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::iter::FusedIterator;
47#[cfg(not(no_global_oom_handling))]
48use core::iter::from_fn;
49#[cfg(not(no_global_oom_handling))]
50use core::num::Saturating;
51#[cfg(not(no_global_oom_handling))]
52use core::ops::Add;
53#[cfg(not(no_global_oom_handling))]
54use core::ops::AddAssign;
55use core::ops::{self, Range, RangeBounds};
56use core::str::pattern::{Pattern, Utf8Pattern};
57use core::{fmt, hash, ptr, slice};
58
59#[cfg(not(no_global_oom_handling))]
60use crate::alloc::Allocator;
61#[cfg(not(no_global_oom_handling))]
62use crate::borrow::{Cow, ToOwned};
63use crate::boxed::Box;
64use crate::collections::TryReserveError;
65use crate::str::{self, CharIndices, Chars, Utf8Error, from_utf8_unchecked_mut};
66#[cfg(not(no_global_oom_handling))]
67use crate::str::{FromStr, from_boxed_utf8_unchecked};
68use crate::vec::{self, Vec};
69
70/// A UTF-8–encoded, growable string.
71///
72/// `String` is the most common string type. It has ownership over the contents
73/// of the string, stored in a heap-allocated buffer (see [Representation](#representation)).
74/// It is closely related to its borrowed counterpart, the primitive [`str`].
75///
76/// # Examples
77///
78/// You can create a `String` from [a literal string][`&str`] with [`String::from`]:
79///
80/// [`String::from`]: From::from
81///
82/// ```
83/// let hello = String::from("Hello, world!");
84/// ```
85///
86/// You can append a [`char`] to a `String` with the [`push`] method, and
87/// append a [`&str`] with the [`push_str`] method:
88///
89/// ```
90/// let mut hello = String::from("Hello, ");
91///
92/// hello.push('w');
93/// hello.push_str("orld!");
94/// ```
95///
96/// [`push`]: String::push
97/// [`push_str`]: String::push_str
98///
99/// If you have a vector of UTF-8 bytes, you can create a `String` from it with
100/// the [`from_utf8`] method:
101///
102/// ```
103/// // some bytes, in a vector
104/// let sparkle_heart = vec![240, 159, 146, 150];
105///
106/// // We know these bytes are valid, so we'll use `unwrap()`.
107/// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
108///
109/// assert_eq!("πŸ’–", sparkle_heart);
110/// ```
111///
112/// [`from_utf8`]: String::from_utf8
113///
114/// # UTF-8
115///
116/// `String`s are always valid UTF-8. If you need a non-UTF-8 string, consider
117/// [`OsString`]. It is similar, but without the UTF-8 constraint. Because UTF-8
118/// is a variable width encoding, `String`s are typically smaller than an array of
119/// the same `char`s:
120///
121/// ```
122/// // `s` is ASCII which represents each `char` as one byte
123/// let s = "hello";
124/// assert_eq!(s.len(), 5);
125///
126/// // A `char` array with the same contents would be longer because
127/// // every `char` is four bytes
128/// let s = ['h', 'e', 'l', 'l', 'o'];
129/// let size: usize = s.into_iter().map(|c| size_of_val(&c)).sum();
130/// assert_eq!(size, 20);
131///
132/// // However, for non-ASCII strings, the difference will be smaller
133/// // and sometimes they are the same
134/// let s = "πŸ’–πŸ’–πŸ’–πŸ’–πŸ’–";
135/// assert_eq!(s.len(), 20);
136///
137/// let s = ['πŸ’–', 'πŸ’–', 'πŸ’–', 'πŸ’–', 'πŸ’–'];
138/// let size: usize = s.into_iter().map(|c| size_of_val(&c)).sum();
139/// assert_eq!(size, 20);
140/// ```
141///
142/// This raises interesting questions as to how `s[i]` should work.
143/// What should `i` be here? Several options include byte indices and
144/// `char` indices but, because of UTF-8 encoding, only byte indices
145/// would provide constant time indexing. Getting the `i`th `char`, for
146/// example, is available using [`chars`]:
147///
148/// ```
149/// let s = "hello";
150/// let third_character = s.chars().nth(2);
151/// assert_eq!(third_character, Some('l'));
152///
153/// let s = "πŸ’–πŸ’–πŸ’–πŸ’–πŸ’–";
154/// let third_character = s.chars().nth(2);
155/// assert_eq!(third_character, Some('πŸ’–'));
156/// ```
157///
158/// Next, what should `s[i]` return? Because indexing returns a reference
159/// to underlying data it could be `&u8`, `&[u8]`, or something similar.
160/// Since we're only providing one index, `&u8` makes the most sense but that
161/// might not be what the user expects and can be explicitly achieved with
162/// [`as_bytes()`]:
163///
164/// ```
165/// // The first byte is 104 - the byte value of `'h'`
166/// let s = "hello";
167/// assert_eq!(s.as_bytes()[0], 104);
168/// // or
169/// assert_eq!(s.as_bytes()[0], b'h');
170///
171/// // The first byte is 240 which isn't obviously useful
172/// let s = "πŸ’–πŸ’–πŸ’–πŸ’–πŸ’–";
173/// assert_eq!(s.as_bytes()[0], 240);
174/// ```
175///
176/// Due to these ambiguities/restrictions, indexing with a `usize` is simply
177/// forbidden:
178///
179/// ```compile_fail,E0277
180/// let s = "hello";
181///
182/// // The following will not compile!
183/// println!("The first letter of s is {}", s[0]);
184/// ```
185///
186/// It is more clear, however, how `&s[i..j]` should work (that is,
187/// indexing with a range). It should accept byte indices (to be constant-time)
188/// and return a `&str` which is UTF-8 encoded. This is also called "string slicing".
189/// Note this will panic if the byte indices provided are not character
190/// boundaries - see [`is_char_boundary`] for more details. See the implementations
191/// for [`SliceIndex<str>`] for more details on string slicing. For a non-panicking
192/// version of string slicing, see [`get`].
193///
194/// [`OsString`]: ../../std/ffi/struct.OsString.html "ffi::OsString"
195/// [`SliceIndex<str>`]: core::slice::SliceIndex
196/// [`as_bytes()`]: str::as_bytes
197/// [`get`]: str::get
198/// [`is_char_boundary`]: str::is_char_boundary
199///
200/// The [`bytes`] and [`chars`] methods return iterators over the bytes and
201/// codepoints of the string, respectively. To iterate over codepoints along
202/// with byte indices, use [`char_indices`].
203///
204/// [`bytes`]: str::bytes
205/// [`chars`]: str::chars
206/// [`char_indices`]: str::char_indices
207///
208/// # Deref
209///
210/// `String` implements <code>[Deref]<Target = [str]></code>, and so inherits all of [`str`]'s
211/// methods. In addition, this means that you can pass a `String` to a
212/// function which takes a [`&str`] by using an ampersand (`&`):
213///
214/// ```
215/// fn takes_str(s: &str) { }
216///
217/// let s = String::from("Hello");
218///
219/// takes_str(&s);
220/// ```
221///
222/// This will create a [`&str`] from the `String` and pass it in. This
223/// conversion is very inexpensive, and so generally, functions will accept
224/// [`&str`]s as arguments unless they need a `String` for some specific
225/// reason.
226///
227/// In certain cases Rust doesn't have enough information to make this
228/// conversion, known as [`Deref`] coercion. In the following example a string
229/// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
230/// `example_func` takes anything that implements the trait. In this case Rust
231/// would need to make two implicit conversions, which Rust doesn't have the
232/// means to do. For that reason, the following example will not compile.
233///
234/// ```compile_fail,E0277
235/// trait TraitExample {}
236///
237/// impl<'a> TraitExample for &'a str {}
238///
239/// fn example_func<A: TraitExample>(example_arg: A) {}
240///
241/// let example_string = String::from("example_string");
242/// example_func(&example_string);
243/// ```
244///
245/// There are two options that would work instead. The first would be to
246/// change the line `example_func(&example_string);` to
247/// `example_func(example_string.as_str());`, using the method [`as_str()`]
248/// to explicitly extract the string slice containing the string. The second
249/// way changes `example_func(&example_string);` to
250/// `example_func(&*example_string);`. In this case we are dereferencing a
251/// `String` to a [`str`], then referencing the [`str`] back to
252/// [`&str`]. The second way is more idiomatic, however both work to do the
253/// conversion explicitly rather than relying on the implicit conversion.
254///
255/// # Representation
256///
257/// A `String` is made up of three components: a pointer to some bytes, a
258/// length, and a capacity. The pointer points to the internal buffer which `String`
259/// uses to store its data. The length is the number of bytes currently stored
260/// in the buffer, and the capacity is the size of the buffer in bytes. As such,
261/// the length will always be less than or equal to the capacity.
262///
263/// This buffer is always stored on the heap.
264///
265/// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
266/// methods:
267///
268/// ```
269/// let story = String::from("Once upon a time...");
270///
271/// // Deconstruct the String into parts.
272/// let (ptr, len, capacity) = story.into_raw_parts();
273///
274/// // story has nineteen bytes
275/// assert_eq!(19, len);
276///
277/// // We can re-build a String out of ptr, len, and capacity. This is all
278/// // unsafe because we are responsible for making sure the components are
279/// // valid:
280/// let s = unsafe { String::from_raw_parts(ptr, len, capacity) } ;
281///
282/// assert_eq!(String::from("Once upon a time..."), s);
283/// ```
284///
285/// [`as_ptr`]: str::as_ptr
286/// [`len`]: String::len
287/// [`capacity`]: String::capacity
288///
289/// If a `String` has enough capacity, adding elements to it will not
290/// re-allocate. For example, consider this program:
291///
292/// ```
293/// let mut s = String::new();
294///
295/// println!("{}", s.capacity());
296///
297/// for _ in 0..5 {
298/// s.push_str("hello");
299/// println!("{}", s.capacity());
300/// }
301/// ```
302///
303/// This will output the following:
304///
305/// ```text
306/// 0
307/// 8
308/// 16
309/// 16
310/// 32
311/// 32
312/// ```
313///
314/// At first, we have no memory allocated at all, but as we append to the
315/// string, it increases its capacity appropriately. If we instead use the
316/// [`with_capacity`] method to allocate the correct capacity initially:
317///
318/// ```
319/// let mut s = String::with_capacity(25);
320///
321/// println!("{}", s.capacity());
322///
323/// for _ in 0..5 {
324/// s.push_str("hello");
325/// println!("{}", s.capacity());
326/// }
327/// ```
328///
329/// [`with_capacity`]: String::with_capacity
330///
331/// We end up with a different output:
332///
333/// ```text
334/// 25
335/// 25
336/// 25
337/// 25
338/// 25
339/// 25
340/// ```
341///
342/// Here, there's no need to allocate more memory inside the loop.
343///
344/// [str]: prim@str "str"
345/// [`str`]: prim@str "str"
346/// [`&str`]: prim@str "&str"
347/// [Deref]: core::ops::Deref "ops::Deref"
348/// [`Deref`]: core::ops::Deref "ops::Deref"
349/// [`as_str()`]: String::as_str
350#[derive(PartialEq, PartialOrd, Eq, Ord)]
351#[stable(feature = "rust1", since = "1.0.0")]
352#[lang = "String"]
353pub struct String {
354 vec: Vec<u8>,
355}
356
357/// A possible error value when converting a `String` from a UTF-8 byte vector.
358///
359/// This type is the error type for the [`from_utf8`] method on [`String`]. It
360/// is designed in such a way to carefully avoid reallocations: the
361/// [`into_bytes`] method will give back the byte vector that was used in the
362/// conversion attempt.
363///
364/// [`from_utf8`]: String::from_utf8
365/// [`into_bytes`]: FromUtf8Error::into_bytes
366///
367/// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
368/// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
369/// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
370/// through the [`utf8_error`] method.
371///
372/// [`Utf8Error`]: str::Utf8Error "std::str::Utf8Error"
373/// [`std::str`]: core::str "std::str"
374/// [`&str`]: prim@str "&str"
375/// [`utf8_error`]: FromUtf8Error::utf8_error
376///
377/// # Examples
378///
379/// ```
380/// // some invalid bytes, in a vector
381/// let bytes = vec![0, 159];
382///
383/// let value = String::from_utf8(bytes);
384///
385/// assert!(value.is_err());
386/// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
387/// ```
388#[stable(feature = "rust1", since = "1.0.0")]
389#[cfg_attr(not(no_global_oom_handling), derive(Clone))]
390#[derive(Debug, PartialEq, Eq)]
391pub struct FromUtf8Error {
392 bytes: Vec<u8>,
393 error: Utf8Error,
394}
395
396/// A possible error value when converting a `String` from a UTF-16 byte slice.
397///
398/// This type is the error type for the [`from_utf16`] method on [`String`].
399///
400/// [`from_utf16`]: String::from_utf16
401///
402/// # Examples
403///
404/// ```
405/// // π„žmu<invalid>ic
406/// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
407/// 0xD800, 0x0069, 0x0063];
408///
409/// assert!(String::from_utf16(v).is_err());
410/// ```
411#[stable(feature = "rust1", since = "1.0.0")]
412#[derive(Debug)]
413pub struct FromUtf16Error(());
414
415impl String {
416 /// Creates a new empty `String`.
417 ///
418 /// Given that the `String` is empty, this will not allocate any initial
419 /// buffer. While that means that this initial operation is very
420 /// inexpensive, it may cause excessive allocation later when you add
421 /// data. If you have an idea of how much data the `String` will hold,
422 /// consider the [`with_capacity`] method to prevent excessive
423 /// re-allocation.
424 ///
425 /// [`with_capacity`]: String::with_capacity
426 ///
427 /// # Examples
428 ///
429 /// ```
430 /// let s = String::new();
431 /// ```
432 #[inline]
433 #[rustc_const_stable(feature = "const_string_new", since = "1.39.0")]
434 #[rustc_diagnostic_item = "string_new"]
435 #[stable(feature = "rust1", since = "1.0.0")]
436 #[must_use]
437 pub const fn new() -> String {
438 String { vec: Vec::new() }
439 }
440
441 /// Creates a new empty `String` with at least the specified capacity.
442 ///
443 /// `String`s have an internal buffer to hold their data. The capacity is
444 /// the length of that buffer, and can be queried with the [`capacity`]
445 /// method. This method creates an empty `String`, but one with an initial
446 /// buffer that can hold at least `capacity` bytes. This is useful when you
447 /// may be appending a bunch of data to the `String`, reducing the number of
448 /// reallocations it needs to do.
449 ///
450 /// [`capacity`]: String::capacity
451 ///
452 /// If the given capacity is `0`, no allocation will occur, and this method
453 /// is identical to the [`new`] method.
454 ///
455 /// [`new`]: String::new
456 ///
457 /// # Panics
458 ///
459 /// Panics if the capacity exceeds `isize::MAX` _bytes_.
460 ///
461 /// # Examples
462 ///
463 /// ```
464 /// let mut s = String::with_capacity(10);
465 ///
466 /// // The String contains no chars, even though it has capacity for more
467 /// assert_eq!(s.len(), 0);
468 ///
469 /// // These are all done without reallocating...
470 /// let cap = s.capacity();
471 /// for _ in 0..10 {
472 /// s.push('a');
473 /// }
474 ///
475 /// assert_eq!(s.capacity(), cap);
476 ///
477 /// // ...but this may make the string reallocate
478 /// s.push('a');
479 /// ```
480 #[cfg(not(no_global_oom_handling))]
481 #[inline]
482 #[stable(feature = "rust1", since = "1.0.0")]
483 #[must_use]
484 pub fn with_capacity(capacity: usize) -> String {
485 String { vec: Vec::with_capacity(capacity) }
486 }
487
488 /// Creates a new empty `String` with at least the specified capacity.
489 ///
490 /// # Errors
491 ///
492 /// Returns [`Err`] if the capacity exceeds `isize::MAX` bytes,
493 /// or if the memory allocator reports failure.
