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1 //! Unicode string slices.
2 //!
3 //! *[See also the `str` primitive type](../../std/primitive.str.html).*
4 //!
5 //! The `&str` type is one of the two main string types, the other being `String`.
6 //! Unlike its `String` counterpart, its contents are borrowed.
7 //!
8 //! # Basic Usage
9 //!
10 //! A basic string declaration of `&str` type:
11 //!
12 //! ```
13 //! let hello_world = "Hello, World!";
14 //! ```
15 //!
16 //! Here we have declared a string literal, also known as a string slice.
17 //! String literals have a static lifetime, which means the string `hello_world`
18 //! is guaranteed to be valid for the duration of the entire program.
19 //! We can explicitly specify `hello_world`'s lifetime as well:
20 //!
21 //! ```
22 //! let hello_world: &'static str = "Hello, world!";
23 //! ```
24
25 #![stable(feature = "rust1", since = "1.0.0")]
26 // Many of the usings in this module are only used in the test configuration.
27 // It's cleaner to just turn off the unused_imports warning than to fix them.
28 #![allow(unused_imports)]
29
30 use core::borrow::{Borrow, BorrowMut};
31 use core::iter::FusedIterator;
32 use core::mem;
33 use core::ptr;
34 use core::str::pattern::{DoubleEndedSearcher, Pattern, ReverseSearcher, Searcher};
35 use core::unicode::conversions;
36
37 use crate::borrow::ToOwned;
38 use crate::boxed::Box;
39 use crate::slice::{Concat, Join, SliceIndex};
40 use crate::string::String;
41 use crate::vec::Vec;
42
43 #[stable(feature = "rust1", since = "1.0.0")]
44 pub use core::str::pattern;
45 #[stable(feature = "encode_utf16", since = "1.8.0")]
46 pub use core::str::EncodeUtf16;
47 #[stable(feature = "split_ascii_whitespace", since = "1.34.0")]
48 pub use core::str::SplitAsciiWhitespace;
49 #[stable(feature = "rust1", since = "1.0.0")]
50 pub use core::str::SplitWhitespace;
51 #[stable(feature = "rust1", since = "1.0.0")]
52 pub use core::str::{from_utf8, from_utf8_mut, Bytes, CharIndices, Chars};
53 #[stable(feature = "rust1", since = "1.0.0")]
54 pub use core::str::{from_utf8_unchecked, from_utf8_unchecked_mut, ParseBoolError};
55 #[stable(feature = "str_escape", since = "1.34.0")]
56 pub use core::str::{EscapeDebug, EscapeDefault, EscapeUnicode};
57 #[stable(feature = "rust1", since = "1.0.0")]
58 pub use core::str::{FromStr, Utf8Error};
59 #[allow(deprecated)]
60 #[stable(feature = "rust1", since = "1.0.0")]
61 pub use core::str::{Lines, LinesAny};
62 #[stable(feature = "rust1", since = "1.0.0")]
63 pub use core::str::{MatchIndices, RMatchIndices};
64 #[stable(feature = "rust1", since = "1.0.0")]
65 pub use core::str::{Matches, RMatches};
66 #[stable(feature = "rust1", since = "1.0.0")]
67 pub use core::str::{RSplit, Split};
68 #[stable(feature = "rust1", since = "1.0.0")]
69 pub use core::str::{RSplitN, SplitN};
70 #[stable(feature = "rust1", since = "1.0.0")]
71 pub use core::str::{RSplitTerminator, SplitTerminator};
72
73 /// Note: `str` in `Concat<str>` is not meaningful here.
74 /// This type parameter of the trait only exists to enable another impl.
