a character
491	/// as `char`s.
492	///
493	/// This will escape the characters similar to the [`Debug`](core::fmt::Debug) implementations
494	/// of `str` or `char`.
495	///
496	/// # Examples
497	///
498	/// As an iterator:
499	///
500	/// ```
501	/// for c in '`\n`'.escape_debug() {
502	/// print!("{c}");
503	/// }
504	/// println!();
505	/// ```
506	///
507	/// Using `println!` directly:
508	///
509	/// ```
510	/// println!("{}", '`\n`'.escape_debug());
511	/// ```
512	///
513	/// Both are equivalent to:
514	///
515	/// ```
516	/// println!("`\\`n");
517	/// ```
518	///
519	/// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
520	///
521	/// ```
522	/// assert_eq!('`\n`'.escape_debug().to_string(), "`\\`n");
523	/// ```
524	#[must_use = "this returns the escaped char as an iterator, \
525	without modifying the original"]
526	#[stable(feature = "char_escape_debug", since = "1.20.0")]
527	#[inline]
528	pub fn escape_debug(self) -> EscapeDebug {
529	self.escape_debug_ext(EscapeDebugExtArgs::ESCAPE_ALL)
530	}
531
532	/// Returns an iterator that yields the literal escape code of a character
533	/// as `char`s.
534	///
535	/// The default is chosen with a bias toward producing literals that are
536	/// legal in a variety of languages, including C++11 and similar C-family
537	/// languages. The exact rules are:
538	///
539	/// Tab is escaped as `\t`.*
540	/// Carriage return is escaped as `\r`.*
541	/// Line feed is escaped as `\n`.*
542	/// Single quote is escaped as `\'`.*
543	/// Double quote is escaped as `\"`.*
544	/// Backslash is escaped as `\\`.*
545	/// Any character in the 'printable ASCII' range `0x20` .. `0x7e`*
546	/// inclusive is not escaped.
547	/// All other characters are given hexadecimal Unicode escapes; see*
548	/// [`escape_unicode`].
549	///
550	/// [`escape_unicode`]: #method.escape_unicode
551	///
552	/// # Examples
553	///
554	/// As an iterator:
555	///
556	/// ```
557	/// for c in '"'.escape_default() {
558	/// print!("{c}");
559	/// }
560	/// println!();
561	/// ```
562	///
563	/// Using `println!` directly:
564	///
565	/// ```
566	/// println!("{}", '"'.escape_default());
567	/// ```
568	///
569	/// Both are equivalent to:
570	///
571	/// ```
572	/// println!("`\\\"`");
573	/// ```
574	///
575	/// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
576	///
577	/// ```
578	/// assert_eq!('"'.escape_default().to_string(), "`\\\"`");
579	/// ```
580	#[must_use = "this returns the escaped char as an iterator, \
581	without modifying the original"]
582	#[stable(feature = "rust1", since = "1.0.0")]
583	#[inline]
584	pub fn escape_default(self) -> EscapeDefault {
585	match self {
586	'`\t`' => EscapeDefault::backslash(ascii::Char::SmallT),
587	'`\r`' => EscapeDefault::backslash(ascii::Char::SmallR),
588	'`\n`' => EscapeDefault::backslash(ascii::Char::SmallN),
589	'`\\`' \| '`\'`' \| '`\"`' => EscapeDefault::backslash(self.as_ascii().unwrap()),
590	'`\x20`'..='`\x7e`' => EscapeDefault::printable(self.as_ascii().unwrap()),
591	_ => EscapeDefault::unicode(self),
592	}
593	}
594
595	/// Returns the number of bytes this `char` would need if encoded in UTF-8.
596	///
597	/// That number of bytes is always between 1 and 4, inclusive.
598	///
599	/// # Examples
600	///
601	/// Basic usage:
602	///
603	/// ```
604	/// let len = 'A'.len_utf8();
605	/// assert_eq!(len, `1`);
606	///
607	/// let len = 'ß'.len_utf8();
608	/// assert_eq!(len, `2`);
609	///
610	/// let len = 'ℝ'.len_utf8();
611	/// assert_eq!(len, `3`);
612	///
613	/// let len = '💣'.len_utf8();
614	/// assert_eq!(len, `4`);
615	/// ```
616	///
617	/// The `&str` type guarantees that its contents are UTF-8, and so we can compare the length it
618	/// would take if each code point was represented as a `char` vs in the `&str` itself:
619	///
620	/// ```
621	/// // as chars
622	/// let eastern = '東';
623	/// let capital = '京';
624	///
625	/// // both can be represented as three bytes
626	/// assert_eq!(`3`, eastern.len_utf8());
627	/// assert_eq!(`3`, capital.len_utf8());
628	///
629	/// // as a &str, these two are encoded in UTF-8
630	/// let tokyo = "東京";
631	///
632	/// let len = eastern.len_utf8() + capital.len_utf8();
633	///
634	/// // we can see that they take six bytes total...
635	/// assert_eq!(`6`, tokyo.len());
636	///
637	/// // ... just like the &str
638	/// assert_eq!(len, tokyo.len());
639	/// ```
640	#[stable(feature = "rust1", since = "1.0.0")]
641	#[rustc_const_stable(feature = "const_char_len_utf", since = "1.52.0")]
642	#[inline]
643	#[must_use]
644	pub const fn len_utf8(self) -> usize {
645	len_utf8(self as u32)
646	}
647
648	/// Returns the number of 16-bit code units this `char` would need if
649	/// encoded in UTF-16.
650	///
651	/// That number of code units is always either 1 or 2, for unicode scalar values in
652	/// the [basic multilingual plane] or [supplementary planes] respectively.
653	///
654	/// See the documentation for [`len_utf8()`] for more explanation of this
655	/// concept. This function is a mirror, but for UTF-16 instead of UTF-8.
656	///
657	/// [basic multilingual plane]: http://www.unicode.org/glossary/#basic_multilingual_plane
658	/// [supplementary planes]: http://www.unicode.org/glossary/#supplementary_planes
659	/// [`len_utf8()`]: #method.len_utf8
660	///
661	/// # Examples
662	///
663	/// Basic usage:
664	///
665	/// ```
666	/// let n = 'ß'.len_utf16();
667	/// assert_eq!(n, `1`);
668	///
669	/// let len = '💣'.len_utf16();
670	/// assert_eq!(len, `2`);
671	/// ```
672	#[stable(feature = "rust1", since = "1.0.0")]
673	#[rustc_const_stable(feature = "const_char_len_utf", since = "1.52.0")]
674	#[inline]
675	#[must_use]
676	pub const fn len_utf16(self) -> usize {
677	len_utf16(self as u32)
678	}
679
680	/// Encodes this character as UTF-8 into the provided byte buffer,
681	/// and then returns the subslice of the buffer that contains the encoded character.
682	///
683	/// # Panics
684	///
685	/// Panics if the buffer is not large enough.
686	/// A buffer of length four is large enough to encode any `char`.
687	///
688	/// # Examples
689	///
690	/// In both of these examples, 'ß' takes two bytes to encode.
