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};
62 use core::ops::{self, Add, AddAssign, Index, IndexMut};
64 use core::str::pattern::Pattern;
65 use std_unicode::lossy;
66 use std_unicode::char::{decode_utf16, REPLACEMENT_CHARACTER};
68 use borrow::{Cow, ToOwned};
69 use range::RangeArgument;
70 use Bound::{Excluded, Included, Unbounded};
71 use str::{self, from_boxed_utf8_unchecked, FromStr, Utf8Error, Chars};
75 /// A UTF-8 encoded, growable string.
77 /// The `String` type is the most common string type that has ownership over the
78 /// contents of the string. It has a close relationship with its borrowed
79 /// counterpart, the primitive [`str`].
81 /// [`str`]: ../../std/primitive.str.html
85 /// You can create a `String` from a literal string with `String::from`:
88 /// let hello = String::from("Hello, world!");
91 /// You can append a [`char`] to a `String` with the [`push`] method, and
92 /// append a [`&str`] with the [`push_str`] method:
95 /// let mut hello = String::from("Hello, ");
98 /// hello.push_str("orld!");
101 /// [`char`]: ../../std/primitive.char.html
102 /// [`push`]: #method.push
103 /// [`push_str`]: #method.push_str
105 /// If you have a vector of UTF-8 bytes, you can create a `String` from it with
106 /// the [`from_utf8`] method:
109 /// // some bytes, in a vector
110 /// let sparkle_heart = vec![240, 159, 146, 150];
112 /// // We know these bytes are valid, so we'll use `unwrap()`.
113 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
115 /// assert_eq!("💖", sparkle_heart);
118 /// [`from_utf8`]: #method.from_utf8
122 /// `String`s are always valid UTF-8. This has a few implications, the first of
123 /// which is that if you need a non-UTF-8 string, consider [`OsString`]. It is
124 /// similar, but without the UTF-8 constraint. The second implication is that
125 /// you cannot index into a `String`:
127 /// ```compile_fail,E0277
130 /// println!("The first letter of s is {}", s[0]); // ERROR!!!
133 /// [`OsString`]: ../../std/ffi/struct.OsString.html
135 /// Indexing is intended to be a constant-time operation, but UTF-8 encoding
136 /// does not allow us to do this. Furthermore, it's not clear what sort of
137 /// thing the index should return: a byte, a codepoint, or a grapheme cluster.
138 /// The [`bytes`] and [`chars`] methods return iterators over the first
139 /// two, respectively.
141 /// [`bytes`]: #method.bytes
142 /// [`chars`]: #method.chars
146 /// `String`s implement [`Deref`]`<Target=str>`, and so inherit all of [`str`]'s
147 /// methods. In addition, this means that you can pass a `String` to a
148 /// function which takes a [`&str`] by using an ampersand (`&`):
151 /// fn takes_str(s: &str) { }
153 /// let s = String::from("Hello");
158 /// [`&str`]: ../../std/primitive.str.html
159 /// [`Deref`]: ../../std/ops/trait.Deref.html
161 /// This will create a [`&str`] from the `String` and pass it in. This
162 /// conversion is very inexpensive, and so generally, functions will accept
163 /// [`&str`]s as arguments unless they need a `String` for some specific
166 /// In certain cases Rust doesn't have enough information to make this
167 /// conversion, known as `Deref` coercion. In the following example a string
168 /// slice `&'a str` implements the trait `TraitExample`, and the function
169 /// `example_func` takes anything that implements the trait. In this case Rust
170 /// would need to make two implicit conversions, which Rust doesn't have the
171 /// means to do. For that reason, the following example will not compile.
173 /// ```compile_fail,E0277
174 /// trait TraitExample {}
176 /// impl<'a> TraitExample for &'a str {}
178 /// fn example_func<A: TraitExample>(example_arg: A) {}
181 /// let example_string = String::from("example_string");
182 /// example_func(&example_string);
186 /// There are two options that would work instead. The first would be to
187 /// change the line `example_func(&example_string);` to
188 /// `example_func(example_string.as_str());`, using the method `as_str()`
189 /// to explicitly extract the string slice containing the string. The second
190 /// way changes `example_func(&example_string);` to
191 /// `example_func(&*example_string);`. In this case we are dereferencing a
192 /// `String` to a `str`, then referencing the `str` back to `&str`. The
193 /// second way is more idiomatic, however both work to do the conversion
194 /// explicitly rather than relying on the implicit conversion.
198 /// A `String` is made up of three components: a pointer to some bytes, a
199 /// length, and a capacity. The pointer points to an internal buffer `String`
200 /// uses to store its data. The length is the number of bytes currently stored
201 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
202 /// the length will always be less than or equal to the capacity.
204 /// This buffer is always stored on the heap.
206 /// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
212 /// let story = String::from("Once upon a time...");
214 /// let ptr = story.as_ptr();
215 /// let len = story.len();
216 /// let capacity = story.capacity();
218 /// // story has nineteen bytes
219 /// assert_eq!(19, len);
221 /// // Now that we have our parts, we throw the story away.
222 /// mem::forget(story);
224 /// // We can re-build a String out of ptr, len, and capacity. This is all
225 /// // unsafe because we are responsible for making sure the components are
227 /// let s = unsafe { String::from_raw_parts(ptr as *mut _, len, capacity) } ;
229 /// assert_eq!(String::from("Once upon a time..."), s);
232 /// [`as_ptr`]: #method.as_ptr
233 /// [`len`]: #method.len
234 /// [`capacity`]: #method.capacity
236 /// If a `String` has enough capacity, adding elements to it will not
237 /// re-allocate. For example, consider this program:
240 /// let mut s = String::new();
242 /// println!("{}", s.capacity());
245 /// s.push_str("hello");
246 /// println!("{}", s.capacity());
250 /// This will output the following:
261 /// At first, we have no memory allocated at all, but as we append to the
262 /// string, it increases its capacity appropriately. If we instead use the
263 /// [`with_capacity`] method to allocate the correct capacity initially:
266 /// let mut s = String::with_capacity(25);
268 /// println!("{}", s.capacity());
271 /// s.push_str("hello");
272 /// println!("{}", s.capacity());
276 /// [`with_capacity`]: #method.with_capacity
278 /// We end up with a different output:
289 /// Here, there's no need to allocate more memory inside the loop.
290 #[derive(PartialOrd, Eq, Ord)]
291 #[stable(feature = "rust1", since = "1.0.0")]
296 /// A possible error value when converting a `String` from a UTF-8 byte vector.
298 /// This type is the error type for the [`from_utf8`] method on [`String`]. It
299 /// is designed in such a way to carefully avoid reallocations: the
300 /// [`into_bytes`] method will give back the byte vector that was used in the
301 /// conversion attempt.
