1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! A UTF-8 encoded, growable string.
13 //! This module contains the [`String`] type, a trait for converting
14 //! [`ToString`]s, and several error types that may result from working with
17 //! [`ToString`]: trait.ToString.html
21 //! There are multiple ways to create a new [`String`] from a string literal:
24 //! let s = "Hello".to_string();
26 //! let s = String::from("world");
27 //! let s: String = "also this".into();
30 //! You can create a new [`String`] from an existing one by concatenating with
33 //! [`String`]: struct.String.html
36 //! let s = "Hello".to_string();
38 //! let message = s + " world!";
41 //! If you have a vector of valid UTF-8 bytes, you can make a `String` out of
42 //! it. You can do the reverse too.
45 //! let sparkle_heart = vec![240, 159, 146, 150];
47 //! // We know these bytes are valid, so we'll use `unwrap()`.
48 //! let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
50 //! assert_eq!("💖", sparkle_heart);
52 //! let bytes = sparkle_heart.into_bytes();
54 //! assert_eq!(bytes, [240, 159, 146, 150]);
57 #![stable(feature = "rust1", since = "1.0.0")]
61 use core::iter::{FromIterator, FusedIterator};
63 use core::ops::{self, Add, AddAssign, Index, IndexMut};
65 use core::str::pattern::Pattern;
66 use std_unicode::char::{decode_utf16, REPLACEMENT_CHARACTER};
67 use std_unicode::str as unicode_str;
69 use borrow::{Cow, ToOwned};
70 use range::RangeArgument;
71 use Bound::{Excluded, Included, Unbounded};
72 use str::{self, FromStr, Utf8Error, Chars};
76 /// A UTF-8 encoded, growable string.
78 /// The `String` type is the most common string type that has ownership over the
79 /// contents of the string. It has a close relationship with its borrowed
80 /// counterpart, the primitive [`str`].
82 /// [`str`]: ../../std/primitive.str.html
86 /// You can create a `String` from a literal string with `String::from`:
89 /// let hello = String::from("Hello, world!");
92 /// You can append a [`char`] to a `String` with the [`push()`] method, and
93 /// append a [`&str`] with the [`push_str()`] method:
96 /// let mut hello = String::from("Hello, ");
99 /// hello.push_str("orld!");
102 /// [`char`]: ../../std/primitive.char.html
103 /// [`push()`]: #method.push
104 /// [`push_str()`]: #method.push_str
106 /// If you have a vector of UTF-8 bytes, you can create a `String` from it with
107 /// the [`from_utf8()`] method:
110 /// // some bytes, in a vector
111 /// let sparkle_heart = vec![240, 159, 146, 150];
113 /// // We know these bytes are valid, so we'll use `unwrap()`.
114 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
116 /// assert_eq!("💖", sparkle_heart);
119 /// [`from_utf8()`]: #method.from_utf8
123 /// `String`s are always valid UTF-8. This has a few implications, the first of
124 /// which is that if you need a non-UTF-8 string, consider [`OsString`]. It is
125 /// similar, but without the UTF-8 constraint. The second implication is that
126 /// you cannot index into a `String`:
131 /// println!("The first letter of s is {}", s[0]); // ERROR!!!
134 /// [`OsString`]: ../../std/ffi/struct.OsString.html
136 /// Indexing is intended to be a constant-time operation, but UTF-8 encoding
137 /// does not allow us to do this. Furthermore, it's not clear what sort of
138 /// thing the index should return: a byte, a codepoint, or a grapheme cluster.
139 /// The [`bytes()`] and [`chars()`] methods return iterators over the first
140 /// two, respectively.
142 /// [`bytes()`]: #method.bytes
143 /// [`chars()`]: #method.chars
147 /// `String`s implement [`Deref`]`<Target=str>`, and so inherit all of [`str`]'s
148 /// methods. In addition, this means that you can pass a `String` to any
149 /// function which takes a [`&str`] by using an ampersand (`&`):
152 /// fn takes_str(s: &str) { }
154 /// let s = String::from("Hello");
159 /// [`&str`]: ../../std/primitive.str.html
160 /// [`Deref`]: ../../std/ops/trait.Deref.html
162 /// This will create a [`&str`] from the `String` and pass it in. This
163 /// conversion is very inexpensive, and so generally, functions will accept
164 /// [`&str`]s as arguments unless they need a `String` for some specific reason.
169 /// A `String` is made up of three components: a pointer to some bytes, a
170 /// length, and a capacity. The pointer points to an internal buffer `String`
171 /// uses to store its data. The length is the number of bytes currently stored
172 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
173 /// the length will always be less than or equal to the capacity.
175 /// This buffer is always stored on the heap.
177 /// You can look at these with the [`as_ptr()`], [`len()`], and [`capacity()`]
183 /// let story = String::from("Once upon a time...");
185 /// let ptr = story.as_ptr();
186 /// let len = story.len();
187 /// let capacity = story.capacity();
189 /// // story has nineteen bytes
190 /// assert_eq!(19, len);
192 /// // Now that we have our parts, we throw the story away.
193 /// mem::forget(story);
195 /// // We can re-build a String out of ptr, len, and capacity. This is all
196 /// // unsafe because we are responsible for making sure the components are
198 /// let s = unsafe { String::from_raw_parts(ptr as *mut _, len, capacity) } ;
200 /// assert_eq!(String::from("Once upon a time..."), s);
203 /// [`as_ptr()`]: #method.as_ptr
204 /// [`len()`]: #method.len
205 /// [`capacity()`]: #method.capacity
207 /// If a `String` has enough capacity, adding elements to it will not
208 /// re-allocate. For example, consider this program:
211 /// let mut s = String::new();
213 /// println!("{}", s.capacity());
216 /// s.push_str("hello");
217 /// println!("{}", s.capacity());
221 /// This will output the following:
232 /// At first, we have no memory allocated at all, but as we append to the
233 /// string, it increases its capacity appropriately. If we instead use the
234 /// [`with_capacity()`] method to allocate the correct capacity initially:
237 /// let mut s = String::with_capacity(25);
239 /// println!("{}", s.capacity());
242 /// s.push_str("hello");
243 /// println!("{}", s.capacity());
247 /// [`with_capacity()`]: #method.with_capacity
249 /// We end up with a different output:
260 /// Here, there's no need to allocate more memory inside the loop.
