1//! A UTF-8–encoded, growable string.
2//!
3//! This module contains the [`String`] type, the [`ToString`] trait for
4//! converting to strings, and several error types that may result from
5//! working with [`String`]s.
6//!
7//! # Examples
8//!
9//! There are multiple ways to create a new [`String`] from a string literal:
10//!
11//! ```
12//! let s = "Hello".to_string();
13//!
14//! let s = String::from("world");
15//! let s: String = "also this".into();
16//! ```
17//!
18//! You can create a new [`String`] from an existing one by concatenating with
19//! `+`:
20//!
21//! ```
22//! let s = "Hello".to_string();
23//!
24//! let message = s + " world!";
25//! ```
26//!
27//! If you have a vector of valid UTF-8 bytes, you can make a [`String`] out of
28//! it. You can do the reverse too.
29//!
30//! ```
31//! let sparkle_heart = vec![240, 159, 146, 150];
32//!
33//! // We know these bytes are valid, so we'll use `unwrap()`.
34//! let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
35//!
36//! assert_eq!("πŸ’–", sparkle_heart);
37//!
38//! let bytes = sparkle_heart.into_bytes();
39//!
40//! assert_eq!(bytes, [240, 159, 146, 150]);
41//! ```
42
43#![stable(feature = "rust1", since = "1.0.0")]
44
45use core::error::Error;
46use core::fmt;
47use core::hash;
48#[cfg(not(no_global_oom_handling))]
49use core::iter::from_fn;
50use core::iter::FusedIterator;
51#[cfg(not(no_global_oom_handling))]
52use core::ops::Add;
53#[cfg(not(no_global_oom_handling))]
54use core::ops::AddAssign;
55#[cfg(not(no_global_oom_handling))]
56use core::ops::Bound::{Excluded, Included, Unbounded};
57use core::ops::{self, Index, IndexMut, Range, RangeBounds};
58use core::ptr;
59use core::slice;
60use core::str::pattern::Pattern;
61#[cfg(not(no_global_oom_handling))]
62use core::str::Utf8Chunks;
63
64#[cfg(not(no_global_oom_handling))]
65use crate::borrow::{Cow, ToOwned};
66use crate::boxed::Box;
67use crate::collections::TryReserveError;
68use crate::str::{self, from_utf8_unchecked_mut, Chars, Utf8Error};
69#[cfg(not(no_global_oom_handling))]
70use crate::str::{from_boxed_utf8_unchecked, FromStr};
71use crate::vec::Vec;
72
73/// A UTF-8–encoded, growable string.
74///
75/// The `String` type is the most common string type that has ownership over the
76/// contents of the string. It has a close relationship with its borrowed
77/// counterpart, the primitive [`str`].
78///
79/// # Examples
80///
81/// You can create a `String` from [a literal string][`&str`] with [`String::from`]:
82///
83/// [`String::from`]: From::from
84///
85/// ```
86/// let hello = String::from("Hello, world!");
87/// ```
88///
89/// You can append a [`char`] to a `String` with the [`push`] method, and
90/// append a [`&str`] with the [`push_str`] method:
91///
92/// ```
93/// let mut hello = String::from("Hello, ");
94///
95/// hello.push('w');
96/// hello.push_str("orld!");
97/// ```
98///
99/// [`push`]: String::push
100/// [`push_str`]: String::push_str
101///
102/// If you have a vector of UTF-8 bytes, you can create a `String` from it with
103/// the [`from_utf8`] method:
104///
105/// ```
106/// // some bytes, in a vector
107/// let sparkle_heart = vec![240, 159, 146, 150];
108///
109/// // We know these bytes are valid, so we'll use `unwrap()`.
110/// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
111///
112/// assert_eq!("πŸ’–", sparkle_heart);
113/// ```
114///
115/// [`from_utf8`]: String::from_utf8
116///
117/// # UTF-8
118///
119/// `String`s are always valid UTF-8. If you need a non-UTF-8 string, consider
120/// [`OsString`]. It is similar, but without the UTF-8 constraint. Because UTF-8
121/// is a variable width encoding, `String`s are typically smaller than an array of
122/// the same `chars`:
123///
124/// ```
125/// use std::mem;
126///
127/// // `s` is ASCII which represents each `char` as one byte
128/// let s = "hello";
129/// assert_eq!(s.len(), 5);
130///
131/// // A `char` array with the same contents would be longer because
132/// // every `char` is four bytes
133/// let s = ['h', 'e', 'l', 'l', 'o'];
134/// let size: usize = s.into_iter().map(|c| mem::size_of_val(&c)).sum();
135/// assert_eq!(size, 20);
136///
137/// // However, for non-ASCII strings, the difference will be smaller
138/// // and sometimes they are the same
139/// let s = "πŸ’–πŸ’–πŸ’–πŸ’–πŸ’–";
140/// assert_eq!(s.len(), 20);
141///
142/// let s = ['πŸ’–', 'πŸ’–', 'πŸ’–', 'πŸ’–', 'πŸ’–'];
143/// let size: usize = s.into_iter().map(|c| mem::size_of_val(&c)).sum();
144/// assert_eq!(size, 20);
145/// ```
146///
147/// This raises interesting questions as to how `s[i]` should work.
148/// What should `i` be here? Several options include byte indices and
149/// `char` indices but, because of UTF-8 encoding, only byte indices
150/// would provide constant time indexing. Getting the `i`th `char`, for
151/// example, is available using [`chars`]:
152///
153/// ```
154/// let s = "hello";
155/// let third_character = s.chars().nth(2);
156/// assert_eq!(third_character, Some('l'));
157///
158/// let s = "πŸ’–πŸ’–πŸ’–πŸ’–πŸ’–";
159/// let third_character = s.chars().nth(2);
160/// assert_eq!(third_character, Some('πŸ’–'));
161/// ```
162///
163/// Next, what should `s[i]` return? Because indexing returns a reference
164/// to underlying data it could be `&u8`, `&[u8]`, or something else similar.
165/// Since we're only providing one index, `&u8` makes the most sense but that
166/// might not be what the user expects and can be explicitly achieved with
167/// [`as_bytes()`]:
168///
169/// ```
170/// // The first byte is 104 - the byte value of `'h'`
171/// let s = "hello";
172/// assert_eq!(s.as_bytes()[0], 104);
173/// // or
174/// assert_eq!(s.as_bytes()[0], b'h');
175///
176/// // The first byte is 240 which isn't obviously useful
177/// let s = "πŸ’–πŸ’–πŸ’–πŸ’–πŸ’–";
178/// assert_eq!(s.as_bytes()[0], 240);
179/// ```
180///
181/// Due to these ambiguities/restrictions, indexing with a `usize` is simply
182/// forbidden:
183///
184/// ```compile_fail,E0277
185/// let s = "hello";
186///
187/// // The following will not compile!
188/// println!("The first letter of s is {}", s[0]);
189/// ```
190///
191/// It is more clear, however, how `&s[i..j]` should work (that is,
192/// indexing with a range). It should accept byte indices (to be constant-time)
193/// and return a `&str` which is UTF-8 encoded. This is also called "string slicing".
194/// Note this will panic if the byte indices provided are not character
195/// boundaries - see [`is_char_boundary`] for more details. See the implementations
196/// for [`SliceIndex<str>`] for more details on string slicing. For a non-panicking
197/// version of string slicing, see [`get`].
198///
199/// [`OsString`]: ../../std/ffi/struct.OsString.html "ffi::OsString"
200/// [`SliceIndex<str>`]: core::slice::SliceIndex
201/// [`as_bytes()`]: str::as_bytes
202/// [`get`]: str::get
203/// [`is_char_boundary`]: str::is_char_boundary
204///
205/// The [`bytes`] and [`chars`] methods return iterators over the bytes and
206/// codepoints of the string, respectively. To iterate over codepoints along
207/// with byte indices, use [`char_indices`].
208///
209/// [`bytes`]: str::bytes
210/// [`chars`]: str::chars
211/// [`char_indices`]: str::char_indices
212///
213/// # Deref
214///
215/// `String` implements <code>[Deref]<Target = [str]></code>, and so inherits all of [`str`]'s
216/// methods. In addition, this means that you can pass a `String` to a
217/// function which takes a [`&str`] by using an ampersand (`&`):
218///
219/// ```
220/// fn takes_str(s: &str) { }
221///
222/// let s = String::from("Hello");
223///
224/// takes_str(&s);
225/// ```
226///
227/// This will create a [`&str`] from the `String` and pass it in. This
228/// conversion is very inexpensive, and so generally, functions will accept
229/// [`&str`]s as arguments unless they need a `String` for some specific
230/// reason.
231///
232/// In certain cases Rust doesn't have enough information to make this
233/// conversion, known as [`Deref`] coercion. In the following example a string
234/// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
235/// `example_func` takes anything that implements the trait. In this case Rust
236/// would need to make two implicit conversions, which Rust doesn't have the
237/// means to do. For that reason, the following example will not compile.
238///
239/// ```compile_fail,E0277
240/// trait TraitExample {}
241///
242/// impl<'a> TraitExample for &'a str {}
243///
244/// fn example_func<A: TraitExample>(example_arg: A) {}
245///
246/// let example_string = String::from("example_string");
247/// example_func(&example_string);
248/// ```
249///
250/// There are two options that would work instead. The first would be to
251/// change the line `example_func(&example_string);` to
252/// `example_func(example_string.as_str());`, using the method [`as_str()`]
253/// to explicitly extract the string slice containing the string. The second
254/// way changes `example_func(&example_string);` to
255/// `example_func(&*example_string);`. In this case we are dereferencing a
256/// `String` to a [`str`], then referencing the [`str`] back to
257/// [`&str`]. The second way is more idiomatic, however both work to do the
258/// conversion explicitly rather than relying on the implicit conversion.
259///
260/// # Representation
261///
262/// A `String` is made up of three components: a pointer to some bytes, a
263/// length, and a capacity. The pointer points to an internal buffer `String`
264/// uses to store its data. The length is the number of bytes currently stored
265/// in the buffer, and the capacity is the size of the buffer in bytes. As such,
266/// the length will always be less than or equal to the capacity.
267///
268/// This buffer is always stored on the heap.
269///
270/// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
271/// methods:
272///
273/// ```
274/// use std::mem;
275///
276/// let story = String::from("Once upon a time...");
277///
278// FIXME Update this when vec_into_raw_parts is stabilized
279/// // Prevent automatically dropping the String's data
280/// let mut story = mem::ManuallyDrop::new(story);
281///
282/// let ptr = story.as_mut_ptr();
283/// let len = story.len();
284/// let capacity = story.capacity();
285///
286/// // story has nineteen bytes
287/// assert_eq!(19, len);
288///
289/// // We can re-build a String out of ptr, len, and capacity. This is all
290/// // unsafe because we are responsible for making sure the components are
291/// // valid:
292/// let s = unsafe { String::from_raw_parts(ptr, len, capacity) } ;
293///
294/// assert_eq!(String::from("Once upon a time..."), s);
295/// ```
296///
297/// [`as_ptr`]: str::as_ptr
298/// [`len`]: String::len
299/// [`capacity`]: String::capacity
300///
301/// If a `String` has enough capacity, adding elements to it will not
302/// re-allocate. For example, consider this program:
303///
304/// ```
305/// let mut s = String::new();
306///
307/// println!("{}", s.capacity());
308///
309/// for _ in 0..5 {
310/// s.push_str("hello");
311/// println!("{}", s.capacity());
312/// }
313/// ```
314///
315/// This will output the following:
316///
317/// ```text
318/// 0
319/// 8
320/// 16
321/// 16
322/// 32
323/// 32
324/// ```
325///
326/// At first, we have no memory allocated at all, but as we append to the
327/// string, it increases its capacity appropriately. If we instead use the
328/// [`with_capacity`] method to allocate the correct capacity initially:
329///
330/// ```
331/// let mut s = String::with_capacity(25);
332///
333/// println!("{}", s.capacity());
334///
335/// for _ in 0..5 {
336/// s.push_str("hello");
337/// println!("{}", s.capacity());
338/// }
339/// ```
340///
341/// [`with_capacity`]: String::with_capacity
342///
343/// We end up with a different output:
344///
345/// ```text
346/// 25
347/// 25
348/// 25
349/// 25
350/// 25
351/// 25
352/// ```
353///
354/// Here, there's no need to allocate more memory inside the loop.
355///
356/// [str]: prim@str "str"
357/// [`str`]: prim@str "str"
358/// [`&str`]: prim@str "&str"
359/// [Deref]: core::ops::Deref "ops::Deref"
360/// [`Deref`]: core::ops::Deref "ops::Deref"
361/// [`as_str()`]: String::as_str
362#[derive(PartialEq, PartialOrd, Eq, Ord)]
363#[stable(feature = "rust1", since = "1.0.0")]
364#[cfg_attr(not(test), lang = "String")]
365pub struct String {
366 vec: Vec<u8>,
367}
368
369/// A possible error value when converting a `String` from a UTF-8 byte vector.
370///
371/// This type is the error type for the [`from_utf8`] method on [`String`]. It
372/// is designed in such a way to carefully avoid reallocations: the
373/// [`into_bytes`] method will give back the byte vector that was used in the
374/// conversion attempt.
375///
376/// [`from_utf8`]: String::from_utf8
377/// [`into_bytes`]: FromUtf8Error::into_bytes
378///
379/// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
380/// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
381/// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
382/// through the [`utf8_error`] method.