691	///
692	/// ```
693	/// let mut b = [`0`; `2`];
694	///
695	/// let result = 'ß'.encode_utf8(&mut b);
696	///
697	/// assert_eq!(result, "ß");
698	///
699	/// assert_eq!(result.len(), `2`);
700	/// ```
701	///
702	/// A buffer that's too small:
703	///
704	/// ```should_panic
705	/// let mut b = [`0`; `1`];
706	///
707	/// // this panics
708	/// 'ß'.encode_utf8(&mut b);
709	/// ```
710	#[stable(feature = "unicode_encode_char", since = "1.15.0")]
711	#[rustc_const_stable(feature = "const_char_encode_utf8", since = "1.83.0")]
712	#[inline]
713	pub const fn encode_utf8(self, dst: &mut [u8]) -> &mut str {
714	// SAFETY: `char` is not a surrogate, so this is valid UTF-8.
715	unsafe { from_utf8_unchecked_mut(encode_utf8_raw(self as u32, dst)) }
716	}
717
718	/// Encodes this character as native endian UTF-16 into the provided `u16` buffer,
719	/// and then returns the subslice of the buffer that contains the encoded character.
720	///
721	/// # Panics
722	///
723	/// Panics if the buffer is not large enough.
724	/// A buffer of length 2 is large enough to encode any `char`.
725	///
726	/// # Examples
727	///
728	/// In both of these examples, '𝕊' takes two `u16`s to encode.
729	///
730	/// ```
731	/// let mut b = [`0`; `2`];
732	///
733	/// let result = '𝕊'.encode_utf16(&mut b);
734	///
735	/// assert_eq!(result.len(), `2`);
736	/// ```
737	///
738	/// A buffer that's too small:
739	///
740	/// ```should_panic
741	/// let mut b = [`0`; `1`];
742	///
743	/// // this panics
744	/// '𝕊'.encode_utf16(&mut b);
745	/// ```
746	#[stable(feature = "unicode_encode_char", since = "1.15.0")]
747	#[rustc_const_stable(feature = "const_char_encode_utf16", since = "1.84.0")]
748	#[inline]
749	pub const fn encode_utf16(self, dst: &mut [u16]) -> &mut [u16] {
750	encode_utf16_raw(self as u32, dst)
751	}
752
753	/// Returns `true` if this `char` has the `Alphabetic` property.
754	///
755	/// `Alphabetic` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
756	/// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
757	///
758	/// [Unicode Standard]: https://www.unicode.org/versions/latest/
759	/// [ucd]: https://www.unicode.org/reports/tr44/
760	/// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
761	///
762	/// # Examples
763	///
764	/// Basic usage:
765	///
766	/// ```
767	/// assert!('a'.is_alphabetic());
768	/// assert!('京'.is_alphabetic());
769	///
770	/// let c = '💝';
771	/// // love is many things, but it is not alphabetic
772	/// assert!(!c.is_alphabetic());
773	/// ```
774	#[must_use]
775	#[stable(feature = "rust1", since = "1.0.0")]
776	#[inline]
777	pub fn is_alphabetic(self) -> bool {
778	match self {
779	'a'..='z' \| 'A'..='Z' => `true`,
780	c => c > '`\x7f`' && unicode::Alphabetic(c),
781	}
782	}
783
784	/// Returns `true` if this `char` has the `Lowercase` property.
785	///
786	/// `Lowercase` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
787	/// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
788	///
789	/// [Unicode Standard]: https://www.unicode.org/versions/latest/
790	/// [ucd]: https://www.unicode.org/reports/tr44/
791	/// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
792	///
793	/// # Examples
794	///
795	/// Basic usage:
796	///
797	/// ```
798	/// assert!('a'.is_lowercase());
799	/// assert!('δ'.is_lowercase());
800	/// assert!(!'A'.is_lowercase());
801	/// assert!(!'Δ'.is_lowercase());
802	///
803	/// // The various Chinese scripts and punctuation do not have case, and so:
804	/// assert!(!'中'.is_lowercase());
805	/// assert!(!' '.is_lowercase());
806	/// ```
807	///
808	/// In a const context:
809	///
810	/// ```
811	/// const CAPITAL_DELTA_IS_LOWERCASE: bool = 'Δ'.is_lowercase();
812	/// assert!(!CAPITAL_DELTA_IS_LOWERCASE);
813	/// ```
814	#[must_use]
815	#[stable(feature = "rust1", since = "1.0.0")]
816	#[rustc_const_stable(feature = "const_unicode_case_lookup", since = "1.84.0")]
817	#[inline]
818	pub const fn is_lowercase(self) -> bool {
819	match self {
820	'a'..='z' => `true`,
821	c => c > '`\x7f`' && unicode::Lowercase(c),
822	}
823	}
824
825	/// Returns `true` if this `char` has the `Uppercase` property.
826	///
827	/// `Uppercase` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
828	/// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
829	///
830	/// [Unicode Standard]: https://www.unicode.org/versions/latest/
831	/// [ucd]: https://www.unicode.org/reports/tr44/
832	/// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
833	///
834	/// # Examples
835	///
836	/// Basic usage:
837	///
838	/// ```
839	/// assert!(!'a'.is_uppercase());
840	/// assert!(!'δ'.is_uppercase());
841	/// assert!('A'.is_uppercase());
842	/// assert!('Δ'.is_uppercase());
843	///
844	/// // The various Chinese scripts and punctuation do not have case, and so:
845	/// assert!(!'中'.is_uppercase());
846	/// assert!(!' '.is_uppercase());
847	/// ```
848	///
849	/// In a const context:
850	///
851	/// ```
852	/// const CAPITAL_DELTA_IS_UPPERCASE: bool = 'Δ'.is_uppercase();
853	/// assert!(CAPITAL_DELTA_IS_UPPERCASE);
854	/// ```
855	#[must_use]
856	#[stable(feature = "rust1", since = "1.0.0")]
857	#[rustc_const_stable(feature = "const_unicode_case_lookup", since = "1.84.0")]
858	#[inline]
859	pub const fn is_uppercase(self) -> bool {
860	match self {
861	'A'..='Z' => `true`,
862	c => c > '`\x7f`' && unicode::Uppercase(c),
863	}
864	}
865
866	/// Returns `true` if this `char` has the `White_Space` property.
867	///
868	/// `White_Space` is specified in the [Unicode Character Database][ucd] [`PropList.txt`].
869	///
870	/// [ucd]: https://www.unicode.org/reports/tr44/
871	/// [`PropList.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/PropList.txt
872	///
873	/// # Examples
874	///
875	/// Basic usage:
876	///
877	/// ```
878	/// assert!(' '.is_whitespace());
879	///
880	/// // line break
881	/// assert!('`\n`'.is_whitespace());
882	///
883	/// // a non-breaking space
884	/// assert!('`\u{A0}`'.is_whitespace());
885	///
886	/// assert!(!'越'.is_whitespace());
887	/// ```
888	#[must_use]
889	#[stable(feature = "rust1", since = "1.0.0")]
890	#[rustc_const_stable(feature = "const_char_classify", since = "1.87.0")]
891	#[inline]
892	pub const fn is_whitespace(self) -> bool {
893	match self {
894	' ' \| '`\x09`'..='`\x0d`' => `true`,
895	c => c > '`\x7f`' && unicode::White_Space(c),
896	}
897	}
898
899	/// Returns `true` if this `char` satisfies either [`is_alphabetic()`] or [`is_numeric()`].