75 #[unstable(feature = "slice_concat_ext", issue = "27747")]
76 impl<S: Borrow<str>> Concat<str> for [S] {
77 type Output = String;
78
79 fn concat(slice: &Self) -> String {
80 Join::join(slice, "")
81 }
82 }
83
84 #[unstable(feature = "slice_concat_ext", issue = "27747")]
85 impl<S: Borrow<str>> Join<&str> for [S] {
86 type Output = String;
87
88 fn join(slice: &Self, sep: &str) -> String {
89 unsafe { String::from_utf8_unchecked(join_generic_copy(slice, sep.as_bytes())) }
90 }
91 }
92
93 macro_rules! spezialize_for_lengths {
94 ($separator:expr, $target:expr, $iter:expr; $($num:expr),*) => {
95 let mut target = $target;
96 let iter = $iter;
97 let sep_bytes = $separator;
98 match $separator.len() {
99 $(
100 // loops with hardcoded sizes run much faster
101 // specialize the cases with small separator lengths
102 $num => {
103 for s in iter {
104 copy_slice_and_advance!(target, sep_bytes);
105 copy_slice_and_advance!(target, s.borrow().as_ref());
106 }
107 },
108 )*
109 _ => {
110 // arbitrary non-zero size fallback
111 for s in iter {
112 copy_slice_and_advance!(target, sep_bytes);
113 copy_slice_and_advance!(target, s.borrow().as_ref());
114 }
115 }
116 }
117 };
118 }
119
120 macro_rules! copy_slice_and_advance {
121 ($target:expr, $bytes:expr) => {
122 let len = $bytes.len();
123 let (head, tail) = { $target }.split_at_mut(len);
124 head.copy_from_slice($bytes);
125 $target = tail;
126 };
127 }
128
129 // Optimized join implementation that works for both Vec<T> (T: Copy) and String's inner vec
130 // Currently (2018-05-13) there is a bug with type inference and specialization (see issue #36262)
131 // For this reason SliceConcat<T> is not specialized for T: Copy and SliceConcat<str> is the
132 // only user of this function. It is left in place for the time when that is fixed.
133 //
134 // the bounds for String-join are S: Borrow<str> and for Vec-join Borrow<[T]>
135 // [T] and str both impl AsRef<[T]> for some T
136 // => s.borrow().as_ref() and we always have slices
137 fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
138 where
139 T: Copy,
140 B: AsRef<[T]> + ?Sized,
141 S: Borrow<B>,
142 {
143 let sep_len = sep.len();
144 let mut iter = slice.iter();
145
146 // the first slice is the only one without a separator preceding it
147 let first = match iter.next() {
148 Some(first) => first,
149 None => return vec![],
150 };
151
152 // compute the exact total length of the joined Vec
153 // if the `len` calculation overflows, we'll panic
154 // we would have run out of memory anyway and the rest of the function requires
155 // the entire Vec pre-allocated for safety
156 let len = sep_len
157 .checked_mul(iter.len())
158 .and_then(|n| {
159 slice.iter().map(|s| s.borrow().as_ref().len()).try_fold(n, usize::checked_add)
160 })
161 .expect("attempt to join into collection with len > usize::MAX");
162
163 // crucial for safety
164 let mut result = Vec::with_capacity(len);
165 assert!(result.capacity() >= len);
166
167 result.extend_from_slice(first.borrow().as_ref());
168
169 unsafe {
170 {
171 let pos = result.len();
172 let target = result.get_unchecked_mut(pos..len);
173
174 // copy separator and slices over without bounds checks
175 // generate loops with hardcoded offsets for small separators
176 // massive improvements possible (~ x2)
177 spezialize_for_lengths!(sep, target, iter; 0, 1, 2, 3, 4);
178 }
179 result.set_len(len);
180 }
181 result
182 }
183
184 #[stable(feature = "rust1", since = "1.0.0")]
185 impl Borrow<str> for String {
186 #[inline]
187 fn borrow(&self) -> &str {
188 &self[..]
189 }
190 }
191
192 #[stable(feature = "string_borrow_mut", since = "1.36.0")]
193 impl BorrowMut<str> for String {
194 #[inline]
195 fn borrow_mut(&mut self) -> &mut str {
196 &mut self[..]
197 }
198 }
199
200 #[stable(feature = "rust1", since = "1.0.0")]
201 impl ToOwned for str {
202 type Owned = String;
203 #[inline]
204 fn to_owned(&self) -> String {
205 unsafe { String::from_utf8_unchecked(self.as_bytes().to_owned()) }
206 }
207
208 fn clone_into(&self, target: &mut String) {
209 let mut b = mem::take(target).into_bytes();
210 self.as_bytes().clone_into(&mut b);
211 *target = unsafe { String::from_utf8_unchecked(b) }
212 }
213 }
214
215 /// Methods for string slices.