383///
384/// [`Utf8Error`]: str::Utf8Error "std::str::Utf8Error"
385/// [`std::str`]: core::str "std::str"
386/// [`&str`]: prim@str "&str"
387/// [`utf8_error`]: FromUtf8Error::utf8_error
388///
389/// # Examples
390///
391/// ```
392/// // some invalid bytes, in a vector
393/// let bytes = vec![0, 159];
394///
395/// let value = String::from_utf8(bytes);
396///
397/// assert!(value.is_err());
398/// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
399/// ```
400#[stable(feature = "rust1", since = "1.0.0")]
401#[cfg_attr(not(no_global_oom_handling), derive(Clone))]
402#[derive(Debug, PartialEq, Eq)]
403pub struct FromUtf8Error {
404 bytes: Vec<u8>,
405 error: Utf8Error,
406}
407
408/// A possible error value when converting a `String` from a UTF-16 byte slice.
409///
410/// This type is the error type for the [`from_utf16`] method on [`String`].
411///
412/// [`from_utf16`]: String::from_utf16
413///
414/// # Examples
415///
416/// ```
417/// // π„žmu<invalid>ic
418/// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
419/// 0xD800, 0x0069, 0x0063];
420///
421/// assert!(String::from_utf16(v).is_err());
422/// ```
423#[stable(feature = "rust1", since = "1.0.0")]
424#[derive(Debug)]
425pub struct FromUtf16Error(());
426
427impl String {
428 /// Creates a new empty `String`.
429 ///
430 /// Given that the `String` is empty, this will not allocate any initial
431 /// buffer. While that means that this initial operation is very
432 /// inexpensive, it may cause excessive allocation later when you add
433 /// data. If you have an idea of how much data the `String` will hold,
434 /// consider the [`with_capacity`] method to prevent excessive
435 /// re-allocation.
436 ///
437 /// [`with_capacity`]: String::with_capacity
438 ///
439 /// # Examples
440 ///
441 /// ```
442 /// let s = String::new();
443 /// ```
444 #[inline]
445 #[rustc_const_stable(feature = "const_string_new", since = "1.39.0")]
446 #[stable(feature = "rust1", since = "1.0.0")]
447 #[must_use]
448 pub const fn new() -> String {
449 String { vec: Vec::new() }
450 }
451
452 /// Creates a new empty `String` with at least the specified capacity.
453 ///
454 /// `String`s have an internal buffer to hold their data. The capacity is
455 /// the length of that buffer, and can be queried with the [`capacity`]
456 /// method. This method creates an empty `String`, but one with an initial
457 /// buffer that can hold at least `capacity` bytes. This is useful when you
458 /// may be appending a bunch of data to the `String`, reducing the number of
459 /// reallocations it needs to do.
460 ///
461 /// [`capacity`]: String::capacity
462 ///
463 /// If the given capacity is `0`, no allocation will occur, and this method
464 /// is identical to the [`new`] method.
465 ///
466 /// [`new`]: String::new
467 ///
468 /// # Examples
469 ///
470 /// ```
471 /// let mut s = String::with_capacity(10);
472 ///
473 /// // The String contains no chars, even though it has capacity for more
474 /// assert_eq!(s.len(), 0);
475 ///
476 /// // These are all done without reallocating...
477 /// let cap = s.capacity();
478 /// for _ in 0..10 {
479 /// s.push('a');
480 /// }
481 ///
482 /// assert_eq!(s.capacity(), cap);
483 ///
484 /// // ...but this may make the string reallocate
485 /// s.push('a');
486 /// ```
487 #[cfg(not(no_global_oom_handling))]
488 #[inline]
489 #[stable(feature = "rust1", since = "1.0.0")]
490 #[must_use]
491 pub fn with_capacity(capacity: usize) -> String {
492 String { vec: Vec::with_capacity(capacity) }
493 }
494
495 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
496 // required for this method definition, is not available. Since we don't
497 // require this method for testing purposes, I'll just stub it
498 // NB see the slice::hack module in slice.rs for more information
499 #[inline]
500 #[cfg(test)]
501 pub fn from_str(_: &str) -> String {
502 panic!("not available with cfg(test)");
503 }
504
505 /// Converts a vector of bytes to a `String`.
506 ///
507 /// A string ([`String`]) is made of bytes ([`u8`]), and a vector of bytes
508 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
509 /// two. Not all byte slices are valid `String`s, however: `String`
510 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
511 /// the bytes are valid UTF-8, and then does the conversion.
512 ///
513 /// If you are sure that the byte slice is valid UTF-8, and you don't want
514 /// to incur the overhead of the validity check, there is an unsafe version
515 /// of this function, [`from_utf8_unchecked`], which has the same behavior
516 /// but skips the check.
517 ///
518 /// This method will take care to not copy the vector, for efficiency's
519 /// sake.
520 ///
521 /// If you need a [`&str`] instead of a `String`, consider
522 /// [`str::from_utf8`].
523 ///
524 /// The inverse of this method is [`into_bytes`].
525 ///
526 /// # Errors
527 ///
528 /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
529 /// provided bytes are not UTF-8. The vector you moved in is also included.
530 ///
531 /// # Examples
532 ///
533 /// Basic usage:
534 ///
535 /// ```
536 /// // some bytes, in a vector
537 /// let sparkle_heart = vec![240, 159, 146, 150];
538 ///
539 /// // We know these bytes are valid, so we'll use `unwrap()`.
540 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
541 ///
542 /// assert_eq!("πŸ’–", sparkle_heart);
543 /// ```
544 ///
545 /// Incorrect bytes:
546 ///
547 /// ```
548 /// // some invalid bytes, in a vector
549 /// let sparkle_heart = vec![0, 159, 146, 150];
550 ///
551 /// assert!(String::from_utf8(sparkle_heart).is_err());
552 /// ```
553 ///
554 /// See the docs for [`FromUtf8Error`] for more details on what you can do
555 /// with this error.
556 ///
557 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
558 /// [`Vec<u8>`]: crate::vec::Vec "Vec"
559 /// [`&str`]: prim@str "&str"
560 /// [`into_bytes`]: String::into_bytes
561 #[inline]
562 #[stable(feature = "rust1", since = "1.0.0")]
563 pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
564 match str::from_utf8(&vec) {
565 Ok(..) => Ok(String { vec }),
566 Err(e) => Err(FromUtf8Error { bytes: vec, error: e }),
567 }
568 }
569
570 /// Converts a slice of bytes to a string, including invalid characters.
571 ///
572 /// Strings are made of bytes ([`u8`]), and a slice of bytes
573 /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
574 /// between the two. Not all byte slices are valid strings, however: strings
575 /// are required to be valid UTF-8. During this conversion,
576 /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
577 /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: οΏ½
578 ///
579 /// [byteslice]: prim@slice
580 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
581 ///
582 /// If you are sure that the byte slice is valid UTF-8, and you don't want
583 /// to incur the overhead of the conversion, there is an unsafe version
584 /// of this function, [`from_utf8_unchecked`], which has the same behavior
585 /// but skips the checks.
586 ///
587 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
588 ///
589 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
590 /// UTF-8, then we need to insert the replacement characters, which will
591 /// change the size of the string, and hence, require a `String`. But if
592 /// it's already valid UTF-8, we don't need a new allocation. This return
593 /// type allows us to handle both cases.
594 ///
595 /// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
596 ///
597 /// # Examples
598 ///
599 /// Basic usage:
600 ///
601 /// ```
602 /// // some bytes, in a vector
603 /// let sparkle_heart = vec![240, 159, 146, 150];
604 ///
605 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
606 ///
607 /// assert_eq!("πŸ’–", sparkle_heart);
608 /// ```
609 ///
610 /// Incorrect bytes:
611 ///
612 /// ```
613 /// // some invalid bytes
614 /// let input = b"Hello \xF0\x90\x80World";
615 /// let output = String::from_utf8_lossy(input);
616 ///
617 /// assert_eq!("Hello οΏ½World", output);
618 /// ```
619 #[must_use]
620 #[cfg(not(no_global_oom_handling))]
621 #[stable(feature = "rust1", since = "1.0.0")]
622 pub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, str> {
623 let mut iter = Utf8Chunks::new(v);
624
625 let first_valid = if let Some(chunk) = iter.next() {
626 let valid = chunk.valid();
627 if chunk.invalid().is_empty() {
628 debug_assert_eq!(valid.len(), v.len());
629 return Cow::Borrowed(valid);
630 }
631 valid
632 } else {
633 return Cow::Borrowed("");
634 };
635
636 const REPLACEMENT: &str = "\u{FFFD}";
637
638 let mut res = String::with_capacity(v.len());
639 res.push_str(first_valid);
640 res.push_str(REPLACEMENT);
641
642 for chunk in iter {
643 res.push_str(chunk.valid());
644 if !chunk.invalid().is_empty() {
645 res.push_str(REPLACEMENT);
646 }
647 }
648
649 Cow::Owned(res)
650 }
651
652 /// Decode a UTF-16–encoded vector `v` into a `String`, returning [`Err`]
653 /// if `v` contains any invalid data.
654 ///
655 /// # Examples
656 ///
657 /// ```
658 /// // π„žmusic
659 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
660 /// 0x0073, 0x0069, 0x0063];
661 /// assert_eq!(String::from("π„žmusic"),
662 /// String::from_utf16(v).unwrap());
663 ///
664 /// // π„žmu<invalid>ic
665 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
666 /// 0xD800, 0x0069, 0x0063];
667 /// assert!(String::from_utf16(v).is_err());
668 /// ```
669 #[cfg(not(no_global_oom_handling))]
670 #[stable(feature = "rust1", since = "1.0.0")]
671 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
672 // This isn't done via collect::<Result<_, _>>() for performance reasons.
673 // FIXME: the function can be simplified again when #48994 is closed.
674 let mut ret = String::with_capacity(v.len());
675 for c in char::decode_utf16(v.iter().cloned()) {
676 if let Ok(c) = c {
677 ret.push(c);
678 } else {
679 return Err(FromUtf16Error(()));
680 }
681 }
682 Ok(ret)
683 }
684
685 /// Decode a UTF-16–encoded slice `v` into a `String`, replacing
686 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
687 ///
688 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
689 /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
690 /// conversion requires a memory allocation.
691 ///
692 /// [`from_utf8_lossy`]: String::from_utf8_lossy
693 /// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
694 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
695 ///
696 /// # Examples
697 ///
698 /// ```
699 /// // π„žmus<invalid>ic<invalid>
700 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
701 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
702 /// 0xD834];
703 ///
704 /// assert_eq!(String::from("π„žmus\u{FFFD}ic\u{FFFD}"),
705 /// String::from_utf16_lossy(v));
706 /// ```
707 #[cfg(not(no_global_oom_handling))]
708 #[must_use]
709 #[inline]
710 #[stable(feature = "rust1", since = "1.0.0")]
711 pub fn from_utf16_lossy(v: &[u16]) -> String {
712 char::decode_utf16(v.iter().cloned())
713 .map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
714 .collect()
715 }
716
717 /// Decode a UTF-16LE–encoded vector `v` into a `String`, returning [`Err`]
718 /// if `v` contains any invalid data.
719 ///
720 /// # Examples
721 ///
722 /// Basic usage:
723 ///
724 /// ```
725 /// #![feature(str_from_utf16_endian)]
726 /// // π„žmusic
727 /// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
728 /// 0x73, 0x00, 0x69, 0x00, 0x63, 0x00];
729 /// assert_eq!(String::from("π„žmusic"),
730 /// String::from_utf16le(v).unwrap());
731 ///
732 /// // π„žmu<invalid>ic
733 /// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
734 /// 0x00, 0xD8, 0x69, 0x00, 0x63, 0x00];
735 /// assert!(String::from_utf16le(v).is_err());
736 /// ```
737 #[cfg(not(no_global_oom_handling))]
738 #[unstable(feature = "str_from_utf16_endian", issue = "116258")]
739 pub fn from_utf16le(v: &[u8]) -> Result<String, FromUtf16Error> {
740 if v.len() % 2 != 0 {
741 return Err(FromUtf16Error(()));
742 }
743 match (cfg!(target_endian = "little"), unsafe { v.align_to::<u16>() }) {
744 (true, ([], v, [])) => Self::from_utf16(v),
745 _ => char::decode_utf16(v.array_chunks::<2>().copied().map(u16::from_le_bytes))
746 .collect::<Result<_, _>>()
747 .map_err(|_| FromUtf16Error(())),
748 }
749 }
750
751 /// Decode a UTF-16LE–encoded slice `v` into a `String`, replacing
752 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
753 ///
754 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
755 /// `from_utf16le_lossy` returns a `String` since the UTF-16 to UTF-8
756 /// conversion requires a memory allocation.