303 /// [`from_utf8`]: struct.String.html#method.from_utf8
304 /// [`String`]: struct.String.html
305 /// [`into_bytes`]: struct.FromUtf8Error.html#method.into_bytes
307 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
308 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
309 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
310 /// through the [`utf8_error`] method.
312 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
313 /// [`std::str`]: ../../std/str/index.html
314 /// [`u8`]: ../../std/primitive.u8.html
315 /// [`&str`]: ../../std/primitive.str.html
316 /// [`utf8_error`]: #method.utf8_error
323 /// // some invalid bytes, in a vector
324 /// let bytes = vec![0, 159];
326 /// let value = String::from_utf8(bytes);
328 /// assert!(value.is_err());
329 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
331 #[stable(feature = "rust1", since = "1.0.0")]
333 pub struct FromUtf8Error {
338 /// A possible error value when converting a `String` from a UTF-16 byte slice.
340 /// This type is the error type for the [`from_utf16`] method on [`String`].
342 /// [`from_utf16`]: struct.String.html#method.from_utf16
343 /// [`String`]: struct.String.html
350 /// // 𝄞mu<invalid>ic
351 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
352 /// 0xD800, 0x0069, 0x0063];
354 /// assert!(String::from_utf16(v).is_err());
356 #[stable(feature = "rust1", since = "1.0.0")]
358 pub struct FromUtf16Error(());
361 /// Creates a new empty `String`.
363 /// Given that the `String` is empty, this will not allocate any initial
364 /// buffer. While that means that this initial operation is very
365 /// inexpensive, but may cause excessive allocation later, when you add
366 /// data. If you have an idea of how much data the `String` will hold,
367 /// consider the [`with_capacity`] method to prevent excessive
370 /// [`with_capacity`]: #method.with_capacity
377 /// let s = String::new();
380 #[stable(feature = "rust1", since = "1.0.0")]
381 pub fn new() -> String {
382 String { vec: Vec::new() }
385 /// Creates a new empty `String` with a particular capacity.
387 /// `String`s have an internal buffer to hold their data. The capacity is
388 /// the length of that buffer, and can be queried with the [`capacity`]
389 /// method. This method creates an empty `String`, but one with an initial
390 /// buffer that can hold `capacity` bytes. This is useful when you may be
391 /// appending a bunch of data to the `String`, reducing the number of
392 /// reallocations it needs to do.
394 /// [`capacity`]: #method.capacity
396 /// If the given capacity is `0`, no allocation will occur, and this method
397 /// is identical to the [`new`] method.
399 /// [`new`]: #method.new
406 /// let mut s = String::with_capacity(10);
408 /// // The String contains no chars, even though it has capacity for more
409 /// assert_eq!(s.len(), 0);
411 /// // These are all done without reallocating...
412 /// let cap = s.capacity();
417 /// assert_eq!(s.capacity(), cap);
419 /// // ...but this may make the vector reallocate
423 #[stable(feature = "rust1", since = "1.0.0")]
424 pub fn with_capacity(capacity: usize) -> String {
425 String { vec: Vec::with_capacity(capacity) }
428 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
429 // required for this method definition, is not available. Since we don't
430 // require this method for testing purposes, I'll just stub it
431 // NB see the slice::hack module in slice.rs for more information
434 pub fn from_str(_: &str) -> String {
435 panic!("not available with cfg(test)");
438 /// Converts a vector of bytes to a `String`.
440 /// A string slice ([`&str`]) is made of bytes ([`u8`]), and a vector of bytes
441 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
442 /// two. Not all byte slices are valid `String`s, however: `String`
443 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
444 /// the bytes are valid UTF-8, and then does the conversion.
446 /// [`&str`]: ../../std/primitive.str.html
447 /// [`u8`]: ../../std/primitive.u8.html
448 /// [`Vec<u8>`]: ../../std/vec/struct.Vec.html
450 /// If you are sure that the byte slice is valid UTF-8, and you don't want
451 /// to incur the overhead of the validity check, there is an unsafe version
452 /// of this function, [`from_utf8_unchecked`], which has the same behavior
453 /// but skips the check.
455 /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
457 /// This method will take care to not copy the vector, for efficiency's
460 /// If you need a `&str` instead of a `String`, consider
461 /// [`str::from_utf8`].
463 /// [`str::from_utf8`]: ../../std/str/fn.from_utf8.html
465 /// The inverse of this method is [`as_bytes`].
467 /// [`as_bytes`]: #method.as_bytes
471 /// Returns `Err` if the slice is not UTF-8 with a description as to why the
472 /// provided bytes are not UTF-8. The vector you moved in is also included.
479 /// // some bytes, in a vector
480 /// let sparkle_heart = vec![240, 159, 146, 150];
482 /// // We know these bytes are valid, so we'll use `unwrap()`.
483 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
485 /// assert_eq!("💖", sparkle_heart);
491 /// // some invalid bytes, in a vector
492 /// let sparkle_heart = vec![0, 159, 146, 150];
494 /// assert!(String::from_utf8(sparkle_heart).is_err());
497 /// See the docs for [`FromUtf8Error`] for more details on what you can do
500 /// [`FromUtf8Error`]: struct.FromUtf8Error.html
502 #[stable(feature = "rust1", since = "1.0.0")]
503 pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
504 match str::from_utf8(&vec) {
505 Ok(..) => Ok(String { vec: vec }),
515 /// Converts a slice of bytes to a string, including invalid characters.
517 /// Strings are made of bytes ([`u8`]), and a slice of bytes
518 /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
519 /// between the two. Not all byte slices are valid strings, however: strings
520 /// are required to be valid UTF-8. During this conversion,
521 /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
522 /// `U+FFFD REPLACEMENT CHARACTER`, which looks like this: �
524 /// [`u8`]: ../../std/primitive.u8.html
525 /// [byteslice]: ../../std/primitive.slice.html
527 /// If you are sure that the byte slice is valid UTF-8, and you don't want
528 /// to incur the overhead of the conversion, there is an unsafe version
529 /// of this function, [`from_utf8_unchecked`], which has the same behavior
530 /// but skips the checks.
532 /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
534 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
535 /// UTF-8, then we need to insert the replacement characters, which will
536 /// change the size of the string, and hence, require a `String`. But if
537 /// it's already valid UTF-8, we don't need a new allocation. This return
538 /// type allows us to handle both cases.
