1 //! Unicode string slices.
3 //! *[See also the `str` primitive type](str).*
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.
10 //! A basic string declaration of `&str` type:
13 //! let hello_world = "Hello, World!";
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:
22 //! let hello_world: &'static str = "Hello, world!";
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)]
30 use core::borrow::{Borrow, BorrowMut};
31 use core::iter::FusedIterator;
34 use core::str::pattern::{DoubleEndedSearcher, Pattern, ReverseSearcher, Searcher};
35 use core::unicode::conversions;
37 use crate::borrow::ToOwned;
38 use crate::boxed::Box;
39 use crate::slice::{Concat, Join, SliceIndex};
40 use crate::string::String;
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 = "split_inclusive", since = "1.51.0")]
50 pub use core::str::SplitInclusive;
51 #[stable(feature = "rust1", since = "1.0.0")]
52 pub use core::str::SplitWhitespace;
53 #[stable(feature = "rust1", since = "1.0.0")]
54 pub use core::str::{from_utf8, from_utf8_mut, Bytes, CharIndices, Chars};
55 #[stable(feature = "rust1", since = "1.0.0")]
56 pub use core::str::{from_utf8_unchecked, from_utf8_unchecked_mut, ParseBoolError};
57 #[stable(feature = "str_escape", since = "1.34.0")]
58 pub use core::str::{EscapeDebug, EscapeDefault, EscapeUnicode};
59 #[stable(feature = "rust1", since = "1.0.0")]
60 pub use core::str::{FromStr, Utf8Error};
62 #[stable(feature = "rust1", since = "1.0.0")]
63 pub use core::str::{Lines, LinesAny};
64 #[stable(feature = "rust1", since = "1.0.0")]
65 pub use core::str::{MatchIndices, RMatchIndices};
66 #[stable(feature = "rust1", since = "1.0.0")]
67 pub use core::str::{Matches, RMatches};
68 #[stable(feature = "rust1", since = "1.0.0")]
69 pub use core::str::{RSplit, Split};
70 #[stable(feature = "rust1", since = "1.0.0")]
71 pub use core::str::{RSplitN, SplitN};
72 #[stable(feature = "rust1", since = "1.0.0")]
73 pub use core::str::{RSplitTerminator, SplitTerminator};
75 /// Note: `str` in `Concat<str>` is not meaningful here.
76 /// This type parameter of the trait only exists to enable another impl.
77 #[cfg(not(no_global_oom_handling))]
78 #[unstable(feature = "slice_concat_ext", issue = "27747")]
79 impl<S: Borrow<str>> Concat<str> for [S] {
82 fn concat(slice: &Self) -> String {
87 #[cfg(not(no_global_oom_handling))]
88 #[unstable(feature = "slice_concat_ext", issue = "27747")]
89 impl<S: Borrow<str>> Join<&str> for [S] {
92 fn join(slice: &Self, sep: &str) -> String {
93 unsafe { String::from_utf8_unchecked(join_generic_copy(slice, sep.as_bytes())) }
97 #[cfg(not(no_global_oom_handling))]
98 macro_rules! specialize_for_lengths {
99 ($separator:expr, $target:expr, $iter:expr; $($num:expr),*) => {{
100 let mut target = $target;
102 let sep_bytes = $separator;
103 match $separator.len() {
105 // loops with hardcoded sizes run much faster
106 // specialize the cases with small separator lengths
109 copy_slice_and_advance!(target, sep_bytes);
110 let content_bytes = s.borrow().as_ref();
111 copy_slice_and_advance!(target, content_bytes);
116 // arbitrary non-zero size fallback
118 copy_slice_and_advance!(target, sep_bytes);
119 let content_bytes = s.borrow().as_ref();
120 copy_slice_and_advance!(target, content_bytes);
128 #[cfg(not(no_global_oom_handling))]
129 macro_rules! copy_slice_and_advance {
130 ($target:expr, $bytes:expr) => {
131 let len = $bytes.len();
132 let (head, tail) = { $target }.split_at_mut(len);
133 head.copy_from_slice($bytes);
138 // Optimized join implementation that works for both Vec<T> (T: Copy) and String's inner vec
139 // Currently (2018-05-13) there is a bug with type inference and specialization (see issue #36262)
140 // For this reason SliceConcat<T> is not specialized for T: Copy and SliceConcat<str> is the
141 // only user of this function. It is left in place for the time when that is fixed.
