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")]
59 use core::char::{decode_utf16, REPLACEMENT_CHARACTER};
62 use core::iter::{FromIterator, FusedIterator};
63 use core::ops::Bound::{Excluded, Included, Unbounded};
64 use core::ops::{self, Add, AddAssign, Index, IndexMut, RangeBounds};
66 use core::str::pattern::Pattern;
69 use collections::CollectionAllocErr;
70 use borrow::{Cow, ToOwned};
72 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 /// [`String::from`]: #method.from
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`:
128 /// ```compile_fail,E0277
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 a
149 /// function which takes a [`&str`] by using an ampersand (`&`):
152 /// fn takes_str(s: &str) { }
154 /// let s = String::from("Hello");
159 /// This will create a [`&str`] from the `String` and pass it in. This
160 /// conversion is very inexpensive, and so generally, functions will accept
161 /// [`&str`]s as arguments unless they need a `String` for some specific
164 /// In certain cases Rust doesn't have enough information to make this
165 /// conversion, known as [`Deref`] coercion. In the following example a string
166 /// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
167 /// `example_func` takes anything that implements the trait. In this case Rust
168 /// would need to make two implicit conversions, which Rust doesn't have the
169 /// means to do. For that reason, the following example will not compile.
171 /// ```compile_fail,E0277
172 /// trait TraitExample {}
174 /// impl<'a> TraitExample for &'a str {}
176 /// fn example_func<A: TraitExample>(example_arg: A) {}
179 /// let example_string = String::from("example_string");
180 /// example_func(&example_string);
184 /// There are two options that would work instead. The first would be to
185 /// change the line `example_func(&example_string);` to
186 /// `example_func(example_string.as_str());`, using the method [`as_str()`]
187 /// to explicitly extract the string slice containing the string. The second
188 /// way changes `example_func(&example_string);` to
189 /// `example_func(&*example_string);`. In this case we are dereferencing a
190 /// `String` to a [`str`][`&str`], then referencing the [`str`][`&str`] back to
191 /// [`&str`]. The second way is more idiomatic, however both work to do the
192 /// conversion explicitly rather than relying on the implicit conversion.
196 /// A `String` is made up of three components: a pointer to some bytes, a
197 /// length, and a capacity. The pointer points to an internal buffer `String`
198 /// uses to store its data. The length is the number of bytes currently stored
199 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
200 /// the length will always be less than or equal to the capacity.
202 /// This buffer is always stored on the heap.
204 /// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
210 /// let story = String::from("Once upon a time...");
212 /// let ptr = story.as_ptr();
213 /// let len = story.len();
214 /// let capacity = story.capacity();
216 /// // story has nineteen bytes
217 /// assert_eq!(19, len);
219 /// // Now that we have our parts, we throw the story away.
220 /// mem::forget(story);
222 /// // We can re-build a String out of ptr, len, and capacity. This is all
223 /// // unsafe because we are responsible for making sure the components are
225 /// let s = unsafe { String::from_raw_parts(ptr as *mut _, len, capacity) } ;
227 /// assert_eq!(String::from("Once upon a time..."), s);
230 /// [`as_ptr`]: #method.as_ptr
231 /// [`len`]: #method.len
232 /// [`capacity`]: #method.capacity
234 /// If a `String` has enough capacity, adding elements to it will not
235 /// re-allocate. For example, consider this program:
238 /// let mut s = String::new();
240 /// println!("{}", s.capacity());
243 /// s.push_str("hello");
244 /// println!("{}", s.capacity());
248 /// This will output the following:
259 /// At first, we have no memory allocated at all, but as we append to the
260 /// string, it increases its capacity appropriately. If we instead use the
261 /// [`with_capacity`] method to allocate the correct capacity initially:
264 /// let mut s = String::with_capacity(25);
266 /// println!("{}", s.capacity());
269 /// s.push_str("hello");
270 /// println!("{}", s.capacity());
274 /// [`with_capacity`]: #method.with_capacity
276 /// We end up with a different output:
287 /// Here, there's no need to allocate more memory inside the loop.
289 /// [`&str`]: ../../std/primitive.str.html
290 /// [`Deref`]: ../../std/ops/trait.Deref.html
291 /// [`as_str()`]: struct.String.html#method.as_str
292 #[derive(PartialOrd, Eq, Ord)]
293 #[stable(feature = "rust1", since = "1.0.0")]
298 /// A possible error value when converting a `String` from a UTF-8 byte vector.
300 /// This type is the error type for the [`from_utf8`] method on [`String`]. It
301 /// is designed in such a way to carefully avoid reallocations: the
302 /// [`into_bytes`] method will give back the byte vector that was used in the
303 /// conversion attempt.
305 /// [`from_utf8`]: struct.String.html#method.from_utf8
306 /// [`String`]: struct.String.html
307 /// [`into_bytes`]: struct.FromUtf8Error.html#method.into_bytes
309 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
310 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
311 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
312 /// through the [`utf8_error`] method.
314 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
315 /// [`std::str`]: ../../std/str/index.html
316 /// [`u8`]: ../../std/primitive.u8.html
317 /// [`&str`]: ../../std/primitive.str.html
318 /// [`utf8_error`]: #method.utf8_error
325 /// // some invalid bytes, in a vector
326 /// let bytes = vec![0, 159];
328 /// let value = String::from_utf8(bytes);
330 /// assert!(value.is_err());
331 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
333 #[stable(feature = "rust1", since = "1.0.0")]
335 pub struct FromUtf8Error {
340 /// A possible error value when converting a `String` from a UTF-16 byte slice.
342 /// This type is the error type for the [`from_utf16`] method on [`String`].
344 /// [`from_utf16`]: struct.String.html#method.from_utf16
345 /// [`String`]: struct.String.html
352 /// // 𝄞mu<invalid>ic
353 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
354 /// 0xD800, 0x0069, 0x0063];
356 /// assert!(String::from_utf16(v).is_err());
358 #[stable(feature = "rust1", since = "1.0.0")]
360 pub struct FromUtf16Error(());
363 /// Creates a new empty `String`.
365 /// Given that the `String` is empty, this will not allocate any initial
366 /// buffer. While that means that this initial operation is very
367 /// inexpensive, it may cause excessive allocation later when you add
368 /// data. If you have an idea of how much data the `String` will hold,
369 /// consider the [`with_capacity`] method to prevent excessive
372 /// [`with_capacity`]: #method.with_capacity
379 /// let s = String::new();
382 #[stable(feature = "rust1", since = "1.0.0")]
383 #[rustc_const_unstable(feature = "const_string_new")]
384 pub const fn new() -> String {
385 String { vec: Vec::new() }
388 /// Creates a new empty `String` with a particular capacity.