494 ///
495 #[inline]
496 #[unstable(feature = "try_with_capacity", issue = "91913")]
497 pub fn try_with_capacity(capacity: usize) -> Result<String, TryReserveError> {
498 Ok(String { vec: Vec::try_with_capacity(capacity)? })
499 }
500
501 /// Converts a vector of bytes to a `String`.
502 ///
503 /// A string ([`String`]) is made of bytes ([`u8`]), and a vector of bytes
504 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
505 /// two. Not all byte slices are valid `String`s, however: `String`
506 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
507 /// the bytes are valid UTF-8, and then does the conversion.
508 ///
509 /// If you are sure that the byte slice is valid UTF-8, and you don't want
510 /// to incur the overhead of the validity check, there is an unsafe version
511 /// of this function, [`from_utf8_unchecked`], which has the same behavior
512 /// but skips the check.
513 ///
514 /// This method will take care to not copy the vector, for efficiency's
515 /// sake.
516 ///
517 /// If you need a [`&str`] instead of a `String`, consider
518 /// [`str::from_utf8`].
519 ///
520 /// The inverse of this method is [`into_bytes`].
521 ///
522 /// # Errors
523 ///
524 /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
525 /// provided bytes are not UTF-8. The vector you moved in is also included.
526 ///
527 /// # Examples
528 ///
529 /// Basic usage:
530 ///
531 /// ```
532 /// // some bytes, in a vector
533 /// let sparkle_heart = vec![240, 159, 146, 150];
534 ///
535 /// // We know these bytes are valid, so we'll use `unwrap()`.
536 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
537 ///
538 /// assert_eq!("πŸ’–", sparkle_heart);
539 /// ```
540 ///
541 /// Incorrect bytes:
542 ///
543 /// ```
544 /// // some invalid bytes, in a vector
545 /// let sparkle_heart = vec![0, 159, 146, 150];
546 ///
547 /// assert!(String::from_utf8(sparkle_heart).is_err());
548 /// ```
549 ///
550 /// See the docs for [`FromUtf8Error`] for more details on what you can do
551 /// with this error.
552 ///
553 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
554 /// [`Vec<u8>`]: crate::vec::Vec "Vec"
555 /// [`&str`]: prim@str "&str"
556 /// [`into_bytes`]: String::into_bytes
557 #[inline]
558 #[stable(feature = "rust1", since = "1.0.0")]
559 #[rustc_diagnostic_item = "string_from_utf8"]
560 pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
561 match str::from_utf8(&vec) {
562 Ok(..) => Ok(String { vec }),
563 Err(e) => Err(FromUtf8Error { bytes: vec, error: e }),
564 }
565 }
566
567 /// Converts a slice of bytes to a string, including invalid characters.
568 ///
569 /// Strings are made of bytes ([`u8`]), and a slice of bytes
570 /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
571 /// between the two. Not all byte slices are valid strings, however: strings
572 /// are required to be valid UTF-8. During this conversion,
573 /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
574 /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: οΏ½
575 ///
576 /// [byteslice]: prim@slice
577 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
578 ///
579 /// If you are sure that the byte slice is valid UTF-8, and you don't want
580 /// to incur the overhead of the conversion, there is an unsafe version
581 /// of this function, [`from_utf8_unchecked`], which has the same behavior
582 /// but skips the checks.
583 ///
584 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
585 ///
586 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
587 /// UTF-8, then we need to insert the replacement characters, which will
588 /// change the size of the string, and hence, require a `String`. But if
589 /// it's already valid UTF-8, we don't need a new allocation. This return
590 /// type allows us to handle both cases.
591 ///
592 /// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
593 ///
594 /// # Examples
595 ///
596 /// Basic usage:
597 ///
598 /// ```
599 /// // some bytes, in a vector
600 /// let sparkle_heart = vec![240, 159, 146, 150];
601 ///
602 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
603 ///
604 /// assert_eq!("πŸ’–", sparkle_heart);
605 /// ```
606 ///
607 /// Incorrect bytes:
608 ///
609 /// ```
610 /// // some invalid bytes
611 /// let input = b"Hello \xF0\x90\x80World";
612 /// let output = String::from_utf8_lossy(input);
613 ///
614 /// assert_eq!("Hello οΏ½World", output);
615 /// ```
616 #[must_use]
617 #[cfg(not(no_global_oom_handling))]
618 #[stable(feature = "rust1", since = "1.0.0")]
619 pub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, str> {
620 let mut iter = v.utf8_chunks();
621
622 let Some(chunk) = iter.next() else {
623 return Cow::Borrowed("");
624 };
625 let first_valid = chunk.valid();
626 if chunk.invalid().is_empty() {
627 debug_assert_eq!(first_valid.len(), v.len());
628 return Cow::Borrowed(first_valid);
629 }
630
631 const REPLACEMENT: &str = "\u{FFFD}";
632
633 let mut res = String::with_capacity(v.len());
634 res.push_str(first_valid);
635 res.push_str(REPLACEMENT);
636
637 for chunk in iter {
638 res.push_str(chunk.valid());
639 if !chunk.invalid().is_empty() {
640 res.push_str(REPLACEMENT);
641 }
642 }
643
644 Cow::Owned(res)
645 }
646
647 /// Converts a [`Vec<u8>`] to a `String`, substituting invalid UTF-8
648 /// sequences with replacement characters.
649 ///
650 /// See [`from_utf8_lossy`] for more details.
651 ///
652 /// [`from_utf8_lossy`]: String::from_utf8_lossy
653 ///
654 /// Note that this function does not guarantee reuse of the original `Vec`
655 /// allocation.
656 ///
657 /// # Examples
658 ///
659 /// Basic usage:
660 ///
661 /// ```
662 /// #![feature(string_from_utf8_lossy_owned)]
663 /// // some bytes, in a vector
664 /// let sparkle_heart = vec![240, 159, 146, 150];
665 ///
666 /// let sparkle_heart = String::from_utf8_lossy_owned(sparkle_heart);
667 ///
668 /// assert_eq!(String::from("πŸ’–"), sparkle_heart);
669 /// ```
670 ///
671 /// Incorrect bytes:
672 ///
673 /// ```
674 /// #![feature(string_from_utf8_lossy_owned)]
675 /// // some invalid bytes
676 /// let input: Vec<u8> = b"Hello \xF0\x90\x80World".into();
677 /// let output = String::from_utf8_lossy_owned(input);
678 ///
679 /// assert_eq!(String::from("Hello οΏ½World"), output);
680 /// ```
681 #[must_use]
682 #[cfg(not(no_global_oom_handling))]
683 #[unstable(feature = "string_from_utf8_lossy_owned", issue = "129436")]
684 pub fn from_utf8_lossy_owned(v: Vec<u8>) -> String {
685 if let Cow::Owned(string) = String::from_utf8_lossy(&v) {
686 string
687 } else {
688 // SAFETY: `String::from_utf8_lossy`'s contract ensures that if
689 // it returns a `Cow::Borrowed`, it is a valid UTF-8 string.
690 // Otherwise, it returns a new allocation of an owned `String`, with
691 // replacement characters for invalid sequences, which is returned
692 // above.
693 unsafe { String::from_utf8_unchecked(v) }
694 }
695 }
696
697 /// Decode a native endian UTF-16–encoded vector `v` into a `String`,
698 /// returning [`Err`] if `v` contains any invalid data.
699 ///
700 /// # Examples
701 ///
702 /// ```
703 /// // π„žmusic
704 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
705 /// 0x0073, 0x0069, 0x0063];
706 /// assert_eq!(String::from("π„žmusic"),
707 /// String::from_utf16(v).unwrap());
708 ///
709 /// // π„žmu<invalid>ic
710 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
711 /// 0xD800, 0x0069, 0x0063];
712 /// assert!(String::from_utf16(v).is_err());
713 /// ```
714 #[cfg(not(no_global_oom_handling))]
715 #[stable(feature = "rust1", since = "1.0.0")]
716 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
717 // This isn't done via collect::<Result<_, _>>() for performance reasons.
718 // FIXME: the function can be simplified again when #48994 is closed.
719 let mut ret = String::with_capacity(v.len());
720 for c in char::decode_utf16(v.iter().cloned()) {
721 let Ok(c) = c else {
722 return Err(FromUtf16Error(()));
723 };
724 ret.push(c);
725 }
726 Ok(ret)
727 }
728
729 /// Decode a native endian UTF-16–encoded slice `v` into a `String`,
730 /// replacing invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
731 ///
732 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
733 /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
734 /// conversion requires a memory allocation.
735 ///
736 /// [`from_utf8_lossy`]: String::from_utf8_lossy
737 /// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
738 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
739 ///
740 /// # Examples
741 ///
742 /// ```
743 /// // π„žmus<invalid>ic<invalid>
744 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
745 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
746 /// 0xD834];
747 ///
748 /// assert_eq!(String::from("π„žmus\u{FFFD}ic\u{FFFD}"),
749 /// String::from_utf16_lossy(v));
750 /// ```
751 #[cfg(not(no_global_oom_handling))]
752 #[must_use]
753 #[inline]
754 #[stable(feature = "rust1", since = "1.0.0")]
755 pub fn from_utf16_lossy(v: &[u16]) -> String {
756 char::decode_utf16(v.iter().cloned())
757 .map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
758 .collect()
759 }
760
761 /// Decode a UTF-16LE–encoded vector `v` into a `String`,
762 /// returning [`Err`] if `v` contains any invalid data.
763 ///
764 /// # Examples
765 ///
766 /// Basic usage:
767 ///
768 /// ```
769 /// #![feature(str_from_utf16_endian)]
770 /// // π„žmusic
771 /// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
772 /// 0x73, 0x00, 0x69, 0x00, 0x63, 0x00];
773 /// assert_eq!(String::from("π„žmusic"),
774 /// String::from_utf16le(v).unwrap());
775 ///
776 /// // π„žmu<invalid>ic
777 /// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
778 /// 0x00, 0xD8, 0x69, 0x00, 0x63, 0x00];
779 /// assert!(String::from_utf16le(v).is_err());
780 /// ```
781 #[cfg(not(no_global_oom_handling))]
782 #[unstable(feature = "str_from_utf16_endian", issue = "116258")]
783 pub fn from_utf16le(v: &[u8]) -> Result<String, FromUtf16Error> {
784 let (chunks, []) = v.as_chunks::<2>() else {
785 return Err(FromUtf16Error(()));
786 };
787 match (cfg!(target_endian = "little"), unsafe { v.align_to::<u16>() }) {
788 (true, ([], v, [])) => Self::from_utf16(v),
789 _ => char::decode_utf16(chunks.iter().copied().map(u16::from_le_bytes))
790 .collect::<Result<_, _>>()
791 .map_err(|_| FromUtf16Error(())),
792 }
793 }
794
795 /// Decode a UTF-16LE–encoded slice `v` into a `String`, replacing
796 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
797 ///
798 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
799 /// `from_utf16le_lossy` returns a `String` since the UTF-16 to UTF-8
800 /// conversion requires a memory allocation.
801 ///
802 /// [`from_utf8_lossy`]: String::from_utf8_lossy
803 /// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
804 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
805 ///
806 /// # Examples
807 ///
808 /// Basic usage:
809 ///
810 /// ```
811 /// #![feature(str_from_utf16_endian)]
812 /// // π„žmus<invalid>ic<invalid>
813 /// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
814 /// 0x73, 0x00, 0x1E, 0xDD, 0x69, 0x00, 0x63, 0x00,
815 /// 0x34, 0xD8];
816 ///
817 /// assert_eq!(String::from("π„žmus\u{FFFD}ic\u{FFFD}"),
818 /// String::from_utf16le_lossy(v));
819 /// ```
820 #[cfg(not(no_global_oom_handling))]
821 #[unstable(feature = "str_from_utf16_endian", issue = "116258")]
822 pub fn from_utf16le_lossy(v: &[u8]) -> String {
823 match (cfg!(target_endian = "little"), unsafe { v.align_to::<u16>() }) {
824 (true, ([], v, [])) => Self::from_utf16_lossy(v),
825 (true, ([], v, [_remainder])) => Self::from_utf16_lossy(v) + "\u{FFFD}",
826 _ => {
827 let (chunks, remainder) = v.as_chunks::<2>();
828 let string = char::decode_utf16(chunks.iter().copied().map(u16::from_le_bytes))
829 .map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
830 .collect();
831 if remainder.is_empty() { string } else { string + "\u{FFFD}" }
832 }
833 }
834 }
835
836 /// Decode a UTF-16BE–encoded vector `v` into a `String`,
837 /// returning [`Err`] if `v` contains any invalid data.
838 ///
839 /// # Examples
840 ///
841 /// Basic usage:
842 ///
843 /// ```
844 /// #![feature(str_from_utf16_endian)]
845 /// // π„žmusic
846 /// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
847 /// 0x00, 0x73, 0x00, 0x69, 0x00, 0x63];
848 /// assert_eq!(String::from("π„žmusic"),
849 /// String::from_utf16be(v).unwrap());
850 ///
851 /// // π„žmu<invalid>ic
852 /// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
853 /// 0xD8, 0x00, 0x00, 0x69, 0x00, 0x63];
854 /// assert!(String::from_utf16be(v).is_err());
855 /// ```
856 #[cfg(not(no_global_oom_handling))]
857 #[unstable(feature = "str_from_utf16_endian", issue = "116258")]
858 pub fn from_utf16be(v: &[u8]) -> Result<String, FromUtf16Error> {
859 let (chunks, []) = v.as_chunks::<2>() else {
860 return Err(FromUtf16Error(()));
861 };
862 match (cfg!(target_endian = "big"), unsafe { v.align_to::<u16>() }) {
863 (true, ([], v, [])) => Self::from_utf16(v),
864 _ => char::decode_utf16(chunks.iter().copied().map(u16::from_be_bytes))
865 .collect::<Result<_, _>>()
866 .map_err(|_| FromUtf16Error(())),
867 }
868 }
869
870 /// Decode a UTF-16BE–encoded slice `v` into a `String`, replacing
871 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
872 ///
873 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
874 /// `from_utf16le_lossy` returns a `String` since the UTF-16 to UTF-8
875 /// conversion requires a memory allocation.
876 ///
877 /// [`from_utf8_lossy`]: String::from_utf8_lossy
878 /// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
879 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
880 ///
881 /// # Examples
882 ///
883 /// Basic usage:
884 ///
885 /// ```
886 /// #![feature(str_from_utf16_endian)]
887 /// // π„žmus<invalid>ic<invalid>
888 /// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
889 /// 0x00, 0x73, 0xDD, 0x1E, 0x00, 0x69, 0x00, 0x63,
890 /// 0xD8, 0x34];
891 ///
892 /// assert_eq!(String::from("π„žmus\u{FFFD}ic\u{FFFD}"),
893 /// String::from_utf16be_lossy(v));
894 /// ```
895 #[cfg(not(no_global_oom_handling))]
896 #[unstable(feature = "str_from_utf16_endian", issue = "116258")]
897 pub fn from_utf16be_lossy(v: &[u8]) -> String {
898 match (cfg!(target_endian = "big"), unsafe { v.align_to::<u16>() }) {
899 (true, ([], v, [])) => Self::from_utf16_lossy(v),
900 (true, ([], v, [_remainder])) => Self::from_utf16_lossy(v) + "\u{FFFD}",
901 _ => {
902 let (chunks, remainder) = v.as_chunks::<2>();
903 let string = char::decode_utf16(chunks.iter().copied().map(u16::from_be_bytes))
904 .map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
905 .collect();
906 if remainder.is_empty() { string } else { string + "\u{FFFD}" }
907 }
908 }
909 }
910
911 /// Decomposes a `String` into its raw components: `(pointer, length, capacity)`.
912 ///
913 /// Returns the raw pointer to the underlying data, the length of
914 /// the string (in bytes), and the allocated capacity of the data
915 /// (in bytes). These are the same arguments in the same order as
916 /// the arguments to [`from_raw_parts`].