757 ///
758 /// [`from_utf8_lossy`]: String::from_utf8_lossy
759 /// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
760 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
761 ///
762 /// # Examples
763 ///
764 /// Basic usage:
765 ///
766 /// ```
767 /// #![feature(str_from_utf16_endian)]
768 /// // π„žmus<invalid>ic<invalid>
769 /// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
770 /// 0x73, 0x00, 0x1E, 0xDD, 0x69, 0x00, 0x63, 0x00,
771 /// 0x34, 0xD8];
772 ///
773 /// assert_eq!(String::from("π„žmus\u{FFFD}ic\u{FFFD}"),
774 /// String::from_utf16le_lossy(v));
775 /// ```
776 #[cfg(not(no_global_oom_handling))]
777 #[unstable(feature = "str_from_utf16_endian", issue = "116258")]
778 pub fn from_utf16le_lossy(v: &[u8]) -> String {
779 match (cfg!(target_endian = "little"), unsafe { v.align_to::<u16>() }) {
780 (true, ([], v, [])) => Self::from_utf16_lossy(v),
781 (true, ([], v, [_remainder])) => Self::from_utf16_lossy(v) + "\u{FFFD}",
782 _ => {
783 let mut iter = v.array_chunks::<2>();
784 let string = char::decode_utf16(iter.by_ref().copied().map(u16::from_le_bytes))
785 .map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
786 .collect();
787 if iter.remainder().is_empty() { string } else { string + "\u{FFFD}" }
788 }
789 }
790 }
791
792 /// Decode a UTF-16BE–encoded vector `v` into a `String`, returning [`Err`]
793 /// if `v` contains any invalid data.
794 ///
795 /// # Examples
796 ///
797 /// Basic usage:
798 ///
799 /// ```
800 /// #![feature(str_from_utf16_endian)]
801 /// // π„žmusic
802 /// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
803 /// 0x00, 0x73, 0x00, 0x69, 0x00, 0x63];
804 /// assert_eq!(String::from("π„žmusic"),
805 /// String::from_utf16be(v).unwrap());
806 ///
807 /// // π„žmu<invalid>ic
808 /// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
809 /// 0xD8, 0x00, 0x00, 0x69, 0x00, 0x63];
810 /// assert!(String::from_utf16be(v).is_err());
811 /// ```
812 #[cfg(not(no_global_oom_handling))]
813 #[unstable(feature = "str_from_utf16_endian", issue = "116258")]
814 pub fn from_utf16be(v: &[u8]) -> Result<String, FromUtf16Error> {
815 if v.len() % 2 != 0 {
816 return Err(FromUtf16Error(()));
817 }
818 match (cfg!(target_endian = "big"), unsafe { v.align_to::<u16>() }) {
819 (true, ([], v, [])) => Self::from_utf16(v),
820 _ => char::decode_utf16(v.array_chunks::<2>().copied().map(u16::from_be_bytes))
821 .collect::<Result<_, _>>()
822 .map_err(|_| FromUtf16Error(())),
823 }
824 }
825
826 /// Decode a UTF-16BE–encoded slice `v` into a `String`, replacing
827 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
828 ///
829 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
830 /// `from_utf16le_lossy` returns a `String` since the UTF-16 to UTF-8
831 /// conversion requires a memory allocation.
832 ///
833 /// [`from_utf8_lossy`]: String::from_utf8_lossy
834 /// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
835 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
836 ///
837 /// # Examples
838 ///
839 /// Basic usage:
840 ///
841 /// ```
842 /// #![feature(str_from_utf16_endian)]
843 /// // π„žmus<invalid>ic<invalid>
844 /// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
845 /// 0x00, 0x73, 0xDD, 0x1E, 0x00, 0x69, 0x00, 0x63,
846 /// 0xD8, 0x34];
847 ///
848 /// assert_eq!(String::from("π„žmus\u{FFFD}ic\u{FFFD}"),
849 /// String::from_utf16be_lossy(v));
850 /// ```
851 #[cfg(not(no_global_oom_handling))]
852 #[unstable(feature = "str_from_utf16_endian", issue = "116258")]
853 pub fn from_utf16be_lossy(v: &[u8]) -> String {
854 match (cfg!(target_endian = "big"), unsafe { v.align_to::<u16>() }) {
855 (true, ([], v, [])) => Self::from_utf16_lossy(v),
856 (true, ([], v, [_remainder])) => Self::from_utf16_lossy(v) + "\u{FFFD}",
857 _ => {
858 let mut iter = v.array_chunks::<2>();
859 let string = char::decode_utf16(iter.by_ref().copied().map(u16::from_be_bytes))
860 .map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
861 .collect();
862 if iter.remainder().is_empty() { string } else { string + "\u{FFFD}" }
863 }
864 }
865 }
866
867 /// Decomposes a `String` into its raw components.
868 ///
869 /// Returns the raw pointer to the underlying data, the length of
870 /// the string (in bytes), and the allocated capacity of the data
871 /// (in bytes). These are the same arguments in the same order as
872 /// the arguments to [`from_raw_parts`].
873 ///
874 /// After calling this function, the caller is responsible for the
875 /// memory previously managed by the `String`. The only way to do
876 /// this is to convert the raw pointer, length, and capacity back
877 /// into a `String` with the [`from_raw_parts`] function, allowing
878 /// the destructor to perform the cleanup.
879 ///
880 /// [`from_raw_parts`]: String::from_raw_parts
881 ///
882 /// # Examples
883 ///
884 /// ```
885 /// #![feature(vec_into_raw_parts)]
886 /// let s = String::from("hello");
887 ///
888 /// let (ptr, len, cap) = s.into_raw_parts();
889 ///
890 /// let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
891 /// assert_eq!(rebuilt, "hello");
892 /// ```
893 #[must_use = "`self` will be dropped if the result is not used"]
894 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
895 pub fn into_raw_parts(self) -> (*mut u8, usize, usize) {
896 self.vec.into_raw_parts()
897 }
898
899 /// Creates a new `String` from a length, capacity, and pointer.
900 ///
901 /// # Safety
902 ///
903 /// This is highly unsafe, due to the number of invariants that aren't
904 /// checked:
905 ///
906 /// * The memory at `buf` needs to have been previously allocated by the
907 /// same allocator the standard library uses, with a required alignment of exactly 1.
908 /// * `length` needs to be less than or equal to `capacity`.
909 /// * `capacity` needs to be the correct value.
910 /// * The first `length` bytes at `buf` need to be valid UTF-8.
911 ///
912 /// Violating these may cause problems like corrupting the allocator's
913 /// internal data structures. For example, it is normally **not** safe to
914 /// build a `String` from a pointer to a C `char` array containing UTF-8
915 /// _unless_ you are certain that array was originally allocated by the
916 /// Rust standard library's allocator.
917 ///
918 /// The ownership of `buf` is effectively transferred to the
919 /// `String` which may then deallocate, reallocate or change the
920 /// contents of memory pointed to by the pointer at will. Ensure
921 /// that nothing else uses the pointer after calling this
922 /// function.
923 ///
924 /// # Examples
925 ///
926 /// ```
927 /// use std::mem;
928 ///
929 /// unsafe {
930 /// let s = String::from("hello");
931 ///
932 // FIXME Update this when vec_into_raw_parts is stabilized
933 /// // Prevent automatically dropping the String's data
934 /// let mut s = mem::ManuallyDrop::new(s);
935 ///
936 /// let ptr = s.as_mut_ptr();
937 /// let len = s.len();
938 /// let capacity = s.capacity();
939 ///
940 /// let s = String::from_raw_parts(ptr, len, capacity);
941 ///
942 /// assert_eq!(String::from("hello"), s);
943 /// }
944 /// ```
945 #[inline]
946 #[stable(feature = "rust1", since = "1.0.0")]
947 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
948 unsafe { String { vec: Vec::from_raw_parts(buf, length, capacity) } }
949 }
950
951 /// Converts a vector of bytes to a `String` without checking that the
952 /// string contains valid UTF-8.
953 ///
954 /// See the safe version, [`from_utf8`], for more details.
955 ///
956 /// [`from_utf8`]: String::from_utf8
957 ///
958 /// # Safety
959 ///
960 /// This function is unsafe because it does not check that the bytes passed
961 /// to it are valid UTF-8. If this constraint is violated, it may cause
962 /// memory unsafety issues with future users of the `String`, as the rest of
963 /// the standard library assumes that `String`s are valid UTF-8.
964 ///
965 /// # Examples
966 ///
967 /// ```
968 /// // some bytes, in a vector
969 /// let sparkle_heart = vec![240, 159, 146, 150];
970 ///
971 /// let sparkle_heart = unsafe {
972 /// String::from_utf8_unchecked(sparkle_heart)
973 /// };
974 ///
975 /// assert_eq!("πŸ’–", sparkle_heart);
976 /// ```
977 #[inline]
978 #[must_use]
979 #[stable(feature = "rust1", since = "1.0.0")]
980 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
981 String { vec: bytes }
982 }
983
984 /// Converts a `String` into a byte vector.
985 ///
986 /// This consumes the `String`, so we do not need to copy its contents.
987 ///
988 /// # Examples
989 ///
990 /// ```
991 /// let s = String::from("hello");
992 /// let bytes = s.into_bytes();
993 ///
994 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
995 /// ```
996 #[inline]
997 #[must_use = "`self` will be dropped if the result is not used"]
998 #[stable(feature = "rust1", since = "1.0.0")]
999 pub fn into_bytes(self) -> Vec<u8> {
1000 self.vec
1001 }
1002
1003 /// Extracts a string slice containing the entire `String`.
1004 ///
1005 /// # Examples
1006 ///
1007 /// ```
1008 /// let s = String::from("foo");
1009 ///
1010 /// assert_eq!("foo", s.as_str());
1011 /// ```
1012 #[inline]
1013 #[must_use]
1014 #[stable(feature = "string_as_str", since = "1.7.0")]
1015 pub fn as_str(&self) -> &str {
1016 self
1017 }
1018
1019 /// Converts a `String` into a mutable string slice.
1020 ///
1021 /// # Examples
1022 ///
1023 /// ```
1024 /// let mut s = String::from("foobar");
1025 /// let s_mut_str = s.as_mut_str();
1026 ///
1027 /// s_mut_str.make_ascii_uppercase();
1028 ///
1029 /// assert_eq!("FOOBAR", s_mut_str);
1030 /// ```
1031 #[inline]
1032 #[must_use]
1033 #[stable(feature = "string_as_str", since = "1.7.0")]
1034 pub fn as_mut_str(&mut self) -> &mut str {
1035 self
1036 }
1037
1038 /// Appends a given string slice onto the end of this `String`.
1039 ///
1040 /// # Examples
1041 ///
1042 /// ```
1043 /// let mut s = String::from("foo");
1044 ///
1045 /// s.push_str("bar");
1046 ///
1047 /// assert_eq!("foobar", s);
1048 /// ```
1049 #[cfg(not(no_global_oom_handling))]
1050 #[inline]
1051 #[stable(feature = "rust1", since = "1.0.0")]
1052 pub fn push_str(&mut self, string: &str) {
1053 self.vec.extend_from_slice(string.as_bytes())
1054 }
1055
1056 /// Copies elements from `src` range to the end of the string.
1057 ///
1058 /// # Panics
1059 ///
1060 /// Panics if the starting point or end point do not lie on a [`char`]
1061 /// boundary, or if they're out of bounds.
1062 ///
1063 /// # Examples
1064 ///
1065 /// ```
1066 /// #![feature(string_extend_from_within)]
1067 /// let mut string = String::from("abcde");
1068 ///
1069 /// string.extend_from_within(2..);
1070 /// assert_eq!(string, "abcdecde");
1071 ///
1072 /// string.extend_from_within(..2);
1073 /// assert_eq!(string, "abcdecdeab");
1074 ///
1075 /// string.extend_from_within(4..8);
1076 /// assert_eq!(string, "abcdecdeabecde");
1077 /// ```
1078 #[cfg(not(no_global_oom_handling))]
1079 #[unstable(feature = "string_extend_from_within", issue = "103806")]
1080 pub fn extend_from_within<R>(&mut self, src: R)
1081 where
1082 R: RangeBounds<usize>,
1083 {
1084 let src @ Range { start, end } = slice::range(src, ..self.len());
1085
1086 assert!(self.is_char_boundary(start));
1087 assert!(self.is_char_boundary(end));
1088
1089 self.vec.extend_from_within(src);
1090 }
1091
1092 /// Returns this `String`'s capacity, in bytes.
1093 ///
1094 /// # Examples
1095 ///
1096 /// ```
1097 /// let s = String::with_capacity(10);
1098 ///
1099 /// assert!(s.capacity() >= 10);
1100 /// ```
1101 #[inline]
1102 #[must_use]
1103 #[stable(feature = "rust1", since = "1.0.0")]
1104 pub fn capacity(&self) -> usize {
1105 self.vec.capacity()
1106 }
1107
1108 /// Reserves capacity for at least `additional` bytes more than the
1109 /// current length. The allocator may reserve more space to speculatively
1110 /// avoid frequent allocations. After calling `reserve`,
1111 /// capacity will be greater than or equal to `self.len() + additional`.
1112 /// Does nothing if capacity is already sufficient.
1113 ///
1114 /// # Panics
1115 ///
1116 /// Panics if the new capacity overflows [`usize`].
1117 ///
1118 /// # Examples
1119 ///
1120 /// Basic usage:
1121 ///
1122 /// ```
1123 /// let mut s = String::new();
1124 ///
1125 /// s.reserve(10);
1126 ///
1127 /// assert!(s.capacity() >= 10);
1128 /// ```
1129 ///
1130 /// This might not actually increase the capacity:
1131 ///
1132 /// ```
1133 /// let mut s = String::with_capacity(10);
1134 /// s.push('a');
1135 /// s.push('b');
1136 ///
1137 /// // s now has a length of 2 and a capacity of at least 10
1138 /// let capacity = s.capacity();
1139 /// assert_eq!(2, s.len());
1140 /// assert!(capacity >= 10);
1141 ///
1142 /// // Since we already have at least an extra 8 capacity, calling this...