261 #[derive(PartialOrd, Eq, Ord)]
262 #[stable(feature = "rust1", since = "1.0.0")]
267 /// A possible error value when converting a `String` from a UTF-8 byte vector.
269 /// This type is the error type for the [`from_utf8()`] method on [`String`]. It
270 /// is designed in such a way to carefully avoid reallocations: the
271 /// [`into_bytes()`] method will give back the byte vector that was used in the
272 /// conversion attempt.
274 /// [`from_utf8()`]: struct.String.html#method.from_utf8
275 /// [`String`]: struct.String.html
276 /// [`into_bytes()`]: struct.FromUtf8Error.html#method.into_bytes
278 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
279 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
280 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
281 /// through the [`utf8_error()`] method.
283 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
284 /// [`std::str`]: ../../std/str/index.html
285 /// [`u8`]: ../../std/primitive.u8.html
286 /// [`&str`]: ../../std/primitive.str.html
287 /// [`utf8_error()`]: #method.utf8_error
294 /// // some invalid bytes, in a vector
295 /// let bytes = vec![0, 159];
297 /// let value = String::from_utf8(bytes);
299 /// assert!(value.is_err());
300 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
302 #[stable(feature = "rust1", since = "1.0.0")]
304 pub struct FromUtf8Error {
309 /// A possible error value when converting a `String` from a UTF-16 byte slice.
311 /// This type is the error type for the [`from_utf16()`] method on [`String`].
313 /// [`from_utf16()`]: struct.String.html#method.from_utf16
314 /// [`String`]: struct.String.html
321 /// // 𝄞mu<invalid>ic
322 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
323 /// 0xD800, 0x0069, 0x0063];
325 /// assert!(String::from_utf16(v).is_err());
327 #[stable(feature = "rust1", since = "1.0.0")]
329 pub struct FromUtf16Error(());
332 /// Creates a new empty `String`.
334 /// Given that the `String` is empty, this will not allocate any initial
335 /// buffer. While that means that this initial operation is very
336 /// inexpensive, but may cause excessive allocation later, when you add
337 /// data. If you have an idea of how much data the `String` will hold,
338 /// consider the [`with_capacity()`] method to prevent excessive
341 /// [`with_capacity()`]: #method.with_capacity
348 /// let s = String::new();
351 #[stable(feature = "rust1", since = "1.0.0")]
352 pub fn new() -> String {
353 String { vec: Vec::new() }
356 /// Creates a new empty `String` with a particular capacity.
358 /// `String`s have an internal buffer to hold their data. The capacity is
359 /// the length of that buffer, and can be queried with the [`capacity()`]
360 /// method. This method creates an empty `String`, but one with an initial
361 /// buffer that can hold `capacity` bytes. This is useful when you may be
362 /// appending a bunch of data to the `String`, reducing the number of
363 /// reallocations it needs to do.
365 /// [`capacity()`]: #method.capacity
367 /// If the given capacity is `0`, no allocation will occur, and this method
368 /// is identical to the [`new()`] method.
370 /// [`new()`]: #method.new
377 /// let mut s = String::with_capacity(10);
379 /// // The String contains no chars, even though it has capacity for more
380 /// assert_eq!(s.len(), 0);
382 /// // These are all done without reallocating...
383 /// let cap = s.capacity();
388 /// assert_eq!(s.capacity(), cap);
390 /// // ...but this may make the vector reallocate
394 #[stable(feature = "rust1", since = "1.0.0")]
395 pub fn with_capacity(capacity: usize) -> String {
396 String { vec: Vec::with_capacity(capacity) }
399 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
400 // required for this method definition, is not available. Since we don't
401 // require this method for testing purposes, I'll just stub it
402 // NB see the slice::hack module in slice.rs for more information
405 pub fn from_str(_: &str) -> String {
406 panic!("not available with cfg(test)");
409 /// Converts a vector of bytes to a `String`.
411 /// A string slice ([`&str`]) is made of bytes ([`u8`]), and a vector of bytes
412 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
413 /// two. Not all byte slices are valid `String`s, however: `String`
414 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
415 /// the bytes are valid UTF-8, and then does the conversion.
417 /// [`&str`]: ../../std/primitive.str.html
418 /// [`u8`]: ../../std/primitive.u8.html
419 /// [`Vec<u8>`]: ../../std/vec/struct.Vec.html
421 /// If you are sure that the byte slice is valid UTF-8, and you don't want
422 /// to incur the overhead of the validity check, there is an unsafe version
423 /// of this function, [`from_utf8_unchecked()`], which has the same behavior
424 /// but skips the check.
426 /// [`from_utf8_unchecked()`]: struct.String.html#method.from_utf8_unchecked
428 /// This method will take care to not copy the vector, for efficiency's
431 /// If you need a `&str` instead of a `String`, consider
432 /// [`str::from_utf8()`].
434 /// [`str::from_utf8()`]: ../../std/str/fn.from_utf8.html
438 /// Returns `Err` if the slice is not UTF-8 with a description as to why the
439 /// provided bytes are not UTF-8. The vector you moved in is also included.
446 /// // some bytes, in a vector
447 /// let sparkle_heart = vec![240, 159, 146, 150];
449 /// // We know these bytes are valid, so we'll use `unwrap()`.
450 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
452 /// assert_eq!("💖", sparkle_heart);
458 /// // some invalid bytes, in a vector
459 /// let sparkle_heart = vec![0, 159, 146, 150];
461 /// assert!(String::from_utf8(sparkle_heart).is_err());
464 /// See the docs for [`FromUtf8Error`] for more details on what you can do
467 /// [`FromUtf8Error`]: struct.FromUtf8Error.html
469 #[stable(feature = "rust1", since = "1.0.0")]
470 pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
471 match str::from_utf8(&vec) {
472 Ok(..) => Ok(String { vec: vec }),
482 /// Converts a slice of bytes to a string, including invalid characters.