143 // the bounds for String-join are S: Borrow<str> and for Vec-join Borrow<[T]>
144 // [T] and str both impl AsRef<[T]> for some T
145 // => s.borrow().as_ref() and we always have slices
146 #[cfg(not(no_global_oom_handling))]
147 fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
150 B: AsRef<[T]> + ?Sized,
153 let sep_len = sep.len();
154 let mut iter = slice.iter();
156 // the first slice is the only one without a separator preceding it
157 let first = match iter.next() {
158 Some(first) => first,
159 None => return vec![],
162 // compute the exact total length of the joined Vec
163 // if the `len` calculation overflows, we'll panic
164 // we would have run out of memory anyway and the rest of the function requires
165 // the entire Vec pre-allocated for safety
166 let reserved_len = sep_len
167 .checked_mul(iter.len())
169 slice.iter().map(|s| s.borrow().as_ref().len()).try_fold(n, usize::checked_add)
171 .expect("attempt to join into collection with len > usize::MAX");
173 // prepare an uninitialized buffer
174 let mut result = Vec::with_capacity(reserved_len);
175 debug_assert!(result.capacity() >= reserved_len);
177 result.extend_from_slice(first.borrow().as_ref());
180 let pos = result.len();
181 let target = result.spare_capacity_mut().get_unchecked_mut(..reserved_len - pos);
183 // Convert the separator and slices to slices of MaybeUninit
184 // to simplify implementation in specialize_for_lengths
185 let sep_uninit = core::slice::from_raw_parts(sep.as_ptr().cast(), sep.len());
186 let iter_uninit = iter.map(|it| {
187 let it = it.borrow().as_ref();
188 core::slice::from_raw_parts(it.as_ptr().cast(), it.len())
191 // copy separator and slices over without bounds checks
192 // generate loops with hardcoded offsets for small separators
193 // massive improvements possible (~ x2)
194 let remain = specialize_for_lengths!(sep_uninit, target, iter_uninit; 0, 1, 2, 3, 4);
196 // A weird borrow implementation may return different
197 // slices for the length calculation and the actual copy.
198 // Make sure we don't expose uninitialized bytes to the caller.
199 let result_len = reserved_len - remain.len();
200 result.set_len(result_len);
205 #[stable(feature = "rust1", since = "1.0.0")]
206 impl Borrow<str> for String {
208 fn borrow(&self) -> &str {
213 #[stable(feature = "string_borrow_mut", since = "1.36.0")]
214 impl BorrowMut<str> for String {
216 fn borrow_mut(&mut self) -> &mut str {
221 #[cfg(not(no_global_oom_handling))]
222 #[stable(feature = "rust1", since = "1.0.0")]
223 impl ToOwned for str {
226 fn to_owned(&self) -> String {
227 unsafe { String::from_utf8_unchecked(self.as_bytes().to_owned()) }
230 fn clone_into(&self, target: &mut String) {
231 let mut b = mem::take(target).into_bytes();
232 self.as_bytes().clone_into(&mut b);
233 *target = unsafe { String::from_utf8_unchecked(b) }
237 /// Methods for string slices.
238 #[lang = "str_alloc"]
241 /// Converts a `Box<str>` into a `Box<[u8]>` without copying or allocating.
248 /// let s = "this is a string";
249 /// let boxed_str = s.to_owned().into_boxed_str();
250 /// let boxed_bytes = boxed_str.into_boxed_bytes();
251 /// assert_eq!(*boxed_bytes, *s.as_bytes());
253 #[stable(feature = "str_box_extras", since = "1.20.0")]
254 #[must_use = "`self` will be dropped if the result is not used"]
256 pub fn into_boxed_bytes(self: Box<str>) -> Box<[u8]> {
260 /// Replaces all matches of a pattern with another string.
262 /// `replace` creates a new [`String`], and copies the data from this string slice into it.
263 /// While doing so, it attempts to find matches of a pattern. If it finds any, it
264 /// replaces them with the replacement string slice.