1143 /// s.reserve(8);
1144 ///
1145 /// // ... doesn't actually increase.
1146 /// assert_eq!(capacity, s.capacity());
1147 /// ```
1148 #[cfg(not(no_global_oom_handling))]
1149 #[inline]
1150 #[stable(feature = "rust1", since = "1.0.0")]
1151 pub fn reserve(&mut self, additional: usize) {
1152 self.vec.reserve(additional)
1153 }
1154
1155 /// Reserves the minimum capacity for at least `additional` bytes more than
1156 /// the current length. Unlike [`reserve`], this will not
1157 /// deliberately over-allocate to speculatively avoid frequent allocations.
1158 /// After calling `reserve_exact`, capacity will be greater than or equal to
1159 /// `self.len() + additional`. Does nothing if the capacity is already
1160 /// sufficient.
1161 ///
1162 /// [`reserve`]: String::reserve
1163 ///
1164 /// # Panics
1165 ///
1166 /// Panics if the new capacity overflows [`usize`].
1167 ///
1168 /// # Examples
1169 ///
1170 /// Basic usage:
1171 ///
1172 /// ```
1173 /// let mut s = String::new();
1174 ///
1175 /// s.reserve_exact(10);
1176 ///
1177 /// assert!(s.capacity() >= 10);
1178 /// ```
1179 ///
1180 /// This might not actually increase the capacity:
1181 ///
1182 /// ```
1183 /// let mut s = String::with_capacity(10);
1184 /// s.push('a');
1185 /// s.push('b');
1186 ///
1187 /// // s now has a length of 2 and a capacity of at least 10
1188 /// let capacity = s.capacity();
1189 /// assert_eq!(2, s.len());
1190 /// assert!(capacity >= 10);
1191 ///
1192 /// // Since we already have at least an extra 8 capacity, calling this...
1193 /// s.reserve_exact(8);
1194 ///
1195 /// // ... doesn't actually increase.
1196 /// assert_eq!(capacity, s.capacity());
1197 /// ```
1198 #[cfg(not(no_global_oom_handling))]
1199 #[inline]
1200 #[stable(feature = "rust1", since = "1.0.0")]
1201 pub fn reserve_exact(&mut self, additional: usize) {
1202 self.vec.reserve_exact(additional)
1203 }
1204
1205 /// Tries to reserve capacity for at least `additional` bytes more than the
1206 /// current length. The allocator may reserve more space to speculatively
1207 /// avoid frequent allocations. After calling `try_reserve`, capacity will be
1208 /// greater than or equal to `self.len() + additional` if it returns
1209 /// `Ok(())`. Does nothing if capacity is already sufficient. This method
1210 /// preserves the contents even if an error occurs.
1211 ///
1212 /// # Errors
1213 ///
1214 /// If the capacity overflows, or the allocator reports a failure, then an error
1215 /// is returned.
1216 ///
1217 /// # Examples
1218 ///
1219 /// ```
1220 /// use std::collections::TryReserveError;
1221 ///
1222 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
1223 /// let mut output = String::new();
1224 ///
1225 /// // Pre-reserve the memory, exiting if we can't
1226 /// output.try_reserve(data.len())?;
1227 ///
1228 /// // Now we know this can't OOM in the middle of our complex work
1229 /// output.push_str(data);
1230 ///
1231 /// Ok(output)
1232 /// }
1233 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1234 /// ```
1235 #[stable(feature = "try_reserve", since = "1.57.0")]
1236 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
1237 self.vec.try_reserve(additional)
1238 }
1239
1240 /// Tries to reserve the minimum capacity for at least `additional` bytes
1241 /// more than the current length. Unlike [`try_reserve`], this will not
1242 /// deliberately over-allocate to speculatively avoid frequent allocations.
1243 /// After calling `try_reserve_exact`, capacity will be greater than or
1244 /// equal to `self.len() + additional` if it returns `Ok(())`.
1245 /// Does nothing if the capacity is already sufficient.
1246 ///
1247 /// Note that the allocator may give the collection more space than it
1248 /// requests. Therefore, capacity can not be relied upon to be precisely
1249 /// minimal. Prefer [`try_reserve`] if future insertions are expected.
1250 ///
1251 /// [`try_reserve`]: String::try_reserve
1252 ///
1253 /// # Errors
1254 ///
1255 /// If the capacity overflows, or the allocator reports a failure, then an error
1256 /// is returned.
1257 ///
1258 /// # Examples
1259 ///
1260 /// ```
1261 /// use std::collections::TryReserveError;
1262 ///
1263 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
1264 /// let mut output = String::new();
1265 ///
1266 /// // Pre-reserve the memory, exiting if we can't
1267 /// output.try_reserve_exact(data.len())?;
1268 ///
1269 /// // Now we know this can't OOM in the middle of our complex work
1270 /// output.push_str(data);
1271 ///
1272 /// Ok(output)
1273 /// }
1274 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1275 /// ```
1276 #[stable(feature = "try_reserve", since = "1.57.0")]
1277 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
1278 self.vec.try_reserve_exact(additional)
1279 }
1280
1281 /// Shrinks the capacity of this `String` to match its length.
1282 ///
1283 /// # Examples
1284 ///
1285 /// ```
1286 /// let mut s = String::from("foo");
1287 ///
1288 /// s.reserve(100);
1289 /// assert!(s.capacity() >= 100);
1290 ///
1291 /// s.shrink_to_fit();
1292 /// assert_eq!(3, s.capacity());
1293 /// ```
1294 #[cfg(not(no_global_oom_handling))]
1295 #[inline]
1296 #[stable(feature = "rust1", since = "1.0.0")]
1297 pub fn shrink_to_fit(&mut self) {
1298 self.vec.shrink_to_fit()
1299 }
1300
1301 /// Shrinks the capacity of this `String` with a lower bound.
1302 ///
1303 /// The capacity will remain at least as large as both the length
1304 /// and the supplied value.
1305 ///
1306 /// If the current capacity is less than the lower limit, this is a no-op.
1307 ///
1308 /// # Examples
1309 ///
1310 /// ```
1311 /// let mut s = String::from("foo");
1312 ///
1313 /// s.reserve(100);
1314 /// assert!(s.capacity() >= 100);
1315 ///
1316 /// s.shrink_to(10);
1317 /// assert!(s.capacity() >= 10);
1318 /// s.shrink_to(0);
1319 /// assert!(s.capacity() >= 3);
1320 /// ```
1321 #[cfg(not(no_global_oom_handling))]
1322 #[inline]
1323 #[stable(feature = "shrink_to", since = "1.56.0")]
1324 pub fn shrink_to(&mut self, min_capacity: usize) {
1325 self.vec.shrink_to(min_capacity)
1326 }
1327
1328 /// Appends the given [`char`] to the end of this `String`.
1329 ///
1330 /// # Examples
1331 ///
1332 /// ```
1333 /// let mut s = String::from("abc");
1334 ///
1335 /// s.push('1');
1336 /// s.push('2');
1337 /// s.push('3');
1338 ///
1339 /// assert_eq!("abc123", s);
1340 /// ```
1341 #[cfg(not(no_global_oom_handling))]
1342 #[inline]
1343 #[stable(feature = "rust1", since = "1.0.0")]
1344 pub fn push(&mut self, ch: char) {
1345 match ch.len_utf8() {
1346 1 => self.vec.push(ch as u8),
1347 _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
1348 }
1349 }
1350
1351 /// Returns a byte slice of this `String`'s contents.
1352 ///
1353 /// The inverse of this method is [`from_utf8`].
1354 ///
1355 /// [`from_utf8`]: String::from_utf8
1356 ///
1357 /// # Examples
1358 ///
1359 /// ```
1360 /// let s = String::from("hello");
1361 ///
1362 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
1363 /// ```
1364 #[inline]
1365 #[must_use]
1366 #[stable(feature = "rust1", since = "1.0.0")]
1367 pub fn as_bytes(&self) -> &[u8] {
1368 &self.vec
1369 }
1370
1371 /// Shortens this `String` to the specified length.
1372 ///
1373 /// If `new_len` is greater than the string's current length, this has no
1374 /// effect.
1375 ///
1376 /// Note that this method has no effect on the allocated capacity
1377 /// of the string
1378 ///
1379 /// # Panics
1380 ///
1381 /// Panics if `new_len` does not lie on a [`char`] boundary.
1382 ///
1383 /// # Examples
1384 ///
1385 /// ```
1386 /// let mut s = String::from("hello");
1387 ///
1388 /// s.truncate(2);
1389 ///
1390 /// assert_eq!("he", s);
1391 /// ```
1392 #[inline]
1393 #[stable(feature = "rust1", since = "1.0.0")]
1394 pub fn truncate(&mut self, new_len: usize) {
1395 if new_len <= self.len() {
1396 assert!(self.is_char_boundary(new_len));
1397 self.vec.truncate(new_len)
1398 }
1399 }
1400
1401 /// Removes the last character from the string buffer and returns it.
1402 ///
1403 /// Returns [`None`] if this `String` is empty.
1404 ///
1405 /// # Examples
1406 ///
1407 /// ```
1408 /// let mut s = String::from("abč");
1409 ///
1410 /// assert_eq!(s.pop(), Some('č'));
1411 /// assert_eq!(s.pop(), Some('b'));
1412 /// assert_eq!(s.pop(), Some('a'));
1413 ///
1414 /// assert_eq!(s.pop(), None);
1415 /// ```
1416 #[inline]
1417 #[stable(feature = "rust1", since = "1.0.0")]
1418 pub fn pop(&mut self) -> Option<char> {
1419 let ch = self.chars().rev().next()?;
1420 let newlen = self.len() - ch.len_utf8();
1421 unsafe {
1422 self.vec.set_len(newlen);
1423 }
1424 Some(ch)
1425 }
1426
1427 /// Removes a [`char`] from this `String` at a byte position and returns it.
1428 ///
1429 /// This is an *O*(*n*) operation, as it requires copying every element in the
1430 /// buffer.
1431 ///
1432 /// # Panics
1433 ///
1434 /// Panics if `idx` is larger than or equal to the `String`'s length,
1435 /// or if it does not lie on a [`char`] boundary.
1436 ///
1437 /// # Examples
1438 ///
1439 /// ```
1440 /// let mut s = String::from("abç");
1441 ///
1442 /// assert_eq!(s.remove(0), 'a');
1443 /// assert_eq!(s.remove(1), 'Γ§');
1444 /// assert_eq!(s.remove(0), 'b');
1445 /// ```
1446 #[inline]
1447 #[stable(feature = "rust1", since = "1.0.0")]
1448 pub fn remove(&mut self, idx: usize) -> char {
1449 let ch = match self[idx..].chars().next() {
1450 Some(ch) => ch,
1451 None => panic!("cannot remove a char from the end of a string"),
1452 };
1453
1454 let next = idx + ch.len_utf8();
1455 let len = self.len();
1456 unsafe {
1457 ptr::copy(self.vec.as_ptr().add(next), self.vec.as_mut_ptr().add(idx), len - next);
1458 self.vec.set_len(len - (next - idx));
1459 }
1460 ch
1461 }
1462
1463 /// Remove all matches of pattern `pat` in the `String`.
1464 ///
1465 /// # Examples
1466 ///
1467 /// ```
1468 /// #![feature(string_remove_matches)]
1469 /// let mut s = String::from("Trees are not green, the sky is not blue.");
1470 /// s.remove_matches("not ");
1471 /// assert_eq!("Trees are green, the sky is blue.", s);
1472 /// ```
1473 ///
1474 /// Matches will be detected and removed iteratively, so in cases where
1475 /// patterns overlap, only the first pattern will be removed:
1476 ///
1477 /// ```
1478 /// #![feature(string_remove_matches)]
1479 /// let mut s = String::from("banana");
1480 /// s.remove_matches("ana");
1481 /// assert_eq!("bna", s);
1482 /// ```
1483 #[cfg(not(no_global_oom_handling))]
1484 #[unstable(feature = "string_remove_matches", reason = "new API", issue = "72826")]
1485 pub fn remove_matches<'a, P>(&'a mut self, pat: P)
1486 where
1487 P: for<'x> Pattern<'x>,
1488 {
1489 use core::str::pattern::Searcher;
1490
1491 let rejections = {
1492 let mut searcher = pat.into_searcher(self);
1493 // Per Searcher::next:
1494 //
1495 // A Match result needs to contain the whole matched pattern,
1496 // however Reject results may be split up into arbitrary many
1497 // adjacent fragments. Both ranges may have zero length.
1498 //
1499 // In practice the implementation of Searcher::next_match tends to
1500 // be more efficient, so we use it here and do some work to invert
1501 // matches into rejections since that's what we want to copy below.
1502 let mut front = 0;
1503 let rejections: Vec<_> = from_fn(|| {
1504 let (start, end) = searcher.next_match()?;
1505 let prev_front = front;
1506 front = end;
1507 Some((prev_front, start))
1508 })
1509 .collect();
1510 rejections.into_iter().chain(core::iter::once((front, self.len())))
1511 };
1512
1513 let mut len = 0;
1514 let ptr = self.vec.as_mut_ptr();
1515
1516 for (start, end) in rejections {
1517 let count = end - start;
1518 if start != len {
1519 // SAFETY: per Searcher::next:
1520 //
1521 // The stream of Match and Reject values up to a Done will
1522 // contain index ranges that are adjacent, non-overlapping,
1523 // covering the whole haystack, and laying on utf8
1524 // boundaries.