484 /// Strings are made of bytes ([`u8`]), and a slice of bytes
485 /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
486 /// between the two. Not all byte slices are valid strings, however: strings
487 /// are required to be valid UTF-8. During this conversion,
488 /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
489 /// `U+FFFD REPLACEMENT CHARACTER`, which looks like this: �
491 /// [`u8`]: ../../std/primitive.u8.html
492 /// [byteslice]: ../../std/primitive.slice.html
494 /// If you are sure that the byte slice is valid UTF-8, and you don't want
495 /// to incur the overhead of the conversion, there is an unsafe version
496 /// of this function, [`from_utf8_unchecked()`], which has the same behavior
497 /// but skips the checks.
499 /// [`from_utf8_unchecked()`]: struct.String.html#method.from_utf8_unchecked
501 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
502 /// UTF-8, then we need to insert the replacement characters, which will
503 /// change the size of the string, and hence, require a `String`. But if
504 /// it's already valid UTF-8, we don't need a new allocation. This return
505 /// type allows us to handle both cases.
507 /// [`Cow<'a, str>`]: ../../std/borrow/enum.Cow.html
514 /// // some bytes, in a vector
515 /// let sparkle_heart = vec![240, 159, 146, 150];
517 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
519 /// assert_eq!("💖", sparkle_heart);
525 /// // some invalid bytes
526 /// let input = b"Hello \xF0\x90\x80World";
527 /// let output = String::from_utf8_lossy(input);
529 /// assert_eq!("Hello �World", output);
531 #[stable(feature = "rust1", since = "1.0.0")]
532 pub fn from_utf8_lossy<'a>(v: &'a [u8]) -> Cow<'a, str> {
534 match str::from_utf8(v) {
535 Ok(s) => return Cow::Borrowed(s),
536 Err(e) => i = e.valid_up_to(),
539 const TAG_CONT_U8: u8 = 128;
540 const REPLACEMENT: &'static [u8] = b"\xEF\xBF\xBD"; // U+FFFD in UTF-8
542 fn unsafe_get(xs: &[u8], i: usize) -> u8 {
543 unsafe { *xs.get_unchecked(i) }
545 fn safe_get(xs: &[u8], i: usize, total: usize) -> u8 {
546 if i >= total { 0 } else { unsafe_get(xs, i) }
549 let mut res = String::with_capacity(total);
552 unsafe { res.as_mut_vec().extend_from_slice(&v[..i]) };
555 // subseqidx is the index of the first byte of the subsequence we're
556 // looking at. It's used to copy a bunch of contiguous good codepoints
557 // at once instead of copying them one by one.
558 let mut subseqidx = i;
562 let byte = unsafe_get(v, i);
565 macro_rules! error { () => ({
568 res.as_mut_vec().extend_from_slice(&v[subseqidx..i_]);
571 res.as_mut_vec().extend_from_slice(REPLACEMENT);
576 // subseqidx handles this
578 let w = unicode_str::utf8_char_width(byte);
582 if safe_get(v, i, total) & 192 != TAG_CONT_U8 {
589 match (byte, safe_get(v, i, total)) {
590 (0xE0, 0xA0...0xBF) => (),
591 (0xE1...0xEC, 0x80...0xBF) => (),
592 (0xED, 0x80...0x9F) => (),
593 (0xEE...0xEF, 0x80...0xBF) => (),
600 if safe_get(v, i, total) & 192 != TAG_CONT_U8 {
607 match (byte, safe_get(v, i, total)) {
608 (0xF0, 0x90...0xBF) => (),
609 (0xF1...0xF3, 0x80...0xBF) => (),
610 (0xF4, 0x80...0x8F) => (),
617 if safe_get(v, i, total) & 192 != TAG_CONT_U8 {
622 if safe_get(v, i, total) & 192 != TAG_CONT_U8 {
635 if subseqidx < total {
636 unsafe { res.as_mut_vec().extend_from_slice(&v[subseqidx..total]) };
641 /// Decode a UTF-16 encoded vector `v` into a `String`, returning `Err`
642 /// if `v` contains any invalid data.
650 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
651 /// 0x0073, 0x0069, 0x0063];
652 /// assert_eq!(String::from("𝄞music"),
653 /// String::from_utf16(v).unwrap());
655 /// // 𝄞mu<invalid>ic
656 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
657 /// 0xD800, 0x0069, 0x0063];
658 /// assert!(String::from_utf16(v).is_err());
660 #[stable(feature = "rust1", since = "1.0.0")]
661 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
662 decode_utf16(v.iter().cloned()).collect::<Result<_, _>>().map_err(|_| FromUtf16Error(()))
665 /// Decode a UTF-16 encoded vector `v` into a string, replacing
666 /// invalid data with the replacement character (U+FFFD).
673 /// // 𝄞mus<invalid>ic<invalid>
674 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
675 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
678 /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
679 /// String::from_utf16_lossy(v));
682 #[stable(feature = "rust1", since = "1.0.0")]
683 pub fn from_utf16_lossy(v: &[u16]) -> String {
684 decode_utf16(v.iter().cloned()).map(|r| r.unwrap_or(REPLACEMENT_CHARACTER)).collect()
687 /// Creates a new `String` from a length, capacity, and pointer.
691 /// This is highly unsafe, due to the number of invariants that aren't
694 /// * The memory at `ptr` needs to have been previously allocated by the
695 /// same allocator the standard library uses.
696 /// * `length` needs to be less than or equal to `capacity`.
697 /// * `capacity` needs to be the correct value.
699 /// Violating these may cause problems like corrupting the allocator's
700 /// internal datastructures.