917 ///
918 /// After calling this function, the caller is responsible for the
919 /// memory previously managed by the `String`. The only way to do
920 /// this is to convert the raw pointer, length, and capacity back
921 /// into a `String` with the [`from_raw_parts`] function, allowing
922 /// the destructor to perform the cleanup.
923 ///
924 /// [`from_raw_parts`]: String::from_raw_parts
925 ///
926 /// # Examples
927 ///
928 /// ```
929 /// let s = String::from("hello");
930 ///
931 /// let (ptr, len, cap) = s.into_raw_parts();
932 ///
933 /// let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
934 /// assert_eq!(rebuilt, "hello");
935 /// ```
936 #[must_use = "losing the pointer will leak memory"]
937 #[stable(feature = "vec_into_raw_parts", since = "1.93.0")]
938 pub fn into_raw_parts(self) -> (*mut u8, usize, usize) {
939 self.vec.into_raw_parts()
940 }
941
942 /// Creates a new `String` from a pointer, a length and a capacity.
943 ///
944 /// # Safety
945 ///
946 /// This is highly unsafe, due to the number of invariants that aren't
947 /// checked:
948 ///
949 /// * all safety requirements for [`Vec::<u8>::from_raw_parts`].
950 /// * all safety requirements for [`String::from_utf8_unchecked`].
951 ///
952 /// Violating these may cause problems like corrupting the allocator's
953 /// internal data structures. For example, it is normally **not** safe to
954 /// build a `String` from a pointer to a C `char` array containing UTF-8
955 /// _unless_ you are certain that array was originally allocated by the
956 /// Rust standard library's allocator.
957 ///
958 /// The ownership of `buf` is effectively transferred to the
959 /// `String` which may then deallocate, reallocate or change the
960 /// contents of memory pointed to by the pointer at will. Ensure
961 /// that nothing else uses the pointer after calling this
962 /// function.
963 ///
964 /// # Examples
965 ///
966 /// ```
967 /// unsafe {
968 /// let s = String::from("hello");
969 ///
970 /// // Deconstruct the String into parts.
971 /// let (ptr, len, capacity) = s.into_raw_parts();
972 ///
973 /// let s = String::from_raw_parts(ptr, len, capacity);
974 ///
975 /// assert_eq!(String::from("hello"), s);
976 /// }
977 /// ```
978 #[inline]
979 #[stable(feature = "rust1", since = "1.0.0")]
980 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
981 unsafe { String { vec: Vec::from_raw_parts(buf, length, capacity) } }
982 }
983
984 /// Converts a vector of bytes to a `String` without checking that the
985 /// string contains valid UTF-8.
986 ///
987 /// See the safe version, [`from_utf8`], for more details.
988 ///
989 /// [`from_utf8`]: String::from_utf8
990 ///
991 /// # Safety
992 ///
993 /// This function is unsafe because it does not check that the bytes passed
994 /// to it are valid UTF-8. If this constraint is violated, it may cause
995 /// memory unsafety issues with future users of the `String`, as the rest of
996 /// the standard library assumes that `String`s are valid UTF-8.
997 ///
998 /// # Examples
999 ///
1000 /// ```
1001 /// // some bytes, in a vector
1002 /// let sparkle_heart = vec![240, 159, 146, 150];
1003 ///
1004 /// let sparkle_heart = unsafe {
1005 /// String::from_utf8_unchecked(sparkle_heart)
1006 /// };
1007 ///
1008 /// assert_eq!("πŸ’–", sparkle_heart);
1009 /// ```
1010 #[inline]
1011 #[must_use]
1012 #[stable(feature = "rust1", since = "1.0.0")]
1013 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
1014 String { vec: bytes }
1015 }
1016
1017 /// Converts a `String` into a byte vector.
1018 ///
1019 /// This consumes the `String`, so we do not need to copy its contents.
1020 ///
1021 /// # Examples
1022 ///
1023 /// ```
1024 /// let s = String::from("hello");
1025 /// let bytes = s.into_bytes();
1026 ///
1027 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
1028 /// ```
1029 #[inline]
1030 #[must_use = "`self` will be dropped if the result is not used"]
1031 #[stable(feature = "rust1", since = "1.0.0")]
1032 #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
1033 #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
1034 pub const fn into_bytes(self) -> Vec<u8> {
1035 self.vec
1036 }
1037
1038 /// Extracts a string slice containing the entire `String`.
1039 ///
1040 /// # Examples
1041 ///
1042 /// ```
1043 /// let s = String::from("foo");
1044 ///
1045 /// assert_eq!("foo", s.as_str());
1046 /// ```
1047 #[inline]
1048 #[must_use]
1049 #[stable(feature = "string_as_str", since = "1.7.0")]
1050 #[rustc_diagnostic_item = "string_as_str"]
1051 #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
1052 pub const fn as_str(&self) -> &str {
1053 // SAFETY: String contents are stipulated to be valid UTF-8, invalid contents are an error
1054 // at construction.
1055 unsafe { str::from_utf8_unchecked(self.vec.as_slice()) }
1056 }
1057
1058 /// Converts a `String` into a mutable string slice.
1059 ///
1060 /// # Examples
1061 ///
1062 /// ```
1063 /// let mut s = String::from("foobar");
1064 /// let s_mut_str = s.as_mut_str();
1065 ///
1066 /// s_mut_str.make_ascii_uppercase();
1067 ///
1068 /// assert_eq!("FOOBAR", s_mut_str);
1069 /// ```
1070 #[inline]
1071 #[must_use]
1072 #[stable(feature = "string_as_str", since = "1.7.0")]
1073 #[rustc_diagnostic_item = "string_as_mut_str"]
1074 #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
1075 pub const fn as_mut_str(&mut self) -> &mut str {
1076 // SAFETY: String contents are stipulated to be valid UTF-8, invalid contents are an error
1077 // at construction.
1078 unsafe { str::from_utf8_unchecked_mut(self.vec.as_mut_slice()) }
1079 }
1080
1081 /// Appends a given string slice onto the end of this `String`.
1082 ///
1083 /// # Panics
1084 ///
1085 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
1086 ///
1087 /// # Examples
1088 ///
1089 /// ```
1090 /// let mut s = String::from("foo");
1091 ///
1092 /// s.push_str("bar");
1093 ///
1094 /// assert_eq!("foobar", s);
1095 /// ```
1096 #[cfg(not(no_global_oom_handling))]
1097 #[inline]
1098 #[stable(feature = "rust1", since = "1.0.0")]
1099 #[rustc_confusables("append", "push")]
1100 #[rustc_diagnostic_item = "string_push_str"]
1101 pub fn push_str(&mut self, string: &str) {
1102 self.vec.extend_from_slice(string.as_bytes())
1103 }
1104
1105 #[cfg(not(no_global_oom_handling))]
1106 #[inline]
1107 fn push_str_slice(&mut self, slice: &[&str]) {
1108 // use saturating arithmetic to ensure that in the case of an overflow, reserve() throws OOM
1109 let additional: Saturating<usize> = slice.iter().map(|x| Saturating(x.len())).sum();
1110 self.reserve(additional.0);
1111 let (ptr, len, cap) = core::mem::take(self).into_raw_parts();
1112 unsafe {
1113 let mut dst = ptr.add(len);
1114 for new in slice {
1115 core::ptr::copy_nonoverlapping(new.as_ptr(), dst, new.len());
1116 dst = dst.add(new.len());
1117 }
1118 *self = String::from_raw_parts(ptr, len + additional.0, cap);
1119 }
1120 }
1121
1122 /// Copies elements from `src` range to the end of the string.
1123 ///
1124 /// # Panics
1125 ///
1126 /// Panics if the range has `start_bound > end_bound`, if the range is
1127 /// bounded on either end and does not lie on a [`char`] boundary, or if the
1128 /// new capacity exceeds `isize::MAX` bytes.
1129 ///
1130 /// # Examples
1131 ///
1132 /// ```
1133 /// let mut string = String::from("abcde");
1134 ///
1135 /// string.extend_from_within(2..);
1136 /// assert_eq!(string, "abcdecde");
1137 ///
1138 /// string.extend_from_within(..2);
1139 /// assert_eq!(string, "abcdecdeab");
1140 ///
1141 /// string.extend_from_within(4..8);
1142 /// assert_eq!(string, "abcdecdeabecde");
1143 /// ```
1144 #[cfg(not(no_global_oom_handling))]
1145 #[stable(feature = "string_extend_from_within", since = "1.87.0")]
1146 #[track_caller]
1147 pub fn extend_from_within<R>(&mut self, src: R)
1148 where
1149 R: RangeBounds<usize>,
1150 {
1151 let src @ Range { start, end } = slice::range(src, ..self.len());
1152
1153 assert!(self.is_char_boundary(start));
1154 assert!(self.is_char_boundary(end));
1155
1156 self.vec.extend_from_within(src);
1157 }
1158
1159 /// Returns this `String`'s capacity, in bytes.
1160 ///
1161 /// # Examples
1162 ///
1163 /// ```
1164 /// let s = String::with_capacity(10);
1165 ///
1166 /// assert!(s.capacity() >= 10);
1167 /// ```
1168 #[inline]
1169 #[must_use]
1170 #[stable(feature = "rust1", since = "1.0.0")]
1171 #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
1172 pub const fn capacity(&self) -> usize {
1173 self.vec.capacity()
1174 }
1175
1176 /// Reserves capacity for at least `additional` bytes more than the
1177 /// current length. The allocator may reserve more space to speculatively
1178 /// avoid frequent allocations. After calling `reserve`,
1179 /// capacity will be greater than or equal to `self.len() + additional`.
1180 /// Does nothing if capacity is already sufficient.
1181 ///
1182 /// # Panics
1183 ///
1184 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
1185 ///
1186 /// # Examples
1187 ///
1188 /// Basic usage:
1189 ///
1190 /// ```
1191 /// let mut s = String::new();
1192 ///
1193 /// s.reserve(10);
1194 ///
1195 /// assert!(s.capacity() >= 10);
1196 /// ```
1197 ///
1198 /// This might not actually increase the capacity:
1199 ///
1200 /// ```
1201 /// let mut s = String::with_capacity(10);
1202 /// s.push('a');
1203 /// s.push('b');
1204 ///
1205 /// // s now has a length of 2 and a capacity of at least 10
1206 /// let capacity = s.capacity();
1207 /// assert_eq!(2, s.len());
1208 /// assert!(capacity >= 10);
1209 ///
1210 /// // Since we already have at least an extra 8 capacity, calling this...
1211 /// s.reserve(8);
1212 ///
1213 /// // ... doesn't actually increase.
1214 /// assert_eq!(capacity, s.capacity());
1215 /// ```
1216 #[cfg(not(no_global_oom_handling))]
1217 #[inline]
1218 #[stable(feature = "rust1", since = "1.0.0")]
1219 pub fn reserve(&mut self, additional: usize) {
1220 self.vec.reserve(additional)
1221 }
1222
1223 /// Reserves the minimum capacity for at least `additional` bytes more than
1224 /// the current length. Unlike [`reserve`], this will not
1225 /// deliberately over-allocate to speculatively avoid frequent allocations.
1226 /// After calling `reserve_exact`, capacity will be greater than or equal to
1227 /// `self.len() + additional`. Does nothing if the capacity is already
1228 /// sufficient.
1229 ///
1230 /// [`reserve`]: String::reserve
1231 ///
1232 /// # Panics
1233 ///
1234 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
1235 ///
1236 /// # Examples
1237 ///
1238 /// Basic usage:
1239 ///
1240 /// ```
1241 /// let mut s = String::new();
1242 ///
1243 /// s.reserve_exact(10);
1244 ///
1245 /// assert!(s.capacity() >= 10);
1246 /// ```
1247 ///
1248 /// This might not actually increase the capacity:
1249 ///
1250 /// ```
1251 /// let mut s = String::with_capacity(10);
1252 /// s.push('a');
1253 /// s.push('b');
1254 ///
1255 /// // s now has a length of 2 and a capacity of at least 10
1256 /// let capacity = s.capacity();
1257 /// assert_eq!(2, s.len());
1258 /// assert!(capacity >= 10);
1259 ///
1260 /// // Since we already have at least an extra 8 capacity, calling this...
1261 /// s.reserve_exact(8);
1262 ///
1263 /// // ... doesn't actually increase.
1264 /// assert_eq!(capacity, s.capacity());
1265 /// ```
1266 #[cfg(not(no_global_oom_handling))]
1267 #[inline]
1268 #[stable(feature = "rust1", since = "1.0.0")]
1269 pub fn reserve_exact(&mut self, additional: usize) {
1270 self.vec.reserve_exact(additional)
1271 }
1272
1273 /// Tries to reserve capacity for at least `additional` bytes more than the
1274 /// current length. The allocator may reserve more space to speculatively
1275 /// avoid frequent allocations. After calling `try_reserve`, capacity will be
1276 /// greater than or equal to `self.len() + additional` if it returns
1277 /// `Ok(())`. Does nothing if capacity is already sufficient. This method
1278 /// preserves the contents even if an error occurs.
1279 ///
1280 /// # Errors
1281 ///
1282 /// If the capacity overflows, or the allocator reports a failure, then an error
1283 /// is returned.
1284 ///
1285 /// # Examples
1286 ///
1287 /// ```
1288 /// use std::collections::TryReserveError;
1289 ///
1290 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
1291 /// let mut output = String::new();
1292 ///
1293 /// // Pre-reserve the memory, exiting if we can't
1294 /// output.try_reserve(data.len())?;
1295 ///
1296 /// // Now we know this can't OOM in the middle of our complex work
1297 /// output.push_str(data);
1298 ///
1299 /// Ok(output)
1300 /// }
1301 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1302 /// ```
1303 #[stable(feature = "try_reserve", since = "1.57.0")]
1304 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
1305 self.vec.try_reserve(additional)
1306 }
1307
1308 /// Tries to reserve the minimum capacity for at least `additional` bytes
1309 /// more than the current length. Unlike [`try_reserve`], this will not
1310 /// deliberately over-allocate to speculatively avoid frequent allocations.
1311 /// After calling `try_reserve_exact`, capacity will be greater than or
1312 /// equal to `self.len() + additional` if it returns `Ok(())`.
1313 /// Does nothing if the capacity is already sufficient.
1314 ///
1315 /// Note that the allocator may give the collection more space than it
1316 /// requests. Therefore, capacity can not be relied upon to be precisely
1317 /// minimal. Prefer [`try_reserve`] if future insertions are expected.
1318 ///
1319 /// [`try_reserve`]: String::try_reserve
1320 ///
1321 /// # Errors
1322 ///
1323 /// If the capacity overflows, or the allocator reports a failure, then an error
1324 /// is returned.
1325 ///
1326 /// # Examples
1327 ///
1328 /// ```
1329 /// use std::collections::TryReserveError;
1330 ///
1331 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
1332 /// let mut output = String::new();
1333 ///
1334 /// // Pre-reserve the memory, exiting if we can't
1335 /// output.try_reserve_exact(data.len())?;
1336 ///
1337 /// // Now we know this can't OOM in the middle of our complex work
1338 /// output.push_str(data);
1339 ///
1340 /// Ok(output)
1341 /// }
1342 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1343 /// ```
1344 #[stable(feature = "try_reserve", since = "1.57.0")]
1345 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
1346 self.vec.try_reserve_exact(additional)
1347 }
1348
1349 /// Shrinks the capacity of this `String` to match its length.
1350 ///
1351 /// # Examples
1352 ///
1353 /// ```
1354 /// let mut s = String::from("foo");
1355 ///
1356 /// s.reserve(100);
1357 /// assert!(s.capacity() >= 100);
1358 ///
1359 /// s.shrink_to_fit();
1360 /// assert_eq!(3, s.capacity());
1361 /// ```
1362 #[cfg(not(no_global_oom_handling))]
1363 #[inline]
1364 #[stable(feature = "rust1", since = "1.0.0")]
1365 pub fn shrink_to_fit(&mut self) {
1366 self.vec.shrink_to_fit()
1367 }
1368
1369 /// Shrinks the capacity of this `String` with a lower bound.