1525 unsafe {
1526 ptr::copy(ptr.add(start), ptr.add(len), count);
1527 }
1528 }
1529 len += count;
1530 }
1531
1532 unsafe {
1533 self.vec.set_len(len);
1534 }
1535 }
1536
1537 /// Retains only the characters specified by the predicate.
1538 ///
1539 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1540 /// This method operates in place, visiting each character exactly once in the
1541 /// original order, and preserves the order of the retained characters.
1542 ///
1543 /// # Examples
1544 ///
1545 /// ```
1546 /// let mut s = String::from("f_o_ob_ar");
1547 ///
1548 /// s.retain(|c| c != '_');
1549 ///
1550 /// assert_eq!(s, "foobar");
1551 /// ```
1552 ///
1553 /// Because the elements are visited exactly once in the original order,
1554 /// external state may be used to decide which elements to keep.
1555 ///
1556 /// ```
1557 /// let mut s = String::from("abcde");
1558 /// let keep = [false, true, true, false, true];
1559 /// let mut iter = keep.iter();
1560 /// s.retain(|_| *iter.next().unwrap());
1561 /// assert_eq!(s, "bce");
1562 /// ```
1563 #[inline]
1564 #[stable(feature = "string_retain", since = "1.26.0")]
1565 pub fn retain<F>(&mut self, mut f: F)
1566 where
1567 F: FnMut(char) -> bool,
1568 {
1569 struct SetLenOnDrop<'a> {
1570 s: &'a mut String,
1571 idx: usize,
1572 del_bytes: usize,
1573 }
1574
1575 impl<'a> Drop for SetLenOnDrop<'a> {
1576 fn drop(&mut self) {
1577 let new_len = self.idx - self.del_bytes;
1578 debug_assert!(new_len <= self.s.len());
1579 unsafe { self.s.vec.set_len(new_len) };
1580 }
1581 }
1582
1583 let len = self.len();
1584 let mut guard = SetLenOnDrop { s: self, idx: 0, del_bytes: 0 };
1585
1586 while guard.idx < len {
1587 let ch =
1588 // SAFETY: `guard.idx` is positive-or-zero and less that len so the `get_unchecked`
1589 // is in bound. `self` is valid UTF-8 like string and the returned slice starts at
1590 // a unicode code point so the `Chars` always return one character.
1591 unsafe { guard.s.get_unchecked(guard.idx..len).chars().next().unwrap_unchecked() };
1592 let ch_len = ch.len_utf8();
1593
1594 if !f(ch) {
1595 guard.del_bytes += ch_len;
1596 } else if guard.del_bytes > 0 {
1597 // SAFETY: `guard.idx` is in bound and `guard.del_bytes` represent the number of
1598 // bytes that are erased from the string so the resulting `guard.idx -
1599 // guard.del_bytes` always represent a valid unicode code point.
1600 //
1601 // `guard.del_bytes` >= `ch.len_utf8()`, so taking a slice with `ch.len_utf8()` len
1602 // is safe.
1603 ch.encode_utf8(unsafe {
1604 crate::slice::from_raw_parts_mut(
1605 guard.s.as_mut_ptr().add(guard.idx - guard.del_bytes),
1606 ch.len_utf8(),
1607 )
1608 });
1609 }
1610
1611 // Point idx to the next char
1612 guard.idx += ch_len;
1613 }
1614
1615 drop(guard);
1616 }
1617
1618 /// Inserts a character into this `String` at a byte position.
1619 ///
1620 /// This is an *O*(*n*) operation as it requires copying every element in the
1621 /// buffer.
1622 ///
1623 /// # Panics
1624 ///
1625 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1626 /// lie on a [`char`] boundary.
1627 ///
1628 /// # Examples
1629 ///
1630 /// ```
1631 /// let mut s = String::with_capacity(3);
1632 ///
1633 /// s.insert(0, 'f');
1634 /// s.insert(1, 'o');
1635 /// s.insert(2, 'o');
1636 ///
1637 /// assert_eq!("foo", s);
1638 /// ```
1639 #[cfg(not(no_global_oom_handling))]
1640 #[inline]
1641 #[stable(feature = "rust1", since = "1.0.0")]
1642 pub fn insert(&mut self, idx: usize, ch: char) {
1643 assert!(self.is_char_boundary(idx));
1644 let mut bits = [0; 4];
1645 let bits = ch.encode_utf8(&mut bits).as_bytes();
1646
1647 unsafe {
1648 self.insert_bytes(idx, bits);
1649 }
1650 }
1651
1652 #[cfg(not(no_global_oom_handling))]
1653 unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1654 let len = self.len();
1655 let amt = bytes.len();
1656 self.vec.reserve(amt);
1657
1658 unsafe {
1659 ptr::copy(self.vec.as_ptr().add(idx), self.vec.as_mut_ptr().add(idx + amt), len - idx);
1660 ptr::copy_nonoverlapping(bytes.as_ptr(), self.vec.as_mut_ptr().add(idx), amt);
1661 self.vec.set_len(len + amt);
1662 }
1663 }
1664
1665 /// Inserts a string slice into this `String` at a byte position.
1666 ///
1667 /// This is an *O*(*n*) operation as it requires copying every element in the
1668 /// buffer.
1669 ///
1670 /// # Panics
1671 ///
1672 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1673 /// lie on a [`char`] boundary.
1674 ///
1675 /// # Examples
1676 ///
1677 /// ```
1678 /// let mut s = String::from("bar");
1679 ///
1680 /// s.insert_str(0, "foo");
1681 ///
1682 /// assert_eq!("foobar", s);
1683 /// ```
1684 #[cfg(not(no_global_oom_handling))]
1685 #[inline]
1686 #[stable(feature = "insert_str", since = "1.16.0")]
1687 pub fn insert_str(&mut self, idx: usize, string: &str) {
1688 assert!(self.is_char_boundary(idx));
1689
1690 unsafe {
1691 self.insert_bytes(idx, string.as_bytes());
1692 }
1693 }
1694
1695 /// Returns a mutable reference to the contents of this `String`.
1696 ///
1697 /// # Safety
1698 ///
1699 /// This function is unsafe because the returned `&mut Vec` allows writing
1700 /// bytes which are not valid UTF-8. If this constraint is violated, using
1701 /// the original `String` after dropping the `&mut Vec` may violate memory
1702 /// safety, as the rest of the standard library assumes that `String`s are
1703 /// valid UTF-8.
1704 ///
1705 /// # Examples
1706 ///
1707 /// ```
1708 /// let mut s = String::from("hello");
1709 ///
1710 /// unsafe {
1711 /// let vec = s.as_mut_vec();
1712 /// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1713 ///
1714 /// vec.reverse();
1715 /// }
1716 /// assert_eq!(s, "olleh");
1717 /// ```
1718 #[inline]
1719 #[stable(feature = "rust1", since = "1.0.0")]
1720 pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1721 &mut self.vec
1722 }
1723
1724 /// Returns the length of this `String`, in bytes, not [`char`]s or
1725 /// graphemes. In other words, it might not be what a human considers the
1726 /// length of the string.
1727 ///
1728 /// # Examples
1729 ///
1730 /// ```
1731 /// let a = String::from("foo");
1732 /// assert_eq!(a.len(), 3);
1733 ///
1734 /// let fancy_f = String::from("Ζ’oo");
1735 /// assert_eq!(fancy_f.len(), 4);
1736 /// assert_eq!(fancy_f.chars().count(), 3);
1737 /// ```
1738 #[inline]
1739 #[must_use]
1740 #[stable(feature = "rust1", since = "1.0.0")]
1741 pub fn len(&self) -> usize {
1742 self.vec.len()
1743 }
1744
1745 /// Returns `true` if this `String` has a length of zero, and `false` otherwise.
1746 ///
1747 /// # Examples
1748 ///
1749 /// ```
1750 /// let mut v = String::new();
1751 /// assert!(v.is_empty());
1752 ///
1753 /// v.push('a');
1754 /// assert!(!v.is_empty());
1755 /// ```
1756 #[inline]
1757 #[must_use]
1758 #[stable(feature = "rust1", since = "1.0.0")]
1759 pub fn is_empty(&self) -> bool {
1760 self.len() == 0
1761 }
1762
1763 /// Splits the string into two at the given byte index.
1764 ///
1765 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1766 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1767 /// boundary of a UTF-8 code point.
1768 ///
1769 /// Note that the capacity of `self` does not change.
1770 ///
1771 /// # Panics
1772 ///
1773 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1774 /// code point of the string.
1775 ///
1776 /// # Examples
1777 ///
1778 /// ```
1779 /// # fn main() {
1780 /// let mut hello = String::from("Hello, World!");
1781 /// let world = hello.split_off(7);
1782 /// assert_eq!(hello, "Hello, ");
1783 /// assert_eq!(world, "World!");
1784 /// # }
1785 /// ```
1786 #[cfg(not(no_global_oom_handling))]
1787 #[inline]
1788 #[stable(feature = "string_split_off", since = "1.16.0")]
1789 #[must_use = "use `.truncate()` if you don't need the other half"]
1790 pub fn split_off(&mut self, at: usize) -> String {
1791 assert!(self.is_char_boundary(at));
1792 let other = self.vec.split_off(at);
1793 unsafe { String::from_utf8_unchecked(other) }
1794 }
1795
1796 /// Truncates this `String`, removing all contents.
1797 ///
1798 /// While this means the `String` will have a length of zero, it does not
1799 /// touch its capacity.
1800 ///
1801 /// # Examples
1802 ///
1803 /// ```
1804 /// let mut s = String::from("foo");
1805 ///
1806 /// s.clear();
1807 ///
1808 /// assert!(s.is_empty());
1809 /// assert_eq!(0, s.len());
1810 /// assert_eq!(3, s.capacity());
1811 /// ```
1812 #[inline]
1813 #[stable(feature = "rust1", since = "1.0.0")]
1814 pub fn clear(&mut self) {
1815 self.vec.clear()
1816 }
1817
1818 /// Removes the specified range from the string in bulk, returning all
1819 /// removed characters as an iterator.
1820 ///
1821 /// The returned iterator keeps a mutable borrow on the string to optimize
1822 /// its implementation.
1823 ///
1824 /// # Panics
1825 ///
1826 /// Panics if the starting point or end point do not lie on a [`char`]
1827 /// boundary, or if they're out of bounds.
1828 ///
1829 /// # Leaking
1830 ///
1831 /// If the returned iterator goes out of scope without being dropped (due to
1832 /// [`core::mem::forget`], for example), the string may still contain a copy
1833 /// of any drained characters, or may have lost characters arbitrarily,
1834 /// including characters outside the range.
1835 ///
1836 /// # Examples
1837 ///
1838 /// ```
1839 /// let mut s = String::from("Ξ± is alpha, Ξ² is beta");
1840 /// let beta_offset = s.find('Ξ²').unwrap_or(s.len());
1841 ///
1842 /// // Remove the range up until the Ξ² from the string
1843 /// let t: String = s.drain(..beta_offset).collect();
1844 /// assert_eq!(t, "Ξ± is alpha, ");
1845 /// assert_eq!(s, "Ξ² is beta");
1846 ///
1847 /// // A full range clears the string, like `clear()` does
1848 /// s.drain(..);
1849 /// assert_eq!(s, "");
1850 /// ```
1851 #[stable(feature = "drain", since = "1.6.0")]
1852 pub fn drain<R>(&mut self, range: R) -> Drain<'_>
1853 where
1854 R: RangeBounds<usize>,
1855 {
1856 // Memory safety
1857 //
1858 // The String version of Drain does not have the memory safety issues
1859 // of the vector version. The data is just plain bytes.
1860 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1861 // the removal will not happen.
1862 let Range { start, end } = slice::range(range, ..self.len());
1863 assert!(self.is_char_boundary(start));
1864 assert!(self.is_char_boundary(end));
1865
1866 // Take out two simultaneous borrows. The &mut String won't be accessed
1867 // until iteration is over, in Drop.
1868 let self_ptr = self as *mut _;
1869 // SAFETY: `slice::range` and `is_char_boundary` do the appropriate bounds checks.
1870 let chars_iter = unsafe { self.get_unchecked(start..end) }.chars();
1871
1872 Drain { start, end, iter: chars_iter, string: self_ptr }
1873 }
1874
1875 /// Removes the specified range in the string,
1876 /// and replaces it with the given string.
1877 /// The given string doesn't need to be the same length as the range.
1878 ///
1879 /// # Panics
1880 ///
1881 /// Panics if the starting point or end point do not lie on a [`char`]
1882 /// boundary, or if they're out of bounds.
1883 ///
1884 /// # Examples
1885 ///
1886 /// ```
1887 /// let mut s = String::from("Ξ± is alpha, Ξ² is beta");
1888 /// let beta_offset = s.find('Ξ²').unwrap_or(s.len());
1889 ///
1890 /// // Replace the range up until the Ξ² from the string
1891 /// s.replace_range(..beta_offset, "Ξ‘ is capital alpha; ");
1892 /// assert_eq!(s, "Ξ‘ is capital alpha; Ξ² is beta");
1893 /// ```
1894 #[cfg(not(no_global_oom_handling))]
1895 #[stable(feature = "splice", since = "1.27.0")]
1896 pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
1897 where
1898 R: RangeBounds<usize>,
1899 {
1900 // Memory safety
1901 //
1902 // Replace_range does not have the memory safety issues of a vector Splice.
1903 // of the vector version. The data is just plain bytes.