900	///
901	/// [`is_alphabetic()`]: #method.is_alphabetic
902	/// [`is_numeric()`]: #method.is_numeric
903	///
904	/// # Examples
905	///
906	/// Basic usage:
907	///
908	/// ```
909	/// assert!('٣'.is_alphanumeric());
910	/// assert!('7'.is_alphanumeric());
911	/// assert!('৬'.is_alphanumeric());
912	/// assert!('¾'.is_alphanumeric());
913	/// assert!('①'.is_alphanumeric());
914	/// assert!('K'.is_alphanumeric());
915	/// assert!('و'.is_alphanumeric());
916	/// assert!('藏'.is_alphanumeric());
917	/// ```
918	#[must_use]
919	#[stable(feature = "rust1", since = "1.0.0")]
920	#[inline]
921	pub fn is_alphanumeric(self) -> bool {
922	self.is_alphabetic() \|\| self.is_numeric()
923	}
924
925	/// Returns `true` if this `char` has the general category for control codes.
926	///
927	/// Control codes (code points with the general category of `Cc`) are described in Chapter 4
928	/// (Character Properties) of the [Unicode Standard] and specified in the [Unicode Character
929	/// Database][ucd] [`UnicodeData.txt`].
930	///
931	/// [Unicode Standard]: https://www.unicode.org/versions/latest/
932	/// [ucd]: https://www.unicode.org/reports/tr44/
933	/// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
934	///
935	/// # Examples
936	///
937	/// Basic usage:
938	///
939	/// ```
940	/// // U+009C, STRING TERMINATOR
941	/// assert!(''.is_control());
942	/// assert!(!'q'.is_control());
943	/// ```
944	#[must_use]
945	#[stable(feature = "rust1", since = "1.0.0")]
946	#[inline]
947	pub fn is_control(self) -> bool {
948	unicode::Cc(self)
949	}
950
951	/// Returns `true` if this `char` has the `Grapheme_Extend` property.
952	///
953	/// `Grapheme_Extend` is described in [Unicode Standard Annex #29 (Unicode Text
954	/// Segmentation)][uax29] and specified in the [Unicode Character Database][ucd]
955	/// [`DerivedCoreProperties.txt`].
956	///
957	/// [uax29]: https://www.unicode.org/reports/tr29/
958	/// [ucd]: https://www.unicode.org/reports/tr44/
959	/// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
960	#[must_use]
961	#[inline]
962	pub(crate) fn is_grapheme_extended(self) -> bool {
963	unicode::Grapheme_Extend(self)
964	}
965
966	/// Returns `true` if this `char` has one of the general categories for numbers.
967	///
968	/// The general categories for numbers (`Nd` for decimal digits, `Nl` for letter-like numeric
969	/// characters, and `No` for other numeric characters) are specified in the [Unicode Character
970	/// Database][ucd] [`UnicodeData.txt`].
971	///
972	/// This method doesn't cover everything that could be considered a number, e.g. ideographic numbers like '三'.
973	/// If you want everything including characters with overlapping purposes then you might want to use
974	/// a unicode or language-processing library that exposes the appropriate character properties instead
975	/// of looking at the unicode categories.
976	///
977	/// If you want to parse ASCII decimal digits (0-9) or ASCII base-N, use
978	/// `is_ascii_digit` or `is_digit` instead.
979	///
980	/// [Unicode Standard]: https://www.unicode.org/versions/latest/
981	/// [ucd]: https://www.unicode.org/reports/tr44/
982	/// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
983	///
984	/// # Examples
985	///
986	/// Basic usage:
987	///
988	/// ```
989	/// assert!('٣'.is_numeric());
990	/// assert!('7'.is_numeric());
991	/// assert!('৬'.is_numeric());
992	/// assert!('¾'.is_numeric());
993	/// assert!('①'.is_numeric());
994	/// assert!(!'K'.is_numeric());
995	/// assert!(!'و'.is_numeric());
996	/// assert!(!'藏'.is_numeric());
997	/// assert!(!'三'.is_numeric());
998	/// ```
999	#[must_use]
1000	#[stable(feature = "rust1", since = "1.0.0")]
1001	#[inline]
1002	pub fn is_numeric(self) -> bool {
1003	match self {
1004	'0'..='9' => `true`,
1005	c => c > '`\x7f`' && unicode::N(c),
1006	}
1007	}
1008
1009	/// Returns an iterator that yields the lowercase mapping of this `char` as one or more
1010	/// `char`s.
1011	///
1012	/// If this `char` does not have a lowercase mapping, the iterator yields the same `char`.
1013	///
1014	/// If this `char` has a one-to-one lowercase mapping given by the [Unicode Character
1015	/// Database][ucd] [`UnicodeData.txt`], the iterator yields that `char`.
1016	///
1017	/// [ucd]: https://www.unicode.org/reports/tr44/
1018	/// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
1019	///
1020	/// If this `char` requires special considerations (e.g. multiple `char`s) the iterator yields
1021	/// the `char`(s) given by [`SpecialCasing.txt`].
1022	///
1023	/// [`SpecialCasing.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/SpecialCasing.txt
1024	///
1025	/// This operation performs an unconditional mapping without tailoring. That is, the conversion
1026	/// is independent of context and language.
1027	///
1028	/// In the [Unicode Standard], Chapter 4 (Character Properties) discusses case mapping in
1029	/// general and Chapter 3 (Conformance) discusses the default algorithm for case conversion.
1030	///
1031	/// [Unicode Standard]: https://www.unicode.org/versions/latest/
1032	///
1033	/// # Examples
1034	///
1035	/// As an iterator:
1036	///
1037	/// ```
1038	/// for c in 'İ'.to_lowercase() {
1039	/// print!("{c}");
1040	/// }
1041	/// println!();
1042	/// ```
1043	///
1044	/// Using `println!` directly:
1045	///
1046	/// ```
1047	/// println!("{}", 'İ'.to_lowercase());
1048	/// ```
1049	///
1050	/// Both are equivalent to:
1051	///
1052	/// ```
1053	/// println!("i`\u{307}`");
1054	/// ```
1055	///
1056	/// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
1057	///
1058	/// ```
1059	/// assert_eq!('C'.to_lowercase().to_string(), "c");
1060	///
1061	/// // Sometimes the result is more than one character:
1062	/// assert_eq!('İ'.to_lowercase().to_string(), "i`\u{307}`");
1063	///
1064	/// // Characters that do not have both uppercase and lowercase
1065	/// // convert into themselves.
1066	/// assert_eq!('山'.to_lowercase().to_string(), "山");
1067	/// ```
1068	#[must_use = "this returns the lowercase character as a new iterator, \
1069	without modifying the original"]
1070	#[stable(feature = "rust1", since = "1.0.0")]
1071	#[inline]
1072	pub fn to_lowercase(self) -> ToLowercase {
1073	ToLowercase(CaseMappingIter::new(conversions::to_lower(self)))
1074	}
1075
1076	/// Returns an iterator that yields the uppercase mapping of this `char` as one or more
1077	/// `char`s.