702 /// The ownership of `ptr` is effectively transferred to the
703 /// `String` which may then deallocate, reallocate or change the
704 /// contents of memory pointed to by the pointer at will. Ensure
705 /// that nothing else uses the pointer after calling this
716 /// let s = String::from("hello");
717 /// let ptr = s.as_ptr();
718 /// let len = s.len();
719 /// let capacity = s.capacity();
723 /// let s = String::from_raw_parts(ptr as *mut _, len, capacity);
725 /// assert_eq!(String::from("hello"), s);
729 #[stable(feature = "rust1", since = "1.0.0")]
730 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
731 String { vec: Vec::from_raw_parts(buf, length, capacity) }
734 /// Converts a vector of bytes to a `String` without checking that the
735 /// string contains valid UTF-8.
737 /// See the safe version, [`from_utf8()`], for more details.
739 /// [`from_utf8()`]: struct.String.html#method.from_utf8
743 /// This function is unsafe because it does not check that the bytes passed
744 /// to it are valid UTF-8. If this constraint is violated, it may cause
745 /// memory unsafety issues with future users of the `String`, as the rest of
746 /// the standard library assumes that `String`s are valid UTF-8.
753 /// // some bytes, in a vector
754 /// let sparkle_heart = vec![240, 159, 146, 150];
756 /// let sparkle_heart = unsafe {
757 /// String::from_utf8_unchecked(sparkle_heart)
760 /// assert_eq!("💖", sparkle_heart);
763 #[stable(feature = "rust1", since = "1.0.0")]
764 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
765 String { vec: bytes }
768 /// Converts a `String` into a byte vector.
770 /// This consumes the `String`, so we do not need to copy its contents.
777 /// let s = String::from("hello");
778 /// let bytes = s.into_bytes();
780 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
783 #[stable(feature = "rust1", since = "1.0.0")]
784 pub fn into_bytes(self) -> Vec<u8> {
788 /// Extracts a string slice containing the entire string.
790 #[stable(feature = "string_as_str", since = "1.7.0")]
791 pub fn as_str(&self) -> &str {
795 /// Extracts a string slice containing the entire string.
797 #[stable(feature = "string_as_str", since = "1.7.0")]
798 pub fn as_mut_str(&mut self) -> &mut str {
802 /// Appends a given string slice onto the end of this `String`.
809 /// let mut s = String::from("foo");
811 /// s.push_str("bar");
813 /// assert_eq!("foobar", s);
816 #[stable(feature = "rust1", since = "1.0.0")]
817 pub fn push_str(&mut self, string: &str) {
818 self.vec.extend_from_slice(string.as_bytes())
821 /// Returns this `String`'s capacity, in bytes.
828 /// let s = String::with_capacity(10);
830 /// assert!(s.capacity() >= 10);
833 #[stable(feature = "rust1", since = "1.0.0")]
834 pub fn capacity(&self) -> usize {
838 /// Ensures that this `String`'s capacity is at least `additional` bytes
839 /// larger than its length.
841 /// The capacity may be increased by more than `additional` bytes if it
842 /// chooses, to prevent frequent reallocations.
844 /// If you do not want this "at least" behavior, see the [`reserve_exact()`]
847 /// [`reserve_exact()`]: #method.reserve_exact
851 /// Panics if the new capacity overflows `usize`.
858 /// let mut s = String::new();
862 /// assert!(s.capacity() >= 10);
865 /// This may not actually increase the capacity:
868 /// let mut s = String::with_capacity(10);
872 /// // s now has a length of 2 and a capacity of 10
873 /// assert_eq!(2, s.len());
874 /// assert_eq!(10, s.capacity());
876 /// // Since we already have an extra 8 capacity, calling this...
879 /// // ... doesn't actually increase.
880 /// assert_eq!(10, s.capacity());
883 #[stable(feature = "rust1", since = "1.0.0")]
884 pub fn reserve(&mut self, additional: usize) {
885 self.vec.reserve(additional)
888 /// Ensures that this `String`'s capacity is `additional` bytes
889 /// larger than its length.
891 /// Consider using the [`reserve()`] method unless you absolutely know
892 /// better than the allocator.
894 /// [`reserve()`]: #method.reserve
898 /// Panics if the new capacity overflows `usize`.
905 /// let mut s = String::new();
907 /// s.reserve_exact(10);
909 /// assert!(s.capacity() >= 10);
912 /// This may not actually increase the capacity:
915 /// let mut s = String::with_capacity(10);
919 /// // s now has a length of 2 and a capacity of 10
920 /// assert_eq!(2, s.len());
921 /// assert_eq!(10, s.capacity());
923 /// // Since we already have an extra 8 capacity, calling this...
924 /// s.reserve_exact(8);
926 /// // ... doesn't actually increase.
927 /// assert_eq!(10, s.capacity());
930 #[stable(feature = "rust1", since = "1.0.0")]
931 pub fn reserve_exact(&mut self, additional: usize) {
932 self.vec.reserve_exact(additional)
935 /// Shrinks the capacity of this `String` to match its length.
942 /// let mut s = String::from("foo");
945 /// assert!(s.capacity() >= 100);
947 /// s.shrink_to_fit();
948 /// assert_eq!(3, s.capacity());
951 #[stable(feature = "rust1", since = "1.0.0")]
952 pub fn shrink_to_fit(&mut self) {
953 self.vec.shrink_to_fit()
956 /// Appends the given `char` to the end of this `String`.
963 /// let mut s = String::from("abc");
969 /// assert_eq!("abc123", s);
972 #[stable(feature = "rust1", since = "1.0.0")]
973 pub fn push(&mut self, ch: char) {
974 match ch.len_utf8() {
975 1 => self.vec.push(ch as u8),
976 _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
980 /// Returns a byte slice of this `String`'s contents.
987 /// let s = String::from("hello");
989 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
992 #[stable(feature = "rust1", since = "1.0.0")]
993 pub fn as_bytes(&self) -> &[u8] {
997 /// Shortens this `String` to the specified length.
999 /// If `new_len` is greater than the string's current length, this has no
1004 /// Panics if `new_len` does not lie on a [`char`] boundary.