390 /// `String`s have an internal buffer to hold their data. The capacity is
391 /// the length of that buffer, and can be queried with the [`capacity`]
392 /// method. This method creates an empty `String`, but one with an initial
393 /// buffer that can hold `capacity` bytes. This is useful when you may be
394 /// appending a bunch of data to the `String`, reducing the number of
395 /// reallocations it needs to do.
397 /// [`capacity`]: #method.capacity
399 /// If the given capacity is `0`, no allocation will occur, and this method
400 /// is identical to the [`new`] method.
402 /// [`new`]: #method.new
409 /// let mut s = String::with_capacity(10);
411 /// // The String contains no chars, even though it has capacity for more
412 /// assert_eq!(s.len(), 0);
414 /// // These are all done without reallocating...
415 /// let cap = s.capacity();
420 /// assert_eq!(s.capacity(), cap);
422 /// // ...but this may make the vector reallocate
426 #[stable(feature = "rust1", since = "1.0.0")]
427 pub fn with_capacity(capacity: usize) -> String {
428 String { vec: Vec::with_capacity(capacity) }
431 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
432 // required for this method definition, is not available. Since we don't
433 // require this method for testing purposes, I'll just stub it
434 // NB see the slice::hack module in slice.rs for more information
437 pub fn from_str(_: &str) -> String {
438 panic!("not available with cfg(test)");
441 /// Converts a vector of bytes to a `String`.
443 /// A string slice ([`&str`]) is made of bytes ([`u8`]), and a vector of bytes
444 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
445 /// two. Not all byte slices are valid `String`s, however: `String`
446 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
447 /// the bytes are valid UTF-8, and then does the conversion.
449 /// If you are sure that the byte slice is valid UTF-8, and you don't want
450 /// to incur the overhead of the validity check, there is an unsafe version
451 /// of this function, [`from_utf8_unchecked`], which has the same behavior
452 /// but skips the check.
454 /// This method will take care to not copy the vector, for efficiency's
457 /// If you need a [`&str`] instead of a `String`, consider
458 /// [`str::from_utf8`].
460 /// The inverse of this method is [`as_bytes`].
464 /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
465 /// provided bytes are not UTF-8. The vector you moved in is also included.
472 /// // some bytes, in a vector
473 /// let sparkle_heart = vec![240, 159, 146, 150];
475 /// // We know these bytes are valid, so we'll use `unwrap()`.
476 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
478 /// assert_eq!("💖", sparkle_heart);
484 /// // some invalid bytes, in a vector
485 /// let sparkle_heart = vec![0, 159, 146, 150];
487 /// assert!(String::from_utf8(sparkle_heart).is_err());
490 /// See the docs for [`FromUtf8Error`] for more details on what you can do
493 /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
494 /// [`&str`]: ../../std/primitive.str.html
495 /// [`u8`]: ../../std/primitive.u8.html
496 /// [`Vec<u8>`]: ../../std/vec/struct.Vec.html
497 /// [`str::from_utf8`]: ../../std/str/fn.from_utf8.html
498 /// [`as_bytes`]: struct.String.html#method.as_bytes
499 /// [`FromUtf8Error`]: struct.FromUtf8Error.html
500 /// [`Err`]: ../../stdresult/enum.Result.html#variant.Err
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 }),
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`][U+FFFD], which looks like this: �
524 /// [`u8`]: ../../std/primitive.u8.html
525 /// [byteslice]: ../../std/primitive.slice.html
526 /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
528 /// If you are sure that the byte slice is valid UTF-8, and you don't want
529 /// to incur the overhead of the conversion, there is an unsafe version
530 /// of this function, [`from_utf8_unchecked`], which has the same behavior
531 /// but skips the checks.
533 /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
535 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
536 /// UTF-8, then we need to insert the replacement characters, which will
537 /// change the size of the string, and hence, require a `String`. But if
538 /// it's already valid UTF-8, we don't need a new allocation. This return
539 /// type allows us to handle both cases.
541 /// [`Cow<'a, str>`]: ../../std/borrow/enum.Cow.html
548 /// // some bytes, in a vector
549 /// let sparkle_heart = vec![240, 159, 146, 150];
551 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
553 /// assert_eq!("💖", sparkle_heart);
559 /// // some invalid bytes
560 /// let input = b"Hello \xF0\x90\x80World";
561 /// let output = String::from_utf8_lossy(input);
563 /// assert_eq!("Hello �World", output);
565 #[stable(feature = "rust1", since = "1.0.0")]
566 pub fn from_utf8_lossy<'a>(v: &'a [u8]) -> Cow<'a, str> {
567 let mut iter = lossy::Utf8Lossy::from_bytes(v).chunks();
569 let (first_valid, first_broken) = if let Some(chunk) = iter.next() {
570 let lossy::Utf8LossyChunk { valid, broken } = chunk;
571 if valid.len() == v.len() {
572 debug_assert!(broken.is_empty());
573 return Cow::Borrowed(valid);
577 return Cow::Borrowed("");
580 const REPLACEMENT: &'static str = "\u{FFFD}";
582 let mut res = String::with_capacity(v.len());
583 res.push_str(first_valid);
584 if !first_broken.is_empty() {
585 res.push_str(REPLACEMENT);
588 for lossy::Utf8LossyChunk { valid, broken } in iter {
590 if !broken.is_empty() {
591 res.push_str(REPLACEMENT);
598 /// Decode a UTF-16 encoded vector `v` into a `String`, returning [`Err`]
599 /// if `v` contains any invalid data.
601 /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
609 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
610 /// 0x0073, 0x0069, 0x0063];
611 /// assert_eq!(String::from("𝄞music"),
612 /// String::from_utf16(v).unwrap());
614 /// // 𝄞mu<invalid>ic
615 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
616 /// 0xD800, 0x0069, 0x0063];
617 /// assert!(String::from_utf16(v).is_err());
619 #[stable(feature = "rust1", since = "1.0.0")]
620 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
621 // This isn't done via collect::<Result<_, _>>() for performance reasons.
622 // FIXME: the function can be simplified again when #48994 is closed.
623 let mut ret = String::with_capacity(v.len());
624 for c in decode_utf16(v.iter().cloned()) {
628 return Err(FromUtf16Error(()));
634 /// Decode a UTF-16 encoded slice `v` into a `String`, replacing
635 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
637 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
638 /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
639 /// conversion requires a memory allocation.