1370 ///
1371 /// The capacity will remain at least as large as both the length
1372 /// and the supplied value.
1373 ///
1374 /// If the current capacity is less than the lower limit, this is a no-op.
1375 ///
1376 /// # Examples
1377 ///
1378 /// ```
1379 /// let mut s = String::from("foo");
1380 ///
1381 /// s.reserve(100);
1382 /// assert!(s.capacity() >= 100);
1383 ///
1384 /// s.shrink_to(10);
1385 /// assert!(s.capacity() >= 10);
1386 /// s.shrink_to(0);
1387 /// assert!(s.capacity() >= 3);
1388 /// ```
1389 #[cfg(not(no_global_oom_handling))]
1390 #[inline]
1391 #[stable(feature = "shrink_to", since = "1.56.0")]
1392 pub fn shrink_to(&mut self, min_capacity: usize) {
1393 self.vec.shrink_to(min_capacity)
1394 }
1395
1396 /// Appends the given [`char`] to the end of this `String`.
1397 ///
1398 /// # Panics
1399 ///
1400 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
1401 ///
1402 /// # Examples
1403 ///
1404 /// ```
1405 /// let mut s = String::from("abc");
1406 ///
1407 /// s.push('1');
1408 /// s.push('2');
1409 /// s.push('3');
1410 ///
1411 /// assert_eq!("abc123", s);
1412 /// ```
1413 #[cfg(not(no_global_oom_handling))]
1414 #[inline]
1415 #[stable(feature = "rust1", since = "1.0.0")]
1416 pub fn push(&mut self, ch: char) {
1417 let len = self.len();
1418 let ch_len = ch.len_utf8();
1419 self.reserve(ch_len);
1420
1421 // SAFETY: Just reserved capacity for at least the length needed to encode `ch`.
1422 unsafe {
1423 core::char::encode_utf8_raw_unchecked(ch as u32, self.vec.as_mut_ptr().add(self.len()));
1424 self.vec.set_len(len + ch_len);
1425 }
1426 }
1427
1428 /// Returns a byte slice of this `String`'s contents.
1429 ///
1430 /// The inverse of this method is [`from_utf8`].
1431 ///
1432 /// [`from_utf8`]: String::from_utf8
1433 ///
1434 /// # Examples
1435 ///
1436 /// ```
1437 /// let s = String::from("hello");
1438 ///
1439 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
1440 /// ```
1441 #[inline]
1442 #[must_use]
1443 #[stable(feature = "rust1", since = "1.0.0")]
1444 #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
1445 pub const fn as_bytes(&self) -> &[u8] {
1446 self.vec.as_slice()
1447 }
1448
1449 /// Shortens this `String` to the specified length.
1450 ///
1451 /// If `new_len` is greater than or equal to the string's current length, this has no
1452 /// effect.
1453 ///
1454 /// Note that this method has no effect on the allocated capacity
1455 /// of the string
1456 ///
1457 /// # Panics
1458 ///
1459 /// Panics if `new_len` does not lie on a [`char`] boundary.
1460 ///
1461 /// # Examples
1462 ///
1463 /// ```
1464 /// let mut s = String::from("hello");
1465 ///
1466 /// s.truncate(2);
1467 ///
1468 /// assert_eq!("he", s);
1469 /// ```
1470 #[inline]
1471 #[stable(feature = "rust1", since = "1.0.0")]
1472 #[track_caller]
1473 pub fn truncate(&mut self, new_len: usize) {
1474 if new_len <= self.len() {
1475 assert!(self.is_char_boundary(new_len));
1476 self.vec.truncate(new_len)
1477 }
1478 }
1479
1480 /// Removes the last character from the string buffer and returns it.
1481 ///
1482 /// Returns [`None`] if this `String` is empty.
1483 ///
1484 /// # Examples
1485 ///
1486 /// ```
1487 /// let mut s = String::from("abč");
1488 ///
1489 /// assert_eq!(s.pop(), Some('č'));
1490 /// assert_eq!(s.pop(), Some('b'));
1491 /// assert_eq!(s.pop(), Some('a'));
1492 ///
1493 /// assert_eq!(s.pop(), None);
1494 /// ```
1495 #[inline]
1496 #[stable(feature = "rust1", since = "1.0.0")]
1497 pub fn pop(&mut self) -> Option<char> {
1498 let ch = self.chars().rev().next()?;
1499 let newlen = self.len() - ch.len_utf8();
1500 unsafe {
1501 self.vec.set_len(newlen);
1502 }
1503 Some(ch)
1504 }
1505
1506 /// Removes a [`char`] from this `String` at byte position `idx` and returns it.
1507 ///
1508 /// Copies all bytes after the removed char to new positions.
1509 ///
1510 /// Note that calling this in a loop can result in quadratic behavior.
1511 ///
1512 /// # Panics
1513 ///
1514 /// Panics if `idx` is larger than or equal to the `String`'s length,
1515 /// or if it does not lie on a [`char`] boundary.
1516 ///
1517 /// # Examples
1518 ///
1519 /// ```
1520 /// let mut s = String::from("abç");
1521 ///
1522 /// assert_eq!(s.remove(0), 'a');
1523 /// assert_eq!(s.remove(1), 'Γ§');
1524 /// assert_eq!(s.remove(0), 'b');
1525 /// ```
1526 #[inline]
1527 #[stable(feature = "rust1", since = "1.0.0")]
1528 #[track_caller]
1529 #[rustc_confusables("delete", "take")]
1530 pub fn remove(&mut self, idx: usize) -> char {
1531 let ch = match self[idx..].chars().next() {
1532 Some(ch) => ch,
1533 None => panic!("cannot remove a char from the end of a string"),
1534 };
1535
1536 let next = idx + ch.len_utf8();
1537 let len = self.len();
1538 unsafe {
1539 ptr::copy(self.vec.as_ptr().add(next), self.vec.as_mut_ptr().add(idx), len - next);
1540 self.vec.set_len(len - (next - idx));
1541 }
1542 ch
1543 }
1544
1545 /// Remove all matches of pattern `pat` in the `String`.
1546 ///
1547 /// # Examples
1548 ///
1549 /// ```
1550 /// #![feature(string_remove_matches)]
1551 /// let mut s = String::from("Trees are not green, the sky is not blue.");
1552 /// s.remove_matches("not ");
1553 /// assert_eq!("Trees are green, the sky is blue.", s);
1554 /// ```
1555 ///
1556 /// Matches will be detected and removed iteratively, so in cases where
1557 /// patterns overlap, only the first pattern will be removed:
1558 ///
1559 /// ```
1560 /// #![feature(string_remove_matches)]
1561 /// let mut s = String::from("banana");
1562 /// s.remove_matches("ana");
1563 /// assert_eq!("bna", s);
1564 /// ```
1565 #[cfg(not(no_global_oom_handling))]
1566 #[unstable(feature = "string_remove_matches", issue = "72826")]
1567 pub fn remove_matches<P: Pattern>(&mut self, pat: P) {
1568 use core::str::pattern::Searcher;
1569
1570 let rejections = {
1571 let mut searcher = pat.into_searcher(self);
1572 // Per Searcher::next:
1573 //
1574 // A Match result needs to contain the whole matched pattern,
1575 // however Reject results may be split up into arbitrary many
1576 // adjacent fragments. Both ranges may have zero length.
1577 //
1578 // In practice the implementation of Searcher::next_match tends to
1579 // be more efficient, so we use it here and do some work to invert
1580 // matches into rejections since that's what we want to copy below.
1581 let mut front = 0;
1582 let rejections: Vec<_> = from_fn(|| {
1583 let (start, end) = searcher.next_match()?;
1584 let prev_front = front;
1585 front = end;
1586 Some((prev_front, start))
1587 })
1588 .collect();
1589 rejections.into_iter().chain(core::iter::once((front, self.len())))
1590 };
1591
1592 let mut len = 0;
1593 let ptr = self.vec.as_mut_ptr();
1594
1595 for (start, end) in rejections {
1596 let count = end - start;
1597 if start != len {
1598 // SAFETY: per Searcher::next:
1599 //
1600 // The stream of Match and Reject values up to a Done will
1601 // contain index ranges that are adjacent, non-overlapping,
1602 // covering the whole haystack, and laying on utf8
1603 // boundaries.
1604 unsafe {
1605 ptr::copy(ptr.add(start), ptr.add(len), count);
1606 }
1607 }
1608 len += count;
1609 }
1610
1611 unsafe {
1612 self.vec.set_len(len);
1613 }
1614 }
1615
1616 /// Retains only the characters specified by the predicate.
1617 ///
1618 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1619 /// This method operates in place, visiting each character exactly once in the
1620 /// original order, and preserves the order of the retained characters.
1621 ///
1622 /// # Examples
1623 ///
1624 /// ```
1625 /// let mut s = String::from("f_o_ob_ar");
1626 ///
1627 /// s.retain(|c| c != '_');
1628 ///
1629 /// assert_eq!(s, "foobar");
1630 /// ```
1631 ///
1632 /// Because the elements are visited exactly once in the original order,
1633 /// external state may be used to decide which elements to keep.
1634 ///
1635 /// ```
1636 /// let mut s = String::from("abcde");
1637 /// let keep = [false, true, true, false, true];
1638 /// let mut iter = keep.iter();
1639 /// s.retain(|_| *iter.next().unwrap());
1640 /// assert_eq!(s, "bce");
1641 /// ```
1642 #[inline]
1643 #[stable(feature = "string_retain", since = "1.26.0")]
1644 pub fn retain<F>(&mut self, mut f: F)
1645 where
1646 F: FnMut(char) -> bool,
1647 {
1648 struct SetLenOnDrop<'a> {
1649 s: &'a mut String,
1650 idx: usize,
1651 del_bytes: usize,
1652 }
1653
1654 impl<'a> Drop for SetLenOnDrop<'a> {
1655 fn drop(&mut self) {
1656 let new_len = self.idx - self.del_bytes;
1657 debug_assert!(new_len <= self.s.len());
1658 unsafe { self.s.vec.set_len(new_len) };
1659 }
1660 }
1661
1662 let len = self.len();
1663 let mut guard = SetLenOnDrop { s: self, idx: 0, del_bytes: 0 };
1664
1665 while guard.idx < len {
1666 let ch =
1667 // SAFETY: `guard.idx` is positive-or-zero and less that len so the `get_unchecked`
1668 // is in bound. `self` is valid UTF-8 like string and the returned slice starts at
1669 // a unicode code point so the `Chars` always return one character.
1670 unsafe { guard.s.get_unchecked(guard.idx..len).chars().next().unwrap_unchecked() };
1671 let ch_len = ch.len_utf8();
1672
1673 if !f(ch) {
1674 guard.del_bytes += ch_len;
1675 } else if guard.del_bytes > 0 {
1676 // SAFETY: `guard.idx` is in bound and `guard.del_bytes` represent the number of
1677 // bytes that are erased from the string so the resulting `guard.idx -
1678 // guard.del_bytes` always represent a valid unicode code point.
1679 //
1680 // `guard.del_bytes` >= `ch.len_utf8()`, so taking a slice with `ch.len_utf8()` len
1681 // is safe.
1682 ch.encode_utf8(unsafe {
1683 crate::slice::from_raw_parts_mut(
1684 guard.s.as_mut_ptr().add(guard.idx - guard.del_bytes),
1685 ch.len_utf8(),
1686 )
1687 });
1688 }
1689
1690 // Point idx to the next char
1691 guard.idx += ch_len;
1692 }
1693
1694 drop(guard);
1695 }
1696
1697 /// Inserts a character into this `String` at byte position `idx`.
1698 ///
1699 /// Reallocates if `self.capacity()` is insufficient, which may involve copying all
1700 /// `self.capacity()` bytes. Makes space for the insertion by copying all bytes of
1701 /// `&self[idx..]` to new positions.
1702 ///
1703 /// Note that calling this in a loop can result in quadratic behavior.
1704 ///
1705 /// # Panics
1706 ///
1707 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1708 /// lie on a [`char`] boundary.
1709 ///
1710 /// # Examples
1711 ///
1712 /// ```
1713 /// let mut s = String::with_capacity(3);
1714 ///
1715 /// s.insert(0, 'f');
1716 /// s.insert(1, 'o');
1717 /// s.insert(2, 'o');
1718 ///
1719 /// assert_eq!("foo", s);
1720 /// ```
1721 #[cfg(not(no_global_oom_handling))]
1722 #[inline]
1723 #[track_caller]
1724 #[stable(feature = "rust1", since = "1.0.0")]
1725 #[rustc_confusables("set")]
1726 pub fn insert(&mut self, idx: usize, ch: char) {
1727 assert!(self.is_char_boundary(idx));
1728
1729 let len = self.len();
1730 let ch_len = ch.len_utf8();
1731 self.reserve(ch_len);
1732
1733 // SAFETY: Move the bytes starting from `idx` to their new location `ch_len`
1734 // bytes ahead. This is safe because sufficient capacity was reserved, and `idx`
1735 // is a char boundary.
1736 unsafe {
1737 ptr::copy(
1738 self.vec.as_ptr().add(idx),
1739 self.vec.as_mut_ptr().add(idx + ch_len),
1740 len - idx,
1741 );
1742 }
1743
1744 // SAFETY: Encode the character into the vacated region if `idx != len`,
1745 // or into the uninitialized spare capacity otherwise.
1746 unsafe {
1747 core::char::encode_utf8_raw_unchecked(ch as u32, self.vec.as_mut_ptr().add(idx));
1748 }
1749
1750 // SAFETY: Update the length to include the newly added bytes.
1751 unsafe {
1752 self.vec.set_len(len + ch_len);
1753 }
1754 }
1755
1756 /// Inserts a string slice into this `String` at byte position `idx`.
1757 ///
1758 /// Reallocates if `self.capacity()` is insufficient, which may involve copying all
1759 /// `self.capacity()` bytes. Makes space for the insertion by copying all bytes of
1760 /// `&self[idx..]` to new positions.
1761 ///
1762 /// Note that calling this in a loop can result in quadratic behavior.
1763 ///
1764 /// # Panics
1765 ///
1766 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1767 /// lie on a [`char`] boundary.
1768 ///
1769 /// # Examples
1770 ///
1771 /// ```
1772 /// let mut s = String::from("bar");
1773 ///
1774 /// s.insert_str(0, "foo");
1775 ///
1776 /// assert_eq!("foobar", s);
1777 /// ```
1778 #[cfg(not(no_global_oom_handling))]
1779 #[inline]
1780 #[track_caller]
1781 #[stable(feature = "insert_str", since = "1.16.0")]
1782 #[rustc_diagnostic_item = "string_insert_str"]
1783 pub fn insert_str(&mut self, idx: usize, string: &str) {
1784 assert!(self.is_char_boundary(idx));
1785
1786 let len = self.len();
1787 let amt = string.len();
1788 self.reserve(amt);
1789
1790 // SAFETY: Move the bytes starting from `idx` to their new location `amt` bytes
1791 // ahead. This is safe because sufficient capacity was just reserved, and `idx`
1792 // is a char boundary.
1793 unsafe {
1794 ptr::copy(self.vec.as_ptr().add(idx), self.vec.as_mut_ptr().add(idx + amt), len - idx);
1795 }
1796
1797 // SAFETY: Copy the new string slice into the vacated region if `idx != len`,
1798 // or into the uninitialized spare capacity otherwise. The borrow checker
1799 // ensures that the source and destination do not overlap.
1800 unsafe {
1801 ptr::copy_nonoverlapping(string.as_ptr(), self.vec.as_mut_ptr().add(idx), amt);
1802 }
1803
1804 // SAFETY: Update the length to include the newly added bytes.
1805 unsafe {
1806 self.vec.set_len(len + amt);
1807 }
1808 }
1809
1810 /// Returns a mutable reference to the contents of this `String`.