1006 /// [`char`]: ../../std/primitive.char.html
1013 /// let mut s = String::from("hello");
1017 /// assert_eq!("he", s);
1020 #[stable(feature = "rust1", since = "1.0.0")]
1021 pub fn truncate(&mut self, new_len: usize) {
1022 if new_len <= self.len() {
1023 assert!(self.is_char_boundary(new_len));
1024 self.vec.truncate(new_len)
1028 /// Removes the last character from the string buffer and returns it.
1030 /// Returns `None` if this `String` is empty.
1037 /// let mut s = String::from("foo");
1039 /// assert_eq!(s.pop(), Some('o'));
1040 /// assert_eq!(s.pop(), Some('o'));
1041 /// assert_eq!(s.pop(), Some('f'));
1043 /// assert_eq!(s.pop(), None);
1046 #[stable(feature = "rust1", since = "1.0.0")]
1047 pub fn pop(&mut self) -> Option<char> {
1048 let ch = match self.chars().rev().next() {
1050 None => return None,
1052 let newlen = self.len() - ch.len_utf8();
1054 self.vec.set_len(newlen);
1059 /// Removes a `char` from this `String` at a byte position and returns it.
1061 /// This is an `O(n)` operation, as it requires copying every element in the
1066 /// Panics if `idx` is larger than or equal to the `String`'s length,
1067 /// or if it does not lie on a [`char`] boundary.
1069 /// [`char`]: ../../std/primitive.char.html
1076 /// let mut s = String::from("foo");
1078 /// assert_eq!(s.remove(0), 'f');
1079 /// assert_eq!(s.remove(1), 'o');
1080 /// assert_eq!(s.remove(0), 'o');
1083 #[stable(feature = "rust1", since = "1.0.0")]
1084 pub fn remove(&mut self, idx: usize) -> char {
1085 let ch = match self[idx..].chars().next() {
1087 None => panic!("cannot remove a char from the end of a string"),
1090 let next = idx + ch.len_utf8();
1091 let len = self.len();
1093 ptr::copy(self.vec.as_ptr().offset(next as isize),
1094 self.vec.as_mut_ptr().offset(idx as isize),
1096 self.vec.set_len(len - (next - idx));
1101 /// Inserts a character into this `String` at a byte position.
1103 /// This is an `O(n)` operation as it requires copying every element in the
1108 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1109 /// lie on a [`char`] boundary.
1111 /// [`char`]: ../../std/primitive.char.html
1118 /// let mut s = String::with_capacity(3);
1120 /// s.insert(0, 'f');
1121 /// s.insert(1, 'o');
1122 /// s.insert(2, 'o');
1124 /// assert_eq!("foo", s);
1127 #[stable(feature = "rust1", since = "1.0.0")]
1128 pub fn insert(&mut self, idx: usize, ch: char) {
1129 assert!(self.is_char_boundary(idx));
1130 let mut bits = [0; 4];
1131 let bits = ch.encode_utf8(&mut bits).as_bytes();
1134 self.insert_bytes(idx, bits);
1138 unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1139 let len = self.len();
1140 let amt = bytes.len();
1141 self.vec.reserve(amt);
1143 ptr::copy(self.vec.as_ptr().offset(idx as isize),
1144 self.vec.as_mut_ptr().offset((idx + amt) as isize),
1146 ptr::copy(bytes.as_ptr(),
1147 self.vec.as_mut_ptr().offset(idx as isize),
1149 self.vec.set_len(len + amt);
1152 /// Inserts a string slice into this `String` at a byte position.
1154 /// This is an `O(n)` operation as it requires copying every element in the
1159 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1160 /// lie on a [`char`] boundary.
1162 /// [`char`]: ../../std/primitive.char.html
1169 /// let mut s = String::from("bar");
1171 /// s.insert_str(0, "foo");
1173 /// assert_eq!("foobar", s);
1176 #[stable(feature = "insert_str", since = "1.16.0")]
1177 pub fn insert_str(&mut self, idx: usize, string: &str) {
1178 assert!(self.is_char_boundary(idx));
1181 self.insert_bytes(idx, string.as_bytes());
1185 /// Returns a mutable reference to the contents of this `String`.
1189 /// This function is unsafe because it does not check that the bytes passed
1190 /// to it are valid UTF-8. If this constraint is violated, it may cause
1191 /// memory unsafety issues with future users of the `String`, as the rest of
1192 /// the standard library assumes that `String`s are valid UTF-8.
1199 /// let mut s = String::from("hello");
1202 /// let vec = s.as_mut_vec();
1203 /// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1207 /// assert_eq!(s, "olleh");
1210 #[stable(feature = "rust1", since = "1.0.0")]
1211 pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1215 /// Returns the length of this `String`, in bytes.
1222 /// let a = String::from("foo");
1224 /// assert_eq!(a.len(), 3);
1227 #[stable(feature = "rust1", since = "1.0.0")]
1228 pub fn len(&self) -> usize {
1232 /// Returns `true` if this `String` has a length of zero.
1234 /// Returns `false` otherwise.
1241 /// let mut v = String::new();
1242 /// assert!(v.is_empty());
1245 /// assert!(!v.is_empty());
1248 #[stable(feature = "rust1", since = "1.0.0")]
1249 pub fn is_empty(&self) -> bool {
1253 /// Divide one string into two at an index.
1255 /// The argument, `mid`, should be a byte offset from the start of the string. It must also
1256 /// be on the boundary of a UTF-8 code point.
1258 /// The two strings returned go from the start of the string to `mid`, and from `mid` to the end
1263 /// Panics if `mid` is not on a `UTF-8` code point boundary, or if it is beyond the last
1264 /// code point of the string.
1270 /// let mut hello = String::from("Hello, World!");
1271 /// let world = hello.split_off(7);
1272 /// assert_eq!(hello, "Hello, ");
1273 /// assert_eq!(world, "World!");
1277 #[stable(feature = "string_split_off", since = "1.16.0")]
1278 pub fn split_off(&mut self, mid: usize) -> String {
1279 assert!(self.is_char_boundary(mid));
1280 let other = self.vec.split_off(mid);
1281 unsafe { String::from_utf8_unchecked(other) }
1284 /// Truncates this `String`, removing all contents.