540 /// [`Cow<'a, str>`]: ../../std/borrow/enum.Cow.html
547 /// // some bytes, in a vector
548 /// let sparkle_heart = vec![240, 159, 146, 150];
550 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
552 /// assert_eq!("💖", sparkle_heart);
558 /// // some invalid bytes
559 /// let input = b"Hello \xF0\x90\x80World";
560 /// let output = String::from_utf8_lossy(input);
562 /// assert_eq!("Hello �World", output);
564 #[stable(feature = "rust1", since = "1.0.0")]
565 pub fn from_utf8_lossy<'a>(v: &'a [u8]) -> Cow<'a, str> {
566 let mut iter = lossy::Utf8Lossy::from_bytes(v).chunks();
568 let (first_valid, first_broken) = if let Some(chunk) = iter.next() {
569 let lossy::Utf8LossyChunk { valid, broken } = chunk;
570 if valid.len() == v.len() {
571 debug_assert!(broken.is_empty());
572 return Cow::Borrowed(valid);
576 return Cow::Borrowed("");
579 const REPLACEMENT: &'static str = "\u{FFFD}";
581 let mut res = String::with_capacity(v.len());
582 res.push_str(first_valid);
583 if !first_broken.is_empty() {
584 res.push_str(REPLACEMENT);
587 for lossy::Utf8LossyChunk { valid, broken } in iter {
589 if !broken.is_empty() {
590 res.push_str(REPLACEMENT);
597 /// Decode a UTF-16 encoded vector `v` into a `String`, returning `Err`
598 /// if `v` contains any invalid data.
606 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
607 /// 0x0073, 0x0069, 0x0063];
608 /// assert_eq!(String::from("𝄞music"),
609 /// String::from_utf16(v).unwrap());
611 /// // 𝄞mu<invalid>ic
612 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
613 /// 0xD800, 0x0069, 0x0063];
614 /// assert!(String::from_utf16(v).is_err());
616 #[stable(feature = "rust1", since = "1.0.0")]
617 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
618 decode_utf16(v.iter().cloned()).collect::<Result<_, _>>().map_err(|_| FromUtf16Error(()))
621 /// Decode a UTF-16 encoded vector `v` into a string, replacing
622 /// invalid data with the replacement character (U+FFFD).
629 /// // 𝄞mus<invalid>ic<invalid>
630 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
631 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
634 /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
635 /// String::from_utf16_lossy(v));
638 #[stable(feature = "rust1", since = "1.0.0")]
639 pub fn from_utf16_lossy(v: &[u16]) -> String {
640 decode_utf16(v.iter().cloned()).map(|r| r.unwrap_or(REPLACEMENT_CHARACTER)).collect()
643 /// Creates a new `String` from a length, capacity, and pointer.
647 /// This is highly unsafe, due to the number of invariants that aren't
650 /// * The memory at `ptr` needs to have been previously allocated by the
651 /// same allocator the standard library uses.
652 /// * `length` needs to be less than or equal to `capacity`.
653 /// * `capacity` needs to be the correct value.
655 /// Violating these may cause problems like corrupting the allocator's
656 /// internal data structures.
658 /// The ownership of `ptr` is effectively transferred to the
659 /// `String` which may then deallocate, reallocate or change the
660 /// contents of memory pointed to by the pointer at will. Ensure
661 /// that nothing else uses the pointer after calling this
672 /// let s = String::from("hello");
673 /// let ptr = s.as_ptr();
674 /// let len = s.len();
675 /// let capacity = s.capacity();
679 /// let s = String::from_raw_parts(ptr as *mut _, len, capacity);
681 /// assert_eq!(String::from("hello"), s);
685 #[stable(feature = "rust1", since = "1.0.0")]
686 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
687 String { vec: Vec::from_raw_parts(buf, length, capacity) }
690 /// Converts a vector of bytes to a `String` without checking that the
691 /// string contains valid UTF-8.
693 /// See the safe version, [`from_utf8`], for more details.
695 /// [`from_utf8`]: struct.String.html#method.from_utf8
699 /// This function is unsafe because it does not check that the bytes passed
700 /// to it are valid UTF-8. If this constraint is violated, it may cause
701 /// memory unsafety issues with future users of the `String`, as the rest of
702 /// the standard library assumes that `String`s are valid UTF-8.
709 /// // some bytes, in a vector
710 /// let sparkle_heart = vec![240, 159, 146, 150];
712 /// let sparkle_heart = unsafe {
713 /// String::from_utf8_unchecked(sparkle_heart)
716 /// assert_eq!("💖", sparkle_heart);
719 #[stable(feature = "rust1", since = "1.0.0")]
720 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
721 String { vec: bytes }
724 /// Converts a `String` into a byte vector.
726 /// This consumes the `String`, so we do not need to copy its contents.
733 /// let s = String::from("hello");
734 /// let bytes = s.into_bytes();
736 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
739 #[stable(feature = "rust1", since = "1.0.0")]
740 pub fn into_bytes(self) -> Vec<u8> {
744 /// Extracts a string slice containing the entire string.
746 #[stable(feature = "string_as_str", since = "1.7.0")]
747 pub fn as_str(&self) -> &str {
751 /// Extracts a string slice containing the entire string.
753 #[stable(feature = "string_as_str", since = "1.7.0")]
754 pub fn as_mut_str(&mut self) -> &mut str {
758 /// Appends a given string slice onto the end of this `String`.
765 /// let mut s = String::from("foo");
767 /// s.push_str("bar");
769 /// assert_eq!("foobar", s);
772 #[stable(feature = "rust1", since = "1.0.0")]
773 pub fn push_str(&mut self, string: &str) {
774 self.vec.extend_from_slice(string.as_bytes())
777 /// Returns this `String`'s capacity, in bytes.
784 /// let s = String::with_capacity(10);
786 /// assert!(s.capacity() >= 10);
789 #[stable(feature = "rust1", since = "1.0.0")]
790 pub fn capacity(&self) -> usize {
794 /// Ensures that this `String`'s capacity is at least `additional` bytes
795 /// larger than its length.
797 /// The capacity may be increased by more than `additional` bytes if it
798 /// chooses, to prevent frequent reallocations.
800 /// If you do not want this "at least" behavior, see the [`reserve_exact`]
803 /// [`reserve_exact`]: #method.reserve_exact
807 /// Panics if the new capacity overflows `usize`.
814 /// let mut s = String::new();
818 /// assert!(s.capacity() >= 10);
821 /// This may not actually increase the capacity:
824 /// let mut s = String::with_capacity(10);
828 /// // s now has a length of 2 and a capacity of 10
829 /// assert_eq!(2, s.len());
830 /// assert_eq!(10, s.capacity());
832 /// // Since we already have an extra 8 capacity, calling this...
835 /// // ... doesn't actually increase.