1078	///
1079	/// If this `char` does not have an uppercase mapping, the iterator yields the same `char`.
1080	///
1081	/// If this `char` has a one-to-one uppercase mapping given by the [Unicode Character
1082	/// Database][ucd] [`UnicodeData.txt`], the iterator yields that `char`.
1083	///
1084	/// [ucd]: https://www.unicode.org/reports/tr44/
1085	/// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
1086	///
1087	/// If this `char` requires special considerations (e.g. multiple `char`s) the iterator yields
1088	/// the `char`(s) given by [`SpecialCasing.txt`].
1089	///
1090	/// [`SpecialCasing.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/SpecialCasing.txt
1091	///
1092	/// This operation performs an unconditional mapping without tailoring. That is, the conversion
1093	/// is independent of context and language.
1094	///
1095	/// In the [Unicode Standard], Chapter 4 (Character Properties) discusses case mapping in
1096	/// general and Chapter 3 (Conformance) discusses the default algorithm for case conversion.
1097	///
1098	/// [Unicode Standard]: https://www.unicode.org/versions/latest/
1099	///
1100	/// # Examples
1101	///
1102	/// As an iterator:
1103	///
1104	/// ```
1105	/// for c in 'ß'.to_uppercase() {
1106	/// print!("{c}");
1107	/// }
1108	/// println!();
1109	/// ```
1110	///
1111	/// Using `println!` directly:
1112	///
1113	/// ```
1114	/// println!("{}", 'ß'.to_uppercase());
1115	/// ```
1116	///
1117	/// Both are equivalent to:
1118	///
1119	/// ```
1120	/// println!("SS");
1121	/// ```
1122	///
1123	/// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
1124	///
1125	/// ```
1126	/// assert_eq!('c'.to_uppercase().to_string(), "C");
1127	///
1128	/// // Sometimes the result is more than one character:
1129	/// assert_eq!('ß'.to_uppercase().to_string(), "SS");
1130	///
1131	/// // Characters that do not have both uppercase and lowercase
1132	/// // convert into themselves.
1133	/// assert_eq!('山'.to_uppercase().to_string(), "山");
1134	/// ```
1135	///
1136	/// # Note on locale
1137	///
1138	/// In Turkish, the equivalent of 'i' in Latin has five forms instead of two:
1139	///
1140	/// 'Dotless': I / ı, sometimes written ï*
1141	/// 'Dotted': İ / i*
1142	///
1143	/// Note that the lowercase dotted 'i' is the same as the Latin. Therefore:
1144	///
1145	/// ```
1146	/// let upper_i = 'i'.to_uppercase().to_string();
1147	/// ```
1148	///
1149	/// The value of `upper_i` here relies on the language of the text: if we're
1150	/// in `en-US`, it should be `"I"`, but if we're in `tr_TR`, it should
1151	/// be `"İ"`. `to_uppercase()` does not take this into account, and so:
1152	///
1153	/// ```
1154	/// let upper_i = 'i'.to_uppercase().to_string();
1155	///
1156	/// assert_eq!(upper_i, "I");
1157	/// ```
1158	///
1159	/// holds across languages.
1160	#[must_use = "this returns the uppercase character as a new iterator, \
1161	without modifying the original"]
1162	#[stable(feature = "rust1", since = "1.0.0")]
1163	#[inline]
1164	pub fn to_uppercase(self) -> ToUppercase {
1165	ToUppercase(CaseMappingIter::new(conversions::to_upper(self)))
1166	}
1167
1168	/// Checks if the value is within the ASCII range.
1169	///
1170	/// # Examples
1171	///
1172	/// ```
1173	/// let ascii = 'a';
1174	/// let non_ascii = '❤';
1175	///
1176	/// assert!(ascii.is_ascii());
1177	/// assert!(!non_ascii.is_ascii());
1178	/// ```
1179	#[must_use]
1180	#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1181	#[rustc_const_stable(feature = "const_char_is_ascii", since = "1.32.0")]
1182	#[rustc_diagnostic_item = "char_is_ascii"]
1183	#[inline]
1184	pub const fn is_ascii(&self) -> bool {
1185	self as u32* <= `0x7F`
1186	}
1187
1188	/// Returns `Some` if the value is within the ASCII range,
1189	/// or `None` if it's not.
1190	///
1191	/// This is preferred to [`Self::is_ascii`] when you're passing the value
1192	/// along to something else that can take [`ascii::Char`] rather than
1193	/// needing to check again for itself whether the value is in ASCII.
1194	#[must_use]
1195	#[unstable(feature = "ascii_char", issue = "110998")]
1196	#[inline]
1197	pub const fn as_ascii(&self) -> Option<ascii::Char> {
1198	if self.is_ascii() {
1199	// SAFETY: Just checked that this is ASCII.
1200	Some(unsafe { ascii::Char::from_u8_unchecked(*self as u8) })
1201	} else {
1202	None
1203	}
1204	}
1205
1206	/// Converts this char into an [ASCII character](`ascii::Char`), without
1207	/// checking whether it is valid.
1208	///
1209	/// # Safety
1210	///
1211	/// This char must be within the ASCII range, or else this is UB.
1212	#[must_use]
1213	#[unstable(feature = "ascii_char", issue = "110998")]
1214	#[inline]
1215	pub const unsafe fn as_ascii_unchecked(&self) -> ascii::Char {
1216	assert_unsafe_precondition!(
1217	check_library_ub,
1218	"as_ascii_unchecked requires that the char is valid ASCII",
1219	(it: &char = self) => it.is_ascii()
1220	);
1221
1222	// SAFETY: the caller promised that this char is ASCII.
1223	unsafe { ascii::Char::from_u8_unchecked(*self as u8) }
1224	}
1225
1226	/// Makes a copy of the value in its ASCII upper case equivalent.
1227	///
1228	/// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
1229	/// but non-ASCII letters are unchanged.
1230	///
1231	/// To uppercase the value in-place, use [`make_ascii_uppercase()`].
1232	///
1233	/// To uppercase ASCII characters in addition to non-ASCII characters, use
1234	/// [`to_uppercase()`].
1235	///
1236	/// # Examples
1237	///
1238	/// ```
1239	/// let ascii = 'a';
1240	/// let non_ascii = '❤';
1241	///
1242	/// assert_eq!('A', ascii.to_ascii_uppercase());
1243	/// assert_eq!('❤', non_ascii.to_ascii_uppercase());
1244	/// ```
1245	///
1246	/// [`make_ascii_uppercase()`]: #method.make_ascii_uppercase
1247	/// [`to_uppercase()`]: #method.to_uppercase
1248	#[must_use = "to uppercase the value in-place, use `make_ascii_uppercase()`"]
1249	#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1250	#[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.52.0")]
1251	#[inline]
1252	pub const fn to_ascii_uppercase(&self) -> char {
1253	if self.is_ascii_lowercase() {
1254	(self as u8).ascii_change_case_unchecked() as char*
1255	} else {
1256	*self
1257	}
1258	}
1259
1260	/// Makes a copy of the value in its ASCII lower case equivalent.