1811 ///
1812 /// # Safety
1813 ///
1814 /// This function is unsafe because the returned `&mut Vec` allows writing
1815 /// bytes which are not valid UTF-8. If this constraint is violated, using
1816 /// the original `String` after dropping the `&mut Vec` may violate memory
1817 /// safety, as the rest of the standard library assumes that `String`s are
1818 /// valid UTF-8.
1819 ///
1820 /// # Examples
1821 ///
1822 /// ```
1823 /// let mut s = String::from("hello");
1824 ///
1825 /// unsafe {
1826 /// let vec = s.as_mut_vec();
1827 /// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1828 ///
1829 /// vec.reverse();
1830 /// }
1831 /// assert_eq!(s, "olleh");
1832 /// ```
1833 #[inline]
1834 #[stable(feature = "rust1", since = "1.0.0")]
1835 #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
1836 pub const unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1837 &mut self.vec
1838 }
1839
1840 /// Returns the length of this `String`, in bytes, not [`char`]s or
1841 /// graphemes. In other words, it might not be what a human considers the
1842 /// length of the string.
1843 ///
1844 /// # Examples
1845 ///
1846 /// ```
1847 /// let a = String::from("foo");
1848 /// assert_eq!(a.len(), 3);
1849 ///
1850 /// let fancy_f = String::from("Ζ’oo");
1851 /// assert_eq!(fancy_f.len(), 4);
1852 /// assert_eq!(fancy_f.chars().count(), 3);
1853 /// ```
1854 #[inline]
1855 #[must_use]
1856 #[stable(feature = "rust1", since = "1.0.0")]
1857 #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
1858 #[rustc_confusables("length", "size")]
1859 #[rustc_no_implicit_autorefs]
1860 pub const fn len(&self) -> usize {
1861 self.vec.len()
1862 }
1863
1864 /// Returns `true` if this `String` has a length of zero, and `false` otherwise.
1865 ///
1866 /// # Examples
1867 ///
1868 /// ```
1869 /// let mut v = String::new();
1870 /// assert!(v.is_empty());
1871 ///
1872 /// v.push('a');
1873 /// assert!(!v.is_empty());
1874 /// ```
1875 #[inline]
1876 #[must_use]
1877 #[stable(feature = "rust1", since = "1.0.0")]
1878 #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
1879 #[rustc_no_implicit_autorefs]
1880 pub const fn is_empty(&self) -> bool {
1881 self.len() == 0
1882 }
1883
1884 /// Splits the string into two at the given byte index.
1885 ///
1886 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1887 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1888 /// boundary of a UTF-8 code point.
1889 ///
1890 /// Note that the capacity of `self` does not change.
1891 ///
1892 /// # Panics
1893 ///
1894 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1895 /// code point of the string.
1896 ///
1897 /// # Examples
1898 ///
1899 /// ```
1900 /// # fn main() {
1901 /// let mut hello = String::from("Hello, World!");
1902 /// let world = hello.split_off(7);
1903 /// assert_eq!(hello, "Hello, ");
1904 /// assert_eq!(world, "World!");
1905 /// # }
1906 /// ```
1907 #[cfg(not(no_global_oom_handling))]
1908 #[inline]
1909 #[track_caller]
1910 #[stable(feature = "string_split_off", since = "1.16.0")]
1911 #[must_use = "use `.truncate()` if you don't need the other half"]
1912 pub fn split_off(&mut self, at: usize) -> String {
1913 assert!(self.is_char_boundary(at));
1914 let other = self.vec.split_off(at);
1915 unsafe { String::from_utf8_unchecked(other) }
1916 }
1917
1918 /// Truncates this `String`, removing all contents.
1919 ///
1920 /// While this means the `String` will have a length of zero, it does not
1921 /// touch its capacity.
1922 ///
1923 /// # Examples
1924 ///
1925 /// ```
1926 /// let mut s = String::from("foo");
1927 ///
1928 /// s.clear();
1929 ///
1930 /// assert!(s.is_empty());
1931 /// assert_eq!(0, s.len());
1932 /// assert_eq!(3, s.capacity());
1933 /// ```
1934 #[inline]
1935 #[stable(feature = "rust1", since = "1.0.0")]
1936 pub fn clear(&mut self) {
1937 self.vec.clear()
1938 }
1939
1940 /// Removes the specified range from the string in bulk, returning all
1941 /// removed characters as an iterator.
1942 ///
1943 /// The returned iterator keeps a mutable borrow on the string to optimize
1944 /// its implementation.
1945 ///
1946 /// # Panics
1947 ///
1948 /// Panics if the range has `start_bound > end_bound`, or, if the range is
1949 /// bounded on either end and does not lie on a [`char`] boundary.
1950 ///
1951 /// # Leaking
1952 ///
1953 /// If the returned iterator goes out of scope without being dropped (due to
1954 /// [`core::mem::forget`], for example), the string may still contain a copy
1955 /// of any drained characters, or may have lost characters arbitrarily,
1956 /// including characters outside the range.
1957 ///
1958 /// # Examples
1959 ///
1960 /// ```
1961 /// let mut s = String::from("Ξ± is alpha, Ξ² is beta");
1962 /// let beta_offset = s.find('Ξ²').unwrap_or(s.len());
1963 ///
1964 /// // Remove the range up until the Ξ² from the string
1965 /// let t: String = s.drain(..beta_offset).collect();
1966 /// assert_eq!(t, "Ξ± is alpha, ");
1967 /// assert_eq!(s, "Ξ² is beta");
1968 ///
1969 /// // A full range clears the string, like `clear()` does
1970 /// s.drain(..);
1971 /// assert_eq!(s, "");
1972 /// ```
1973 #[stable(feature = "drain", since = "1.6.0")]
1974 #[track_caller]
1975 pub fn drain<R>(&mut self, range: R) -> Drain<'_>
1976 where
1977 R: RangeBounds<usize>,
1978 {
1979 // Memory safety
1980 //
1981 // The String version of Drain does not have the memory safety issues
1982 // of the vector version. The data is just plain bytes.
1983 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1984 // the removal will not happen.
1985 let Range { start, end } = slice::range(range, ..self.len());
1986 assert!(self.is_char_boundary(start));
1987 assert!(self.is_char_boundary(end));
1988
1989 // Take out two simultaneous borrows. The &mut String won't be accessed
1990 // until iteration is over, in Drop.
1991 let self_ptr = self as *mut _;
1992 // SAFETY: `slice::range` and `is_char_boundary` do the appropriate bounds checks.
1993 let chars_iter = unsafe { self.get_unchecked(start..end) }.chars();
1994
1995 Drain { start, end, iter: chars_iter, string: self_ptr }
1996 }
1997
1998 /// Converts a `String` into an iterator over the [`char`]s of the string.
1999 ///
2000 /// As a string consists of valid UTF-8, we can iterate through a string
2001 /// by [`char`]. This method returns such an iterator.
2002 ///
2003 /// It's important to remember that [`char`] represents a Unicode Scalar
2004 /// Value, and might not match your idea of what a 'character' is. Iteration
2005 /// over grapheme clusters may be what you actually want. That functionality
2006 /// is not provided by Rust's standard library, check crates.io instead.
2007 ///
2008 /// # Examples
2009 ///
2010 /// Basic usage:
2011 ///
2012 /// ```
2013 /// #![feature(string_into_chars)]
2014 ///
2015 /// let word = String::from("goodbye");
2016 ///
2017 /// let mut chars = word.into_chars();
2018 ///
2019 /// assert_eq!(Some('g'), chars.next());
2020 /// assert_eq!(Some('o'), chars.next());
2021 /// assert_eq!(Some('o'), chars.next());
2022 /// assert_eq!(Some('d'), chars.next());
2023 /// assert_eq!(Some('b'), chars.next());
2024 /// assert_eq!(Some('y'), chars.next());
2025 /// assert_eq!(Some('e'), chars.next());
2026 ///
2027 /// assert_eq!(None, chars.next());
2028 /// ```
2029 ///
2030 /// Remember, [`char`]s might not match your intuition about characters:
2031 ///
2032 /// ```
2033 /// #![feature(string_into_chars)]
2034 ///
2035 /// let y = String::from("y̆");
2036 ///
2037 /// let mut chars = y.into_chars();
2038 ///
2039 /// assert_eq!(Some('y'), chars.next()); // not 'y̆'
2040 /// assert_eq!(Some('\u{0306}'), chars.next());
2041 ///
2042 /// assert_eq!(None, chars.next());
2043 /// ```
2044 ///
2045 /// [`char`]: prim@char
2046 #[inline]
2047 #[must_use = "`self` will be dropped if the result is not used"]
2048 #[unstable(feature = "string_into_chars", issue = "133125")]
2049 pub fn into_chars(self) -> IntoChars {
2050 IntoChars { bytes: self.into_bytes().into_iter() }
2051 }
2052
2053 /// Removes the specified range in the string,
2054 /// and replaces it with the given string.
2055 /// The given string doesn't need to be the same length as the range.
2056 ///
2057 /// # Panics
2058 ///
2059 /// Panics if the range has `start_bound > end_bound`, or, if the range is
2060 /// bounded on either end and does not lie on a [`char`] boundary.
2061 ///
2062 /// # Examples
2063 ///
2064 /// ```
2065 /// let mut s = String::from("Ξ± is alpha, Ξ² is beta");
2066 /// let beta_offset = s.find('Ξ²').unwrap_or(s.len());
2067 ///
2068 /// // Replace the range up until the Ξ² from the string
2069 /// s.replace_range(..beta_offset, "Ξ‘ is capital alpha; ");
2070 /// assert_eq!(s, "Ξ‘ is capital alpha; Ξ² is beta");
2071 /// ```
2072 #[cfg(not(no_global_oom_handling))]
2073 #[stable(feature = "splice", since = "1.27.0")]
2074 #[track_caller]
2075 pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
2076 where
2077 R: RangeBounds<usize>,
2078 {
2079 // We avoid #81138 (nondeterministic RangeBounds impls) because we only use `range` once, here.
2080 let checked_range = slice::range(range, ..self.len());
2081
2082 assert!(
2083 self.is_char_boundary(checked_range.start),
2084 "start of range should be a character boundary"
2085 );
2086 assert!(
2087 self.is_char_boundary(checked_range.end),
2088 "end of range should be a character boundary"
2089 );
2090
2091 unsafe { self.as_mut_vec() }.splice(checked_range, replace_with.bytes());
2092 }
2093
2094 /// Replaces the leftmost occurrence of a pattern with another string, in-place.
2095 ///
2096 /// This method can be preferred over [`string = string.replacen(..., 1);`][replacen],
2097 /// as it can use the `String`'s existing capacity to prevent a reallocation if
2098 /// sufficient space is available.
2099 ///
2100 /// # Examples
2101 ///
2102 /// Basic usage:
2103 ///
2104 /// ```
2105 /// #![feature(string_replace_in_place)]
2106 ///
2107 /// let mut s = String::from("Test Results: ❌❌❌");
2108 ///
2109 /// // Replace the leftmost ❌ with a βœ…
2110 /// s.replace_first('❌', "βœ…");
2111 /// assert_eq!(s, "Test Results: βœ…βŒβŒ");
2112 /// ```
2113 ///
2114 /// [replacen]: ../../std/primitive.str.html#method.replacen
2115 #[cfg(not(no_global_oom_handling))]
2116 #[unstable(feature = "string_replace_in_place", issue = "147949")]
2117 pub fn replace_first<P: Pattern>(&mut self, from: P, to: &str) {
2118 let range = match self.match_indices(from).next() {
2119 Some((start, match_str)) => start..start + match_str.len(),
2120 None => return,
2121 };
2122
2123 self.replace_range(range, to);
2124 }
2125
2126 /// Replaces the rightmost occurrence of a pattern with another string, in-place.
2127 ///
2128 /// # Examples
2129 ///
2130 /// Basic usage:
2131 ///
2132 /// ```
2133 /// #![feature(string_replace_in_place)]
2134 ///
2135 /// let mut s = String::from("Test Results: ❌❌❌");
2136 ///
2137 /// // Replace the rightmost ❌ with a βœ…
2138 /// s.replace_last('❌', "βœ…");
2139 /// assert_eq!(s, "Test Results: βŒβŒβœ…");
2140 /// ```
2141 #[cfg(not(no_global_oom_handling))]
2142 #[unstable(feature = "string_replace_in_place", issue = "147949")]
2143 pub fn replace_last<P: Pattern>(&mut self, from: P, to: &str)
2144 where
2145 for<'a> P::Searcher<'a>: core::str::pattern::ReverseSearcher<'a>,
2146 {
2147 let range = match self.rmatch_indices(from).next() {
2148 Some((start, match_str)) => start..start + match_str.len(),
2149 None => return,
2150 };
2151
2152 self.replace_range(range, to);
2153 }
2154
2155 /// Converts this `String` into a <code>[Box]<[str]></code>.
2156 ///
2157 /// Before doing the conversion, this method discards excess capacity like [`shrink_to_fit`].
2158 /// Note that this call may reallocate and copy the bytes of the string.
2159 ///
2160 /// [`shrink_to_fit`]: String::shrink_to_fit
2161 /// [str]: prim@str "str"
2162 ///
2163 /// # Examples
2164 ///
2165 /// ```
2166 /// let s = String::from("hello");
2167 ///
2168 /// let b = s.into_boxed_str();
2169 /// ```
2170 #[cfg(not(no_global_oom_handling))]
2171 #[stable(feature = "box_str", since = "1.4.0")]
2172 #[must_use = "`self` will be dropped if the result is not used"]
2173 #[inline]
2174 pub fn into_boxed_str(self) -> Box<str> {
2175 let slice = self.vec.into_boxed_slice();
2176 unsafe { from_boxed_utf8_unchecked(slice) }
2177 }
2178
2179 /// Consumes and leaks the `String`, returning a mutable reference to the contents,
2180 /// `&'a mut str`.
2181 ///
2182 /// The caller has free choice over the returned lifetime, including `'static`. Indeed,
2183 /// this function is ideally used for data that lives for the remainder of the program's life,
2184 /// as dropping the returned reference will cause a memory leak.
2185 ///
2186 /// It does not reallocate or shrink the `String`, so the leaked allocation may include unused
2187 /// capacity that is not part of the returned slice. If you want to discard excess capacity,
2188 /// call [`into_boxed_str`], and then [`Box::leak`] instead. However, keep in mind that
2189 /// trimming the capacity may result in a reallocation and copy.
2190 ///
2191 /// [`into_boxed_str`]: Self::into_boxed_str
2192 ///
2193 /// # Examples
2194 ///
2195 /// ```
2196 /// let x = String::from("bucket");
2197 /// let static_ref: &'static mut str = x.leak();
2198 /// assert_eq!(static_ref, "bucket");
2199 /// # // FIXME(https://github.com/rust-lang/miri/issues/3670):
2200 /// # // use -Zmiri-disable-leak-check instead of unleaking in tests meant to leak.
2201 /// # drop(unsafe { Box::from_raw(static_ref) });
2202 /// ```
2203 #[stable(feature = "string_leak", since = "1.72.0")]
2204 #[inline]
2205 pub fn leak<'a>(self) -> &'a mut str {
2206 let slice = self.vec.leak();
2207 unsafe { from_utf8_unchecked_mut(slice) }
2208 }
2209}
2210
2211impl FromUtf8Error {
2212 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
2213 ///
2214 /// # Examples
2215 ///
2216 /// ```
2217 /// // some invalid bytes, in a vector
2218 /// let bytes = vec![0, 159];
2219 ///
2220 /// let value = String::from_utf8(bytes);
2221 ///
2222 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
2223 /// ```
2224 #[must_use]
2225 #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
2226 pub fn as_bytes(&self) -> &[u8] {
2227 &self.bytes[..]
2228 }
2229
2230 /// Converts the bytes into a `String` lossily, substituting invalid UTF-8
2231 /// sequences with replacement characters.