836 /// assert_eq!(10, s.capacity());
839 #[stable(feature = "rust1", since = "1.0.0")]
840 pub fn reserve(&mut self, additional: usize) {
841 self.vec.reserve(additional)
844 /// Ensures that this `String`'s capacity is `additional` bytes
845 /// larger than its length.
847 /// Consider using the [`reserve`] method unless you absolutely know
848 /// better than the allocator.
850 /// [`reserve`]: #method.reserve
854 /// Panics if the new capacity overflows `usize`.
861 /// let mut s = String::new();
863 /// s.reserve_exact(10);
865 /// assert!(s.capacity() >= 10);
868 /// This may not actually increase the capacity:
871 /// let mut s = String::with_capacity(10);
875 /// // s now has a length of 2 and a capacity of 10
876 /// assert_eq!(2, s.len());
877 /// assert_eq!(10, s.capacity());
879 /// // Since we already have an extra 8 capacity, calling this...
880 /// s.reserve_exact(8);
882 /// // ... doesn't actually increase.
883 /// assert_eq!(10, s.capacity());
886 #[stable(feature = "rust1", since = "1.0.0")]
887 pub fn reserve_exact(&mut self, additional: usize) {
888 self.vec.reserve_exact(additional)
891 /// Shrinks the capacity of this `String` to match its length.
898 /// let mut s = String::from("foo");
901 /// assert!(s.capacity() >= 100);
903 /// s.shrink_to_fit();
904 /// assert_eq!(3, s.capacity());
907 #[stable(feature = "rust1", since = "1.0.0")]
908 pub fn shrink_to_fit(&mut self) {
909 self.vec.shrink_to_fit()
912 /// Appends the given `char` to the end of this `String`.
919 /// let mut s = String::from("abc");
925 /// assert_eq!("abc123", s);
928 #[stable(feature = "rust1", since = "1.0.0")]
929 pub fn push(&mut self, ch: char) {
930 match ch.len_utf8() {
931 1 => self.vec.push(ch as u8),
932 _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
936 /// Returns a byte slice of this `String`'s contents.
938 /// The inverse of this method is [`from_utf8`].
940 /// [`from_utf8`]: #method.from_utf8
947 /// let s = String::from("hello");
949 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
952 #[stable(feature = "rust1", since = "1.0.0")]
953 pub fn as_bytes(&self) -> &[u8] {
957 /// Shortens this `String` to the specified length.
959 /// If `new_len` is greater than the string's current length, this has no
962 /// Note that this method has no effect on the allocated capacity
967 /// Panics if `new_len` does not lie on a [`char`] boundary.
969 /// [`char`]: ../../std/primitive.char.html
976 /// let mut s = String::from("hello");
980 /// assert_eq!("he", s);
983 #[stable(feature = "rust1", since = "1.0.0")]
984 pub fn truncate(&mut self, new_len: usize) {
985 if new_len <= self.len() {
986 assert!(self.is_char_boundary(new_len));
987 self.vec.truncate(new_len)
991 /// Removes the last character from the string buffer and returns it.
993 /// Returns `None` if this `String` is empty.
1000 /// let mut s = String::from("foo");
1002 /// assert_eq!(s.pop(), Some('o'));
1003 /// assert_eq!(s.pop(), Some('o'));
1004 /// assert_eq!(s.pop(), Some('f'));
1006 /// assert_eq!(s.pop(), None);
1009 #[stable(feature = "rust1", since = "1.0.0")]
1010 pub fn pop(&mut self) -> Option<char> {
1011 let ch = match self.chars().rev().next() {
1013 None => return None,
1015 let newlen = self.len() - ch.len_utf8();
1017 self.vec.set_len(newlen);
1022 /// Removes a `char` from this `String` at a byte position and returns it.
1024 /// This is an `O(n)` operation, as it requires copying every element in the
1029 /// Panics if `idx` is larger than or equal to the `String`'s length,
1030 /// or if it does not lie on a [`char`] boundary.
1032 /// [`char`]: ../../std/primitive.char.html
1039 /// let mut s = String::from("foo");
1041 /// assert_eq!(s.remove(0), 'f');
1042 /// assert_eq!(s.remove(1), 'o');
1043 /// assert_eq!(s.remove(0), 'o');
1046 #[stable(feature = "rust1", since = "1.0.0")]
1047 pub fn remove(&mut self, idx: usize) -> char {
1048 let ch = match self[idx..].chars().next() {
1050 None => panic!("cannot remove a char from the end of a string"),
1053 let next = idx + ch.len_utf8();
1054 let len = self.len();
1056 ptr::copy(self.vec.as_ptr().offset(next as isize),
1057 self.vec.as_mut_ptr().offset(idx as isize),
1059 self.vec.set_len(len - (next - idx));
1064 /// Retains only the characters specified by the predicate.
1066 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1067 /// This method operates in place and preserves the order of the retained
1073 /// #![feature(string_retain)]
1075 /// let mut s = String::from("f_o_ob_ar");
1077 /// s.retain(|c| c != '_');
1079 /// assert_eq!(s, "foobar");
1082 #[unstable(feature = "string_retain", issue = "43874")]
1083 pub fn retain<F>(&mut self, mut f: F)
1084 where F: FnMut(char) -> bool
1086 let len = self.len();
1087 let mut del_bytes = 0;
1092 self.slice_unchecked(idx, len).chars().next().unwrap()
1094 let ch_len = ch.len_utf8();
1097 del_bytes += ch_len;
1098 } else if del_bytes > 0 {
1100 ptr::copy(self.vec.as_ptr().offset(idx as isize),
1101 self.vec.as_mut_ptr().offset((idx - del_bytes) as isize),
1106 // Point idx to the next char
1111 unsafe { self.vec.set_len(len - del_bytes); }
1115 /// Inserts a character into this `String` at a byte position.
1117 /// This is an `O(n)` operation as it requires copying every element in the
1122 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1123 /// lie on a [`char`] boundary.
1125 /// [`char`]: ../../std/primitive.char.html
1132 /// let mut s = String::with_capacity(3);
1134 /// s.insert(0, 'f');
1135 /// s.insert(1, 'o');
1136 /// s.insert(2, 'o');
1138 /// assert_eq!("foo", s);
1141 #[stable(feature = "rust1", since = "1.0.0")]
1142 pub fn insert(&mut self, idx: usize, ch: char) {
1143 assert!(self.is_char_boundary(idx));
1144 let mut bits = [0; 4];
1145 let bits = ch.encode_utf8(&mut bits).as_bytes();
1148 self.insert_bytes(idx, bits);
1152 unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1153 let len = self.len();
1154 let amt = bytes.len();
1155 self.vec.reserve(amt);
1157 ptr::copy(self.vec.as_ptr().offset(idx as isize),
1158 self.vec.as_mut_ptr().offset((idx + amt) as isize),
1160 ptr::copy(bytes.as_ptr(),
1161 self.vec.as_mut_ptr().offset(idx as isize),
1163 self.vec.set_len(len + amt);
1166 /// Inserts a string slice into this `String` at a byte position.