641 /// [`from_utf8_lossy`]: #method.from_utf8_lossy
642 /// [`Cow<'a, str>`]: ../borrow/enum.Cow.html
643 /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
650 /// // 𝄞mus<invalid>ic<invalid>
651 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
652 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
655 /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
656 /// String::from_utf16_lossy(v));
659 #[stable(feature = "rust1", since = "1.0.0")]
660 pub fn from_utf16_lossy(v: &[u16]) -> String {
661 decode_utf16(v.iter().cloned()).map(|r| r.unwrap_or(REPLACEMENT_CHARACTER)).collect()
664 /// Creates a new `String` from a length, capacity, and pointer.
668 /// This is highly unsafe, due to the number of invariants that aren't
671 /// * The memory at `ptr` needs to have been previously allocated by the
672 /// same allocator the standard library uses.
673 /// * `length` needs to be less than or equal to `capacity`.
674 /// * `capacity` needs to be the correct value.
676 /// Violating these may cause problems like corrupting the allocator's
677 /// internal data structures.
679 /// The ownership of `ptr` is effectively transferred to the
680 /// `String` which may then deallocate, reallocate or change the
681 /// contents of memory pointed to by the pointer at will. Ensure
682 /// that nothing else uses the pointer after calling this
693 /// let s = String::from("hello");
694 /// let ptr = s.as_ptr();
695 /// let len = s.len();
696 /// let capacity = s.capacity();
700 /// let s = String::from_raw_parts(ptr as *mut _, len, capacity);
702 /// assert_eq!(String::from("hello"), s);
706 #[stable(feature = "rust1", since = "1.0.0")]
707 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
708 String { vec: Vec::from_raw_parts(buf, length, capacity) }
711 /// Converts a vector of bytes to a `String` without checking that the
712 /// string contains valid UTF-8.
714 /// See the safe version, [`from_utf8`], for more details.
716 /// [`from_utf8`]: struct.String.html#method.from_utf8
720 /// This function is unsafe because it does not check that the bytes passed
721 /// to it are valid UTF-8. If this constraint is violated, it may cause
722 /// memory unsafety issues with future users of the `String`, as the rest of
723 /// the standard library assumes that `String`s are valid UTF-8.
730 /// // some bytes, in a vector
731 /// let sparkle_heart = vec![240, 159, 146, 150];
733 /// let sparkle_heart = unsafe {
734 /// String::from_utf8_unchecked(sparkle_heart)
737 /// assert_eq!("💖", sparkle_heart);
740 #[stable(feature = "rust1", since = "1.0.0")]
741 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
742 String { vec: bytes }
745 /// Converts a `String` into a byte vector.
747 /// This consumes the `String`, so we do not need to copy its contents.
754 /// let s = String::from("hello");
755 /// let bytes = s.into_bytes();
757 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
760 #[stable(feature = "rust1", since = "1.0.0")]
761 pub fn into_bytes(self) -> Vec<u8> {
765 /// Extracts a string slice containing the entire `String`.
772 /// let s = String::from("foo");
774 /// assert_eq!("foo", s.as_str());
777 #[stable(feature = "string_as_str", since = "1.7.0")]
778 pub fn as_str(&self) -> &str {
782 /// Converts a `String` into a mutable string slice.
789 /// let mut s = String::from("foobar");
790 /// let s_mut_str = s.as_mut_str();
792 /// s_mut_str.make_ascii_uppercase();
794 /// assert_eq!("FOOBAR", s_mut_str);
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`]
849 /// Panics if the new capacity overflows [`usize`].
851 /// [`reserve_exact`]: struct.String.html#method.reserve_exact
852 /// [`usize`]: ../../std/primitive.usize.html
859 /// let mut s = String::new();
863 /// assert!(s.capacity() >= 10);
866 /// This may not actually increase the capacity:
869 /// let mut s = String::with_capacity(10);
873 /// // s now has a length of 2 and a capacity of 10
874 /// assert_eq!(2, s.len());
875 /// assert_eq!(10, s.capacity());
877 /// // Since we already have an extra 8 capacity, calling this...
880 /// // ... doesn't actually increase.
881 /// assert_eq!(10, s.capacity());
884 #[stable(feature = "rust1", since = "1.0.0")]
885 pub fn reserve(&mut self, additional: usize) {
886 self.vec.reserve(additional)
889 /// Ensures that this `String`'s capacity is `additional` bytes
890 /// larger than its length.
892 /// Consider using the [`reserve`] method unless you absolutely know
893 /// better than the allocator.
895 /// [`reserve`]: #method.reserve
899 /// Panics if the new capacity overflows `usize`.
906 /// let mut s = String::new();
908 /// s.reserve_exact(10);
910 /// assert!(s.capacity() >= 10);
913 /// This may not actually increase the capacity:
916 /// let mut s = String::with_capacity(10);
920 /// // s now has a length of 2 and a capacity of 10
921 /// assert_eq!(2, s.len());
922 /// assert_eq!(10, s.capacity());
924 /// // Since we already have an extra 8 capacity, calling this...
925 /// s.reserve_exact(8);
927 /// // ... doesn't actually increase.
928 /// assert_eq!(10, s.capacity());
931 #[stable(feature = "rust1", since = "1.0.0")]
932 pub fn reserve_exact(&mut self, additional: usize) {
933 self.vec.reserve_exact(additional)
936 /// Tries to reserve capacity for at least `additional` more elements to be inserted
937 /// in the given `String`. The collection may reserve more space to avoid
938 /// frequent reallocations. After calling `reserve`, capacity will be
939 /// greater than or equal to `self.len() + additional`. Does nothing if
940 /// capacity is already sufficient.
944 /// If the capacity overflows, or the allocator reports a failure, then an error
950 /// #![feature(try_reserve)]
951 /// use std::collections::CollectionAllocErr;
953 /// fn process_data(data: &str) -> Result<String, CollectionAllocErr> {
954 /// let mut output = String::new();
956 /// // Pre-reserve the memory, exiting if we can't
957 /// output.try_reserve(data.len())?;
959 /// // Now we know this can't OOM in the middle of our complex work
960 /// output.push_str(data);
964 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
966 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
967 pub fn try_reserve(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
968 self.vec.try_reserve(additional)
971 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
972 /// be inserted in the given `String`. After calling `reserve_exact`,
973 /// capacity will be greater than or equal to `self.len() + additional`.
974 /// Does nothing if the capacity is already sufficient.
976 /// Note that the allocator may give the collection more space than it
977 /// requests. Therefore capacity can not be relied upon to be precisely
978 /// minimal. Prefer `reserve` if future insertions are expected.