2232 ///
2233 /// See [`String::from_utf8_lossy`] for more details on replacement of
2234 /// invalid sequences, and [`String::from_utf8_lossy_owned`] for the
2235 /// `String` function which corresponds to this function.
2236 ///
2237 /// # Examples
2238 ///
2239 /// ```
2240 /// #![feature(string_from_utf8_lossy_owned)]
2241 /// // some invalid bytes
2242 /// let input: Vec<u8> = b"Hello \xF0\x90\x80World".into();
2243 /// let output = String::from_utf8(input).unwrap_or_else(|e| e.into_utf8_lossy());
2244 ///
2245 /// assert_eq!(String::from("Hello οΏ½World"), output);
2246 /// ```
2247 #[must_use]
2248 #[cfg(not(no_global_oom_handling))]
2249 #[unstable(feature = "string_from_utf8_lossy_owned", issue = "129436")]
2250 pub fn into_utf8_lossy(self) -> String {
2251 const REPLACEMENT: &str = "\u{FFFD}";
2252
2253 let mut res = {
2254 let mut v = Vec::with_capacity(self.bytes.len());
2255
2256 // `Utf8Error::valid_up_to` returns the maximum index of validated
2257 // UTF-8 bytes. Copy the valid bytes into the output buffer.
2258 v.extend_from_slice(&self.bytes[..self.error.valid_up_to()]);
2259
2260 // SAFETY: This is safe because the only bytes present in the buffer
2261 // were validated as UTF-8 by the call to `String::from_utf8` which
2262 // produced this `FromUtf8Error`.
2263 unsafe { String::from_utf8_unchecked(v) }
2264 };
2265
2266 let iter = self.bytes[self.error.valid_up_to()..].utf8_chunks();
2267
2268 for chunk in iter {
2269 res.push_str(chunk.valid());
2270 if !chunk.invalid().is_empty() {
2271 res.push_str(REPLACEMENT);
2272 }
2273 }
2274
2275 res
2276 }
2277
2278 /// Returns the bytes that were attempted to convert to a `String`.
2279 ///
2280 /// This method is carefully constructed to avoid allocation. It will
2281 /// consume the error, moving out the bytes, so that a copy of the bytes
2282 /// does not need to be made.
2283 ///
2284 /// # Examples
2285 ///
2286 /// ```
2287 /// // some invalid bytes, in a vector
2288 /// let bytes = vec![0, 159];
2289 ///
2290 /// let value = String::from_utf8(bytes);
2291 ///
2292 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
2293 /// ```
2294 #[must_use = "`self` will be dropped if the result is not used"]
2295 #[stable(feature = "rust1", since = "1.0.0")]
2296 pub fn into_bytes(self) -> Vec<u8> {
2297 self.bytes
2298 }
2299
2300 /// Fetch a `Utf8Error` to get more details about the conversion failure.
2301 ///
2302 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
2303 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
2304 /// an analogue to `FromUtf8Error`. See its documentation for more details
2305 /// on using it.
2306 ///
2307 /// [`std::str`]: core::str "std::str"
2308 /// [`&str`]: prim@str "&str"
2309 ///
2310 /// # Examples
2311 ///
2312 /// ```
2313 /// // some invalid bytes, in a vector
2314 /// let bytes = vec![0, 159];
2315 ///
2316 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
2317 ///
2318 /// // the first byte is invalid here
2319 /// assert_eq!(1, error.valid_up_to());
2320 /// ```
2321 #[must_use]
2322 #[stable(feature = "rust1", since = "1.0.0")]
2323 pub fn utf8_error(&self) -> Utf8Error {
2324 self.error
2325 }
2326}
2327
2328#[stable(feature = "rust1", since = "1.0.0")]
2329impl fmt::Display for FromUtf8Error {
2330 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2331 fmt::Display::fmt(&self.error, f)
2332 }
2333}
2334
2335#[stable(feature = "rust1", since = "1.0.0")]
2336impl fmt::Display for FromUtf16Error {
2337 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2338 fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
2339 }
2340}
2341
2342#[stable(feature = "rust1", since = "1.0.0")]
2343impl Error for FromUtf8Error {}
2344
2345#[stable(feature = "rust1", since = "1.0.0")]
2346impl Error for FromUtf16Error {}
2347
2348#[cfg(not(no_global_oom_handling))]
2349#[stable(feature = "rust1", since = "1.0.0")]
2350impl Clone for String {
2351 fn clone(&self) -> Self {
2352 String { vec: self.vec.clone() }
2353 }
2354
2355 /// Clones the contents of `source` into `self`.
2356 ///
2357 /// This method is preferred over simply assigning `source.clone()` to `self`,
2358 /// as it avoids reallocation if possible.
2359 fn clone_from(&mut self, source: &Self) {
2360 self.vec.clone_from(&source.vec);
2361 }
2362}
2363
2364#[cfg(not(no_global_oom_handling))]
2365#[stable(feature = "rust1", since = "1.0.0")]
2366impl FromIterator<char> for String {
2367 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
2368 let mut buf: String = String::new();
2369 buf.extend(iter);
2370 buf
2371 }
2372}
2373
2374#[cfg(not(no_global_oom_handling))]
2375#[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
2376impl<'a> FromIterator<&'a char> for String {
2377 fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
2378 let mut buf: String = String::new();
2379 buf.extend(iter);
2380 buf
2381 }
2382}
2383
2384#[cfg(not(no_global_oom_handling))]
2385#[stable(feature = "rust1", since = "1.0.0")]
2386impl<'a> FromIterator<&'a str> for String {
2387 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
2388 let mut buf: String = String::new();
2389 buf.extend(iter);
2390 buf
2391 }
2392}
2393
2394#[cfg(not(no_global_oom_handling))]
2395#[stable(feature = "extend_string", since = "1.4.0")]
2396impl FromIterator<String> for String {
2397 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
2398 let mut iterator = iter.into_iter();
2399
2400 // Because we're iterating over `String`s, we can avoid at least
2401 // one allocation by getting the first string from the iterator
2402 // and appending to it all the subsequent strings.
2403 match iterator.next() {
2404 None => String::new(),
2405 Some(mut buf: String) => {
2406 buf.extend(iterator);
2407 buf
2408 }
2409 }
2410 }
2411}
2412
2413#[cfg(not(no_global_oom_handling))]
2414#[stable(feature = "box_str2", since = "1.45.0")]
2415impl<A: Allocator> FromIterator<Box<str, A>> for String {
2416 fn from_iter<I: IntoIterator<Item = Box<str, A>>>(iter: I) -> String {
2417 let mut buf: String = String::new();
2418 buf.extend(iter);
2419 buf
2420 }
2421}
2422
2423#[cfg(not(no_global_oom_handling))]
2424#[stable(feature = "herd_cows", since = "1.19.0")]
2425impl<'a> FromIterator<Cow<'a, str>> for String {
2426 fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
2427 let mut iterator = iter.into_iter();
2428
2429 // Because we're iterating over CoWs, we can (potentially) avoid at least
2430 // one allocation by getting the first item and appending to it all the
2431 // subsequent items.
2432 match iterator.next() {
2433 None => String::new(),
2434 Some(cow) => {
2435 let mut buf: String = cow.into_owned();
2436 buf.extend(iterator);
2437 buf
2438 }
2439 }
2440 }
2441}
2442
2443#[cfg(not(no_global_oom_handling))]
2444#[unstable(feature = "ascii_char", issue = "110998")]
2445impl FromIterator<core::ascii::Char> for String {
2446 fn from_iter<T: IntoIterator<Item = core::ascii::Char>>(iter: T) -> Self {
2447 let buf: Vec = iter.into_iter().map(core::ascii::Char::to_u8).collect();
2448 // SAFETY: `buf` is guaranteed to be valid UTF-8 because the `core::ascii::Char` type
2449 // only contains ASCII values (0x00-0x7F), which are valid UTF-8.
2450 unsafe { String::from_utf8_unchecked(bytes:buf) }
2451 }
2452}
2453
2454#[cfg(not(no_global_oom_handling))]
2455#[unstable(feature = "ascii_char", issue = "110998")]
2456impl<'a> FromIterator<&'a core::ascii::Char> for String {
2457 fn from_iter<T: IntoIterator<Item = &'a core::ascii::Char>>(iter: T) -> Self {
2458 let buf: Vec = iter.into_iter().copied().map(core::ascii::Char::to_u8).collect();
2459 // SAFETY: `buf` is guaranteed to be valid UTF-8 because the `core::ascii::Char` type
2460 // only contains ASCII values (0x00-0x7F), which are valid UTF-8.
2461 unsafe { String::from_utf8_unchecked(bytes:buf) }
2462 }
2463}
2464
2465#[cfg(not(no_global_oom_handling))]
2466#[stable(feature = "rust1", since = "1.0.0")]
2467impl Extend<char> for String {
2468 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
2469 let iterator = iter.into_iter();
2470 let (lower_bound: usize, _) = iterator.size_hint();
2471 self.reserve(additional:lower_bound);
2472 iterator.for_each(move |c: char| self.push(ch:c));
2473 }
2474
2475 #[inline]
2476 fn extend_one(&mut self, c: char) {
2477 self.push(ch:c);
2478 }
2479
2480 #[inline]
2481 fn extend_reserve(&mut self, additional: usize) {
2482 self.reserve(additional);
2483 }
2484}
2485
2486#[cfg(not(no_global_oom_handling))]
2487#[stable(feature = "extend_ref", since = "1.2.0")]
2488impl<'a> Extend<&'a char> for String {
2489 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
2490 self.extend(iter.into_iter().cloned());
2491 }
2492
2493 #[inline]
2494 fn extend_one(&mut self, &c: char: &'a char) {
2495 self.push(ch:c);
2496 }
2497
2498 #[inline]
2499 fn extend_reserve(&mut self, additional: usize) {
2500 self.reserve(additional);
2501 }
2502}
2503
2504#[cfg(not(no_global_oom_handling))]
2505#[stable(feature = "rust1", since = "1.0.0")]
2506impl<'a> Extend<&'a str> for String {
2507 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
2508 <I as SpecExtendStr>::spec_extend_into(self:iter, self)
2509 }
2510
2511 #[inline]
2512 fn extend_one(&mut self, s: &'a str) {
2513 self.push_str(string:s);
2514 }
2515}
2516
2517#[cfg(not(no_global_oom_handling))]
2518trait SpecExtendStr {
2519 fn spec_extend_into(self, s: &mut String);
2520}
2521
2522#[cfg(not(no_global_oom_handling))]
2523impl<'a, T: IntoIterator<Item = &'a str>> SpecExtendStr for T {
2524 default fn spec_extend_into(self, target: &mut String) {
2525 self.into_iter().for_each(move |s: &str| target.push_str(string:s));
2526 }
2527}
2528
2529#[cfg(not(no_global_oom_handling))]
2530impl SpecExtendStr for [&str] {
2531 fn spec_extend_into(self, target: &mut String) {
2532 target.push_str_slice(&self);
2533 }
2534}
2535
2536#[cfg(not(no_global_oom_handling))]
2537impl<const N: usize> SpecExtendStr for [&str; N] {
2538 fn spec_extend_into(self, target: &mut String) {
2539 target.push_str_slice(&self[..]);
2540 }
2541}
2542
2543#[cfg(not(no_global_oom_handling))]
2544#[stable(feature = "box_str2", since = "1.45.0")]
2545impl<A: Allocator> Extend<Box<str, A>> for String {
2546 fn extend<I: IntoIterator<Item = Box<str, A>>>(&mut self, iter: I) {
2547 iter.into_iter().for_each(move |s: str| self.push_str(&s));
2548 }
2549}
2550
2551#[cfg(not(no_global_oom_handling))]
2552#[stable(feature = "extend_string", since = "1.4.0")]
2553impl Extend<String> for String {
2554 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
2555 iter.into_iter().for_each(move |s: str| self.push_str(&s));
2556 }
2557
2558 #[inline]
2559 fn extend_one(&mut self, s: String) {
2560 self.push_str(&s);
2561 }
2562}
2563
2564#[cfg(not(no_global_oom_handling))]
2565#[stable(feature = "herd_cows", since = "1.19.0")]
2566impl<'a> Extend<Cow<'a, str>> for String {
2567 fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
2568 iter.into_iter().for_each(move |s: str| self.push_str(&s));
2569 }
2570
2571 #[inline]
2572 fn extend_one(&mut self, s: Cow<'a, str>) {
2573 self.push_str(&s);
2574 }
2575}
2576
2577#[cfg(not(no_global_oom_handling))]
2578#[unstable(feature = "ascii_char", issue = "110998")]
2579impl Extend<core::ascii::Char> for String {
2580 #[inline]
2581 fn extend<I: IntoIterator<Item = core::ascii::Char>>(&mut self, iter: I) {
2582 self.vec.extend(iter.into_iter().map(|c| c.to_u8()));
2583 }
2584
2585 #[inline]
2586 fn extend_one(&mut self, c: core::ascii::Char) {
2587 self.vec.push(c.to_u8());
2588 }
2589}
2590
2591#[cfg(not(no_global_oom_handling))]
2592#[unstable(feature = "ascii_char", issue = "110998")]
2593impl<'a> Extend<&'a core::ascii::Char> for String {
2594 #[inline]
2595 fn extend<I: IntoIterator<Item = &'a core::ascii::Char>>(&mut self, iter: I) {
2596 self.extend(iter.into_iter().cloned());
2597 }
2598
2599 #[inline]
2600 fn extend_one(&mut self, c: &'a core::ascii::Char) {
2601 self.vec.push(c.to_u8());
2602 }
2603}
2604
2605/// A convenience impl that delegates to the impl for `&str`.
2606///
2607/// # Examples
2608///
2609/// ```
2610/// assert_eq!(String::from("Hello world").find("world"), Some(6));
2611/// ```
2612#[unstable(
2613 feature = "pattern",
2614 reason = "API not fully fleshed out and ready to be stabilized",
2615 issue = "27721"
2616)]
2617impl<'b> Pattern for &'b String {
2618 type Searcher<'a> = <&'b str as Pattern>::Searcher<'a>;
2619
2620 fn into_searcher(self, haystack: &str) -> <&'b str as Pattern>::Searcher<'_> {
2621 self[..].into_searcher(haystack)
2622 }
2623
2624 #[inline]
2625 fn is_contained_in(self, haystack: &str) -> bool {
2626 self[..].is_contained_in(haystack)
2627 }
2628
2629 #[inline]
2630 fn is_prefix_of(self, haystack: &str) -> bool {
2631 self[..].is_prefix_of(haystack)
2632 }
2633
2634 #[inline]
2635 fn strip_prefix_of(self, haystack: &str) -> Option<&str> {
2636 self[..].strip_prefix_of(haystack)
2637 }
2638
2639 #[inline]
2640 fn is_suffix_of<'a>(self, haystack: &'a str) -> bool
2641 where
2642 Self::Searcher<'a>: core::str::pattern::ReverseSearcher<'a>,
2643 {
2644 self[..].is_suffix_of(haystack)
2645 }
2646
2647 #[inline]
2648 fn strip_suffix_of<'a>(self, haystack: &'a str) -> Option<&'a str>
2649 where
2650 Self::Searcher<'a>: core::str::pattern::ReverseSearcher<'a>,
2651 {
2652 self[..].strip_suffix_of(haystack)
2653 }
2654
2655 #[inline]
2656 fn as_utf8_pattern(&self) -> Option<Utf8Pattern<'_>> {
2657 Some(Utf8Pattern::StringPattern(self.as_bytes()))
2658 }
2659}
2660
2661macro_rules! impl_eq {
2662 ($lhs:ty, $rhs: ty) => {
2663 #[stable(feature = "rust1", since = "1.0.0")]
2664 #[allow(unused_lifetimes)]
2665 impl<'a, 'b> PartialEq<$rhs> for $lhs {
2666 #[inline]
2667 fn eq(&self, other: &$rhs) -> bool {
2668 PartialEq::eq(&self[..], &other[..])
2669 }
2670 #[inline]
2671 fn ne(&self, other: &$rhs) -> bool {
2672 PartialEq::ne(&self[..], &other[..])
2673 }
2674 }
2675
2676 #[stable(feature = "rust1", since = "1.0.0")]
2677 #[allow(unused_lifetimes)]
2678 impl<'a, 'b> PartialEq<$lhs> for $rhs {
2679 #[inline]
2680 fn eq(&self, other: &$lhs) -> bool {
2681 PartialEq::eq(&self[..], &other[..])
2682 }
2683 #[inline]
2684 fn ne(&self, other: &$lhs) -> bool {
2685 PartialEq::ne(&self[..], &other[..])
2686 }
2687 }
2688 };
2689}
2690
2691impl_eq! { String, str }
2692impl_eq! { String, &'a str }
2693#[cfg(not(no_global_oom_handling))]
2694impl_eq! { Cow<'a, str>, str }
2695#[cfg(not(no_global_oom_handling))]
2696impl_eq! { Cow<'a, str>, &'b str }
2697#[cfg(not(no_global_oom_handling))]
2698impl_eq! { Cow<'a, str>, String }
2699
2700#[stable(feature = "rust1", since = "1.0.0")]
2701#[rustc_const_unstable(feature = "const_default", issue = "143894")]
2702impl const Default for String {
2703 /// Creates an empty `String`.