1168 /// This is an `O(n)` operation as it requires copying every element in the
1173 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1174 /// lie on a [`char`] boundary.
1176 /// [`char`]: ../../std/primitive.char.html
1183 /// let mut s = String::from("bar");
1185 /// s.insert_str(0, "foo");
1187 /// assert_eq!("foobar", s);
1190 #[stable(feature = "insert_str", since = "1.16.0")]
1191 pub fn insert_str(&mut self, idx: usize, string: &str) {
1192 assert!(self.is_char_boundary(idx));
1195 self.insert_bytes(idx, string.as_bytes());
1199 /// Returns a mutable reference to the contents of this `String`.
1203 /// This function is unsafe because it does not check that the bytes passed
1204 /// to it are valid UTF-8. If this constraint is violated, it may cause
1205 /// memory unsafety issues with future users of the `String`, as the rest of
1206 /// the standard library assumes that `String`s are valid UTF-8.
1213 /// let mut s = String::from("hello");
1216 /// let vec = s.as_mut_vec();
1217 /// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1221 /// assert_eq!(s, "olleh");
1224 #[stable(feature = "rust1", since = "1.0.0")]
1225 pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1229 /// Returns the length of this `String`, in bytes.
1236 /// let a = String::from("foo");
1238 /// assert_eq!(a.len(), 3);
1241 #[stable(feature = "rust1", since = "1.0.0")]
1242 pub fn len(&self) -> usize {
1246 /// Returns `true` if this `String` has a length of zero.
1248 /// Returns `false` otherwise.
1255 /// let mut v = String::new();
1256 /// assert!(v.is_empty());
1259 /// assert!(!v.is_empty());
1262 #[stable(feature = "rust1", since = "1.0.0")]
1263 pub fn is_empty(&self) -> bool {
1267 /// Splits the string into two at the given index.
1269 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1270 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1271 /// boundary of a UTF-8 code point.
1273 /// Note that the capacity of `self` does not change.
1277 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1278 /// code point of the string.
1284 /// let mut hello = String::from("Hello, World!");
1285 /// let world = hello.split_off(7);
1286 /// assert_eq!(hello, "Hello, ");
1287 /// assert_eq!(world, "World!");
1291 #[stable(feature = "string_split_off", since = "1.16.0")]
1292 pub fn split_off(&mut self, at: usize) -> String {
1293 assert!(self.is_char_boundary(at));
1294 let other = self.vec.split_off(at);
1295 unsafe { String::from_utf8_unchecked(other) }
1298 /// Truncates this `String`, removing all contents.
1300 /// While this means the `String` will have a length of zero, it does not
1301 /// touch its capacity.
1308 /// let mut s = String::from("foo");
1312 /// assert!(s.is_empty());
1313 /// assert_eq!(0, s.len());
1314 /// assert_eq!(3, s.capacity());
1317 #[stable(feature = "rust1", since = "1.0.0")]
1318 pub fn clear(&mut self) {
1322 /// Creates a draining iterator that removes the specified range in the string
1323 /// and yields the removed chars.
1325 /// Note: The element range is removed even if the iterator is not
1326 /// consumed until the end.
1330 /// Panics if the starting point or end point do not lie on a [`char`]
1331 /// boundary, or if they're out of bounds.
1333 /// [`char`]: ../../std/primitive.char.html
1340 /// let mut s = String::from("α is alpha, β is beta");
1341 /// let beta_offset = s.find('β').unwrap_or(s.len());
1343 /// // Remove the range up until the β from the string
1344 /// let t: String = s.drain(..beta_offset).collect();
1345 /// assert_eq!(t, "α is alpha, ");
1346 /// assert_eq!(s, "β is beta");
1348 /// // A full range clears the string
1350 /// assert_eq!(s, "");
1352 #[stable(feature = "drain", since = "1.6.0")]
1353 pub fn drain<R>(&mut self, range: R) -> Drain
1354 where R: RangeArgument<usize>
1358 // The String version of Drain does not have the memory safety issues
1359 // of the vector version. The data is just plain bytes.
1360 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1361 // the removal will not happen.
1362 let len = self.len();
1363 let start = match range.start() {
1365 Excluded(&n) => n + 1,
1368 let end = match range.end() {
1369 Included(&n) => n + 1,
1374 // Take out two simultaneous borrows. The &mut String won't be accessed
1375 // until iteration is over, in Drop.
1376 let self_ptr = self as *mut _;
1377 // slicing does the appropriate bounds checks
1378 let chars_iter = self[start..end].chars();
1388 /// Creates a splicing iterator that removes the specified range in the string,
1389 /// replaces with the given string, and yields the removed chars.
1390 /// The given string doesn’t need to be the same length as the range.
1392 /// Note: The element range is removed when the `Splice` is dropped,
1393 /// even if the iterator is not consumed until the end.
1397 /// Panics if the starting point or end point do not lie on a [`char`]
1398 /// boundary, or if they're out of bounds.
1400 /// [`char`]: ../../std/primitive.char.html
1407 /// #![feature(splice)]
1408 /// let mut s = String::from("α is alpha, β is beta");
1409 /// let beta_offset = s.find('β').unwrap_or(s.len());
1411 /// // Replace the range up until the β from the string
1412 /// let t: String = s.splice(..beta_offset, "Α is capital alpha; ").collect();
1413 /// assert_eq!(t, "α is alpha, ");
1414 /// assert_eq!(s, "Α is capital alpha; β is beta");
1416 #[unstable(feature = "splice", reason = "recently added", issue = "32310")]
1417 pub fn splice<'a, 'b, R>(&'a mut self, range: R, replace_with: &'b str) -> Splice<'a, 'b>
1418 where R: RangeArgument<usize>
1422 // The String version of Splice does not have the memory safety issues
1423 // of the vector version. The data is just plain bytes.
1424 // Because the range removal happens in Drop, if the Splice iterator is leaked,
1425 // the removal will not happen.
1426 let len = self.len();
1427 let start = match range.start() {
1429 Excluded(&n) => n + 1,
1432 let end = match range.end() {
1433 Included(&n) => n + 1,
1438 // Take out two simultaneous borrows. The &mut String won't be accessed
1439 // until iteration is over, in Drop.
1440 let self_ptr = self as *mut _;
1441 // slicing does the appropriate bounds checks
1442 let chars_iter = self[start..end].chars();
1453 /// Converts this `String` into a `Box<str>`.