982 /// If the capacity overflows, or the allocator reports a failure, then an error
988 /// #![feature(try_reserve)]
989 /// use std::collections::CollectionAllocErr;
991 /// fn process_data(data: &str) -> Result<String, CollectionAllocErr> {
992 /// let mut output = String::new();
994 /// // Pre-reserve the memory, exiting if we can't
995 /// output.try_reserve(data.len())?;
997 /// // Now we know this can't OOM in the middle of our complex work
998 /// output.push_str(data);
1002 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1004 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
1005 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
1006 self.vec.try_reserve_exact(additional)
1009 /// Shrinks the capacity of this `String` to match its length.
1016 /// let mut s = String::from("foo");
1019 /// assert!(s.capacity() >= 100);
1021 /// s.shrink_to_fit();
1022 /// assert_eq!(3, s.capacity());
1025 #[stable(feature = "rust1", since = "1.0.0")]
1026 pub fn shrink_to_fit(&mut self) {
1027 self.vec.shrink_to_fit()
1030 /// Shrinks the capacity of this `String` with a lower bound.
1032 /// The capacity will remain at least as large as both the length
1033 /// and the supplied value.
1035 /// Panics if the current capacity is smaller than the supplied
1036 /// minimum capacity.
1041 /// #![feature(shrink_to)]
1042 /// let mut s = String::from("foo");
1045 /// assert!(s.capacity() >= 100);
1047 /// s.shrink_to(10);
1048 /// assert!(s.capacity() >= 10);
1050 /// assert!(s.capacity() >= 3);
1053 #[unstable(feature = "shrink_to", reason = "new API", issue="56431")]
1054 pub fn shrink_to(&mut self, min_capacity: usize) {
1055 self.vec.shrink_to(min_capacity)
1058 /// Appends the given [`char`] to the end of this `String`.
1060 /// [`char`]: ../../std/primitive.char.html
1067 /// let mut s = String::from("abc");
1073 /// assert_eq!("abc123", s);
1076 #[stable(feature = "rust1", since = "1.0.0")]
1077 pub fn push(&mut self, ch: char) {
1078 match ch.len_utf8() {
1079 1 => self.vec.push(ch as u8),
1080 _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
1084 /// Returns a byte slice of this `String`'s contents.
1086 /// The inverse of this method is [`from_utf8`].
1088 /// [`from_utf8`]: #method.from_utf8
1095 /// let s = String::from("hello");
1097 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
1100 #[stable(feature = "rust1", since = "1.0.0")]
1101 pub fn as_bytes(&self) -> &[u8] {
1105 /// Shortens this `String` to the specified length.
1107 /// If `new_len` is greater than the string's current length, this has no
1110 /// Note that this method has no effect on the allocated capacity
1115 /// Panics if `new_len` does not lie on a [`char`] boundary.
1117 /// [`char`]: ../../std/primitive.char.html
1124 /// let mut s = String::from("hello");
1128 /// assert_eq!("he", s);
1131 #[stable(feature = "rust1", since = "1.0.0")]
1132 pub fn truncate(&mut self, new_len: usize) {
1133 if new_len <= self.len() {
1134 assert!(self.is_char_boundary(new_len));
1135 self.vec.truncate(new_len)
1139 /// Removes the last character from the string buffer and returns it.
1141 /// Returns [`None`] if this `String` is empty.
1143 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1150 /// let mut s = String::from("foo");
1152 /// assert_eq!(s.pop(), Some('o'));
1153 /// assert_eq!(s.pop(), Some('o'));
1154 /// assert_eq!(s.pop(), Some('f'));
1156 /// assert_eq!(s.pop(), None);
1159 #[stable(feature = "rust1", since = "1.0.0")]
1160 pub fn pop(&mut self) -> Option<char> {
1161 let ch = self.chars().rev().next()?;
1162 let newlen = self.len() - ch.len_utf8();
1164 self.vec.set_len(newlen);
1169 /// Removes a [`char`] from this `String` at a byte position and returns it.
1171 /// This is an `O(n)` operation, as it requires copying every element in the
1176 /// Panics if `idx` is larger than or equal to the `String`'s length,
1177 /// or if it does not lie on a [`char`] boundary.
1179 /// [`char`]: ../../std/primitive.char.html
1186 /// let mut s = String::from("foo");
1188 /// assert_eq!(s.remove(0), 'f');
1189 /// assert_eq!(s.remove(1), 'o');
1190 /// assert_eq!(s.remove(0), 'o');
1193 #[stable(feature = "rust1", since = "1.0.0")]
1194 pub fn remove(&mut self, idx: usize) -> char {
1195 let ch = match self[idx..].chars().next() {
1197 None => panic!("cannot remove a char from the end of a string"),
1200 let next = idx + ch.len_utf8();
1201 let len = self.len();
1203 ptr::copy(self.vec.as_ptr().add(next),
1204 self.vec.as_mut_ptr().add(idx),
1206 self.vec.set_len(len - (next - idx));
1211 /// Retains only the characters specified by the predicate.
1213 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1214 /// This method operates in place and preserves the order of the retained
1220 /// let mut s = String::from("f_o_ob_ar");
1222 /// s.retain(|c| c != '_');
1224 /// assert_eq!(s, "foobar");
1227 #[stable(feature = "string_retain", since = "1.26.0")]
1228 pub fn retain<F>(&mut self, mut f: F)
1229 where F: FnMut(char) -> bool
1231 let len = self.len();
1232 let mut del_bytes = 0;
1237 self.get_unchecked(idx..len).chars().next().unwrap()
1239 let ch_len = ch.len_utf8();
1242 del_bytes += ch_len;
1243 } else if del_bytes > 0 {
1245 ptr::copy(self.vec.as_ptr().add(idx),
1246 self.vec.as_mut_ptr().add(idx - del_bytes),
1251 // Point idx to the next char
1256 unsafe { self.vec.set_len(len - del_bytes); }
1260 /// Inserts a character into this `String` at a byte position.
1262 /// This is an `O(n)` operation as it requires copying every element in the
1267 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1268 /// lie on a [`char`] boundary.