1261	///
1262	/// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
1263	/// but non-ASCII letters are unchanged.
1264	///
1265	/// To lowercase the value in-place, use [`make_ascii_lowercase()`].
1266	///
1267	/// To lowercase ASCII characters in addition to non-ASCII characters, use
1268	/// [`to_lowercase()`].
1269	///
1270	/// # Examples
1271	///
1272	/// ```
1273	/// let ascii = 'A';
1274	/// let non_ascii = '❤';
1275	///
1276	/// assert_eq!('a', ascii.to_ascii_lowercase());
1277	/// assert_eq!('❤', non_ascii.to_ascii_lowercase());
1278	/// ```
1279	///
1280	/// [`make_ascii_lowercase()`]: #method.make_ascii_lowercase
1281	/// [`to_lowercase()`]: #method.to_lowercase
1282	#[must_use = "to lowercase the value in-place, use `make_ascii_lowercase()`"]
1283	#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1284	#[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.52.0")]
1285	#[inline]
1286	pub const fn to_ascii_lowercase(&self) -> char {
1287	if self.is_ascii_uppercase() {
1288	(self as u8).ascii_change_case_unchecked() as char*
1289	} else {
1290	*self
1291	}
1292	}
1293
1294	/// Checks that two values are an ASCII case-insensitive match.
1295	///
1296	/// Equivalent to <code>[to_ascii_lowercase]\(a) == [to_ascii_lowercase]\(b)</code>.
1297	///
1298	/// # Examples
1299	///
1300	/// ```
1301	/// let upper_a = 'A';
1302	/// let lower_a = 'a';
1303	/// let lower_z = 'z';
1304	///
1305	/// assert!(upper_a.eq_ignore_ascii_case(&lower_a));
1306	/// assert!(upper_a.eq_ignore_ascii_case(&upper_a));
1307	/// assert!(!upper_a.eq_ignore_ascii_case(&lower_z));
1308	/// ```
1309	///
1310	/// [to_ascii_lowercase]: #method.to_ascii_lowercase
1311	#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1312	#[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.52.0")]
1313	#[inline]
1314	pub const fn eq_ignore_ascii_case(&self, other: &char) -> bool {
1315	self.to_ascii_lowercase() == other.to_ascii_lowercase()
1316	}
1317
1318	/// Converts this type to its ASCII upper case equivalent in-place.
1319	///
1320	/// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
1321	/// but non-ASCII letters are unchanged.
1322	///
1323	/// To return a new uppercased value without modifying the existing one, use
1324	/// [`to_ascii_uppercase()`].
1325	///
1326	/// # Examples
1327	///
1328	/// ```
1329	/// let mut ascii = 'a';
1330	///
1331	/// ascii.make_ascii_uppercase();
1332	///
1333	/// assert_eq!('A', ascii);
1334	/// ```
1335	///
1336	/// [`to_ascii_uppercase()`]: #method.to_ascii_uppercase
1337	#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1338	#[rustc_const_stable(feature = "const_make_ascii", since = "1.84.0")]
1339	#[inline]
1340	pub const fn make_ascii_uppercase(&mut self) {
1341	*self = self.to_ascii_uppercase();
1342	}
1343
1344	/// Converts this type to its ASCII lower case equivalent in-place.
1345	///
1346	/// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
1347	/// but non-ASCII letters are unchanged.
1348	///
1349	/// To return a new lowercased value without modifying the existing one, use
1350	/// [`to_ascii_lowercase()`].
1351	///
1352	/// # Examples
1353	///
1354	/// ```
1355	/// let mut ascii = 'A';
1356	///
1357	/// ascii.make_ascii_lowercase();
1358	///
1359	/// assert_eq!('a', ascii);
1360	/// ```
1361	///
1362	/// [`to_ascii_lowercase()`]: #method.to_ascii_lowercase
1363	#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
1364	#[rustc_const_stable(feature = "const_make_ascii", since = "1.84.0")]
1365	#[inline]
1366	pub const fn make_ascii_lowercase(&mut self) {
1367	*self = self.to_ascii_lowercase();
1368	}
1369
1370	/// Checks if the value is an ASCII alphabetic character:
1371	///
1372	/// - U+0041 'A' ..= U+005A 'Z', or
1373	/// - U+0061 'a' ..= U+007A 'z'.
1374	///
1375	/// # Examples
1376	///
1377	/// ```
1378	/// let uppercase_a = 'A';
1379	/// let uppercase_g = 'G';
1380	/// let a = 'a';
1381	/// let g = 'g';
1382	/// let zero = '0';
1383	/// let percent = '%';
1384	/// let space = ' ';
1385	/// let lf = '`\n`';
1386	/// let esc = '`\x1b`';
1387	///
1388	/// assert!(uppercase_a.is_ascii_alphabetic());
1389	/// assert!(uppercase_g.is_ascii_alphabetic());
1390	/// assert!(a.is_ascii_alphabetic());
1391	/// assert!(g.is_ascii_alphabetic());
1392	/// assert!(!zero.is_ascii_alphabetic());
1393	/// assert!(!percent.is_ascii_alphabetic());
1394	/// assert!(!space.is_ascii_alphabetic());
1395	/// assert!(!lf.is_ascii_alphabetic());
1396	/// assert!(!esc.is_ascii_alphabetic());
1397	/// ```
1398	#[must_use]
1399	#[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1400	#[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1401	#[inline]
1402	pub const fn is_ascii_alphabetic(&self) -> bool {
1403	matches!(*self, 'A'..='Z' \| 'a'..='z')
1404	}
1405
1406	/// Checks if the value is an ASCII uppercase character:
1407	/// U+0041 'A' ..= U+005A 'Z'.
1408	///
1409	/// # Examples
1410	///
1411	/// ```
1412	/// let uppercase_a = 'A';
1413	/// let uppercase_g = 'G';
1414	/// let a = 'a';
1415	/// let g = 'g';
1416	/// let zero = '0';
1417	/// let percent = '%';
1418	/// let space = ' ';
1419	/// let lf = '`\n`';
1420	/// let esc = '`\x1b`';
1421	///
1422	/// assert!(uppercase_a.is_ascii_uppercase());
1423	/// assert!(uppercase_g.is_ascii_uppercase());
1424	/// assert!(!a.is_ascii_uppercase());
1425	/// assert!(!g.is_ascii_uppercase());
1426	/// assert!(!zero.is_ascii_uppercase());
1427	/// assert!(!percent.is_ascii_uppercase());
1428	/// assert!(!space.is_ascii_uppercase());
1429	/// assert!(!lf.is_ascii_uppercase());
1430	/// assert!(!esc.is_ascii_uppercase());
1431	/// ```
1432	#[must_use]
1433	#[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1434	#[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1435	#[inline]
1436	pub const fn is_ascii_uppercase(&self) -> bool {
1437	matches!(*self, 'A'..='Z')
1438	}
1439
1440	/// Checks if the value is an ASCII lowercase character:
1441	/// U+0061 'a' ..= U+007A 'z'.