1455 /// This will drop any excess capacity.
1462 /// let s = String::from("hello");
1464 /// let b = s.into_boxed_str();
1466 #[stable(feature = "box_str", since = "1.4.0")]
1467 pub fn into_boxed_str(self) -> Box<str> {
1468 let slice = self.vec.into_boxed_slice();
1469 unsafe { from_boxed_utf8_unchecked(slice) }
1473 impl FromUtf8Error {
1474 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1481 /// #![feature(from_utf8_error_as_bytes)]
1482 /// // some invalid bytes, in a vector
1483 /// let bytes = vec![0, 159];
1485 /// let value = String::from_utf8(bytes);
1487 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1489 #[unstable(feature = "from_utf8_error_as_bytes", reason = "recently added", issue = "40895")]
1490 pub fn as_bytes(&self) -> &[u8] {
1494 /// Returns the bytes that were attempted to convert to a `String`.
1496 /// This method is carefully constructed to avoid allocation. It will
1497 /// consume the error, moving out the bytes, so that a copy of the bytes
1498 /// does not need to be made.
1505 /// // some invalid bytes, in a vector
1506 /// let bytes = vec![0, 159];
1508 /// let value = String::from_utf8(bytes);
1510 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1512 #[stable(feature = "rust1", since = "1.0.0")]
1513 pub fn into_bytes(self) -> Vec<u8> {
1517 /// Fetch a `Utf8Error` to get more details about the conversion failure.
1519 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1520 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1521 /// an analogue to `FromUtf8Error`. See its documentation for more details
1524 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
1525 /// [`std::str`]: ../../std/str/index.html
1526 /// [`u8`]: ../../std/primitive.u8.html
1527 /// [`&str`]: ../../std/primitive.str.html
1534 /// // some invalid bytes, in a vector
1535 /// let bytes = vec![0, 159];
1537 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1539 /// // the first byte is invalid here
1540 /// assert_eq!(1, error.valid_up_to());
1542 #[stable(feature = "rust1", since = "1.0.0")]
1543 pub fn utf8_error(&self) -> Utf8Error {
1548 #[stable(feature = "rust1", since = "1.0.0")]
1549 impl fmt::Display for FromUtf8Error {
1550 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1551 fmt::Display::fmt(&self.error, f)
1555 #[stable(feature = "rust1", since = "1.0.0")]
1556 impl fmt::Display for FromUtf16Error {
1557 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1558 fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
1562 #[stable(feature = "rust1", since = "1.0.0")]
1563 impl Clone for String {
1564 fn clone(&self) -> Self {
1565 String { vec: self.vec.clone() }
1568 fn clone_from(&mut self, source: &Self) {
1569 self.vec.clone_from(&source.vec);
1573 #[stable(feature = "rust1", since = "1.0.0")]
1574 impl FromIterator<char> for String {
1575 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
1576 let mut buf = String::new();
1582 #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
1583 impl<'a> FromIterator<&'a char> for String {
1584 fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
1585 let mut buf = String::new();
1591 #[stable(feature = "rust1", since = "1.0.0")]
1592 impl<'a> FromIterator<&'a str> for String {
1593 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
1594 let mut buf = String::new();
1600 #[stable(feature = "extend_string", since = "1.4.0")]
1601 impl FromIterator<String> for String {
1602 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
1603 let mut buf = String::new();
1609 #[stable(feature = "herd_cows", since = "1.19.0")]
1610 impl<'a> FromIterator<Cow<'a, str>> for String {
1611 fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
1612 let mut buf = String::new();
1618 #[stable(feature = "rust1", since = "1.0.0")]
1619 impl Extend<char> for String {
1620 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
1621 let iterator = iter.into_iter();
1622 let (lower_bound, _) = iterator.size_hint();
1623 self.reserve(lower_bound);
1624 for ch in iterator {
1630 #[stable(feature = "extend_ref", since = "1.2.0")]
1631 impl<'a> Extend<&'a char> for String {
1632 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
1633 self.extend(iter.into_iter().cloned());
1637 #[stable(feature = "rust1", since = "1.0.0")]
1638 impl<'a> Extend<&'a str> for String {
1639 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
1646 #[stable(feature = "extend_string", since = "1.4.0")]
1647 impl Extend<String> for String {
1648 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
1655 #[stable(feature = "herd_cows", since = "1.19.0")]
1656 impl<'a> Extend<Cow<'a, str>> for String {
1657 fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
1664 /// A convenience impl that delegates to the impl for `&str`
1665 #[unstable(feature = "pattern",
1666 reason = "API not fully fleshed out and ready to be stabilized",
1668 impl<'a, 'b> Pattern<'a> for &'b String {
1669 type Searcher = <&'b str as Pattern<'a>>::Searcher;
1671 fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
1672 self[..].into_searcher(haystack)
1676 fn is_contained_in(self, haystack: &'a str) -> bool {
1677 self[..].is_contained_in(haystack)
1681 fn is_prefix_of(self, haystack: &'a str) -> bool {
1682 self[..].is_prefix_of(haystack)
1686 #[stable(feature = "rust1", since = "1.0.0")]
1687 impl PartialEq for String {
1689 fn eq(&self, other: &String) -> bool {
1690 PartialEq::eq(&self[..], &other[..])
1693 fn ne(&self, other: &String) -> bool {
1694 PartialEq::ne(&self[..], &other[..])
1698 macro_rules! impl_eq {
1699 ($lhs:ty, $rhs: ty) => {
1700 #[stable(feature = "rust1", since = "1.0.0")]
1701 impl<'a, 'b> PartialEq<$rhs> for $lhs {
1703 fn eq(&self, other: &$rhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1705 fn ne(&self, other: &$rhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1708 #[stable(feature = "rust1", since = "1.0.0")]
1709 impl<'a, 'b> PartialEq<$lhs> for $rhs {
1711 fn eq(&self, other: &$lhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1713 fn ne(&self, other: &$lhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1719 impl_eq! { String, str }
1720 impl_eq! { String, &'a str }
1721 impl_eq! { Cow<'a, str>, str }
1722 impl_eq! { Cow<'a, str>, &'b str }
1723 impl_eq! { Cow<'a, str>, String }
1725 #[stable(feature = "rust1", since = "1.0.0")]
1726 impl Default for String {
1727 /// Creates an empty `String`.