2704 #[inline]
2705 fn default() -> String {
2706 String::new()
2707 }
2708}
2709
2710#[stable(feature = "rust1", since = "1.0.0")]
2711impl fmt::Display for String {
2712 #[inline]
2713 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2714 fmt::Display::fmt(&**self, f)
2715 }
2716}
2717
2718#[stable(feature = "rust1", since = "1.0.0")]
2719impl fmt::Debug for String {
2720 #[inline]
2721 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2722 fmt::Debug::fmt(&**self, f)
2723 }
2724}
2725
2726#[stable(feature = "rust1", since = "1.0.0")]
2727impl hash::Hash for String {
2728 #[inline]
2729 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
2730 (**self).hash(hasher)
2731 }
2732}
2733
2734/// Implements the `+` operator for concatenating two strings.
2735///
2736/// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
2737/// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
2738/// every operation, which would lead to *O*(*n*^2) running time when building an *n*-byte string by
2739/// repeated concatenation.
2740///
2741/// The string on the right-hand side is only borrowed; its contents are copied into the returned
2742/// `String`.
2743///
2744/// # Examples
2745///
2746/// Concatenating two `String`s takes the first by value and borrows the second:
2747///
2748/// ```
2749/// let a = String::from("hello");
2750/// let b = String::from(" world");
2751/// let c = a + &b;
2752/// // `a` is moved and can no longer be used here.
2753/// ```
2754///
2755/// If you want to keep using the first `String`, you can clone it and append to the clone instead:
2756///
2757/// ```
2758/// let a = String::from("hello");
2759/// let b = String::from(" world");
2760/// let c = a.clone() + &b;
2761/// // `a` is still valid here.
2762/// ```
2763///
2764/// Concatenating `&str` slices can be done by converting the first to a `String`:
2765///
2766/// ```
2767/// let a = "hello";
2768/// let b = " world";
2769/// let c = a.to_string() + b;
2770/// ```
2771#[cfg(not(no_global_oom_handling))]
2772#[stable(feature = "rust1", since = "1.0.0")]
2773impl Add<&str> for String {
2774 type Output = String;
2775
2776 #[inline]
2777 fn add(mut self, other: &str) -> String {
2778 self.push_str(string:other);
2779 self
2780 }
2781}
2782
2783/// Implements the `+=` operator for appending to a `String`.
2784///
2785/// This has the same behavior as the [`push_str`][String::push_str] method.
2786#[cfg(not(no_global_oom_handling))]
2787#[stable(feature = "stringaddassign", since = "1.12.0")]
2788impl AddAssign<&str> for String {
2789 #[inline]
2790 fn add_assign(&mut self, other: &str) {
2791 self.push_str(string:other);
2792 }
2793}
2794
2795#[stable(feature = "rust1", since = "1.0.0")]
2796impl<I> ops::Index<I> for String
2797where
2798 I: slice::SliceIndex<str>,
2799{
2800 type Output = I::Output;
2801
2802 #[inline]
2803 fn index(&self, index: I) -> &I::Output {
2804 index.index(self.as_str())
2805 }
2806}
2807
2808#[stable(feature = "rust1", since = "1.0.0")]
2809impl<I> ops::IndexMut<I> for String
2810where
2811 I: slice::SliceIndex<str>,
2812{
2813 #[inline]
2814 fn index_mut(&mut self, index: I) -> &mut I::Output {
2815 index.index_mut(self.as_mut_str())
2816 }
2817}
2818
2819#[stable(feature = "rust1", since = "1.0.0")]
2820impl ops::Deref for String {
2821 type Target = str;
2822
2823 #[inline]
2824 fn deref(&self) -> &str {
2825 self.as_str()
2826 }
2827}
2828
2829#[unstable(feature = "deref_pure_trait", issue = "87121")]
2830unsafe impl ops::DerefPure for String {}
2831
2832#[stable(feature = "derefmut_for_string", since = "1.3.0")]
2833impl ops::DerefMut for String {
2834 #[inline]
2835 fn deref_mut(&mut self) -> &mut str {
2836 self.as_mut_str()
2837 }
2838}
2839
2840/// A type alias for [`Infallible`].
2841///
2842/// This alias exists for backwards compatibility, and may be eventually deprecated.
2843///
2844/// [`Infallible`]: core::convert::Infallible "convert::Infallible"
2845#[stable(feature = "str_parse_error", since = "1.5.0")]
2846pub type ParseError = core::convert::Infallible;
2847
2848#[cfg(not(no_global_oom_handling))]
2849#[stable(feature = "rust1", since = "1.0.0")]
2850impl FromStr for String {
2851 type Err = core::convert::Infallible;
2852 #[inline]
2853 fn from_str(s: &str) -> Result<String, Self::Err> {
2854 Ok(String::from(s))
2855 }
2856}
2857
2858/// A trait for converting a value to a `String`.
2859///
2860/// This trait is automatically implemented for any type which implements the
2861/// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
2862/// [`Display`] should be implemented instead, and you get the `ToString`
2863/// implementation for free.
2864///
2865/// [`Display`]: fmt::Display
2866#[rustc_diagnostic_item = "ToString"]
2867#[stable(feature = "rust1", since = "1.0.0")]
2868pub trait ToString {
2869 /// Converts the given value to a `String`.
2870 ///
2871 /// # Examples
2872 ///
2873 /// ```
2874 /// let i = 5;
2875 /// let five = String::from("5");
2876 ///
2877 /// assert_eq!(five, i.to_string());
2878 /// ```
2879 #[rustc_conversion_suggestion]
2880 #[stable(feature = "rust1", since = "1.0.0")]
2881 #[rustc_diagnostic_item = "to_string_method"]
2882 fn to_string(&self) -> String;
2883}
2884
2885/// # Panics
2886///
2887/// In this implementation, the `to_string` method panics
2888/// if the `Display` implementation returns an error.
2889/// This indicates an incorrect `Display` implementation
2890/// since `fmt::Write for String` never returns an error itself.
2891#[cfg(not(no_global_oom_handling))]
2892#[stable(feature = "rust1", since = "1.0.0")]
2893impl<T: fmt::Display + ?Sized> ToString for T {
2894 #[inline]
2895 fn to_string(&self) -> String {
2896 <Self as SpecToString>::spec_to_string(self)
2897 }
2898}
2899
2900#[cfg(not(no_global_oom_handling))]
2901trait SpecToString {
2902 fn spec_to_string(&self) -> String;
2903}
2904
2905#[cfg(not(no_global_oom_handling))]
2906impl<T: fmt::Display + ?Sized> SpecToString for T {
2907 // A common guideline is to not inline generic functions. However,
2908 // removing `#[inline]` from this method causes non-negligible regressions.
2909 // See <https://github.com/rust-lang/rust/pull/74852>, the last attempt
2910 // to try to remove it.
2911 #[inline]
2912 default fn spec_to_string(&self) -> String {
2913 let mut buf: String = String::new();
2914 let mut formatter =
2915 core::fmt::Formatter::new(&mut buf, core::fmt::FormattingOptions::new());
2916 // Bypass format_args!() to avoid write_str with zero-length strs
2917 fmt::Display::fmt(self, &mut formatter)
2918 .expect("a Display implementation returned an error unexpectedly");
2919 buf
2920 }
2921}
2922
2923#[cfg(not(no_global_oom_handling))]
2924impl SpecToString for core::ascii::Char {
2925 #[inline]
2926 fn spec_to_string(&self) -> String {
2927 self.as_str().to_owned()
2928 }
2929}
2930
2931#[cfg(not(no_global_oom_handling))]
2932impl SpecToString for char {
2933 #[inline]
2934 fn spec_to_string(&self) -> String {
2935 String::from(self.encode_utf8(&mut [0; char::MAX_LEN_UTF8]))
2936 }
2937}
2938
2939#[cfg(not(no_global_oom_handling))]
2940impl SpecToString for bool {
2941 #[inline]
2942 fn spec_to_string(&self) -> String {
2943 String::from(if *self { "true" } else { "false" })
2944 }
2945}
2946
2947macro_rules! impl_to_string {
2948 ($($signed:ident, $unsigned:ident,)*) => {
2949 $(
2950 #[cfg(not(no_global_oom_handling))]
2951 #[cfg(not(feature = "optimize_for_size"))]
2952 impl SpecToString for $signed {
2953 #[inline]
2954 fn spec_to_string(&self) -> String {
2955 const SIZE: usize = $signed::MAX.ilog10() as usize + 1;
2956 let mut buf = [core::mem::MaybeUninit::<u8>::uninit(); SIZE];
2957 // Only difference between signed and unsigned are these 8 lines.
2958 let mut out;
2959 if *self < 0 {
2960 out = String::with_capacity(SIZE + 1);
2961 out.push('-');
2962 } else {
2963 out = String::with_capacity(SIZE);
2964 }
2965
2966 // SAFETY: `buf` is always big enough to contain all the digits.
2967 unsafe { out.push_str(self.unsigned_abs()._fmt(&mut buf)); }
2968 out
2969 }
2970 }
2971 #[cfg(not(no_global_oom_handling))]
2972 #[cfg(not(feature = "optimize_for_size"))]
2973 impl SpecToString for $unsigned {
2974 #[inline]
2975 fn spec_to_string(&self) -> String {
2976 const SIZE: usize = $unsigned::MAX.ilog10() as usize + 1;
2977 let mut buf = [core::mem::MaybeUninit::<u8>::uninit(); SIZE];
2978
2979 // SAFETY: `buf` is always big enough to contain all the digits.
2980 unsafe { self._fmt(&mut buf).to_string() }
2981 }
2982 }
2983 )*
2984 }
2985}
2986
2987impl_to_string! {
2988 i8, u8,
2989 i16, u16,
2990 i32, u32,
2991 i64, u64,
2992 isize, usize,
2993 i128, u128,
2994}
2995
2996#[cfg(not(no_global_oom_handling))]
2997#[cfg(feature = "optimize_for_size")]
2998impl SpecToString for u8 {
2999 #[inline]
3000 fn spec_to_string(&self) -> String {
3001 let mut buf = String::with_capacity(3);
3002 let mut n = *self;
3003 if n >= 10 {
3004 if n >= 100 {
3005 buf.push((b'0' + n / 100) as char);
3006 n %= 100;
3007 }
3008 buf.push((b'0' + n / 10) as char);
3009 n %= 10;
3010 }
3011 buf.push((b'0' + n) as char);
3012 buf
3013 }
3014}
3015
3016#[cfg(not(no_global_oom_handling))]
3017#[cfg(feature = "optimize_for_size")]
3018impl SpecToString for i8 {
3019 #[inline]
3020 fn spec_to_string(&self) -> String {
3021 let mut buf = String::with_capacity(4);
3022 if self.is_negative() {
3023 buf.push('-');
3024 }
3025 let mut n = self.unsigned_abs();
3026 if n >= 10 {
3027 if n >= 100 {
3028 buf.push('1');
3029 n -= 100;
3030 }
3031 buf.push((b'0' + n / 10) as char);
3032 n %= 10;
3033 }
3034 buf.push((b'0' + n) as char);
3035 buf
3036 }
3037}
3038
3039#[cfg(not(no_global_oom_handling))]
3040macro_rules! to_string_str {
3041 {$($type:ty,)*} => {
3042 $(
3043 impl SpecToString for $type {
3044 #[inline]
3045 fn spec_to_string(&self) -> String {
3046 let s: &str = self;
3047 String::from(s)
3048 }
3049 }
3050 )*
3051 };
3052}
3053
3054#[cfg(not(no_global_oom_handling))]
3055to_string_str! {
3056 Cow<'_, str>,
3057 String,
3058 // Generic/generated code can sometimes have multiple, nested references
3059 // for strings, including `&&&str`s that would never be written
3060 // by hand.
3061 &&&&&&&&&&&&str,
3062 &&&&&&&&&&&str,
3063 &&&&&&&&&&str,
3064 &&&&&&&&&str,
3065 &&&&&&&&str,
3066 &&&&&&&str,
3067 &&&&&&str,
3068 &&&&&str,
3069 &&&&str,
3070 &&&str,
3071 &&str,
3072 &str,
3073 str,
3074}
3075
3076#[cfg(not(no_global_oom_handling))]
3077impl SpecToString for fmt::Arguments<'_> {
3078 #[inline]
3079 fn spec_to_string(&self) -> String {
3080 crate::fmt::format(*self)
3081 }
3082}
3083
3084#[stable(feature = "rust1", since = "1.0.0")]
3085impl AsRef<str> for String {
3086 #[inline]
3087 fn as_ref(&self) -> &str {
3088 self
3089 }
3090}
3091
3092#[stable(feature = "string_as_mut", since = "1.43.0")]
3093impl AsMut<str> for String {
3094 #[inline]
3095 fn as_mut(&mut self) -> &mut str {
3096 self
3097 }
3098}
3099
3100#[stable(feature = "rust1", since = "1.0.0")]
3101impl AsRef<[u8]> for String {
3102 #[inline]
3103 fn as_ref(&self) -> &[u8] {
3104 self.as_bytes()
3105 }
3106}
3107
3108#[cfg(not(no_global_oom_handling))]
3109#[stable(feature = "rust1", since = "1.0.0")]
3110impl From<&str> for String {
3111 /// Converts a `&str` into a [`String`].
3112 ///
3113 /// The result is allocated on the heap.
3114 #[inline]
3115 fn from(s: &str) -> String {
3116 s.to_owned()
3117 }
3118}
3119
3120#[cfg(not(no_global_oom_handling))]
3121#[stable(feature = "from_mut_str_for_string", since = "1.44.0")]
3122impl From<&mut str> for String {
3123 /// Converts a `&mut str` into a [`String`].
3124 ///
3125 /// The result is allocated on the heap.
3126 #[inline]
3127 fn from(s: &mut str) -> String {
3128 s.to_owned()
3129 }
3130}
3131
3132#[cfg(not(no_global_oom_handling))]
3133#[stable(feature = "from_ref_string", since = "1.35.0")]
3134impl From<&String> for String {
3135 /// Converts a `&String` into a [`String`].
3136 ///
3137 /// This clones `s` and returns the clone.
3138 #[inline]
3139 fn from(s: &String) -> String {
3140 s.clone()
3141 }
3142}
3143
3144// note: test pulls in std, which causes errors here
3145#[stable(feature = "string_from_box", since = "1.18.0")]
3146impl From<Box<str>> for String {
3147 /// Converts the given boxed `str` slice to a [`String`].
3148 /// It is notable that the `str` slice is owned.