1270 /// [`char`]: ../../std/primitive.char.html
1277 /// let mut s = String::with_capacity(3);
1279 /// s.insert(0, 'f');
1280 /// s.insert(1, 'o');
1281 /// s.insert(2, 'o');
1283 /// assert_eq!("foo", s);
1286 #[stable(feature = "rust1", since = "1.0.0")]
1287 pub fn insert(&mut self, idx: usize, ch: char) {
1288 assert!(self.is_char_boundary(idx));
1289 let mut bits = [0; 4];
1290 let bits = ch.encode_utf8(&mut bits).as_bytes();
1293 self.insert_bytes(idx, bits);
1297 unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1298 let len = self.len();
1299 let amt = bytes.len();
1300 self.vec.reserve(amt);
1302 ptr::copy(self.vec.as_ptr().add(idx),
1303 self.vec.as_mut_ptr().add(idx + amt),
1305 ptr::copy(bytes.as_ptr(),
1306 self.vec.as_mut_ptr().add(idx),
1308 self.vec.set_len(len + amt);
1311 /// Inserts a string slice into this `String` at a byte position.
1313 /// This is an `O(n)` operation as it requires copying every element in the
1318 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1319 /// lie on a [`char`] boundary.
1321 /// [`char`]: ../../std/primitive.char.html
1328 /// let mut s = String::from("bar");
1330 /// s.insert_str(0, "foo");
1332 /// assert_eq!("foobar", s);
1335 #[stable(feature = "insert_str", since = "1.16.0")]
1336 pub fn insert_str(&mut self, idx: usize, string: &str) {
1337 assert!(self.is_char_boundary(idx));
1340 self.insert_bytes(idx, string.as_bytes());
1344 /// Returns a mutable reference to the contents of this `String`.
1348 /// This function is unsafe because it does not check that the bytes passed
1349 /// to it are valid UTF-8. If this constraint is violated, it may cause
1350 /// memory unsafety issues with future users of the `String`, as the rest of
1351 /// the standard library assumes that `String`s are valid UTF-8.
1358 /// let mut s = String::from("hello");
1361 /// let vec = s.as_mut_vec();
1362 /// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1366 /// assert_eq!(s, "olleh");
1369 #[stable(feature = "rust1", since = "1.0.0")]
1370 pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1374 /// Returns the length of this `String`, in bytes.
1381 /// let a = String::from("foo");
1383 /// assert_eq!(a.len(), 3);
1386 #[stable(feature = "rust1", since = "1.0.0")]
1387 pub fn len(&self) -> usize {
1391 /// Returns `true` if this `String` has a length of zero.
1393 /// Returns `false` otherwise.
1400 /// let mut v = String::new();
1401 /// assert!(v.is_empty());
1404 /// assert!(!v.is_empty());
1407 #[stable(feature = "rust1", since = "1.0.0")]
1408 pub fn is_empty(&self) -> bool {
1412 /// Splits the string into two at the given index.
1414 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1415 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1416 /// boundary of a UTF-8 code point.
1418 /// Note that the capacity of `self` does not change.
1422 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1423 /// code point of the string.
1429 /// let mut hello = String::from("Hello, World!");
1430 /// let world = hello.split_off(7);
1431 /// assert_eq!(hello, "Hello, ");
1432 /// assert_eq!(world, "World!");
1436 #[stable(feature = "string_split_off", since = "1.16.0")]
1437 pub fn split_off(&mut self, at: usize) -> String {
1438 assert!(self.is_char_boundary(at));
1439 let other = self.vec.split_off(at);
1440 unsafe { String::from_utf8_unchecked(other) }
1443 /// Truncates this `String`, removing all contents.
1445 /// While this means the `String` will have a length of zero, it does not
1446 /// touch its capacity.
1453 /// let mut s = String::from("foo");
1457 /// assert!(s.is_empty());
1458 /// assert_eq!(0, s.len());
1459 /// assert_eq!(3, s.capacity());
1462 #[stable(feature = "rust1", since = "1.0.0")]
1463 pub fn clear(&mut self) {
1467 /// Creates a draining iterator that removes the specified range in the `String`
1468 /// and yields the removed `chars`.
1470 /// Note: The element range is removed even if the iterator is not
1471 /// consumed until the end.
1475 /// Panics if the starting point or end point do not lie on a [`char`]
1476 /// boundary, or if they're out of bounds.
1478 /// [`char`]: ../../std/primitive.char.html
1485 /// let mut s = String::from("α is alpha, β is beta");
1486 /// let beta_offset = s.find('β').unwrap_or(s.len());
1488 /// // Remove the range up until the β from the string
1489 /// let t: String = s.drain(..beta_offset).collect();
1490 /// assert_eq!(t, "α is alpha, ");
1491 /// assert_eq!(s, "β is beta");
1493 /// // A full range clears the string
1495 /// assert_eq!(s, "");
1497 #[stable(feature = "drain", since = "1.6.0")]
1498 pub fn drain<R>(&mut self, range: R) -> Drain
1499 where R: RangeBounds<usize>
1503 // The String version of Drain does not have the memory safety issues
1504 // of the vector version. The data is just plain bytes.
1505 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1506 // the removal will not happen.
1507 let len = self.len();
1508 let start = match range.start_bound() {
1510 Excluded(&n) => n + 1,
1513 let end = match range.end_bound() {
1514 Included(&n) => n + 1,
1519 // Take out two simultaneous borrows. The &mut String won't be accessed
1520 // until iteration is over, in Drop.
1521 let self_ptr = self as *mut _;
1522 // slicing does the appropriate bounds checks
1523 let chars_iter = self[start..end].chars();
1533 /// Removes the specified range in the string,
1534 /// and replaces it with the given string.
1535 /// The given string doesn't need to be the same length as the range.
1539 /// Panics if the starting point or end point do not lie on a [`char`]
1540 /// boundary, or if they're out of bounds.
1542 /// [`char`]: ../../std/primitive.char.html
1543 /// [`Vec::splice`]: ../../std/vec/struct.Vec.html#method.splice
1550 /// let mut s = String::from("α is alpha, β is beta");
1551 /// let beta_offset = s.find('β').unwrap_or(s.len());
1553 /// // Replace the range up until the β from the string
1554 /// s.replace_range(..beta_offset, "Α is capital alpha; ");
1555 /// assert_eq!(s, "Α is capital alpha; β is beta");
1557 #[stable(feature = "splice", since = "1.27.0")]
1558 pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
1559 where R: RangeBounds<usize>
1563 // Replace_range does not have the memory safety issues of a vector Splice.
1564 // of the vector version. The data is just plain bytes.
1566 match range.start_bound() {
1567 Included(&n) => assert!(self.is_char_boundary(n)),
1568 Excluded(&n) => assert!(self.is_char_boundary(n + 1)),
1571 match range.end_bound() {
1572 Included(&n) => assert!(self.is_char_boundary(n + 1)),
1573 Excluded(&n) => assert!(self.is_char_boundary(n)),
1579 }.splice(range, replace_with.bytes());
1582 /// Converts this `String` into a [`Box`]`<`[`str`]`>`.