1286 /// While this means the `String` will have a length of zero, it does not
1287 /// touch its capacity.
1294 /// let mut s = String::from("foo");
1298 /// assert!(s.is_empty());
1299 /// assert_eq!(0, s.len());
1300 /// assert_eq!(3, s.capacity());
1303 #[stable(feature = "rust1", since = "1.0.0")]
1304 pub fn clear(&mut self) {
1308 /// Create a draining iterator that removes the specified range in the string
1309 /// and yields the removed chars.
1311 /// Note: The element range is removed even if the iterator is not
1312 /// consumed until the end.
1316 /// Panics if the starting point or end point do not lie on a [`char`]
1317 /// boundary, or if they're out of bounds.
1319 /// [`char`]: ../../std/primitive.char.html
1326 /// let mut s = String::from("α is alpha, β is beta");
1327 /// let beta_offset = s.find('β').unwrap_or(s.len());
1329 /// // Remove the range up until the β from the string
1330 /// let t: String = s.drain(..beta_offset).collect();
1331 /// assert_eq!(t, "α is alpha, ");
1332 /// assert_eq!(s, "β is beta");
1334 /// // A full range clears the string
1336 /// assert_eq!(s, "");
1338 #[stable(feature = "drain", since = "1.6.0")]
1339 pub fn drain<R>(&mut self, range: R) -> Drain
1340 where R: RangeArgument<usize>
1344 // The String version of Drain does not have the memory safety issues
1345 // of the vector version. The data is just plain bytes.
1346 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1347 // the removal will not happen.
1348 let len = self.len();
1349 let start = match range.start() {
1351 Excluded(&n) => n + 1,
1354 let end = match range.end() {
1355 Included(&n) => n + 1,
1360 // Take out two simultaneous borrows. The &mut String won't be accessed
1361 // until iteration is over, in Drop.
1362 let self_ptr = self as *mut _;
1363 // slicing does the appropriate bounds checks
1364 let chars_iter = self[start..end].chars();
1374 /// Converts this `String` into a `Box<str>`.
1376 /// This will drop any excess capacity.
1383 /// let s = String::from("hello");
1385 /// let b = s.into_boxed_str();
1387 #[stable(feature = "box_str", since = "1.4.0")]
1388 pub fn into_boxed_str(self) -> Box<str> {
1389 let slice = self.vec.into_boxed_slice();
1390 unsafe { mem::transmute::<Box<[u8]>, Box<str>>(slice) }
1394 impl FromUtf8Error {
1395 /// Returns the bytes that were attempted to convert to a `String`.
1397 /// This method is carefully constructed to avoid allocation. It will
1398 /// consume the error, moving out the bytes, so that a copy of the bytes
1399 /// does not need to be made.
1406 /// // some invalid bytes, in a vector
1407 /// let bytes = vec![0, 159];
1409 /// let value = String::from_utf8(bytes);
1411 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1413 #[stable(feature = "rust1", since = "1.0.0")]
1414 pub fn into_bytes(self) -> Vec<u8> {
1418 /// Fetch a `Utf8Error` to get more details about the conversion failure.
1420 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1421 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1422 /// an analogue to `FromUtf8Error`. See its documentation for more details
1425 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
1426 /// [`std::str`]: ../../std/str/index.html
1427 /// [`u8`]: ../../std/primitive.u8.html
1428 /// [`&str`]: ../../std/primitive.str.html
1435 /// // some invalid bytes, in a vector
1436 /// let bytes = vec![0, 159];
1438 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1440 /// // the first byte is invalid here
1441 /// assert_eq!(1, error.valid_up_to());
1443 #[stable(feature = "rust1", since = "1.0.0")]
1444 pub fn utf8_error(&self) -> Utf8Error {
1449 #[stable(feature = "rust1", since = "1.0.0")]
1450 impl fmt::Display for FromUtf8Error {
1451 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1452 fmt::Display::fmt(&self.error, f)
1456 #[stable(feature = "rust1", since = "1.0.0")]
1457 impl fmt::Display for FromUtf16Error {
1458 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1459 fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
1463 #[stable(feature = "rust1", since = "1.0.0")]
1464 impl Clone for String {
1465 fn clone(&self) -> Self {
1466 String { vec: self.vec.clone() }
1469 fn clone_from(&mut self, source: &Self) {
1470 self.vec.clone_from(&source.vec);
1474 #[stable(feature = "rust1", since = "1.0.0")]
1475 impl FromIterator<char> for String {
1476 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
1477 let mut buf = String::new();
1483 #[stable(feature = "rust1", since = "1.0.0")]
1484 impl<'a> FromIterator<&'a str> for String {
1485 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
1486 let mut buf = String::new();
1492 #[stable(feature = "extend_string", since = "1.4.0")]
1493 impl FromIterator<String> for String {
1494 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
1495 let mut buf = String::new();
1501 #[stable(feature = "rust1", since = "1.0.0")]
1502 impl Extend<char> for String {
1503 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
1504 let iterator = iter.into_iter();
1505 let (lower_bound, _) = iterator.size_hint();
1506 self.reserve(lower_bound);
1507 for ch in iterator {
1513 #[stable(feature = "extend_ref", since = "1.2.0")]
1514 impl<'a> Extend<&'a char> for String {
1515 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
1516 self.extend(iter.into_iter().cloned());
1520 #[stable(feature = "rust1", since = "1.0.0")]
1521 impl<'a> Extend<&'a str> for String {
1522 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
1529 #[stable(feature = "extend_string", since = "1.4.0")]
1530 impl Extend<String> for String {
1531 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
1538 /// A convenience impl that delegates to the impl for `&str`
1539 #[unstable(feature = "pattern",
1540 reason = "API not fully fleshed out and ready to be stabilized",
1542 impl<'a, 'b> Pattern<'a> for &'b String {
1543 type Searcher = <&'b str as Pattern<'a>>::Searcher;
1545 fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
1546 self[..].into_searcher(haystack)
1550 fn is_contained_in(self, haystack: &'a str) -> bool {
1551 self[..].is_contained_in(haystack)
1555 fn is_prefix_of(self, haystack: &'a str) -> bool {
1556 self[..].is_prefix_of(haystack)
1560 #[stable(feature = "rust1", since = "1.0.0")]