271 /// let s = "this is old";
273 /// assert_eq!("this is new", s.replace("old", "new"));
276 /// When the pattern doesn't match:
279 /// let s = "this is old";
280 /// assert_eq!(s, s.replace("cookie monster", "little lamb"));
282 #[cfg(not(no_global_oom_handling))]
283 #[must_use = "this returns the replaced string as a new allocation, \
284 without modifying the original"]
285 #[stable(feature = "rust1", since = "1.0.0")]
287 pub fn replace<'a, P: Pattern<'a>>(&'a self, from: P, to: &str) -> String {
288 let mut result = String::new();
289 let mut last_end = 0;
290 for (start, part) in self.match_indices(from) {
291 result.push_str(unsafe { self.get_unchecked(last_end..start) });
293 last_end = start + part.len();
295 result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
299 /// Replaces first N matches of a pattern with another string.
301 /// `replacen` creates a new [`String`], and copies the data from this string slice into it.
302 /// While doing so, it attempts to find matches of a pattern. If it finds any, it
303 /// replaces them with the replacement string slice at most `count` times.
310 /// let s = "foo foo 123 foo";
311 /// assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
312 /// assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
313 /// assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));
316 /// When the pattern doesn't match:
319 /// let s = "this is old";
320 /// assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));
322 #[cfg(not(no_global_oom_handling))]
323 #[must_use = "this returns the replaced string as a new allocation, \
324 without modifying the original"]
325 #[stable(feature = "str_replacen", since = "1.16.0")]
326 pub fn replacen<'a, P: Pattern<'a>>(&'a self, pat: P, to: &str, count: usize) -> String {
327 // Hope to reduce the times of re-allocation
328 let mut result = String::with_capacity(32);
329 let mut last_end = 0;
330 for (start, part) in self.match_indices(pat).take(count) {
331 result.push_str(unsafe { self.get_unchecked(last_end..start) });
333 last_end = start + part.len();
335 result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
339 /// Returns the lowercase equivalent of this string slice, as a new [`String`].
341 /// 'Lowercase' is defined according to the terms of the Unicode Derived Core Property
344 /// Since some characters can expand into multiple characters when changing
345 /// the case, this function returns a [`String`] instead of modifying the
346 /// parameter in-place.
355 /// assert_eq!("hello", s.to_lowercase());
358 /// A tricky example, with sigma:
363 /// assert_eq!("σ", sigma.to_lowercase());
365 /// // but at the end of a word, it's ς, not σ:
366 /// let odysseus = "ὈΔΥΣΣΕΎΣ";
368 /// assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());
371 /// Languages without case are not changed:
374 /// let new_year = "农历新年";
376 /// assert_eq!(new_year, new_year.to_lowercase());
378 #[cfg(not(no_global_oom_handling))]
379 #[must_use = "this returns the lowercase string as a new String, \
380 without modifying the original"]
381 #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
382 pub fn to_lowercase(&self) -> String {
383 let mut s = String::with_capacity(self.len());
384 for (i, c) in self[..].char_indices() {
386 // Σ maps to σ, except at the end of a word where it maps to ς.
387 // This is the only conditional (contextual) but language-independent mapping
388 // in `SpecialCasing.txt`,
389 // so hard-code it rather than have a generic "condition" mechanism.
390 // See https://github.com/rust-lang/rust/issues/26035
391 map_uppercase_sigma(self, i, &mut s)
393 match conversions::to_lower(c) {
394 [a, '\0', _] => s.push(a),
409 fn map_uppercase_sigma(from: &str, i: usize, to: &mut String) {
410 // See https://www.unicode.org/versions/Unicode7.0.0/ch03.pdf#G33992
411 // for the definition of `Final_Sigma`.
412 debug_assert!('Σ'.len_utf8() == 2);
413 let is_word_final = case_ignoreable_then_cased(from[..i].chars().rev())
414 && !case_ignoreable_then_cased(from[i + 2..].chars());
415 to.push_str(if is_word_final { "ς" } else { "σ" });
418 fn case_ignoreable_then_cased<I: Iterator<Item = char>>(iter: I) -> bool {
419 use core::unicode::{Case_Ignorable, Cased};
420 match iter.skip_while(|&c| Case_Ignorable(c)).next() {
427 /// Returns the uppercase equivalent of this string slice, as a new [`String`].
429 /// 'Uppercase' is defined according to the terms of the Unicode Derived Core Property
432 /// Since some characters can expand into multiple characters when changing
433 /// the case, this function returns a [`String`] instead of modifying the
434 /// parameter in-place.