1584 /// This will drop any excess capacity.
1586 /// [`Box`]: ../../std/boxed/struct.Box.html
1587 /// [`str`]: ../../std/primitive.str.html
1594 /// let s = String::from("hello");
1596 /// let b = s.into_boxed_str();
1598 #[stable(feature = "box_str", since = "1.4.0")]
1600 pub fn into_boxed_str(self) -> Box<str> {
1601 let slice = self.vec.into_boxed_slice();
1602 unsafe { from_boxed_utf8_unchecked(slice) }
1606 impl FromUtf8Error {
1607 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1614 /// // some invalid bytes, in a vector
1615 /// let bytes = vec![0, 159];
1617 /// let value = String::from_utf8(bytes);
1619 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1621 #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
1622 pub fn as_bytes(&self) -> &[u8] {
1626 /// Returns the bytes that were attempted to convert to a `String`.
1628 /// This method is carefully constructed to avoid allocation. It will
1629 /// consume the error, moving out the bytes, so that a copy of the bytes
1630 /// does not need to be made.
1637 /// // some invalid bytes, in a vector
1638 /// let bytes = vec![0, 159];
1640 /// let value = String::from_utf8(bytes);
1642 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1644 #[stable(feature = "rust1", since = "1.0.0")]
1645 pub fn into_bytes(self) -> Vec<u8> {
1649 /// Fetch a `Utf8Error` to get more details about the conversion failure.
1651 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1652 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1653 /// an analogue to `FromUtf8Error`. See its documentation for more details
1656 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
1657 /// [`std::str`]: ../../std/str/index.html
1658 /// [`u8`]: ../../std/primitive.u8.html
1659 /// [`&str`]: ../../std/primitive.str.html
1666 /// // some invalid bytes, in a vector
1667 /// let bytes = vec![0, 159];
1669 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1671 /// // the first byte is invalid here
1672 /// assert_eq!(1, error.valid_up_to());
1674 #[stable(feature = "rust1", since = "1.0.0")]
1675 pub fn utf8_error(&self) -> Utf8Error {
1680 #[stable(feature = "rust1", since = "1.0.0")]
1681 impl fmt::Display for FromUtf8Error {
1682 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1683 fmt::Display::fmt(&self.error, f)
1687 #[stable(feature = "rust1", since = "1.0.0")]
1688 impl fmt::Display for FromUtf16Error {
1689 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1690 fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
1694 #[stable(feature = "rust1", since = "1.0.0")]
1695 impl Clone for String {
1696 fn clone(&self) -> Self {
1697 String { vec: self.vec.clone() }
1700 fn clone_from(&mut self, source: &Self) {
1701 self.vec.clone_from(&source.vec);
1705 #[stable(feature = "rust1", since = "1.0.0")]
1706 impl FromIterator<char> for String {
1707 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
1708 let mut buf = String::new();
1714 #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
1715 impl<'a> FromIterator<&'a char> for String {
1716 fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
1717 let mut buf = String::new();
1723 #[stable(feature = "rust1", since = "1.0.0")]
1724 impl<'a> FromIterator<&'a str> for String {
1725 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
1726 let mut buf = String::new();
1732 #[stable(feature = "extend_string", since = "1.4.0")]
1733 impl FromIterator<String> for String {
1734 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
1735 let mut buf = String::new();
1741 #[stable(feature = "herd_cows", since = "1.19.0")]
1742 impl<'a> FromIterator<Cow<'a, str>> for String {
1743 fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
1744 let mut buf = String::new();
1750 #[stable(feature = "rust1", since = "1.0.0")]
1751 impl Extend<char> for String {
1752 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
1753 let iterator = iter.into_iter();
1754 let (lower_bound, _) = iterator.size_hint();
1755 self.reserve(lower_bound);
1756 for ch in iterator {
1762 #[stable(feature = "extend_ref", since = "1.2.0")]
1763 impl<'a> Extend<&'a char> for String {
1764 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
1765 self.extend(iter.into_iter().cloned());
1769 #[stable(feature = "rust1", since = "1.0.0")]
1770 impl<'a> Extend<&'a str> for String {
1771 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
1778 #[stable(feature = "extend_string", since = "1.4.0")]
1779 impl Extend<String> for String {
1780 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
1787 #[stable(feature = "herd_cows", since = "1.19.0")]
1788 impl<'a> Extend<Cow<'a, str>> for String {
1789 fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
1796 /// A convenience impl that delegates to the impl for `&str`
1797 #[unstable(feature = "pattern",
1798 reason = "API not fully fleshed out and ready to be stabilized",
1800 impl<'a, 'b> Pattern<'a> for &'b String {
1801 type Searcher = <&'b str as Pattern<'a>>::Searcher;
1803 fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
1804 self[..].into_searcher(haystack)
1808 fn is_contained_in(self, haystack: &'a str) -> bool {
1809 self[..].is_contained_in(haystack)
1813 fn is_prefix_of(self, haystack: &'a str) -> bool {
1814 self[..].is_prefix_of(haystack)
1818 #[stable(feature = "rust1", since = "1.0.0")]
1819 impl PartialEq for String {
1821 fn eq(&self, other: &String) -> bool {
1822 PartialEq::eq(&self[..], &other[..])
1825 fn ne(&self, other: &String) -> bool {
1826 PartialEq::ne(&self[..], &other[..])
1830 macro_rules! impl_eq {
1831 ($lhs:ty, $rhs: ty) => {
1832 #[stable(feature = "rust1", since = "1.0.0")]
1833 impl<'a, 'b> PartialEq<$rhs> for $lhs {
1835 fn eq(&self, other: &$rhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1837 fn ne(&self, other: &$rhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1840 #[stable(feature = "rust1", since = "1.0.0")]
1841 impl<'a, 'b> PartialEq<$lhs> for $rhs {
1843 fn eq(&self, other: &$lhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1845 fn ne(&self, other: &$lhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1851 impl_eq! { String, str }
1852 impl_eq! { String, &'a str }
1853 impl_eq! { Cow<'a, str>, str }
1854 impl_eq! { Cow<'a, str>, &'b str }
1855 impl_eq! { Cow<'a, str>, String }
1857 #[stable(feature = "rust1", since = "1.0.0")]
1858 impl Default for String {
1859 /// Creates an empty `String`.