1442	///
1443	/// # Examples
1444	///
1445	/// ```
1446	/// let uppercase_a = 'A';
1447	/// let uppercase_g = 'G';
1448	/// let a = 'a';
1449	/// let g = 'g';
1450	/// let zero = '0';
1451	/// let percent = '%';
1452	/// let space = ' ';
1453	/// let lf = '`\n`';
1454	/// let esc = '`\x1b`';
1455	///
1456	/// assert!(!uppercase_a.is_ascii_lowercase());
1457	/// assert!(!uppercase_g.is_ascii_lowercase());
1458	/// assert!(a.is_ascii_lowercase());
1459	/// assert!(g.is_ascii_lowercase());
1460	/// assert!(!zero.is_ascii_lowercase());
1461	/// assert!(!percent.is_ascii_lowercase());
1462	/// assert!(!space.is_ascii_lowercase());
1463	/// assert!(!lf.is_ascii_lowercase());
1464	/// assert!(!esc.is_ascii_lowercase());
1465	/// ```
1466	#[must_use]
1467	#[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1468	#[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1469	#[inline]
1470	pub const fn is_ascii_lowercase(&self) -> bool {
1471	matches!(*self, 'a'..='z')
1472	}
1473
1474	/// Checks if the value is an ASCII alphanumeric character:
1475	///
1476	/// - U+0041 'A' ..= U+005A 'Z', or
1477	/// - U+0061 'a' ..= U+007A 'z', or
1478	/// - U+0030 '0' ..= U+0039 '9'.
1479	///
1480	/// # Examples
1481	///
1482	/// ```
1483	/// let uppercase_a = 'A';
1484	/// let uppercase_g = 'G';
1485	/// let a = 'a';
1486	/// let g = 'g';
1487	/// let zero = '0';
1488	/// let percent = '%';
1489	/// let space = ' ';
1490	/// let lf = '`\n`';
1491	/// let esc = '`\x1b`';
1492	///
1493	/// assert!(uppercase_a.is_ascii_alphanumeric());
1494	/// assert!(uppercase_g.is_ascii_alphanumeric());
1495	/// assert!(a.is_ascii_alphanumeric());
1496	/// assert!(g.is_ascii_alphanumeric());
1497	/// assert!(zero.is_ascii_alphanumeric());
1498	/// assert!(!percent.is_ascii_alphanumeric());
1499	/// assert!(!space.is_ascii_alphanumeric());
1500	/// assert!(!lf.is_ascii_alphanumeric());
1501	/// assert!(!esc.is_ascii_alphanumeric());
1502	/// ```
1503	#[must_use]
1504	#[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1505	#[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1506	#[inline]
1507	pub const fn is_ascii_alphanumeric(&self) -> bool {
1508	matches!(self, '0'..='9') \| matches!(self, 'A'..='Z') \| matches!(*self, 'a'..='z')
1509	}
1510
1511	/// Checks if the value is an ASCII decimal digit:
1512	/// U+0030 '0' ..= U+0039 '9'.
1513	///
1514	/// # Examples
1515	///
1516	/// ```
1517	/// let uppercase_a = 'A';
1518	/// let uppercase_g = 'G';
1519	/// let a = 'a';
1520	/// let g = 'g';
1521	/// let zero = '0';
1522	/// let percent = '%';
1523	/// let space = ' ';
1524	/// let lf = '`\n`';
1525	/// let esc = '`\x1b`';
1526	///
1527	/// assert!(!uppercase_a.is_ascii_digit());
1528	/// assert!(!uppercase_g.is_ascii_digit());
1529	/// assert!(!a.is_ascii_digit());
1530	/// assert!(!g.is_ascii_digit());
1531	/// assert!(zero.is_ascii_digit());
1532	/// assert!(!percent.is_ascii_digit());
1533	/// assert!(!space.is_ascii_digit());
1534	/// assert!(!lf.is_ascii_digit());
1535	/// assert!(!esc.is_ascii_digit());
1536	/// ```
1537	#[must_use]
1538	#[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1539	#[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1540	#[inline]
1541	pub const fn is_ascii_digit(&self) -> bool {
1542	matches!(*self, '0'..='9')
1543	}
1544
1545	/// Checks if the value is an ASCII octal digit:
1546	/// U+0030 '0' ..= U+0037 '7'.
1547	///
1548	/// # Examples
1549	///
1550	/// ```
1551	/// #![feature(is_ascii_octdigit)]
1552	///
1553	/// let uppercase_a = 'A';
1554	/// let a = 'a';
1555	/// let zero = '0';
1556	/// let seven = '7';
1557	/// let nine = '9';
1558	/// let percent = '%';
1559	/// let lf = '`\n`';
1560	///
1561	/// assert!(!uppercase_a.is_ascii_octdigit());
1562	/// assert!(!a.is_ascii_octdigit());
1563	/// assert!(zero.is_ascii_octdigit());
1564	/// assert!(seven.is_ascii_octdigit());
1565	/// assert!(!nine.is_ascii_octdigit());
1566	/// assert!(!percent.is_ascii_octdigit());
1567	/// assert!(!lf.is_ascii_octdigit());
1568	/// ```
1569	#[must_use]
1570	#[unstable(feature = "is_ascii_octdigit", issue = "101288")]
1571	#[inline]
1572	pub const fn is_ascii_octdigit(&self) -> bool {
1573	matches!(*self, '0'..='7')
1574	}
1575
1576	/// Checks if the value is an ASCII hexadecimal digit:
1577	///
1578	/// - U+0030 '0' ..= U+0039 '9', or
1579	/// - U+0041 'A' ..= U+0046 'F', or
1580	/// - U+0061 'a' ..= U+0066 'f'.