1904
1905 // WARNING: Inlining this variable would be unsound (#81138)
1906 let start = range.start_bound();
1907 match start {
1908 Included(&n) => assert!(self.is_char_boundary(n)),
1909 Excluded(&n) => assert!(self.is_char_boundary(n + 1)),
1910 Unbounded => {}
1911 };
1912 // WARNING: Inlining this variable would be unsound (#81138)
1913 let end = range.end_bound();
1914 match end {
1915 Included(&n) => assert!(self.is_char_boundary(n + 1)),
1916 Excluded(&n) => assert!(self.is_char_boundary(n)),
1917 Unbounded => {}
1918 };
1919
1920 // Using `range` again would be unsound (#81138)
1921 // We assume the bounds reported by `range` remain the same, but
1922 // an adversarial implementation could change between calls
1923 unsafe { self.as_mut_vec() }.splice((start, end), replace_with.bytes());
1924 }
1925
1926 /// Converts this `String` into a <code>[Box]<[str]></code>.
1927 ///
1928 /// This will drop any excess capacity.
1929 ///
1930 /// [str]: prim@str "str"
1931 ///
1932 /// # Examples
1933 ///
1934 /// ```
1935 /// let s = String::from("hello");
1936 ///
1937 /// let b = s.into_boxed_str();
1938 /// ```
1939 #[cfg(not(no_global_oom_handling))]
1940 #[stable(feature = "box_str", since = "1.4.0")]
1941 #[must_use = "`self` will be dropped if the result is not used"]
1942 #[inline]
1943 pub fn into_boxed_str(self) -> Box<str> {
1944 let slice = self.vec.into_boxed_slice();
1945 unsafe { from_boxed_utf8_unchecked(slice) }
1946 }
1947
1948 /// Consumes and leaks the `String`, returning a mutable reference to the contents,
1949 /// `&'a mut str`.
1950 ///
1951 /// The caller has free choice over the returned lifetime, including `'static`. Indeed,
1952 /// this function is ideally used for data that lives for the remainder of the program's life,
1953 /// as dropping the returned reference will cause a memory leak.
1954 ///
1955 /// It does not reallocate or shrink the `String`,
1956 /// so the leaked allocation may include unused capacity that is not part
1957 /// of the returned slice. If you don't want that, call [`into_boxed_str`],
1958 /// and then [`Box::leak`].
1959 ///
1960 /// [`into_boxed_str`]: Self::into_boxed_str
1961 ///
1962 /// # Examples
1963 ///
1964 /// ```
1965 /// let x = String::from("bucket");
1966 /// let static_ref: &'static mut str = x.leak();
1967 /// assert_eq!(static_ref, "bucket");
1968 /// ```
1969 #[stable(feature = "string_leak", since = "1.72.0")]
1970 #[inline]
1971 pub fn leak<'a>(self) -> &'a mut str {
1972 let slice = self.vec.leak();
1973 unsafe { from_utf8_unchecked_mut(slice) }
1974 }
1975}
1976
1977impl FromUtf8Error {
1978 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1979 ///
1980 /// # Examples
1981 ///
1982 /// ```
1983 /// // some invalid bytes, in a vector
1984 /// let bytes = vec![0, 159];
1985 ///
1986 /// let value = String::from_utf8(bytes);
1987 ///
1988 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1989 /// ```
1990 #[must_use]
1991 #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
1992 pub fn as_bytes(&self) -> &[u8] {
1993 &self.bytes[..]
1994 }
1995
1996 /// Returns the bytes that were attempted to convert to a `String`.
1997 ///
1998 /// This method is carefully constructed to avoid allocation. It will
1999 /// consume the error, moving out the bytes, so that a copy of the bytes
2000 /// does not need to be made.
2001 ///
2002 /// # Examples
2003 ///
2004 /// ```
2005 /// // some invalid bytes, in a vector
2006 /// let bytes = vec![0, 159];
2007 ///
2008 /// let value = String::from_utf8(bytes);
2009 ///
2010 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
2011 /// ```
2012 #[must_use = "`self` will be dropped if the result is not used"]
2013 #[stable(feature = "rust1", since = "1.0.0")]
2014 pub fn into_bytes(self) -> Vec<u8> {
2015 self.bytes
2016 }
2017
2018 /// Fetch a `Utf8Error` to get more details about the conversion failure.
2019 ///
2020 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
2021 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
2022 /// an analogue to `FromUtf8Error`. See its documentation for more details
2023 /// on using it.
2024 ///
2025 /// [`std::str`]: core::str "std::str"
2026 /// [`&str`]: prim@str "&str"
2027 ///
2028 /// # Examples
2029 ///
2030 /// ```
2031 /// // some invalid bytes, in a vector
2032 /// let bytes = vec![0, 159];
2033 ///
2034 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
2035 ///
2036 /// // the first byte is invalid here
2037 /// assert_eq!(1, error.valid_up_to());
2038 /// ```
2039 #[must_use]
2040 #[stable(feature = "rust1", since = "1.0.0")]
2041 pub fn utf8_error(&self) -> Utf8Error {
2042 self.error
2043 }
2044}
2045
2046#[stable(feature = "rust1", since = "1.0.0")]
2047impl fmt::Display for FromUtf8Error {
2048 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2049 fmt::Display::fmt(&self.error, f)
2050 }
2051}
2052
2053#[stable(feature = "rust1", since = "1.0.0")]
2054impl fmt::Display for FromUtf16Error {
2055 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2056 fmt::Display::fmt(self:"invalid utf-16: lone surrogate found", f)
2057 }
2058}
2059
2060#[stable(feature = "rust1", since = "1.0.0")]
2061impl Error for FromUtf8Error {
2062 #[allow(deprecated)]
2063 fn description(&self) -> &str {
2064 "invalid utf-8"
2065 }
2066}
2067
2068#[stable(feature = "rust1", since = "1.0.0")]
2069impl Error for FromUtf16Error {
2070 #[allow(deprecated)]
2071 fn description(&self) -> &str {
2072 "invalid utf-16"
2073 }
2074}
2075
2076#[cfg(not(no_global_oom_handling))]
2077#[stable(feature = "rust1", since = "1.0.0")]
2078impl Clone for String {
2079 fn clone(&self) -> Self {
2080 String { vec: self.vec.clone() }
2081 }
2082
2083 fn clone_from(&mut self, source: &Self) {
2084 self.vec.clone_from(&source.vec);
2085 }
2086}
2087
2088#[cfg(not(no_global_oom_handling))]
2089#[stable(feature = "rust1", since = "1.0.0")]
2090impl FromIterator<char> for String {
2091 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
2092 let mut buf: String = String::new();
2093 buf.extend(iter);
2094 buf
2095 }
2096}
2097
2098#[cfg(not(no_global_oom_handling))]
2099#[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
2100impl<'a> FromIterator<&'a char> for String {
2101 fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
2102 let mut buf: String = String::new();
2103 buf.extend(iter);
2104 buf
2105 }
2106}
2107
2108#[cfg(not(no_global_oom_handling))]
2109#[stable(feature = "rust1", since = "1.0.0")]
2110impl<'a> FromIterator<&'a str> for String {
2111 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
2112 let mut buf: String = String::new();
2113 buf.extend(iter);
2114 buf
2115 }
2116}
2117
2118#[cfg(not(no_global_oom_handling))]
2119#[stable(feature = "extend_string", since = "1.4.0")]
2120impl FromIterator<String> for String {
2121 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
2122 let mut iterator: ::IntoIter = iter.into_iter();
2123
2124 // Because we're iterating over `String`s, we can avoid at least
2125 // one allocation by getting the first string from the iterator
2126 // and appending to it all the subsequent strings.
2127 match iterator.next() {
2128 None => String::new(),
2129 Some(mut buf: String) => {
2130 buf.extend(iter:iterator);
2131 buf
2132 }
2133 }
2134 }
2135}
2136
2137#[cfg(not(no_global_oom_handling))]
2138#[stable(feature = "box_str2", since = "1.45.0")]
2139impl FromIterator<Box<str>> for String {
2140 fn from_iter<I: IntoIterator<Item = Box<str>>>(iter: I) -> String {
2141 let mut buf: String = String::new();
2142 buf.extend(iter);
2143 buf
2144 }
2145}
2146
2147#[cfg(not(no_global_oom_handling))]
2148#[stable(feature = "herd_cows", since = "1.19.0")]
2149impl<'a> FromIterator<Cow<'a, str>> for String {
2150 fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
2151 let mut iterator: ::IntoIter = iter.into_iter();
2152
2153 // Because we're iterating over CoWs, we can (potentially) avoid at least
2154 // one allocation by getting the first item and appending to it all the
2155 // subsequent items.
2156 match iterator.next() {
2157 None => String::new(),
2158 Some(cow: Cow<'_, str>) => {
2159 let mut buf: String = cow.into_owned();
2160 buf.extend(iter:iterator);
2161 buf
2162 }
2163 }
2164 }
2165}
2166
2167#[cfg(not(no_global_oom_handling))]
2168#[stable(feature = "rust1", since = "1.0.0")]
2169impl Extend<char> for String {
2170 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
2171 let iterator: ::IntoIter = iter.into_iter();
2172 let (lower_bound: usize, _) = iterator.size_hint();
2173 self.reserve(additional:lower_bound);
2174 iterator.for_each(move |c: char| self.push(ch:c));
2175 }
2176
2177 #[inline]
2178 fn extend_one(&mut self, c: char) {
2179 self.push(ch:c);
2180 }
2181
2182 #[inline]
2183 fn extend_reserve(&mut self, additional: usize) {
2184 self.reserve(additional);
2185 }
2186}
2187
2188#[cfg(not(no_global_oom_handling))]
2189#[stable(feature = "extend_ref", since = "1.2.0")]
2190impl<'a> Extend<&'a char> for String {
2191 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
2192 self.extend(iter:iter.into_iter().cloned());
2193 }
2194
2195 #[inline]
2196 fn extend_one(&mut self, &c: char: &'a char) {
2197 self.push(ch:c);
2198 }
2199
2200 #[inline]
2201 fn extend_reserve(&mut self, additional: usize) {
2202 self.reserve(additional);
2203 }
2204}
2205
2206#[cfg(not(no_global_oom_handling))]
2207#[stable(feature = "rust1", since = "1.0.0")]
2208impl<'a> Extend<&'a str> for String {
2209 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
2210 iter.into_iter().for_each(move |s: &str| self.push_str(string:s));
2211 }
2212
2213 #[inline]
2214 fn extend_one(&mut self, s: &'a str) {
2215 self.push_str(string:s);
2216 }
2217}
2218
2219#[cfg(not(no_global_oom_handling))]
2220#[stable(feature = "box_str2", since = "1.45.0")]
2221impl Extend<Box<str>> for String {
2222 fn extend<I: IntoIterator<Item = Box<str>>>(&mut self, iter: I) {
2223 iter.into_iter().for_each(move |s: Box| self.push_str(&s));
2224 }
2225}
2226
2227#[cfg(not(no_global_oom_handling))]
2228#[stable(feature = "extend_string", since = "1.4.0")]
2229impl Extend<String> for String {
2230 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
2231 iter.into_iter().for_each(move |s: String| self.push_str(&s));
2232 }
2233
2234 #[inline]
2235 fn extend_one(&mut self, s: String) {
2236 self.push_str(&s);
2237 }
2238}
2239
2240#[cfg(not(no_global_oom_handling))]
2241#[stable(feature = "herd_cows", since = "1.19.0")]
2242impl<'a> Extend<Cow<'a, str>> for String {
2243 fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
2244 iter.into_iter().for_each(move |s: Cow<'_, str>| self.push_str(&s));
2245 }
2246
2247 #[inline]
2248 fn extend_one(&mut self, s: Cow<'a, str>) {
2249 self.push_str(&s);
2250 }
2251}
2252
2253/// A convenience impl that delegates to the impl for `&str`.
2254///
2255/// # Examples
2256///
2257/// ```
2258/// assert_eq!(String::from("Hello world").find("world"), Some(6));
2259/// ```
2260#[unstable(
2261 feature = "pattern",
2262 reason = "API not fully fleshed out and ready to be stabilized",
2263 issue = "27721"
2264)]
2265impl<'a, 'b> Pattern<'a> for &'b String {
2266 type Searcher = <&'b str as Pattern<'a>>::Searcher;
2267
2268 fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
2269 self[..].into_searcher(haystack)
2270 }
2271
2272 #[inline]
2273 fn is_contained_in(self, haystack: &'a str) -> bool {
2274 self[..].is_contained_in(haystack)
2275 }
2276
2277 #[inline]
2278 fn is_prefix_of(self, haystack: &'a str) -> bool {
2279 self[..].is_prefix_of(haystack)
2280 }
2281
2282 #[inline]
2283 fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str> {
2284 self[..].strip_prefix_of(haystack)
2285 }
2286
2287 #[inline]
2288 fn is_suffix_of(self, haystack: &'a str) -> bool {
2289 self[..].is_suffix_of(haystack)
2290 }
2291
2292 #[inline]
2293 fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str> {
2294 self[..].strip_suffix_of(haystack)
2295 }
2296}
2297
2298macro_rules! impl_eq {
2299 ($lhs:ty, $rhs: ty) => {
2300 #[stable(feature = "rust1", since = "1.0.0")]
2301 #[allow(unused_lifetimes)]
2302 impl<'a, 'b> PartialEq<$rhs> for $lhs {
2303 #[inline]
2304 fn eq(&self, other: &$rhs) -> bool {
2305 PartialEq::eq(&self[..], &other[..])
2306 }
2307 #[inline]
2308 fn ne(&self, other: &$rhs) -> bool {
2309 PartialEq::ne(&self[..], &other[..])
2310 }
2311 }
2312
2313 #[stable(feature = "rust1", since = "1.0.0")]
2314 #[allow(unused_lifetimes)]
2315 impl<'a, 'b> PartialEq<$lhs> for $rhs {
2316 #[inline]
2317 fn eq(&self, other: &$lhs) -> bool {
2318 PartialEq::eq(&self[..], &other[..])
2319 }
2320 #[inline]
2321 fn ne(&self, other: &$lhs) -> bool {
2322 PartialEq::ne(&self[..], &other[..])
2323 }
2324 }
2325 };
2326}
2327
2328impl_eq! { String, str }
2329impl_eq! { String, &'a str }
2330#[cfg(not(no_global_oom_handling))]
2331impl_eq! { Cow<'a, str>, str }
2332#[cfg(not(no_global_oom_handling))]
2333impl_eq! { Cow<'a, str>, &'b str }
2334#[cfg(not(no_global_oom_handling))]
2335impl_eq! { Cow<'a, str>, String }
2336
2337#[stable(feature = "rust1", since = "1.0.0")]
2338impl Default for String {
2339 /// Creates an empty `String`.