216 #[lang = "str_alloc"]
217 #[cfg(not(test))]
218 impl str {
219 /// Converts a `Box<str>` into a `Box<[u8]>` without copying or allocating.
220 ///
221 /// # Examples
222 ///
223 /// Basic usage:
224 ///
225 /// ```
226 /// let s = "this is a string";
227 /// let boxed_str = s.to_owned().into_boxed_str();
228 /// let boxed_bytes = boxed_str.into_boxed_bytes();
229 /// assert_eq!(*boxed_bytes, *s.as_bytes());
230 /// ```
231 #[stable(feature = "str_box_extras", since = "1.20.0")]
232 #[inline]
233 pub fn into_boxed_bytes(self: Box<str>) -> Box<[u8]> {
234 self.into()
235 }
236
237 /// Replaces all matches of a pattern with another string.
238 ///
239 /// `replace` creates a new [`String`], and copies the data from this string slice into it.
240 /// While doing so, it attempts to find matches of a pattern. If it finds any, it
241 /// replaces them with the replacement string slice.
242 ///
243 /// [`String`]: string/struct.String.html
244 ///
245 /// # Examples
246 ///
247 /// Basic usage:
248 ///
249 /// ```
250 /// let s = "this is old";
251 ///
252 /// assert_eq!("this is new", s.replace("old", "new"));
253 /// ```
254 ///
255 /// When the pattern doesn't match:
256 ///
257 /// ```
258 /// let s = "this is old";
259 /// assert_eq!(s, s.replace("cookie monster", "little lamb"));
260 /// ```
261 #[must_use = "this returns the replaced string as a new allocation, \
262 without modifying the original"]
263 #[stable(feature = "rust1", since = "1.0.0")]
264 #[inline]
265 pub fn replace<'a, P: Pattern<'a>>(&'a self, from: P, to: &str) -> String {
266 let mut result = String::new();
267 let mut last_end = 0;
268 for (start, part) in self.match_indices(from) {
269 result.push_str(unsafe { self.get_unchecked(last_end..start) });
270 result.push_str(to);
271 last_end = start + part.len();
272 }
273 result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
274 result
275 }
276
277 /// Replaces first N matches of a pattern with another string.
278 ///
279 /// `replacen` creates a new [`String`], and copies the data from this string slice into it.
280 /// While doing so, it attempts to find matches of a pattern. If it finds any, it
281 /// replaces them with the replacement string slice at most `count` times.
282 ///
283 /// [`String`]: string/struct.String.html
284 ///
285 /// # Examples
286 ///
287 /// Basic usage:
288 ///
289 /// ```
290 /// let s = "foo foo 123 foo";
291 /// assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
292 /// assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
293 /// assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));
294 /// ```
295 ///
296 /// When the pattern doesn't match:
297 ///
298 /// ```
299 /// let s = "this is old";
300 /// assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));
301 /// ```
302 #[must_use = "this returns the replaced string as a new allocation, \
303 without modifying the original"]
304 #[stable(feature = "str_replacen", since = "1.16.0")]
305 pub fn replacen<'a, P: Pattern<'a>>(&'a self, pat: P, to: &str, count: usize) -> String {
306 // Hope to reduce the times of re-allocation
307 let mut result = String::with_capacity(32);
308 let mut last_end = 0;
309 for (start, part) in self.match_indices(pat).take(count) {
310 result.push_str(unsafe { self.get_unchecked(last_end..start) });
311 result.push_str(to);
312 last_end = start + part.len();
313 }
314 result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
315 result
316 }
317
318 /// Returns the lowercase equivalent of this string slice, as a new [`String`].
319 ///
320 /// 'Lowercase' is defined according to the terms of the Unicode Derived Core Property
321 /// `Lowercase`.
322 ///
323 /// Since some characters can expand into multiple characters when changing
324 /// the case, this function returns a [`String`] instead of modifying the
325 /// parameter in-place.