1581	///
1582	/// # Examples
1583	///
1584	/// ```
1585	/// let uppercase_a = 'A';
1586	/// let uppercase_g = 'G';
1587	/// let a = 'a';
1588	/// let g = 'g';
1589	/// let zero = '0';
1590	/// let percent = '%';
1591	/// let space = ' ';
1592	/// let lf = '`\n`';
1593	/// let esc = '`\x1b`';
1594	///
1595	/// assert!(uppercase_a.is_ascii_hexdigit());
1596	/// assert!(!uppercase_g.is_ascii_hexdigit());
1597	/// assert!(a.is_ascii_hexdigit());
1598	/// assert!(!g.is_ascii_hexdigit());
1599	/// assert!(zero.is_ascii_hexdigit());
1600	/// assert!(!percent.is_ascii_hexdigit());
1601	/// assert!(!space.is_ascii_hexdigit());
1602	/// assert!(!lf.is_ascii_hexdigit());
1603	/// assert!(!esc.is_ascii_hexdigit());
1604	/// ```
1605	#[must_use]
1606	#[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1607	#[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1608	#[inline]
1609	pub const fn is_ascii_hexdigit(&self) -> bool {
1610	matches!(self, '0'..='9') \| matches!(self, 'A'..='F') \| matches!(*self, 'a'..='f')
1611	}
1612
1613	/// Checks if the value is an ASCII punctuation character:
1614	///
1615	/// - U+0021 ..= U+002F `! " # $ % & ' ( ) + , - . /`, or*
1616	/// - U+003A ..= U+0040 `: ; < = > ? @`, or
1617	/// - U+005B ..= U+0060 ``[ \ ] ^ _ ` ``, or
1618	/// - U+007B ..= U+007E `{ \| } ~`
1619	///
1620	/// # Examples
1621	///
1622	/// ```
1623	/// let uppercase_a = 'A';
1624	/// let uppercase_g = 'G';
1625	/// let a = 'a';
1626	/// let g = 'g';
1627	/// let zero = '0';
1628	/// let percent = '%';
1629	/// let space = ' ';
1630	/// let lf = '`\n`';
1631	/// let esc = '`\x1b`';
1632	///
1633	/// assert!(!uppercase_a.is_ascii_punctuation());
1634	/// assert!(!uppercase_g.is_ascii_punctuation());
1635	/// assert!(!a.is_ascii_punctuation());
1636	/// assert!(!g.is_ascii_punctuation());
1637	/// assert!(!zero.is_ascii_punctuation());
1638	/// assert!(percent.is_ascii_punctuation());
1639	/// assert!(!space.is_ascii_punctuation());
1640	/// assert!(!lf.is_ascii_punctuation());
1641	/// assert!(!esc.is_ascii_punctuation());
1642	/// ```
1643	#[must_use]
1644	#[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1645	#[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1646	#[inline]
1647	pub const fn is_ascii_punctuation(&self) -> bool {
1648	matches!(*self, '!'..='/')
1649	\| matches!(*self, ':'..='@')
1650	\| matches!(*self, '['..='`')
1651	\| matches!(*self, '{'..='~')
1652	}
1653
1654	/// Checks if the value is an ASCII graphic character:
1655	/// U+0021 '!' ..= U+007E '~'.
1656	///
1657	/// # Examples
1658	///
1659	/// ```
1660	/// let uppercase_a = 'A';
1661	/// let uppercase_g = 'G';
1662	/// let a = 'a';
1663	/// let g = 'g';
1664	/// let zero = '0';
1665	/// let percent = '%';
1666	/// let space = ' ';
1667	/// let lf = '`\n`';
1668	/// let esc = '`\x1b`';
1669	///
1670	/// assert!(uppercase_a.is_ascii_graphic());
1671	/// assert!(uppercase_g.is_ascii_graphic());
1672	/// assert!(a.is_ascii_graphic());
1673	/// assert!(g.is_ascii_graphic());
1674	/// assert!(zero.is_ascii_graphic());
1675	/// assert!(percent.is_ascii_graphic());
1676	/// assert!(!space.is_ascii_graphic());
1677	/// assert!(!lf.is_ascii_graphic());
1678	/// assert!(!esc.is_ascii_graphic());
1679	/// ```
1680	#[must_use]
1681	#[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1682	#[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1683	#[inline]
1684	pub const fn is_ascii_graphic(&self) -> bool {
1685	matches!(*self, '!'..='~')
1686	}
1687
1688	/// Checks if the value is an ASCII whitespace character:
1689	/// U+0020 SPACE, U+0009 HORIZONTAL TAB, U+000A LINE FEED,
1690	/// U+000C FORM FEED, or U+000D CARRIAGE RETURN.
1691	///
1692	/// Rust uses the WhatWG Infra Standard's [definition of ASCII
1693	/// whitespace][infra-aw]. There are several other definitions in
1694	/// wide use. For instance, [the POSIX locale][pct] includes
1695	/// U+000B VERTICAL TAB as well as all the above characters,
1696	/// but—from the very same specification—[the default rule for
1697	/// "field splitting" in the Bourne shell][bfs] considers only
1698	/// SPACE, HORIZONTAL TAB, and LINE FEED as whitespace.
1699	///
1700	/// If you are writing a program that will process an existing
1701	/// file format, check what that format's definition of whitespace is
1702	/// before using this function.
1703	///
1704	/// [infra-aw]: https://infra.spec.whatwg.org/#ascii-whitespace
1705	/// [pct]: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap07.html#tag_07_03_01
1706	/// [bfs]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_05
1707	///
1708	/// # Examples
1709	///
1710	/// ```
1711	/// let uppercase_a = 'A';
1712	/// let uppercase_g = 'G';
1713	/// let a = 'a';
1714	/// let g = 'g';
1715	/// let zero = '0';
1716	/// let percent = '%';
1717	/// let space = ' ';
1718	/// let lf = '`\n`';
1719	/// let esc = '`\x1b`';
1720	///
1721	/// assert!(!uppercase_a.is_ascii_whitespace());
1722	/// assert!(!uppercase_g.is_ascii_whitespace());
1723	/// assert!(!a.is_ascii_whitespace());
1724	/// assert!(!g.is_ascii_whitespace());
1725	/// assert!(!zero.is_ascii_whitespace());
1726	/// assert!(!percent.is_ascii_whitespace());
1727	/// assert!(space.is_ascii_whitespace());
1728	/// assert!(lf.is_ascii_whitespace());
1729	/// assert!(!esc.is_ascii_whitespace());
1730	/// ```
1731	#[must_use]
1732	#[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1733	#[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1734	#[inline]
1735	pub const fn is_ascii_whitespace(&self) -> bool {
1736	matches!(*self, '`\t`' \| '`\n`' \| '`\x0C`' \| '`\r`' \| ' ')
1737	}
1738
1739	/// Checks if the value is an ASCII control character:
1740	/// U+0000 NUL ..= U+001F UNIT SEPARATOR, or U+007F DELETE.
1741	/// Note that most ASCII whitespace characters are control
1742	/// characters, but SPACE is not.
1743	///
1744	/// # Examples
1745	///
1746	/// ```
1747	/// let uppercase_a = 'A';
1748	/// let uppercase_g = 'G';
1749	/// let a = 'a';
1750	/// let g = 'g';
1751	/// let zero = '0';
1752	/// let percent = '%';
1753	/// let space = ' ';
1754	/// let lf = '`\n`';
1755	/// let esc = '`\x1b`';
1756	///
1757	/// assert!(!uppercase_a.is_ascii_control());
1758	/// assert!(!uppercase_g.is_ascii_control());
1759	/// assert!(!a.is_ascii_control());
1760	/// assert!(!g.is_ascii_control());
1761	/// assert!(!zero.is_ascii_control());
1762	/// assert!(!percent.is_ascii_control());
1763	/// assert!(!space.is_ascii_control());
1764	/// assert!(lf.is_ascii_control());
1765	/// assert!(esc.is_ascii_control());
1766	/// ```
1767	#[must_use]
1768	#[stable(feature = "ascii_ctype_on_intrinsics", since = "1.24.0")]
1769	#[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
1770	#[inline]
1771	pub const fn is_ascii_control(&self) -> bool {
1772	matches!(*self, '`\0`'..='`\x1F`' \| '`\x7F`')
1773	}
1774	}
1775
1776	pub(crate) struct EscapeDebugExtArgs {
1777	/// Escape Extended Grapheme codepoints?
1778	pub(crate) escape_grapheme_extended: bool,
1779
1780	/// Escape single quotes?