443 /// assert_eq!("HELLO", s.to_uppercase());
446 /// Scripts without case are not changed:
449 /// let new_year = "农历新年";
451 /// assert_eq!(new_year, new_year.to_uppercase());
454 /// One character can become multiple:
456 /// let s = "tschüß";
458 /// assert_eq!("TSCHÜSS", s.to_uppercase());
460 #[cfg(not(no_global_oom_handling))]
461 #[must_use = "this returns the uppercase string as a new String, \
462 without modifying the original"]
463 #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
464 pub fn to_uppercase(&self) -> String {
465 let mut s = String::with_capacity(self.len());
466 for c in self[..].chars() {
467 match conversions::to_upper(c) {
468 [a, '\0', _] => s.push(a),
483 /// Converts a [`Box<str>`] into a [`String`] without copying or allocating.
490 /// let string = String::from("birthday gift");
491 /// let boxed_str = string.clone().into_boxed_str();
493 /// assert_eq!(boxed_str.into_string(), string);
495 #[stable(feature = "box_str", since = "1.4.0")]
496 #[must_use = "`self` will be dropped if the result is not used"]
498 pub fn into_string(self: Box<str>) -> String {
499 let slice = Box::<[u8]>::from(self);
500 unsafe { String::from_utf8_unchecked(slice.into_vec()) }
503 /// Creates a new [`String`] by repeating a string `n` times.
507 /// This function will panic if the capacity would overflow.
514 /// assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));
517 /// A panic upon overflow:
520 /// // this will panic at runtime
521 /// let huge = "0123456789abcdef".repeat(usize::MAX);
523 #[cfg(not(no_global_oom_handling))]
525 #[stable(feature = "repeat_str", since = "1.16.0")]
526 pub fn repeat(&self, n: usize) -> String {
527 unsafe { String::from_utf8_unchecked(self.as_bytes().repeat(n)) }
530 /// Returns a copy of this string where each character is mapped to its
531 /// ASCII upper case equivalent.
533 /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
534 /// but non-ASCII letters are unchanged.
536 /// To uppercase the value in-place, use [`make_ascii_uppercase`].
538 /// To uppercase ASCII characters in addition to non-ASCII characters, use
539 /// [`to_uppercase`].
544 /// let s = "Grüße, Jürgen ❤";
546 /// assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());
549 /// [`make_ascii_uppercase`]: str::make_ascii_uppercase
550 /// [`to_uppercase`]: #method.to_uppercase
551 #[cfg(not(no_global_oom_handling))]
552 #[must_use = "to uppercase the value in-place, use `make_ascii_uppercase()`"]
553 #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
555 pub fn to_ascii_uppercase(&self) -> String {
556 let mut bytes = self.as_bytes().to_vec();
557 bytes.make_ascii_uppercase();
558 // make_ascii_uppercase() preserves the UTF-8 invariant.
559 unsafe { String::from_utf8_unchecked(bytes) }
562 /// Returns a copy of this string where each character is mapped to its
563 /// ASCII lower case equivalent.
565 /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
566 /// but non-ASCII letters are unchanged.
568 /// To lowercase the value in-place, use [`make_ascii_lowercase`].
570 /// To lowercase ASCII characters in addition to non-ASCII characters, use
571 /// [`to_lowercase`].
576 /// let s = "Grüße, Jürgen ❤";
578 /// assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());
581 /// [`make_ascii_lowercase`]: str::make_ascii_lowercase
582 /// [`to_lowercase`]: #method.to_lowercase
583 #[cfg(not(no_global_oom_handling))]
584 #[must_use = "to lowercase the value in-place, use `make_ascii_lowercase()`"]
585 #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
587 pub fn to_ascii_lowercase(&self) -> String {
588 let mut bytes = self.as_bytes().to_vec();
589 bytes.make_ascii_lowercase();
590 // make_ascii_lowercase() preserves the UTF-8 invariant.
591 unsafe { String::from_utf8_unchecked(bytes) }
595 /// Converts a boxed slice of bytes to a boxed string slice without checking
596 /// that the string contains valid UTF-8.
603 /// let smile_utf8 = Box::new([226, 152, 186]);
604 /// let smile = unsafe { std::str::from_boxed_utf8_unchecked(smile_utf8) };
606 /// assert_eq!("☺", &*smile);
608 #[stable(feature = "str_box_extras", since = "1.20.0")]
611 pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
612 unsafe { Box::from_raw(Box::into_raw(v) as *mut str) }