326 ///
327 /// [`String`]: string/struct.String.html
328 ///
329 /// # Examples
330 ///
331 /// Basic usage:
332 ///
333 /// ```
334 /// let s = "HELLO";
335 ///
336 /// assert_eq!("hello", s.to_lowercase());
337 /// ```
338 ///
339 /// A tricky example, with sigma:
340 ///
341 /// ```
342 /// let sigma = "Σ";
343 ///
344 /// assert_eq!("σ", sigma.to_lowercase());
345 ///
346 /// // but at the end of a word, it's ς, not σ:
347 /// let odysseus = "ὈΔΥΣΣΕΎΣ";
348 ///
349 /// assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());
350 /// ```
351 ///
352 /// Languages without case are not changed:
353 ///
354 /// ```
355 /// let new_year = "农历新年";
356 ///
357 /// assert_eq!(new_year, new_year.to_lowercase());
358 /// ```
359 #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
360 pub fn to_lowercase(&self) -> String {
361 let mut s = String::with_capacity(self.len());
362 for (i, c) in self[..].char_indices() {
363 if c == 'Σ' {
364 // Σ maps to σ, except at the end of a word where it maps to ς.
365 // This is the only conditional (contextual) but language-independent mapping
366 // in `SpecialCasing.txt`,
367 // so hard-code it rather than have a generic "condition" mechanism.
368 // See https://github.com/rust-lang/rust/issues/26035
369 map_uppercase_sigma(self, i, &mut s)
370 } else {
371 match conversions::to_lower(c) {
372 [a, '\0', _] => s.push(a),
373 [a, b, '\0'] => {
374 s.push(a);
375 s.push(b);
376 }
377 [a, b, c] => {
378 s.push(a);
379 s.push(b);
380 s.push(c);
381 }
382 }
383 }
384 }
385 return s;
386
387 fn map_uppercase_sigma(from: &str, i: usize, to: &mut String) {
388 // See http://www.unicode.org/versions/Unicode7.0.0/ch03.pdf#G33992
389 // for the definition of `Final_Sigma`.
390 debug_assert!('Σ'.len_utf8() == 2);
391 let is_word_final = case_ignoreable_then_cased(from[..i].chars().rev())
392 && !case_ignoreable_then_cased(from[i + 2..].chars());
393 to.push_str(if is_word_final { "ς" } else { "σ" });
394 }
395
396 fn case_ignoreable_then_cased<I: Iterator<Item = char>>(iter: I) -> bool {
397 use core::unicode::derived_property::{Case_Ignorable, Cased};
398 match iter.skip_while(|&c| Case_Ignorable(c)).next() {
399 Some(c) => Cased(c),
400 None => false,
401 }
402 }
403 }
404
405 /// Returns the uppercase equivalent of this string slice, as a new [`String`].
406 ///
407 /// 'Uppercase' is defined according to the terms of the Unicode Derived Core Property
408 /// `Uppercase`.
409 ///
410 /// Since some characters can expand into multiple characters when changing
411 /// the case, this function returns a [`String`] instead of modifying the
412 /// parameter in-place.
413 ///
414 /// [`String`]: string/struct.String.html
415 ///
416 /// # Examples
417 ///
418 /// Basic usage:
419 ///
420 /// ```
421 /// let s = "hello";
422 ///
423 /// assert_eq!("HELLO", s.to_uppercase());
424 /// ```
425 ///
426 /// Scripts without case are not changed:
427 ///
428 /// ```
429 /// let new_year = "农历新年";
430 ///
431 /// assert_eq!(new_year, new_year.to_uppercase());
432 /// ```
433 ///
434 /// One character can become multiple:
435 /// ```
436 /// let s = "tschüß";
437 ///
438 /// assert_eq!("TSCHÜSS", s.to_uppercase());
439 /// ```
440 #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
441 pub fn to_uppercase(&self) -> String {
442 let mut s = String::with_capacity(self.len());
443 for c in self[..].chars() {
444 match conversions::to_upper(c) {
445 [a, '\0', _] => s.push(a),
446 [a, b, '\0'] => {
447 s.push(a);
448 s.push(b);
449 }
450 [a, b, c] => {
451 s.push(a);
452 s.push(b);
453 s.push(c);
454 }
455 }
456 }
457 s
458 }
459
460 /// Converts a [`Box<str>`] into a [`String`] without copying or allocating.