1561 impl PartialEq for String {
1563 fn eq(&self, other: &String) -> bool {
1564 PartialEq::eq(&self[..], &other[..])
1567 fn ne(&self, other: &String) -> bool {
1568 PartialEq::ne(&self[..], &other[..])
1572 macro_rules! impl_eq {
1573 ($lhs:ty, $rhs: ty) => {
1574 #[stable(feature = "rust1", since = "1.0.0")]
1575 impl<'a, 'b> PartialEq<$rhs> for $lhs {
1577 fn eq(&self, other: &$rhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1579 fn ne(&self, other: &$rhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1582 #[stable(feature = "rust1", since = "1.0.0")]
1583 impl<'a, 'b> PartialEq<$lhs> for $rhs {
1585 fn eq(&self, other: &$lhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1587 fn ne(&self, other: &$lhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1593 impl_eq! { String, str }
1594 impl_eq! { String, &'a str }
1595 impl_eq! { Cow<'a, str>, str }
1596 impl_eq! { Cow<'a, str>, &'b str }
1597 impl_eq! { Cow<'a, str>, String }
1599 #[stable(feature = "rust1", since = "1.0.0")]
1600 impl Default for String {
1601 /// Creates an empty `String`.
1603 fn default() -> String {
1608 #[stable(feature = "rust1", since = "1.0.0")]
1609 impl fmt::Display for String {
1611 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1612 fmt::Display::fmt(&**self, f)
1616 #[stable(feature = "rust1", since = "1.0.0")]
1617 impl fmt::Debug for String {
1619 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1620 fmt::Debug::fmt(&**self, f)
1624 #[stable(feature = "rust1", since = "1.0.0")]
1625 impl hash::Hash for String {
1627 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
1628 (**self).hash(hasher)
1632 #[stable(feature = "rust1", since = "1.0.0")]
1633 impl<'a> Add<&'a str> for String {
1634 type Output = String;
1637 fn add(mut self, other: &str) -> String {
1638 self.push_str(other);
1643 #[stable(feature = "stringaddassign", since = "1.12.0")]
1644 impl<'a> AddAssign<&'a str> for String {
1646 fn add_assign(&mut self, other: &str) {
1647 self.push_str(other);
1651 #[stable(feature = "rust1", since = "1.0.0")]
1652 impl ops::Index<ops::Range<usize>> for String {
1656 fn index(&self, index: ops::Range<usize>) -> &str {
1660 #[stable(feature = "rust1", since = "1.0.0")]
1661 impl ops::Index<ops::RangeTo<usize>> for String {
1665 fn index(&self, index: ops::RangeTo<usize>) -> &str {
1669 #[stable(feature = "rust1", since = "1.0.0")]
1670 impl ops::Index<ops::RangeFrom<usize>> for String {
1674 fn index(&self, index: ops::RangeFrom<usize>) -> &str {
1678 #[stable(feature = "rust1", since = "1.0.0")]
1679 impl ops::Index<ops::RangeFull> for String {
1683 fn index(&self, _index: ops::RangeFull) -> &str {
1684 unsafe { str::from_utf8_unchecked(&self.vec) }
1687 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1688 impl ops::Index<ops::RangeInclusive<usize>> for String {
1692 fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
1693 Index::index(&**self, index)
1696 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1697 impl ops::Index<ops::RangeToInclusive<usize>> for String {
1701 fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
1702 Index::index(&**self, index)
1706 #[stable(feature = "derefmut_for_string", since = "1.2.0")]
1707 impl ops::IndexMut<ops::Range<usize>> for String {
1709 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
1710 &mut self[..][index]
1713 #[stable(feature = "derefmut_for_string", since = "1.2.0")]
1714 impl ops::IndexMut<ops::RangeTo<usize>> for String {
1716 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
1717 &mut self[..][index]
1720 #[stable(feature = "derefmut_for_string", since = "1.2.0")]
1721 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
1723 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
1724 &mut self[..][index]
1727 #[stable(feature = "derefmut_for_string", since = "1.2.0")]
1728 impl ops::IndexMut<ops::RangeFull> for String {
1730 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
1731 unsafe { mem::transmute(&mut *self.vec) }
1734 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1735 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
1737 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
1738 IndexMut::index_mut(&mut **self, index)
1741 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1742 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
1744 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
1745 IndexMut::index_mut(&mut **self, index)
1749 #[stable(feature = "rust1", since = "1.0.0")]
1750 impl ops::Deref for String {
1754 fn deref(&self) -> &str {
1755 unsafe { str::from_utf8_unchecked(&self.vec) }
1759 #[stable(feature = "derefmut_for_string", since = "1.2.0")]
1760 impl ops::DerefMut for String {
1762 fn deref_mut(&mut self) -> &mut str {
1763 unsafe { mem::transmute(&mut *self.vec) }
1767 /// An error when parsing a `String`.
1769 /// This `enum` is slightly awkward: it will never actually exist. This error is
1770 /// part of the type signature of the implementation of [`FromStr`] on
1771 /// [`String`]. The return type of [`from_str()`], requires that an error be
1772 /// defined, but, given that a [`String`] can always be made into a new
1773 /// [`String`] without error, this type will never actually be returned. As
1774 /// such, it is only here to satisfy said signature, and is useless otherwise.