2340 #[inline]
2341 fn default() -> String {
2342 String::new()
2343 }
2344}
2345
2346#[stable(feature = "rust1", since = "1.0.0")]
2347impl fmt::Display for String {
2348 #[inline]
2349 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2350 fmt::Display::fmt(&**self, f)
2351 }
2352}
2353
2354#[stable(feature = "rust1", since = "1.0.0")]
2355impl fmt::Debug for String {
2356 #[inline]
2357 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2358 fmt::Debug::fmt(&**self, f)
2359 }
2360}
2361
2362#[stable(feature = "rust1", since = "1.0.0")]
2363impl hash::Hash for String {
2364 #[inline]
2365 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
2366 (**self).hash(state:hasher)
2367 }
2368}
2369
2370/// Implements the `+` operator for concatenating two strings.
2371///
2372/// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
2373/// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
2374/// every operation, which would lead to *O*(*n*^2) running time when building an *n*-byte string by
2375/// repeated concatenation.
2376///
2377/// The string on the right-hand side is only borrowed; its contents are copied into the returned
2378/// `String`.
2379///
2380/// # Examples
2381///
2382/// Concatenating two `String`s takes the first by value and borrows the second:
2383///
2384/// ```
2385/// let a = String::from("hello");
2386/// let b = String::from(" world");
2387/// let c = a + &b;
2388/// // `a` is moved and can no longer be used here.
2389/// ```
2390///
2391/// If you want to keep using the first `String`, you can clone it and append to the clone instead:
2392///
2393/// ```
2394/// let a = String::from("hello");
2395/// let b = String::from(" world");
2396/// let c = a.clone() + &b;
2397/// // `a` is still valid here.
2398/// ```
2399///
2400/// Concatenating `&str` slices can be done by converting the first to a `String`:
2401///
2402/// ```
2403/// let a = "hello";
2404/// let b = " world";
2405/// let c = a.to_string() + b;
2406/// ```
2407#[cfg(not(no_global_oom_handling))]
2408#[stable(feature = "rust1", since = "1.0.0")]
2409impl Add<&str> for String {
2410 type Output = String;
2411
2412 #[inline]
2413 fn add(mut self, other: &str) -> String {
2414 self.push_str(string:other);
2415 self
2416 }
2417}
2418
2419/// Implements the `+=` operator for appending to a `String`.
2420///
2421/// This has the same behavior as the [`push_str`][String::push_str] method.
2422#[cfg(not(no_global_oom_handling))]
2423#[stable(feature = "stringaddassign", since = "1.12.0")]
2424impl AddAssign<&str> for String {
2425 #[inline]
2426 fn add_assign(&mut self, other: &str) {
2427 self.push_str(string:other);
2428 }
2429}
2430
2431#[stable(feature = "rust1", since = "1.0.0")]
2432impl ops::Index<ops::Range<usize>> for String {
2433 type Output = str;
2434
2435 #[inline]
2436 fn index(&self, index: ops::Range<usize>) -> &str {
2437 &self[..][index]
2438 }
2439}
2440#[stable(feature = "rust1", since = "1.0.0")]
2441impl ops::Index<ops::RangeTo<usize>> for String {
2442 type Output = str;
2443
2444 #[inline]
2445 fn index(&self, index: ops::RangeTo<usize>) -> &str {
2446 &self[..][index]
2447 }
2448}
2449#[stable(feature = "rust1", since = "1.0.0")]
2450impl ops::Index<ops::RangeFrom<usize>> for String {
2451 type Output = str;
2452
2453 #[inline]
2454 fn index(&self, index: ops::RangeFrom<usize>) -> &str {
2455 &self[..][index]
2456 }
2457}
2458#[stable(feature = "rust1", since = "1.0.0")]
2459impl ops::Index<ops::RangeFull> for String {
2460 type Output = str;
2461
2462 #[inline]
2463 fn index(&self, _index: ops::RangeFull) -> &str {
2464 unsafe { str::from_utf8_unchecked(&self.vec) }
2465 }
2466}
2467#[stable(feature = "inclusive_range", since = "1.26.0")]
2468impl ops::Index<ops::RangeInclusive<usize>> for String {
2469 type Output = str;
2470
2471 #[inline]
2472 fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
2473 Index::index(&**self, index)
2474 }
2475}
2476#[stable(feature = "inclusive_range", since = "1.26.0")]
2477impl ops::Index<ops::RangeToInclusive<usize>> for String {
2478 type Output = str;
2479
2480 #[inline]
2481 fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
2482 Index::index(&**self, index)
2483 }
2484}
2485
2486#[stable(feature = "derefmut_for_string", since = "1.3.0")]
2487impl ops::IndexMut<ops::Range<usize>> for String {
2488 #[inline]
2489 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
2490 &mut self[..][index]
2491 }
2492}
2493#[stable(feature = "derefmut_for_string", since = "1.3.0")]
2494impl ops::IndexMut<ops::RangeTo<usize>> for String {
2495 #[inline]
2496 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
2497 &mut self[..][index]
2498 }
2499}
2500#[stable(feature = "derefmut_for_string", since = "1.3.0")]
2501impl ops::IndexMut<ops::RangeFrom<usize>> for String {
2502 #[inline]
2503 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
2504 &mut self[..][index]
2505 }
2506}
2507#[stable(feature = "derefmut_for_string", since = "1.3.0")]
2508impl ops::IndexMut<ops::RangeFull> for String {
2509 #[inline]
2510 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
2511 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2512 }
2513}
2514#[stable(feature = "inclusive_range", since = "1.26.0")]
2515impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
2516 #[inline]
2517 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
2518 IndexMut::index_mut(&mut **self, index)
2519 }
2520}
2521#[stable(feature = "inclusive_range", since = "1.26.0")]
2522impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
2523 #[inline]
2524 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
2525 IndexMut::index_mut(&mut **self, index)
2526 }
2527}
2528
2529#[stable(feature = "rust1", since = "1.0.0")]
2530impl ops::Deref for String {
2531 type Target = str;
2532
2533 #[inline]
2534 fn deref(&self) -> &str {
2535 unsafe { str::from_utf8_unchecked(&self.vec) }
2536 }
2537}
2538
2539#[stable(feature = "derefmut_for_string", since = "1.3.0")]
2540impl ops::DerefMut for String {
2541 #[inline]
2542 fn deref_mut(&mut self) -> &mut str {
2543 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2544 }
2545}
2546
2547/// A type alias for [`Infallible`].
2548///
2549/// This alias exists for backwards compatibility, and may be eventually deprecated.
2550///
2551/// [`Infallible`]: core::convert::Infallible "convert::Infallible"
2552#[stable(feature = "str_parse_error", since = "1.5.0")]
2553pub type ParseError = core::convert::Infallible;
2554
2555#[cfg(not(no_global_oom_handling))]
2556#[stable(feature = "rust1", since = "1.0.0")]
2557impl FromStr for String {
2558 type Err = core::convert::Infallible;
2559 #[inline]
2560 fn from_str(s: &str) -> Result<String, Self::Err> {
2561 Ok(String::from(s))
2562 }
2563}
2564
2565/// A trait for converting a value to a `String`.
2566///
2567/// This trait is automatically implemented for any type which implements the
2568/// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
2569/// [`Display`] should be implemented instead, and you get the `ToString`
2570/// implementation for free.
2571///
2572/// [`Display`]: fmt::Display
2573#[cfg_attr(not(test), rustc_diagnostic_item = "ToString")]
2574#[stable(feature = "rust1", since = "1.0.0")]
2575pub trait ToString {
2576 /// Converts the given value to a `String`.
2577 ///
2578 /// # Examples
2579 ///
2580 /// ```
2581 /// let i = 5;
2582 /// let five = String::from("5");
2583 ///
2584 /// assert_eq!(five, i.to_string());
2585 /// ```
2586 #[rustc_conversion_suggestion]
2587 #[stable(feature = "rust1", since = "1.0.0")]
2588 #[cfg_attr(not(test), rustc_diagnostic_item = "to_string_method")]
2589 fn to_string(&self) -> String;
2590}
2591
2592/// # Panics
2593///
2594/// In this implementation, the `to_string` method panics
2595/// if the `Display` implementation returns an error.
2596/// This indicates an incorrect `Display` implementation
2597/// since `fmt::Write for String` never returns an error itself.
2598#[cfg(not(no_global_oom_handling))]
2599#[stable(feature = "rust1", since = "1.0.0")]
2600impl<T: fmt::Display + ?Sized> ToString for T {
2601 // A common guideline is to not inline generic functions. However,
2602 // removing `#[inline]` from this method causes non-negligible regressions.
2603 // See <https://github.com/rust-lang/rust/pull/74852>, the last attempt
2604 // to try to remove it.
2605 #[inline]
2606 default fn to_string(&self) -> String {
2607 let mut buf: String = String::new();
2608 let mut formatter: Formatter<'_> = core::fmt::Formatter::new(&mut buf);
2609 // Bypass format_args!() to avoid write_str with zero-length strs
2610 fmt::Display::fmt(self, &mut formatter)
2611 .expect(msg:"a Display implementation returned an error unexpectedly");
2612 buf
2613 }
2614}
2615
2616#[doc(hidden)]
2617#[cfg(not(no_global_oom_handling))]
2618#[unstable(feature = "ascii_char", issue = "110998")]
2619impl ToString for core::ascii::Char {
2620 #[inline]
2621 fn to_string(&self) -> String {
2622 self.as_str().to_owned()
2623 }
2624}
2625
2626#[doc(hidden)]
2627#[cfg(not(no_global_oom_handling))]
2628#[stable(feature = "char_to_string_specialization", since = "1.46.0")]
2629impl ToString for char {
2630 #[inline]
2631 fn to_string(&self) -> String {
2632 String::from(self.encode_utf8(&mut [0; 4]))
2633 }
2634}
2635
2636#[doc(hidden)]
2637#[cfg(not(no_global_oom_handling))]
2638#[stable(feature = "bool_to_string_specialization", since = "1.68.0")]
2639impl ToString for bool {
2640 #[inline]
2641 fn to_string(&self) -> String {
2642 String::from(if *self { "true" } else { "false" })
2643 }
2644}
2645
2646#[doc(hidden)]
2647#[cfg(not(no_global_oom_handling))]
2648#[stable(feature = "u8_to_string_specialization", since = "1.54.0")]
2649impl ToString for u8 {
2650 #[inline]
2651 fn to_string(&self) -> String {
2652 let mut buf: String = String::with_capacity(3);
2653 let mut n: u8 = *self;
2654 if n >= 10 {
2655 if n >= 100 {
2656 buf.push((b'0' + n / 100) as char);
2657 n %= 100;
2658 }
2659 buf.push((b'0' + n / 10) as char);
2660 n %= 10;
2661 }
2662 buf.push((b'0' + n) as char);
2663 buf
2664 }
2665}
2666
2667#[doc(hidden)]
2668#[cfg(not(no_global_oom_handling))]
2669#[stable(feature = "i8_to_string_specialization", since = "1.54.0")]
2670impl ToString for i8 {
2671 #[inline]
2672 fn to_string(&self) -> String {
2673 let mut buf: String = String::with_capacity(4);
2674 if self.is_negative() {
2675 buf.push(ch:'-');
2676 }
2677 let mut n: u8 = self.unsigned_abs();
2678 if n >= 10 {
2679 if n >= 100 {
2680 buf.push(ch:'1');
2681 n -= 100;
2682 }
2683 buf.push((b'0' + n / 10) as char);
2684 n %= 10;
2685 }
2686 buf.push((b'0' + n) as char);
2687 buf
2688 }
2689}
2690
2691#[doc(hidden)]
2692#[cfg(not(no_global_oom_handling))]
2693#[stable(feature = "str_to_string_specialization", since = "1.9.0")]
2694impl ToString for str {
2695 #[inline]
2696 fn to_string(&self) -> String {
2697 String::from(self)
2698 }
2699}
2700
2701#[doc(hidden)]
2702#[cfg(not(no_global_oom_handling))]
2703#[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
2704impl ToString for Cow<'_, str> {
2705 #[inline]
2706 fn to_string(&self) -> String {
2707 self[..].to_owned()
2708 }
2709}
2710
2711#[doc(hidden)]
2712#[cfg(not(no_global_oom_handling))]
2713#[stable(feature = "string_to_string_specialization", since = "1.17.0")]
2714impl ToString for String {
2715 #[inline]
2716 fn to_string(&self) -> String {
2717 self.to_owned()
2718 }
2719}
2720
2721#[doc(hidden)]
2722#[cfg(not(no_global_oom_handling))]
2723#[stable(feature = "fmt_arguments_to_string_specialization", since = "1.71.0")]
2724impl ToString for fmt::Arguments<'_> {
2725 #[inline]
2726 fn to_string(&self) -> String {
2727 crate::fmt::format(*self)
2728 }
2729}
2730
2731#[stable(feature = "rust1", since = "1.0.0")]
2732impl AsRef<str> for String {
2733 #[inline]
2734 fn as_ref(&self) -> &str {
2735 self
2736 }
2737}
2738
2739#[stable(feature = "string_as_mut", since = "1.43.0")]
2740impl AsMut<str> for String {
2741 #[inline]
2742 fn as_mut(&mut self) -> &mut str {
2743 self
2744 }
2745}
2746
2747#[stable(feature = "rust1", since = "1.0.0")]
2748impl AsRef<[u8]> for String {
2749 #[inline]
2750 fn as_ref(&self) -> &[u8] {
2751 self.as_bytes()
2752 }
2753}
2754
2755#[cfg(not(no_global_oom_handling))]
2756#[stable(feature = "rust1", since = "1.0.0")]
2757impl From<&str> for String {
2758 /// Converts a `&str` into a [`String`].