1861 fn default() -> String {
1866 #[stable(feature = "rust1", since = "1.0.0")]
1867 impl fmt::Display for String {
1869 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1870 fmt::Display::fmt(&**self, f)
1874 #[stable(feature = "rust1", since = "1.0.0")]
1875 impl fmt::Debug for String {
1877 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1878 fmt::Debug::fmt(&**self, f)
1882 #[stable(feature = "rust1", since = "1.0.0")]
1883 impl hash::Hash for String {
1885 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
1886 (**self).hash(hasher)
1890 /// Implements the `+` operator for concatenating two strings.
1892 /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
1893 /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
1894 /// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by
1895 /// repeated concatenation.
1897 /// The string on the right-hand side is only borrowed; its contents are copied into the returned
1902 /// Concatenating two `String`s takes the first by value and borrows the second:
1905 /// let a = String::from("hello");
1906 /// let b = String::from(" world");
1908 /// // `a` is moved and can no longer be used here.
1911 /// If you want to keep using the first `String`, you can clone it and append to the clone instead:
1914 /// let a = String::from("hello");
1915 /// let b = String::from(" world");
1916 /// let c = a.clone() + &b;
1917 /// // `a` is still valid here.
1920 /// Concatenating `&str` slices can be done by converting the first to a `String`:
1923 /// let a = "hello";
1924 /// let b = " world";
1925 /// let c = a.to_string() + b;
1927 #[stable(feature = "rust1", since = "1.0.0")]
1928 impl<'a> Add<&'a str> for String {
1929 type Output = String;
1932 fn add(mut self, other: &str) -> String {
1933 self.push_str(other);
1938 /// Implements the `+=` operator for appending to a `String`.
1940 /// This has the same behavior as the [`push_str`][String::push_str] method.
1941 #[stable(feature = "stringaddassign", since = "1.12.0")]
1942 impl<'a> AddAssign<&'a str> for String {
1944 fn add_assign(&mut self, other: &str) {
1945 self.push_str(other);
1949 #[stable(feature = "rust1", since = "1.0.0")]
1950 impl ops::Index<ops::Range<usize>> for String {
1954 fn index(&self, index: ops::Range<usize>) -> &str {
1958 #[stable(feature = "rust1", since = "1.0.0")]
1959 impl ops::Index<ops::RangeTo<usize>> for String {
1963 fn index(&self, index: ops::RangeTo<usize>) -> &str {
1967 #[stable(feature = "rust1", since = "1.0.0")]
1968 impl ops::Index<ops::RangeFrom<usize>> for String {
1972 fn index(&self, index: ops::RangeFrom<usize>) -> &str {
1976 #[stable(feature = "rust1", since = "1.0.0")]
1977 impl ops::Index<ops::RangeFull> for String {
1981 fn index(&self, _index: ops::RangeFull) -> &str {
1982 unsafe { str::from_utf8_unchecked(&self.vec) }
1985 #[stable(feature = "inclusive_range", since = "1.26.0")]
1986 impl ops::Index<ops::RangeInclusive<usize>> for String {
1990 fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
1991 Index::index(&**self, index)
1994 #[stable(feature = "inclusive_range", since = "1.26.0")]
1995 impl ops::Index<ops::RangeToInclusive<usize>> for String {
1999 fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
2000 Index::index(&**self, index)
2004 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2005 impl ops::IndexMut<ops::Range<usize>> for String {
2007 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
2008 &mut self[..][index]
2011 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2012 impl ops::IndexMut<ops::RangeTo<usize>> for String {
2014 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
2015 &mut self[..][index]
2018 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2019 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
2021 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
2022 &mut self[..][index]
2025 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2026 impl ops::IndexMut<ops::RangeFull> for String {
2028 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
2029 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2032 #[stable(feature = "inclusive_range", since = "1.26.0")]
2033 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
2035 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
2036 IndexMut::index_mut(&mut **self, index)
2039 #[stable(feature = "inclusive_range", since = "1.26.0")]
2040 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
2042 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
2043 IndexMut::index_mut(&mut **self, index)
2047 #[stable(feature = "rust1", since = "1.0.0")]
2048 impl ops::Deref for String {
2052 fn deref(&self) -> &str {
2053 unsafe { str::from_utf8_unchecked(&self.vec) }
2057 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2058 impl ops::DerefMut for String {
2060 fn deref_mut(&mut self) -> &mut str {
2061 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2065 /// An error when parsing a `String`.
2067 /// This `enum` is slightly awkward: it will never actually exist. This error is
2068 /// part of the type signature of the implementation of [`FromStr`] on
2069 /// [`String`]. The return type of [`from_str`], requires that an error be
2070 /// defined, but, given that a [`String`] can always be made into a new
2071 /// [`String`] without error, this type will never actually be returned. As
2072 /// such, it is only here to satisfy said signature, and is useless otherwise.
2074 /// [`FromStr`]: ../../std/str/trait.FromStr.html
2075 /// [`String`]: struct.String.html
2076 /// [`from_str`]: ../../std/str/trait.FromStr.html#tymethod.from_str
2077 #[stable(feature = "str_parse_error", since = "1.5.0")]
2079 pub enum ParseError {}
2081 #[stable(feature = "rust1", since = "1.0.0")]
2082 impl FromStr for String {
2083 type Err = ParseError;
2085 fn from_str(s: &str) -> Result<String, ParseError> {
2090 #[stable(feature = "str_parse_error", since = "1.5.0")]
2091 impl Clone for ParseError {
2092 fn clone(&self) -> ParseError {
2097 #[stable(feature = "str_parse_error", since = "1.5.0")]
2098 impl fmt::Debug for ParseError {
2099 fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
2104 #[stable(feature = "str_parse_error2", since = "1.8.0")]
2105 impl fmt::Display for ParseError {
2106 fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
2111 #[stable(feature = "str_parse_error", since = "1.5.0")]
2112 impl PartialEq for ParseError {
2113 fn eq(&self, _: &ParseError) -> bool {
2118 #[stable(feature = "str_parse_error", since = "1.5.0")]
2119 impl Eq for ParseError {}
2121 /// A trait for converting a value to a `String`.
2123 /// This trait is automatically implemented for any type which implements the
2124 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
2125 /// [`Display`] should be implemented instead, and you get the `ToString`
2126 /// implementation for free.
2128 /// [`Display`]: ../../std/fmt/trait.Display.html
2129 #[stable(feature = "rust1", since = "1.0.0")]
2130 pub trait ToString {
2131 /// Converts the given value to a `String`.