1729 fn default() -> String {
1734 #[stable(feature = "rust1", since = "1.0.0")]
1735 impl fmt::Display for String {
1737 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1738 fmt::Display::fmt(&**self, f)
1742 #[stable(feature = "rust1", since = "1.0.0")]
1743 impl fmt::Debug for String {
1745 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1746 fmt::Debug::fmt(&**self, f)
1750 #[stable(feature = "rust1", since = "1.0.0")]
1751 impl hash::Hash for String {
1753 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
1754 (**self).hash(hasher)
1758 /// Implements the `+` operator for concatenating two strings.
1760 /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
1761 /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
1762 /// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by
1763 /// repeated concatenation.
1765 /// The string on the right-hand side is only borrowed; its contents are copied into the returned
1770 /// Concatenating two `String`s takes the first by value and borrows the second:
1773 /// let a = String::from("hello");
1774 /// let b = String::from(" world");
1776 /// // `a` is moved and can no longer be used here.
1779 /// If you want to keep using the first `String`, you can clone it and append to the clone instead:
1782 /// let a = String::from("hello");
1783 /// let b = String::from(" world");
1784 /// let c = a.clone() + &b;
1785 /// // `a` is still valid here.
1788 /// Concatenating `&str` slices can be done by converting the first to a `String`:
1791 /// let a = "hello";
1792 /// let b = " world";
1793 /// let c = a.to_string() + b;
1795 #[stable(feature = "rust1", since = "1.0.0")]
1796 impl<'a> Add<&'a str> for String {
1797 type Output = String;
1800 fn add(mut self, other: &str) -> String {
1801 self.push_str(other);
1806 /// Implements the `+=` operator for appending to a `String`.
1808 /// This has the same behavior as the [`push_str`] method.
1810 /// [`push_str`]: struct.String.html#method.push_str
1811 #[stable(feature = "stringaddassign", since = "1.12.0")]
1812 impl<'a> AddAssign<&'a str> for String {
1814 fn add_assign(&mut self, other: &str) {
1815 self.push_str(other);
1819 #[stable(feature = "rust1", since = "1.0.0")]
1820 impl ops::Index<ops::Range<usize>> for String {
1824 fn index(&self, index: ops::Range<usize>) -> &str {
1828 #[stable(feature = "rust1", since = "1.0.0")]
1829 impl ops::Index<ops::RangeTo<usize>> for String {
1833 fn index(&self, index: ops::RangeTo<usize>) -> &str {
1837 #[stable(feature = "rust1", since = "1.0.0")]
1838 impl ops::Index<ops::RangeFrom<usize>> for String {
1842 fn index(&self, index: ops::RangeFrom<usize>) -> &str {
1846 #[stable(feature = "rust1", since = "1.0.0")]
1847 impl ops::Index<ops::RangeFull> for String {
1851 fn index(&self, _index: ops::RangeFull) -> &str {
1852 unsafe { str::from_utf8_unchecked(&self.vec) }
1855 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1856 impl ops::Index<ops::RangeInclusive<usize>> for String {
1860 fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
1861 Index::index(&**self, index)
1864 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1865 impl ops::Index<ops::RangeToInclusive<usize>> for String {
1869 fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
1870 Index::index(&**self, index)
1874 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
1875 impl ops::IndexMut<ops::Range<usize>> for String {
1877 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
1878 &mut self[..][index]
1881 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
1882 impl ops::IndexMut<ops::RangeTo<usize>> for String {
1884 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
1885 &mut self[..][index]
1888 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
1889 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
1891 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
1892 &mut self[..][index]
1895 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
1896 impl ops::IndexMut<ops::RangeFull> for String {
1898 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
1899 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
1902 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1903 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
1905 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
1906 IndexMut::index_mut(&mut **self, index)
1909 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1910 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
1912 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
1913 IndexMut::index_mut(&mut **self, index)
1917 #[stable(feature = "rust1", since = "1.0.0")]
1918 impl ops::Deref for String {
1922 fn deref(&self) -> &str {
1923 unsafe { str::from_utf8_unchecked(&self.vec) }
1927 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
1928 impl ops::DerefMut for String {
1930 fn deref_mut(&mut self) -> &mut str {
1931 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
1935 /// An error when parsing a `String`.
1937 /// This `enum` is slightly awkward: it will never actually exist. This error is
1938 /// part of the type signature of the implementation of [`FromStr`] on
1939 /// [`String`]. The return type of [`from_str`], requires that an error be
1940 /// defined, but, given that a [`String`] can always be made into a new
1941 /// [`String`] without error, this type will never actually be returned. As
1942 /// such, it is only here to satisfy said signature, and is useless otherwise.
1944 /// [`FromStr`]: ../../std/str/trait.FromStr.html
1945 /// [`String`]: struct.String.html
1946 /// [`from_str`]: ../../std/str/trait.FromStr.html#tymethod.from_str
1947 #[stable(feature = "str_parse_error", since = "1.5.0")]
1949 pub enum ParseError {}
1951 #[stable(feature = "rust1", since = "1.0.0")]
1952 impl FromStr for String {
1953 type Err = ParseError;
1955 fn from_str(s: &str) -> Result<String, ParseError> {
1960 #[stable(feature = "str_parse_error", since = "1.5.0")]
1961 impl Clone for ParseError {
1962 fn clone(&self) -> ParseError {
1967 #[stable(feature = "str_parse_error", since = "1.5.0")]
1968 impl fmt::Debug for ParseError {
1969 fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
1974 #[stable(feature = "str_parse_error2", since = "1.8.0")]
1975 impl fmt::Display for ParseError {
1976 fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
1981 #[stable(feature = "str_parse_error", since = "1.5.0")]
1982 impl PartialEq for ParseError {
1983 fn eq(&self, _: &ParseError) -> bool {
1988 #[stable(feature = "str_parse_error", since = "1.5.0")]
1989 impl Eq for ParseError {}
1991 /// A trait for converting a value to a `String`.
1993 /// This trait is automatically implemented for any type which implements the
1994 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
1995 /// [`Display`] should be implemented instead, and you get the `ToString`
1996 /// implementation for free.
1998 /// [`Display`]: ../../std/fmt/trait.Display.html
1999 #[stable(feature = "rust1", since = "1.0.0")]
2000 pub trait ToString {
2001 /// Converts the given value to a `String`.
2009 /// let five = String::from("5");
2011 /// assert_eq!(five, i.to_string());
2013 #[stable(feature = "rust1", since = "1.0.0")]
2014 fn to_string(&self) -> String;
2019 /// In this implementation, the `to_string` method panics
2020 /// if the `Display` implementation returns an error.
2021 /// This indicates an incorrect `Display` implementation
2022 /// since `fmt::Write for String` never returns an error itself.