1776 /// [`FromStr`]: ../../std/str/trait.FromStr.html
1777 /// [`String`]: struct.String.html
1778 /// [`from_str()`]: ../../std/str/trait.FromStr.html#tymethod.from_str
1779 #[stable(feature = "str_parse_error", since = "1.5.0")]
1781 pub enum ParseError {}
1783 #[stable(feature = "rust1", since = "1.0.0")]
1784 impl FromStr for String {
1785 type Err = ParseError;
1787 fn from_str(s: &str) -> Result<String, ParseError> {
1792 #[stable(feature = "str_parse_error", since = "1.5.0")]
1793 impl Clone for ParseError {
1794 fn clone(&self) -> ParseError {
1799 #[stable(feature = "str_parse_error", since = "1.5.0")]
1800 impl fmt::Debug for ParseError {
1801 fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
1806 #[stable(feature = "str_parse_error2", since = "1.8.0")]
1807 impl fmt::Display for ParseError {
1808 fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
1813 #[stable(feature = "str_parse_error", since = "1.5.0")]
1814 impl PartialEq for ParseError {
1815 fn eq(&self, _: &ParseError) -> bool {
1820 #[stable(feature = "str_parse_error", since = "1.5.0")]
1821 impl Eq for ParseError {}
1823 /// A trait for converting a value to a `String`.
1825 /// This trait is automatically implemented for any type which implements the
1826 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
1827 /// [`Display`] should be implemented instead, and you get the `ToString`
1828 /// implementation for free.
1830 /// [`Display`]: ../../std/fmt/trait.Display.html
1831 #[stable(feature = "rust1", since = "1.0.0")]
1832 pub trait ToString {
1833 /// Converts the given value to a `String`.
1841 /// let five = String::from("5");
1843 /// assert_eq!(five, i.to_string());
1845 #[stable(feature = "rust1", since = "1.0.0")]
1846 fn to_string(&self) -> String;
1849 #[stable(feature = "rust1", since = "1.0.0")]
1850 impl<T: fmt::Display + ?Sized> ToString for T {
1852 default fn to_string(&self) -> String {
1853 use core::fmt::Write;
1854 let mut buf = String::new();
1855 let _ = buf.write_fmt(format_args!("{}", self));
1856 buf.shrink_to_fit();
1861 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
1862 impl ToString for str {
1864 fn to_string(&self) -> String {
1869 #[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
1870 impl<'a> ToString for Cow<'a, str> {
1872 fn to_string(&self) -> String {
1877 #[stable(feature = "string_to_string_specialization", since = "1.17.0")]
1878 impl ToString for String {
1880 fn to_string(&self) -> String {
1885 #[stable(feature = "rust1", since = "1.0.0")]
1886 impl AsRef<str> for String {
1888 fn as_ref(&self) -> &str {
1893 #[stable(feature = "rust1", since = "1.0.0")]
1894 impl AsRef<[u8]> for String {
1896 fn as_ref(&self) -> &[u8] {
1901 #[stable(feature = "rust1", since = "1.0.0")]
1902 impl<'a> From<&'a str> for String {
1903 fn from(s: &'a str) -> String {
1908 #[stable(feature = "string_from_cow_str", since = "1.14.0")]
1909 impl<'a> From<Cow<'a, str>> for String {
1910 fn from(s: Cow<'a, str>) -> String {
1915 #[stable(feature = "rust1", since = "1.0.0")]
1916 impl<'a> From<&'a str> for Cow<'a, str> {
1918 fn from(s: &'a str) -> Cow<'a, str> {
1923 #[stable(feature = "rust1", since = "1.0.0")]
1924 impl<'a> From<String> for Cow<'a, str> {
1926 fn from(s: String) -> Cow<'a, str> {
1931 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
1932 impl<'a> FromIterator<char> for Cow<'a, str> {
1933 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
1934 Cow::Owned(FromIterator::from_iter(it))
1938 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
1939 impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
1940 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
1941 Cow::Owned(FromIterator::from_iter(it))
1945 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
1946 impl<'a> FromIterator<String> for Cow<'a, str> {
1947 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
1948 Cow::Owned(FromIterator::from_iter(it))
1952 #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
1953 impl From<String> for Vec<u8> {
1954 fn from(string: String) -> Vec<u8> {
1959 #[stable(feature = "rust1", since = "1.0.0")]
1960 impl fmt::Write for String {
1962 fn write_str(&mut self, s: &str) -> fmt::Result {
1968 fn write_char(&mut self, c: char) -> fmt::Result {
1974 /// A draining iterator for `String`.
1976 /// This struct is created by the [`drain()`] method on [`String`]. See its
1977 /// documentation for more.
1979 /// [`drain()`]: struct.String.html#method.drain
1980 /// [`String`]: struct.String.html
1981 #[stable(feature = "drain", since = "1.6.0")]
1982 pub struct Drain<'a> {
1983 /// Will be used as &'a mut String in the destructor
1984 string: *mut String,
1985 /// Start of part to remove
1987 /// End of part to remove
1989 /// Current remaining range to remove
1993 #[stable(feature = "collection_debug", since = "1.17.0")]
1994 impl<'a> fmt::Debug for Drain<'a> {
1995 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1996 f.pad("Drain { .. }")
2000 #[stable(feature = "drain", since = "1.6.0")]
2001 unsafe impl<'a> Sync for Drain<'a> {}
2002 #[stable(feature = "drain", since = "1.6.0")]
2003 unsafe impl<'a> Send for Drain<'a> {}
2005 #[stable(feature = "drain", since = "1.6.0")]
2006 impl<'a> Drop for Drain<'a> {
2007 fn drop(&mut self) {
2009 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
2010 // panic code being inserted again.
2011 let self_vec = (*self.string).as_mut_vec();
2012 if self.start <= self.end && self.end <= self_vec.len() {
2013 self_vec.drain(self.start..self.end);
2019 #[stable(feature = "drain", since = "1.6.0")]
2020 impl<'a> Iterator for Drain<'a> {
2024 fn next(&mut self) -> Option<char> {
2028 fn size_hint(&self) -> (usize, Option<usize>) {
2029 self.iter.size_hint()
2033 #[stable(feature = "drain", since = "1.6.0")]
2034 impl<'a> DoubleEndedIterator for Drain<'a> {
2036 fn next_back(&mut self) -> Option<char> {
2037 self.iter.next_back()
2041 #[unstable(feature = "fused", issue = "35602")]
2042 impl<'a> FusedIterator for Drain<'a> {}