2759 ///
2760 /// The result is allocated on the heap.
2761 #[inline]
2762 fn from(s: &str) -> String {
2763 s.to_owned()
2764 }
2765}
2766
2767#[cfg(not(no_global_oom_handling))]
2768#[stable(feature = "from_mut_str_for_string", since = "1.44.0")]
2769impl From<&mut str> for String {
2770 /// Converts a `&mut str` into a [`String`].
2771 ///
2772 /// The result is allocated on the heap.
2773 #[inline]
2774 fn from(s: &mut str) -> String {
2775 s.to_owned()
2776 }
2777}
2778
2779#[cfg(not(no_global_oom_handling))]
2780#[stable(feature = "from_ref_string", since = "1.35.0")]
2781impl From<&String> for String {
2782 /// Converts a `&String` into a [`String`].
2783 ///
2784 /// This clones `s` and returns the clone.
2785 #[inline]
2786 fn from(s: &String) -> String {
2787 s.clone()
2788 }
2789}
2790
2791// note: test pulls in std, which causes errors here
2792#[cfg(not(test))]
2793#[stable(feature = "string_from_box", since = "1.18.0")]
2794impl From<Box<str>> for String {
2795 /// Converts the given boxed `str` slice to a [`String`].
2796 /// It is notable that the `str` slice is owned.
2797 ///
2798 /// # Examples
2799 ///
2800 /// ```
2801 /// let s1: String = String::from("hello world");
2802 /// let s2: Box<str> = s1.into_boxed_str();
2803 /// let s3: String = String::from(s2);
2804 ///
2805 /// assert_eq!("hello world", s3)
2806 /// ```
2807 fn from(s: Box<str>) -> String {
2808 s.into_string()
2809 }
2810}
2811
2812#[cfg(not(no_global_oom_handling))]
2813#[stable(feature = "box_from_str", since = "1.20.0")]
2814impl From<String> for Box<str> {
2815 /// Converts the given [`String`] to a boxed `str` slice that is owned.
2816 ///
2817 /// # Examples
2818 ///
2819 /// ```
2820 /// let s1: String = String::from("hello world");
2821 /// let s2: Box<str> = Box::from(s1);
2822 /// let s3: String = String::from(s2);
2823 ///
2824 /// assert_eq!("hello world", s3)
2825 /// ```
2826 fn from(s: String) -> Box<str> {
2827 s.into_boxed_str()
2828 }
2829}
2830
2831#[cfg(not(no_global_oom_handling))]
2832#[stable(feature = "string_from_cow_str", since = "1.14.0")]
2833impl<'a> From<Cow<'a, str>> for String {
2834 /// Converts a clone-on-write string to an owned
2835 /// instance of [`String`].
2836 ///
2837 /// This extracts the owned string,
2838 /// clones the string if it is not already owned.
2839 ///
2840 /// # Example
2841 ///
2842 /// ```
2843 /// # use std::borrow::Cow;
2844 /// // If the string is not owned...
2845 /// let cow: Cow<'_, str> = Cow::Borrowed("eggplant");
2846 /// // It will allocate on the heap and copy the string.
2847 /// let owned: String = String::from(cow);
2848 /// assert_eq!(&owned[..], "eggplant");
2849 /// ```
2850 fn from(s: Cow<'a, str>) -> String {
2851 s.into_owned()
2852 }
2853}
2854
2855#[cfg(not(no_global_oom_handling))]
2856#[stable(feature = "rust1", since = "1.0.0")]
2857impl<'a> From<&'a str> for Cow<'a, str> {
2858 /// Converts a string slice into a [`Borrowed`] variant.
2859 /// No heap allocation is performed, and the string
2860 /// is not copied.
2861 ///
2862 /// # Example
2863 ///
2864 /// ```
2865 /// # use std::borrow::Cow;
2866 /// assert_eq!(Cow::from("eggplant"), Cow::Borrowed("eggplant"));
2867 /// ```
2868 ///
2869 /// [`Borrowed`]: crate::borrow::Cow::Borrowed "borrow::Cow::Borrowed"
2870 #[inline]
2871 fn from(s: &'a str) -> Cow<'a, str> {
2872 Cow::Borrowed(s)
2873 }
2874}
2875
2876#[cfg(not(no_global_oom_handling))]
2877#[stable(feature = "rust1", since = "1.0.0")]
2878impl<'a> From<String> for Cow<'a, str> {
2879 /// Converts a [`String`] into an [`Owned`] variant.
2880 /// No heap allocation is performed, and the string
2881 /// is not copied.
2882 ///
2883 /// # Example
2884 ///
2885 /// ```
2886 /// # use std::borrow::Cow;
2887 /// let s = "eggplant".to_string();
2888 /// let s2 = "eggplant".to_string();
2889 /// assert_eq!(Cow::from(s), Cow::<'static, str>::Owned(s2));
2890 /// ```
2891 ///
2892 /// [`Owned`]: crate::borrow::Cow::Owned "borrow::Cow::Owned"
2893 #[inline]
2894 fn from(s: String) -> Cow<'a, str> {
2895 Cow::Owned(s)
2896 }
2897}
2898
2899#[cfg(not(no_global_oom_handling))]
2900#[stable(feature = "cow_from_string_ref", since = "1.28.0")]
2901impl<'a> From<&'a String> for Cow<'a, str> {
2902 /// Converts a [`String`] reference into a [`Borrowed`] variant.
2903 /// No heap allocation is performed, and the string
2904 /// is not copied.
2905 ///
2906 /// # Example
2907 ///
2908 /// ```
2909 /// # use std::borrow::Cow;
2910 /// let s = "eggplant".to_string();
2911 /// assert_eq!(Cow::from(&s), Cow::Borrowed("eggplant"));
2912 /// ```
2913 ///
2914 /// [`Borrowed`]: crate::borrow::Cow::Borrowed "borrow::Cow::Borrowed"
2915 #[inline]
2916 fn from(s: &'a String) -> Cow<'a, str> {
2917 Cow::Borrowed(s.as_str())
2918 }
2919}
2920
2921#[cfg(not(no_global_oom_handling))]
2922#[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2923impl<'a> FromIterator<char> for Cow<'a, str> {
2924 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
2925 Cow::Owned(FromIterator::from_iter(it))
2926 }
2927}
2928
2929#[cfg(not(no_global_oom_handling))]
2930#[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2931impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
2932 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
2933 Cow::Owned(FromIterator::from_iter(it))
2934 }
2935}
2936
2937#[cfg(not(no_global_oom_handling))]
2938#[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2939impl<'a> FromIterator<String> for Cow<'a, str> {
2940 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
2941 Cow::Owned(FromIterator::from_iter(it))
2942 }
2943}
2944
2945#[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
2946impl From<String> for Vec<u8> {
2947 /// Converts the given [`String`] to a vector [`Vec`] that holds values of type [`u8`].
2948 ///
2949 /// # Examples
2950 ///
2951 /// ```
2952 /// let s1 = String::from("hello world");
2953 /// let v1 = Vec::from(s1);
2954 ///
2955 /// for b in v1 {
2956 /// println!("{b}");
2957 /// }
2958 /// ```
2959 fn from(string: String) -> Vec<u8> {
2960 string.into_bytes()
2961 }
2962}
2963
2964#[cfg(not(no_global_oom_handling))]
2965#[stable(feature = "rust1", since = "1.0.0")]
2966impl fmt::Write for String {
2967 #[inline]
2968 fn write_str(&mut self, s: &str) -> fmt::Result {
2969 self.push_str(string:s);
2970 Ok(())
2971 }
2972
2973 #[inline]
2974 fn write_char(&mut self, c: char) -> fmt::Result {
2975 self.push(ch:c);
2976 Ok(())
2977 }
2978}
2979
2980/// A draining iterator for `String`.
2981///
2982/// This struct is created by the [`drain`] method on [`String`]. See its
2983/// documentation for more.
2984///
2985/// [`drain`]: String::drain
2986#[stable(feature = "drain", since = "1.6.0")]
2987pub struct Drain<'a> {
2988 /// Will be used as &'a mut String in the destructor
2989 string: *mut String,
2990 /// Start of part to remove
2991 start: usize,
2992 /// End of part to remove
2993 end: usize,
2994 /// Current remaining range to remove
2995 iter: Chars<'a>,
2996}
2997
2998#[stable(feature = "collection_debug", since = "1.17.0")]
2999impl fmt::Debug for Drain<'_> {
3000 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
3001 f.debug_tuple(name:"Drain").field(&self.as_str()).finish()
3002 }
3003}
3004
3005#[stable(feature = "drain", since = "1.6.0")]
3006unsafe impl Sync for Drain<'_> {}
3007#[stable(feature = "drain", since = "1.6.0")]
3008unsafe impl Send for Drain<'_> {}
3009
3010#[stable(feature = "drain", since = "1.6.0")]
3011impl Drop for Drain<'_> {
3012 fn drop(&mut self) {
3013 unsafe {
3014 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
3015 // panic code being inserted again.
3016 let self_vec: &mut Vec = (*self.string).as_mut_vec();
3017 if self.start <= self.end && self.end <= self_vec.len() {
3018 self_vec.drain(self.start..self.end);
3019 }
3020 }
3021 }
3022}
3023
3024impl<'a> Drain<'a> {
3025 /// Returns the remaining (sub)string of this iterator as a slice.
3026 ///
3027 /// # Examples
3028 ///
3029 /// ```
3030 /// let mut s = String::from("abc");
3031 /// let mut drain = s.drain(..);
3032 /// assert_eq!(drain.as_str(), "abc");
3033 /// let _ = drain.next().unwrap();
3034 /// assert_eq!(drain.as_str(), "bc");
3035 /// ```
3036 #[must_use]
3037 #[stable(feature = "string_drain_as_str", since = "1.55.0")]
3038 pub fn as_str(&self) -> &str {
3039 self.iter.as_str()
3040 }
3041}
3042
3043#[stable(feature = "string_drain_as_str", since = "1.55.0")]
3044impl<'a> AsRef<str> for Drain<'a> {
3045 fn as_ref(&self) -> &str {
3046 self.as_str()
3047 }
3048}
3049
3050#[stable(feature = "string_drain_as_str", since = "1.55.0")]
3051impl<'a> AsRef<[u8]> for Drain<'a> {
3052 fn as_ref(&self) -> &[u8] {
3053 self.as_str().as_bytes()
3054 }
3055}
3056
3057#[stable(feature = "drain", since = "1.6.0")]
3058impl Iterator for Drain<'_> {
3059 type Item = char;
3060
3061 #[inline]
3062 fn next(&mut self) -> Option<char> {
3063 self.iter.next()
3064 }
3065
3066 fn size_hint(&self) -> (usize, Option<usize>) {
3067 self.iter.size_hint()
3068 }
3069
3070 #[inline]
3071 fn last(mut self) -> Option<char> {
3072 self.next_back()
3073 }
3074}
3075
3076#[stable(feature = "drain", since = "1.6.0")]
3077impl DoubleEndedIterator for Drain<'_> {
3078 #[inline]
3079 fn next_back(&mut self) -> Option<char> {
3080 self.iter.next_back()
3081 }
3082}
3083
3084#[stable(feature = "fused", since = "1.26.0")]
3085impl FusedIterator for Drain<'_> {}
3086
3087#[cfg(not(no_global_oom_handling))]
3088#[stable(feature = "from_char_for_string", since = "1.46.0")]
3089impl From<char> for String {
3090 /// Allocates an owned [`String`] from a single character.
3091 ///
3092 /// # Example
3093 /// ```rust
3094 /// let c: char = 'a';
3095 /// let s: String = String::from(c);
3096 /// assert_eq!("a", &s[..]);
3097 /// ```
3098 #[inline]
3099 fn from(c: char) -> Self {
3100 c.to_string()
3101 }
3102}
3103