1781	pub(crate) escape_single_quote: bool,
1782
1783	/// Escape double quotes?
1784	pub(crate) escape_double_quote: bool,
1785	}
1786
1787	impl EscapeDebugExtArgs {
1788	pub(crate) const ESCAPE_ALL: Self = Self {
1789	escape_grapheme_extended: `true`,
1790	escape_single_quote: `true`,
1791	escape_double_quote: `true`,
1792	};
1793	}
1794
1795	#[inline]
1796	#[must_use]
1797	const fn len_utf8(code: u32) -> usize {
1798	match code {
1799	..MAX_ONE_B => `1`,
1800	..MAX_TWO_B => `2`,
1801	..MAX_THREE_B => `3`,
1802	_ => `4`,
1803	}
1804	}
1805
1806	#[inline]
1807	#[must_use]
1808	const fn len_utf16(code: u32) -> usize {
1809	if (code & `0xFFFF`) == code { `1` } else { `2` }
1810	}
1811
1812	/// Encodes a raw `u32` value as UTF-8 into the provided byte buffer,
1813	/// and then returns the subslice of the buffer that contains the encoded character.
1814	///
1815	/// Unlike `char::encode_utf8`, this method also handles codepoints in the surrogate range.
1816	/// (Creating a `char` in the surrogate range is UB.)
1817	/// The result is valid [generalized UTF-8] but not valid UTF-8.
1818	///
1819	/// [generalized UTF-8]: https://simonsapin.github.io/wtf-8/#generalized-utf8
1820	///
1821	/// # Panics
1822	///
1823	/// Panics if the buffer is not large enough.
1824	/// A buffer of length four is large enough to encode any `char`.
1825	#[unstable(feature = "char_internals", reason = "exposed only for libstd", issue = "none")]
1826	#[doc(hidden)]
1827	#[inline]
1828	pub const fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> &mut [u8] {
1829	let len: usize = len_utf8(code);
1830	if dst.len() < len {
1831	const_panic!(
1832	"encode_utf8: buffer does not have enough bytes to encode code point",
1833	"encode_utf8: need {len} bytes to encode U+{code:`04`X} but buffer has just {dst_len}",
1834	code: u32 = code,
1835	len: usize = len,
1836	dst_len: usize = dst.len(),
1837	);
1838	}
1839
1840	// SAFETY: `dst` is checked to be at least the length needed to encode the codepoint.
1841	unsafe { encode_utf8_raw_unchecked(code, dst.as_mut_ptr()) };
1842
1843	// SAFETY: `<&mut [u8]>::as_mut_ptr` is guaranteed to return a valid pointer and `len` has been tested to be within bounds.
1844	unsafe { slice::from_raw_parts_mut(data:dst.as_mut_ptr(), len) }
1845	}
1846
1847	/// Encodes a raw `u32` value as UTF-8 into the byte buffer pointed to by `dst`.
1848	///
1849	/// Unlike `char::encode_utf8`, this method also handles codepoints in the surrogate range.
1850	/// (Creating a `char` in the surrogate range is UB.)
1851	/// The result is valid [generalized UTF-8] but not valid UTF-8.
1852	///
1853	/// [generalized UTF-8]: https://simonsapin.github.io/wtf-8/#generalized-utf8
1854	///
1855	/// # Safety
1856	///
1857	/// The behavior is undefined if the buffer pointed to by `dst` is not
1858	/// large enough to hold the encoded codepoint. A buffer of length four
1859	/// is large enough to encode any `char`.
1860	///
1861	/// For a safe version of this function, see the [`encode_utf8_raw`] function.
1862	#[unstable(feature = "char_internals", reason = "exposed only for libstd", issue = "none")]
1863	#[doc(hidden)]
1864	#[inline]
1865	pub const unsafe fn encode_utf8_raw_unchecked(code: u32, dst: *mut u8) {
1866	let len = len_utf8(code);
1867	// SAFETY: The caller must guarantee that the buffer pointed to by `dst`
1868	// is at least `len` bytes long.
1869	unsafe {
1870	match len {
1871	`1` => {
1872	*dst = code as u8;
1873	}
1874	`2` => {
1875	*dst = (code >> `6` & `0x1F`) as u8 \| TAG_TWO_B;
1876	*dst.add(`1`) = (code & `0x3F`) as u8 \| TAG_CONT;
1877	}
1878	`3` => {
1879	*dst = (code >> `12` & `0x0F`) as u8 \| TAG_THREE_B;
1880	*dst.add(`1`) = (code >> `6` & `0x3F`) as u8 \| TAG_CONT;
1881	*dst.add(`2`) = (code & `0x3F`) as u8 \| TAG_CONT;
1882	}
1883	`4` => {
1884	*dst = (code >> `18` & `0x07`) as u8 \| TAG_FOUR_B;
1885	*dst.add(`1`) = (code >> `12` & `0x3F`) as u8 \| TAG_CONT;
1886	*dst.add(`2`) = (code >> `6` & `0x3F`) as u8 \| TAG_CONT;
1887	*dst.add(`3`) = (code & `0x3F`) as u8 \| TAG_CONT;
1888	}
1889	// SAFETY: `char` always takes between 1 and 4 bytes to encode in UTF-8.
1890	_ => crate::hint::unreachable_unchecked(),
1891	}
1892	}
1893	}
1894
1895	/// Encodes a raw `u32` value as native endian UTF-16 into the provided `u16` buffer,
1896	/// and then returns the subslice of the buffer that contains the encoded character.
1897	///
1898	/// Unlike `char::encode_utf16`, this method also handles codepoints in the surrogate range.
1899	/// (Creating a `char` in the surrogate range is UB.)
1900	///
1901	/// # Panics
1902	///
1903	/// Panics if the buffer is not large enough.
1904	/// A buffer of length 2 is large enough to encode any `char`.
1905	#[unstable(feature = "char_internals", reason = "exposed only for libstd", issue = "none")]
1906	#[doc(hidden)]
1907	#[inline]
1908	pub const fn encode_utf16_raw(mut code: u32, dst: &mut [u16]) -> &mut [u16] {
1909	let len: usize = len_utf16(code);
1910	match (len, &mut *dst) {
1911	(`1`, [a: &mut u16, ..]) => {
1912	a = code as u16*;
1913	}
1914	(`2`, [a: &mut u16, b: &mut u16, ..]) => {
1915	code -= `0x1_0000`;
1916	a = (code >> `10`) as u16* \| `0xD800`;
1917	b = (code & `0x3FF`) as u16* \| `0xDC00`;
1918	}
1919	_ => {
1920	const_panic!(
1921	"encode_utf16: buffer does not have enough bytes to encode code point",
1922	"encode_utf16: need {len} bytes to encode U+{code:`04`X} but buffer has just {dst_len}",
1923	code: u32 = code,
1924	len: usize = len,
1925	dst_len: usize = dst.len(),
1926	)
1927	}
1928	};
1929	// SAFETY: `<&mut [u16]>::as_mut_ptr` is guaranteed to return a valid pointer and `len` has been tested to be within bounds.
1930	unsafe { slice::from_raw_parts_mut(data:dst.as_mut_ptr(), len) }
1931	}
1932