2023 #[stable(feature = "rust1", since = "1.0.0")]
2024 impl<T: fmt::Display + ?Sized> ToString for T {
2026 default fn to_string(&self) -> String {
2027 use core::fmt::Write;
2028 let mut buf = String::new();
2029 buf.write_fmt(format_args!("{}", self))
2030 .expect("a Display implementation return an error unexpectedly");
2031 buf.shrink_to_fit();
2036 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
2037 impl ToString for str {
2039 fn to_string(&self) -> String {
2044 #[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
2045 impl<'a> ToString for Cow<'a, str> {
2047 fn to_string(&self) -> String {
2052 #[stable(feature = "string_to_string_specialization", since = "1.17.0")]
2053 impl ToString for String {
2055 fn to_string(&self) -> String {
2060 #[stable(feature = "rust1", since = "1.0.0")]
2061 impl AsRef<str> for String {
2063 fn as_ref(&self) -> &str {
2068 #[stable(feature = "rust1", since = "1.0.0")]
2069 impl AsRef<[u8]> for String {
2071 fn as_ref(&self) -> &[u8] {
2076 #[stable(feature = "rust1", since = "1.0.0")]
2077 impl<'a> From<&'a str> for String {
2078 fn from(s: &'a str) -> String {
2083 // note: test pulls in libstd, which causes errors here
2085 #[stable(feature = "string_from_box", since = "1.18.0")]
2086 impl From<Box<str>> for String {
2087 fn from(s: Box<str>) -> String {
2092 #[stable(feature = "box_from_str", since = "1.20.0")]
2093 impl From<String> for Box<str> {
2094 fn from(s: String) -> Box<str> {
2099 #[stable(feature = "string_from_cow_str", since = "1.14.0")]
2100 impl<'a> From<Cow<'a, str>> for String {
2101 fn from(s: Cow<'a, str>) -> String {
2106 #[stable(feature = "rust1", since = "1.0.0")]
2107 impl<'a> From<&'a str> for Cow<'a, str> {
2109 fn from(s: &'a str) -> Cow<'a, str> {
2114 #[stable(feature = "rust1", since = "1.0.0")]
2115 impl<'a> From<String> for Cow<'a, str> {
2117 fn from(s: String) -> Cow<'a, str> {
2122 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2123 impl<'a> FromIterator<char> for Cow<'a, str> {
2124 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
2125 Cow::Owned(FromIterator::from_iter(it))
2129 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2130 impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
2131 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
2132 Cow::Owned(FromIterator::from_iter(it))
2136 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2137 impl<'a> FromIterator<String> for Cow<'a, str> {
2138 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
2139 Cow::Owned(FromIterator::from_iter(it))
2143 #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
2144 impl From<String> for Vec<u8> {
2145 fn from(string: String) -> Vec<u8> {
2150 #[stable(feature = "rust1", since = "1.0.0")]
2151 impl fmt::Write for String {
2153 fn write_str(&mut self, s: &str) -> fmt::Result {
2159 fn write_char(&mut self, c: char) -> fmt::Result {
2165 /// A draining iterator for `String`.
2167 /// This struct is created by the [`drain`] method on [`String`]. See its
2168 /// documentation for more.
2170 /// [`drain`]: struct.String.html#method.drain
2171 /// [`String`]: struct.String.html
2172 #[stable(feature = "drain", since = "1.6.0")]
2173 pub struct Drain<'a> {
2174 /// Will be used as &'a mut String in the destructor
2175 string: *mut String,
2176 /// Start of part to remove
2178 /// End of part to remove
2180 /// Current remaining range to remove
2184 #[stable(feature = "collection_debug", since = "1.17.0")]
2185 impl<'a> fmt::Debug for Drain<'a> {
2186 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2187 f.pad("Drain { .. }")
2191 #[stable(feature = "drain", since = "1.6.0")]
2192 unsafe impl<'a> Sync for Drain<'a> {}
2193 #[stable(feature = "drain", since = "1.6.0")]
2194 unsafe impl<'a> Send for Drain<'a> {}
2196 #[stable(feature = "drain", since = "1.6.0")]
2197 impl<'a> Drop for Drain<'a> {
2198 fn drop(&mut self) {
2200 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
2201 // panic code being inserted again.
2202 let self_vec = (*self.string).as_mut_vec();
2203 if self.start <= self.end && self.end <= self_vec.len() {
2204 self_vec.drain(self.start..self.end);
2210 #[stable(feature = "drain", since = "1.6.0")]
2211 impl<'a> Iterator for Drain<'a> {
2215 fn next(&mut self) -> Option<char> {
2219 fn size_hint(&self) -> (usize, Option<usize>) {
2220 self.iter.size_hint()
2224 #[stable(feature = "drain", since = "1.6.0")]
2225 impl<'a> DoubleEndedIterator for Drain<'a> {
2227 fn next_back(&mut self) -> Option<char> {
2228 self.iter.next_back()
2232 #[unstable(feature = "fused", issue = "35602")]
2233 impl<'a> FusedIterator for Drain<'a> {}
2235 /// A splicing iterator for `String`.
2237 /// This struct is created by the [`splice()`] method on [`String`]. See its
2238 /// documentation for more.
2240 /// [`splice()`]: struct.String.html#method.splice
2241 /// [`String`]: struct.String.html
2243 #[unstable(feature = "splice", reason = "recently added", issue = "32310")]
2244 pub struct Splice<'a, 'b> {
2245 /// Will be used as &'a mut String in the destructor
2246 string: *mut String,
2247 /// Start of part to remove
2249 /// End of part to remove
2251 /// Current remaining range to remove
2253 replace_with: &'b str,
2256 #[unstable(feature = "splice", reason = "recently added", issue = "32310")]
2257 unsafe impl<'a, 'b> Sync for Splice<'a, 'b> {}
2258 #[unstable(feature = "splice", reason = "recently added", issue = "32310")]
2259 unsafe impl<'a, 'b> Send for Splice<'a, 'b> {}
2261 #[unstable(feature = "splice", reason = "recently added", issue = "32310")]
2262 impl<'a, 'b> Drop for Splice<'a, 'b> {
2263 fn drop(&mut self) {
2265 let vec = (*self.string).as_mut_vec();
2266 vec.splice(self.start..self.end, self.replace_with.bytes());
2271 #[unstable(feature = "splice", reason = "recently added", issue = "32310")]
2272 impl<'a, 'b> Iterator for Splice<'a, 'b> {
2276 fn next(&mut self) -> Option<char> {
2280 fn size_hint(&self) -> (usize, Option<usize>) {
2281 self.iter.size_hint()
2285 #[unstable(feature = "splice", reason = "recently added", issue = "32310")]
2286 impl<'a, 'b> DoubleEndedIterator for Splice<'a, 'b> {
2288 fn next_back(&mut self) -> Option<char> {
2289 self.iter.next_back()