461 ///
462 /// [`String`]: string/struct.String.html
463 /// [`Box<str>`]: boxed/struct.Box.html
464 ///
465 /// # Examples
466 ///
467 /// Basic usage:
468 ///
469 /// ```
470 /// let string = String::from("birthday gift");
471 /// let boxed_str = string.clone().into_boxed_str();
472 ///
473 /// assert_eq!(boxed_str.into_string(), string);
474 /// ```
475 #[stable(feature = "box_str", since = "1.4.0")]
476 #[inline]
477 pub fn into_string(self: Box<str>) -> String {
478 let slice = Box::<[u8]>::from(self);
479 unsafe { String::from_utf8_unchecked(slice.into_vec()) }
480 }
481
482 /// Creates a new [`String`] by repeating a string `n` times.
483 ///
484 /// # Panics
485 ///
486 /// This function will panic if the capacity would overflow.
487 ///
488 /// [`String`]: string/struct.String.html
489 ///
490 /// # Examples
491 ///
492 /// Basic usage:
493 ///
494 /// ```
495 /// assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));
496 /// ```
497 ///
498 /// A panic upon overflow:
499 ///
500 /// ```should_panic
501 /// // this will panic at runtime
502 /// "0123456789abcdef".repeat(usize::MAX);
503 /// ```
504 #[stable(feature = "repeat_str", since = "1.16.0")]
505 pub fn repeat(&self, n: usize) -> String {
506 unsafe { String::from_utf8_unchecked(self.as_bytes().repeat(n)) }
507 }
508
509 /// Returns a copy of this string where each character is mapped to its
510 /// ASCII upper case equivalent.
511 ///
512 /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
513 /// but non-ASCII letters are unchanged.
514 ///
515 /// To uppercase the value in-place, use [`make_ascii_uppercase`].
516 ///
517 /// To uppercase ASCII characters in addition to non-ASCII characters, use
518 /// [`to_uppercase`].
519 ///
520 /// # Examples
521 ///
522 /// ```
523 /// let s = "Grüße, Jürgen ❤";
524 ///
525 /// assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());
526 /// ```
527 ///
528 /// [`make_ascii_uppercase`]: #method.make_ascii_uppercase
529 /// [`to_uppercase`]: #method.to_uppercase
530 #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
531 #[inline]
532 pub fn to_ascii_uppercase(&self) -> String {
533 let mut bytes = self.as_bytes().to_vec();
534 bytes.make_ascii_uppercase();
535 // make_ascii_uppercase() preserves the UTF-8 invariant.
536 unsafe { String::from_utf8_unchecked(bytes) }
537 }
538
539 /// Returns a copy of this string where each character is mapped to its
540 /// ASCII lower case equivalent.
541 ///
542 /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
543 /// but non-ASCII letters are unchanged.
544 ///
545 /// To lowercase the value in-place, use [`make_ascii_lowercase`].
546 ///
547 /// To lowercase ASCII characters in addition to non-ASCII characters, use
548 /// [`to_lowercase`].
549 ///
550 /// # Examples
551 ///
552 /// ```
553 /// let s = "Grüße, Jürgen ❤";
554 ///
555 /// assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());
556 /// ```
557 ///
558 /// [`make_ascii_lowercase`]: #method.make_ascii_lowercase
559 /// [`to_lowercase`]: #method.to_lowercase
560 #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
561 #[inline]
562 pub fn to_ascii_lowercase(&self) -> String {
563 let mut bytes = self.as_bytes().to_vec();
564 bytes.make_ascii_lowercase();
565 // make_ascii_lowercase() preserves the UTF-8 invariant.
566 unsafe { String::from_utf8_unchecked(bytes) }
567 }
568 }
569
570 /// Converts a boxed slice of bytes to a boxed string slice without checking
571 /// that the string contains valid UTF-8.
572 ///
573 /// # Examples
574 ///
575 /// Basic usage:
576 ///
577 /// ```
578 /// let smile_utf8 = Box::new([226, 152, 186]);
579 /// let smile = unsafe { std::str::from_boxed_utf8_unchecked(smile_utf8) };
580 ///
581 /// assert_eq!("☺", &*smile);
582 /// ```
583 #[stable(feature = "str_box_extras", since = "1.20.0")]
584 #[inline]
585 pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
586 unsafe { Box::from_raw(Box::into_raw(v) as *mut str) }
587 }