3149 ///
3150 /// # Examples
3151 ///
3152 /// ```
3153 /// let s1: String = String::from("hello world");
3154 /// let s2: Box<str> = s1.into_boxed_str();
3155 /// let s3: String = String::from(s2);
3156 ///
3157 /// assert_eq!("hello world", s3)
3158 /// ```
3159 fn from(s: Box<str>) -> String {
3160 s.into_string()
3161 }
3162}
3163
3164#[cfg(not(no_global_oom_handling))]
3165#[stable(feature = "box_from_str", since = "1.20.0")]
3166impl From<String> for Box<str> {
3167 /// Converts the given [`String`] to a boxed `str` slice that is owned.
3168 ///
3169 /// # Examples
3170 ///
3171 /// ```
3172 /// let s1: String = String::from("hello world");
3173 /// let s2: Box<str> = Box::from(s1);
3174 /// let s3: String = String::from(s2);
3175 ///
3176 /// assert_eq!("hello world", s3)
3177 /// ```
3178 fn from(s: String) -> Box<str> {
3179 s.into_boxed_str()
3180 }
3181}
3182
3183#[cfg(not(no_global_oom_handling))]
3184#[stable(feature = "string_from_cow_str", since = "1.14.0")]
3185impl<'a> From<Cow<'a, str>> for String {
3186 /// Converts a clone-on-write string to an owned
3187 /// instance of [`String`].
3188 ///
3189 /// This extracts the owned string,
3190 /// clones the string if it is not already owned.
3191 ///
3192 /// # Example
3193 ///
3194 /// ```
3195 /// # use std::borrow::Cow;
3196 /// // If the string is not owned...
3197 /// let cow: Cow<'_, str> = Cow::Borrowed("eggplant");
3198 /// // It will allocate on the heap and copy the string.
3199 /// let owned: String = String::from(cow);
3200 /// assert_eq!(&owned[..], "eggplant");
3201 /// ```
3202 fn from(s: Cow<'a, str>) -> String {
3203 s.into_owned()
3204 }
3205}
3206
3207#[cfg(not(no_global_oom_handling))]
3208#[stable(feature = "rust1", since = "1.0.0")]
3209impl<'a> From<&'a str> for Cow<'a, str> {
3210 /// Converts a string slice into a [`Borrowed`] variant.
3211 /// No heap allocation is performed, and the string
3212 /// is not copied.
3213 ///
3214 /// # Example
3215 ///
3216 /// ```
3217 /// # use std::borrow::Cow;
3218 /// assert_eq!(Cow::from("eggplant"), Cow::Borrowed("eggplant"));
3219 /// ```
3220 ///
3221 /// [`Borrowed`]: crate::borrow::Cow::Borrowed "borrow::Cow::Borrowed"
3222 #[inline]
3223 fn from(s: &'a str) -> Cow<'a, str> {
3224 Cow::Borrowed(s)
3225 }
3226}
3227
3228#[cfg(not(no_global_oom_handling))]
3229#[stable(feature = "rust1", since = "1.0.0")]
3230impl<'a> From<String> for Cow<'a, str> {
3231 /// Converts a [`String`] into an [`Owned`] variant.
3232 /// No heap allocation is performed, and the string
3233 /// is not copied.
3234 ///
3235 /// # Example
3236 ///
3237 /// ```
3238 /// # use std::borrow::Cow;
3239 /// let s = "eggplant".to_string();
3240 /// let s2 = "eggplant".to_string();
3241 /// assert_eq!(Cow::from(s), Cow::<'static, str>::Owned(s2));
3242 /// ```
3243 ///
3244 /// [`Owned`]: crate::borrow::Cow::Owned "borrow::Cow::Owned"
3245 #[inline]
3246 fn from(s: String) -> Cow<'a, str> {
3247 Cow::Owned(s)
3248 }
3249}
3250
3251#[cfg(not(no_global_oom_handling))]
3252#[stable(feature = "cow_from_string_ref", since = "1.28.0")]
3253impl<'a> From<&'a String> for Cow<'a, str> {
3254 /// Converts a [`String`] reference into a [`Borrowed`] variant.
3255 /// No heap allocation is performed, and the string
3256 /// is not copied.
3257 ///
3258 /// # Example
3259 ///
3260 /// ```
3261 /// # use std::borrow::Cow;
3262 /// let s = "eggplant".to_string();
3263 /// assert_eq!(Cow::from(&s), Cow::Borrowed("eggplant"));
3264 /// ```
3265 ///
3266 /// [`Borrowed`]: crate::borrow::Cow::Borrowed "borrow::Cow::Borrowed"
3267 #[inline]
3268 fn from(s: &'a String) -> Cow<'a, str> {
3269 Cow::Borrowed(s.as_str())
3270 }
3271}
3272
3273#[cfg(not(no_global_oom_handling))]
3274#[stable(feature = "cow_str_from_iter", since = "1.12.0")]
3275impl<'a> FromIterator<char> for Cow<'a, str> {
3276 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
3277 Cow::Owned(FromIterator::from_iter(it))
3278 }
3279}
3280
3281#[cfg(not(no_global_oom_handling))]
3282#[stable(feature = "cow_str_from_iter", since = "1.12.0")]
3283impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
3284 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
3285 Cow::Owned(FromIterator::from_iter(it))
3286 }
3287}
3288
3289#[cfg(not(no_global_oom_handling))]
3290#[stable(feature = "cow_str_from_iter", since = "1.12.0")]
3291impl<'a> FromIterator<String> for Cow<'a, str> {
3292 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
3293 Cow::Owned(FromIterator::from_iter(it))
3294 }
3295}
3296
3297#[cfg(not(no_global_oom_handling))]
3298#[unstable(feature = "ascii_char", issue = "110998")]
3299impl<'a> FromIterator<core::ascii::Char> for Cow<'a, str> {
3300 fn from_iter<T: IntoIterator<Item = core::ascii::Char>>(it: T) -> Self {
3301 Cow::Owned(FromIterator::from_iter(it))
3302 }
3303}
3304
3305#[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
3306impl From<String> for Vec<u8> {
3307 /// Converts the given [`String`] to a vector [`Vec`] that holds values of type [`u8`].
3308 ///
3309 /// # Examples
3310 ///
3311 /// ```
3312 /// let s1 = String::from("hello world");
3313 /// let v1 = Vec::from(s1);
3314 ///
3315 /// for b in v1 {
3316 /// println!("{b}");
3317 /// }
3318 /// ```
3319 fn from(string: String) -> Vec<u8> {
3320 string.into_bytes()
3321 }
3322}
3323
3324#[stable(feature = "try_from_vec_u8_for_string", since = "1.87.0")]
3325impl TryFrom<Vec<u8>> for String {
3326 type Error = FromUtf8Error;
3327 /// Converts the given [`Vec<u8>`] into a [`String`] if it contains valid UTF-8 data.
3328 ///
3329 /// # Examples
3330 ///
3331 /// ```
3332 /// let s1 = b"hello world".to_vec();
3333 /// let v1 = String::try_from(s1).unwrap();
3334 /// assert_eq!(v1, "hello world");
3335 ///
3336 /// ```
3337 fn try_from(bytes: Vec<u8>) -> Result<Self, Self::Error> {
3338 Self::from_utf8(vec:bytes)
3339 }
3340}
3341
3342#[cfg(not(no_global_oom_handling))]
3343#[stable(feature = "rust1", since = "1.0.0")]
3344impl fmt::Write for String {
3345 #[inline]
3346 fn write_str(&mut self, s: &str) -> fmt::Result {
3347 self.push_str(string:s);
3348 Ok(())
3349 }
3350
3351 #[inline]
3352 fn write_char(&mut self, c: char) -> fmt::Result {
3353 self.push(ch:c);
3354 Ok(())
3355 }
3356}
3357
3358/// An iterator over the [`char`]s of a string.
3359///
3360/// This struct is created by the [`into_chars`] method on [`String`].
3361/// See its documentation for more.
3362///
3363/// [`char`]: prim@char
3364/// [`into_chars`]: String::into_chars
3365#[cfg_attr(not(no_global_oom_handling), derive(Clone))]
3366#[must_use = "iterators are lazy and do nothing unless consumed"]
3367#[unstable(feature = "string_into_chars", issue = "133125")]
3368pub struct IntoChars {
3369 bytes: vec::IntoIter<u8>,
3370}
3371
3372#[unstable(feature = "string_into_chars", issue = "133125")]
3373impl fmt::Debug for IntoChars {
3374 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
3375 f.debug_tuple("IntoChars").field(&self.as_str()).finish()
3376 }
3377}
3378
3379impl IntoChars {
3380 /// Views the underlying data as a subslice of the original data.
3381 ///
3382 /// # Examples
3383 ///
3384 /// ```
3385 /// #![feature(string_into_chars)]
3386 ///
3387 /// let mut chars = String::from("abc").into_chars();
3388 ///
3389 /// assert_eq!(chars.as_str(), "abc");
3390 /// chars.next();
3391 /// assert_eq!(chars.as_str(), "bc");
3392 /// chars.next();
3393 /// chars.next();
3394 /// assert_eq!(chars.as_str(), "");
3395 /// ```
3396 #[unstable(feature = "string_into_chars", issue = "133125")]
3397 #[must_use]
3398 #[inline]
3399 pub fn as_str(&self) -> &str {
3400 // SAFETY: `bytes` is a valid UTF-8 string.
3401 unsafe { str::from_utf8_unchecked(self.bytes.as_slice()) }
3402 }
3403
3404 /// Consumes the `IntoChars`, returning the remaining string.
3405 ///
3406 /// # Examples
3407 ///
3408 /// ```
3409 /// #![feature(string_into_chars)]
3410 ///
3411 /// let chars = String::from("abc").into_chars();
3412 /// assert_eq!(chars.into_string(), "abc");
3413 ///
3414 /// let mut chars = String::from("def").into_chars();
3415 /// chars.next();
3416 /// assert_eq!(chars.into_string(), "ef");
3417 /// ```
3418 #[cfg(not(no_global_oom_handling))]
3419 #[unstable(feature = "string_into_chars", issue = "133125")]
3420 #[inline]
3421 pub fn into_string(self) -> String {
3422 // Safety: `bytes` are kept in UTF-8 form, only removing whole `char`s at a time.
3423 unsafe { String::from_utf8_unchecked(self.bytes.collect()) }
3424 }
3425
3426 #[inline]
3427 fn iter(&self) -> CharIndices<'_> {
3428 self.as_str().char_indices()
3429 }
3430}
3431
3432#[unstable(feature = "string_into_chars", issue = "133125")]
3433impl Iterator for IntoChars {
3434 type Item = char;
3435
3436 #[inline]
3437 fn next(&mut self) -> Option<char> {
3438 let mut iter = self.iter();
3439 match iter.next() {
3440 None => None,
3441 Some((_, ch)) => {
3442 let offset = iter.offset();
3443 // `offset` is a valid index.
3444 let _ = self.bytes.advance_by(offset);
3445 Some(ch)
3446 }
3447 }
3448 }
3449
3450 #[inline]
3451 fn count(self) -> usize {
3452 self.iter().count()
3453 }
3454
3455 #[inline]
3456 fn size_hint(&self) -> (usize, Option<usize>) {
3457 self.iter().size_hint()
3458 }
3459
3460 #[inline]
3461 fn last(mut self) -> Option<char> {
3462 self.next_back()
3463 }
3464}
3465
3466#[unstable(feature = "string_into_chars", issue = "133125")]
3467impl DoubleEndedIterator for IntoChars {
3468 #[inline]
3469 fn next_back(&mut self) -> Option<char> {
3470 let len = self.as_str().len();
3471 let mut iter = self.iter();
3472 match iter.next_back() {
3473 None => None,
3474 Some((idx, ch)) => {
3475 // `idx` is a valid index.
3476 let _ = self.bytes.advance_back_by(len - idx);
3477 Some(ch)
3478 }
3479 }
3480 }
3481}
3482
3483#[unstable(feature = "string_into_chars", issue = "133125")]
3484impl FusedIterator for IntoChars {}
3485
3486/// A draining iterator for `String`.
3487///
3488/// This struct is created by the [`drain`] method on [`String`]. See its
3489/// documentation for more.
3490///
3491/// [`drain`]: String::drain
3492#[stable(feature = "drain", since = "1.6.0")]
3493pub struct Drain<'a> {
3494 /// Will be used as &'a mut String in the destructor
3495 string: *mut String,
3496 /// Start of part to remove
3497 start: usize,
3498 /// End of part to remove
3499 end: usize,
3500 /// Current remaining range to remove
3501 iter: Chars<'a>,
3502}
3503
3504#[stable(feature = "collection_debug", since = "1.17.0")]
3505impl fmt::Debug for Drain<'_> {
3506 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
3507 f.debug_tuple("Drain").field(&self.as_str()).finish()
3508 }
3509}
3510
3511#[stable(feature = "drain", since = "1.6.0")]
3512unsafe impl Sync for Drain<'_> {}
3513#[stable(feature = "drain", since = "1.6.0")]
3514unsafe impl Send for Drain<'_> {}
3515
3516#[stable(feature = "drain", since = "1.6.0")]
3517impl Drop for Drain<'_> {
3518 fn drop(&mut self) {
3519 unsafe {
3520 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
3521 // panic code being inserted again.
3522 let self_vec: &mut Vec = (*self.string).as_mut_vec();
3523 if self.start <= self.end && self.end <= self_vec.len() {
3524 self_vec.drain(self.start..self.end);
3525 }
3526 }
3527 }
3528}
3529
3530impl<'a> Drain<'a> {
3531 /// Returns the remaining (sub)string of this iterator as a slice.
3532 ///
3533 /// # Examples
3534 ///
3535 /// ```
3536 /// let mut s = String::from("abc");
3537 /// let mut drain = s.drain(..);
3538 /// assert_eq!(drain.as_str(), "abc");
3539 /// let _ = drain.next().unwrap();
3540 /// assert_eq!(drain.as_str(), "bc");
3541 /// ```
3542 #[must_use]
3543 #[stable(feature = "string_drain_as_str", since = "1.55.0")]
3544 pub fn as_str(&self) -> &str {
3545 self.iter.as_str()
3546 }
3547}
3548
3549#[stable(feature = "string_drain_as_str", since = "1.55.0")]
3550impl<'a> AsRef<str> for Drain<'a> {
3551 fn as_ref(&self) -> &str {
3552 self.as_str()
3553 }
3554}
3555
3556#[stable(feature = "string_drain_as_str", since = "1.55.0")]
3557impl<'a> AsRef<[u8]> for Drain<'a> {
3558 fn as_ref(&self) -> &[u8] {
3559 self.as_str().as_bytes()
3560 }
3561}
3562
3563#[stable(feature = "drain", since = "1.6.0")]
3564impl Iterator for Drain<'_> {
3565 type Item = char;
3566
3567 #[inline]
3568 fn next(&mut self) -> Option<char> {
3569 self.iter.next()
3570 }
3571
3572 fn size_hint(&self) -> (usize, Option<usize>) {
3573 self.iter.size_hint()
3574 }
3575
3576 #[inline]
3577 fn last(mut self) -> Option<char> {
3578 self.next_back()
3579 }
3580}
3581
3582#[stable(feature = "drain", since = "1.6.0")]
3583impl DoubleEndedIterator for Drain<'_> {
3584 #[inline]
3585 fn next_back(&mut self) -> Option<char> {
3586 self.iter.next_back()
3587 }
3588}
3589
3590#[stable(feature = "fused", since = "1.26.0")]
3591impl FusedIterator for Drain<'_> {}
3592
3593#[cfg(not(no_global_oom_handling))]
3594#[stable(feature = "from_char_for_string", since = "1.46.0")]
3595impl From<char> for String {
3596 /// Allocates an owned [`String`] from a single character.
3597 ///
3598 /// # Example
3599 /// ```rust
3600 /// let c: char = 'a';
3601 /// let s: String = String::from(c);
3602 /// assert_eq!("a", &s[..]);
3603 /// ```
3604 #[inline]
3605 fn from(c: char) -> Self {
3606 c.to_string()
3607 }
3608}
3609