2139 /// let five = String::from("5");
2141 /// assert_eq!(five, i.to_string());
2143 #[rustc_conversion_suggestion]
2144 #[stable(feature = "rust1", since = "1.0.0")]
2145 fn to_string(&self) -> String;
2150 /// In this implementation, the `to_string` method panics
2151 /// if the `Display` implementation returns an error.
2152 /// This indicates an incorrect `Display` implementation
2153 /// since `fmt::Write for String` never returns an error itself.
2154 #[stable(feature = "rust1", since = "1.0.0")]
2155 impl<T: fmt::Display + ?Sized> ToString for T {
2157 default fn to_string(&self) -> String {
2158 use core::fmt::Write;
2159 let mut buf = String::new();
2160 buf.write_fmt(format_args!("{}", self))
2161 .expect("a Display implementation return an error unexpectedly");
2162 buf.shrink_to_fit();
2167 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
2168 impl ToString for str {
2170 fn to_string(&self) -> String {
2175 #[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
2176 impl<'a> ToString for Cow<'a, str> {
2178 fn to_string(&self) -> String {
2183 #[stable(feature = "string_to_string_specialization", since = "1.17.0")]
2184 impl ToString for String {
2186 fn to_string(&self) -> String {
2191 #[stable(feature = "rust1", since = "1.0.0")]
2192 impl AsRef<str> for String {
2194 fn as_ref(&self) -> &str {
2199 #[stable(feature = "rust1", since = "1.0.0")]
2200 impl AsRef<[u8]> for String {
2202 fn as_ref(&self) -> &[u8] {
2207 #[stable(feature = "rust1", since = "1.0.0")]
2208 impl<'a> From<&'a str> for String {
2210 fn from(s: &'a str) -> String {
2215 // note: test pulls in libstd, which causes errors here
2217 #[stable(feature = "string_from_box", since = "1.18.0")]
2218 impl From<Box<str>> for String {
2219 /// Converts the given boxed `str` slice to a `String`.
2220 /// It is notable that the `str` slice is owned.
2227 /// let s1: String = String::from("hello world");
2228 /// let s2: Box<str> = s1.into_boxed_str();
2229 /// let s3: String = String::from(s2);
2231 /// assert_eq!("hello world", s3)
2233 fn from(s: Box<str>) -> String {
2238 #[stable(feature = "box_from_str", since = "1.20.0")]
2239 impl From<String> for Box<str> {
2240 /// Converts the given `String` to a boxed `str` slice that is owned.
2247 /// let s1: String = String::from("hello world");
2248 /// let s2: Box<str> = Box::from(s1);
2249 /// let s3: String = String::from(s2);
2251 /// assert_eq!("hello world", s3)
2253 fn from(s: String) -> Box<str> {
2258 #[stable(feature = "string_from_cow_str", since = "1.14.0")]
2259 impl<'a> From<Cow<'a, str>> for String {
2260 fn from(s: Cow<'a, str>) -> String {
2265 #[stable(feature = "rust1", since = "1.0.0")]
2266 impl<'a> From<&'a str> for Cow<'a, str> {
2268 fn from(s: &'a str) -> Cow<'a, str> {
2273 #[stable(feature = "rust1", since = "1.0.0")]
2274 impl<'a> From<String> for Cow<'a, str> {
2276 fn from(s: String) -> Cow<'a, str> {
2281 #[stable(feature = "cow_from_string_ref", since = "1.28.0")]
2282 impl<'a> From<&'a String> for Cow<'a, str> {
2284 fn from(s: &'a String) -> Cow<'a, str> {
2285 Cow::Borrowed(s.as_str())
2289 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2290 impl<'a> FromIterator<char> for Cow<'a, str> {
2291 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
2292 Cow::Owned(FromIterator::from_iter(it))
2296 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2297 impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
2298 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
2299 Cow::Owned(FromIterator::from_iter(it))
2303 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2304 impl<'a> FromIterator<String> for Cow<'a, str> {
2305 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
2306 Cow::Owned(FromIterator::from_iter(it))
2310 #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
2311 impl From<String> for Vec<u8> {
2312 /// Converts the given `String` to a vector `Vec` that holds values of type `u8`.
2319 /// let s1 = String::from("hello world");
2320 /// let v1 = Vec::from(s1);
2323 /// println!("{}", b);
2326 fn from(string: String) -> Vec<u8> {
2331 #[stable(feature = "rust1", since = "1.0.0")]
2332 impl fmt::Write for String {
2334 fn write_str(&mut self, s: &str) -> fmt::Result {
2340 fn write_char(&mut self, c: char) -> fmt::Result {
2346 /// A draining iterator for `String`.
2348 /// This struct is created by the [`drain`] method on [`String`]. See its
2349 /// documentation for more.
2351 /// [`drain`]: struct.String.html#method.drain
2352 /// [`String`]: struct.String.html
2353 #[stable(feature = "drain", since = "1.6.0")]
2354 pub struct Drain<'a> {
2355 /// Will be used as &'a mut String in the destructor
2356 string: *mut String,
2357 /// Start of part to remove
2359 /// End of part to remove
2361 /// Current remaining range to remove
2365 #[stable(feature = "collection_debug", since = "1.17.0")]
2366 impl<'a> fmt::Debug for Drain<'a> {
2367 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2368 f.pad("Drain { .. }")
2372 #[stable(feature = "drain", since = "1.6.0")]
2373 unsafe impl<'a> Sync for Drain<'a> {}
2374 #[stable(feature = "drain", since = "1.6.0")]
2375 unsafe impl<'a> Send for Drain<'a> {}
2377 #[stable(feature = "drain", since = "1.6.0")]
2378 impl<'a> Drop for Drain<'a> {
2379 fn drop(&mut self) {
2381 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
2382 // panic code being inserted again.
2383 let self_vec = (*self.string).as_mut_vec();
2384 if self.start <= self.end && self.end <= self_vec.len() {
2385 self_vec.drain(self.start..self.end);
2391 #[stable(feature = "drain", since = "1.6.0")]
2392 impl<'a> Iterator for Drain<'a> {
2396 fn next(&mut self) -> Option<char> {
2400 fn size_hint(&self) -> (usize, Option<usize>) {
2401 self.iter.size_hint()
2405 #[stable(feature = "drain", since = "1.6.0")]
2406 impl<'a> DoubleEndedIterator for Drain<'a> {
2408 fn next_back(&mut self) -> Option<char> {
2409 self.iter.next_back()
2413 #[stable(feature = "fused", since = "1.26.0")]
2414 impl<'a> FusedIterator for Drain<'a> {}