1 //! A UTF-8 encoded, growable string.
3 //! This module contains the [`String`] type, a trait for converting
4 //! [`ToString`]s, and several error types that may result from working with
7 //! [`ToString`]: trait.ToString.html
11 //! There are multiple ways to create a new [`String`] from a string literal:
14 //! let s = "Hello".to_string();
16 //! let s = String::from("world");
17 //! let s: String = "also this".into();
20 //! You can create a new [`String`] from an existing one by concatenating with
23 //! [`String`]: struct.String.html
26 //! let s = "Hello".to_string();
28 //! let message = s + " world!";
31 //! If you have a vector of valid UTF-8 bytes, you can make a [`String`] out of
32 //! it. You can do the reverse too.
35 //! let sparkle_heart = vec![240, 159, 146, 150];
37 //! // We know these bytes are valid, so we'll use `unwrap()`.
38 //! let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
40 //! assert_eq!("💖", sparkle_heart);
42 //! let bytes = sparkle_heart.into_bytes();
44 //! assert_eq!(bytes, [240, 159, 146, 150]);
47 #![stable(feature = "rust1", since = "1.0.0")]
49 use core::char::{decode_utf16, REPLACEMENT_CHARACTER};
52 use core::iter::{FromIterator, FusedIterator};
53 use core::ops::{self, Add, AddAssign, Index, IndexMut, RangeBounds};
54 use core::ops::Bound::{Excluded, Included, Unbounded};
56 use core::str::{pattern::Pattern, lossy};
58 use crate::borrow::{Cow, ToOwned};
59 use crate::collections::TryReserveError;
60 use crate::boxed::Box;
61 use crate::str::{self, from_boxed_utf8_unchecked, FromStr, Utf8Error, Chars};
64 /// A UTF-8 encoded, growable string.
66 /// The `String` type is the most common string type that has ownership over the
67 /// contents of the string. It has a close relationship with its borrowed
68 /// counterpart, the primitive [`str`].
70 /// [`str`]: ../../std/primitive.str.html
74 /// You can create a `String` from a literal string with [`String::from`]:
77 /// let hello = String::from("Hello, world!");
80 /// You can append a [`char`] to a `String` with the [`push`] method, and
81 /// append a [`&str`] with the [`push_str`] method:
84 /// let mut hello = String::from("Hello, ");
87 /// hello.push_str("orld!");
90 /// [`String::from`]: #method.from
91 /// [`char`]: ../../std/primitive.char.html
92 /// [`push`]: #method.push
93 /// [`push_str`]: #method.push_str
95 /// If you have a vector of UTF-8 bytes, you can create a `String` from it with
96 /// the [`from_utf8`] method:
99 /// // some bytes, in a vector
100 /// let sparkle_heart = vec![240, 159, 146, 150];
102 /// // We know these bytes are valid, so we'll use `unwrap()`.
103 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
105 /// assert_eq!("💖", sparkle_heart);
108 /// [`from_utf8`]: #method.from_utf8
112 /// `String`s are always valid UTF-8. This has a few implications, the first of
113 /// which is that if you need a non-UTF-8 string, consider [`OsString`]. It is
114 /// similar, but without the UTF-8 constraint. The second implication is that
115 /// you cannot index into a `String`:
117 /// ```compile_fail,E0277
120 /// println!("The first letter of s is {}", s[0]); // ERROR!!!
123 /// [`OsString`]: ../../std/ffi/struct.OsString.html
125 /// Indexing is intended to be a constant-time operation, but UTF-8 encoding
126 /// does not allow us to do this. Furthermore, it's not clear what sort of
127 /// thing the index should return: a byte, a codepoint, or a grapheme cluster.
128 /// The [`bytes`] and [`chars`] methods return iterators over the first
129 /// two, respectively.
131 /// [`bytes`]: #method.bytes
132 /// [`chars`]: #method.chars
136 /// `String`s implement [`Deref`]`<Target=str>`, and so inherit all of [`str`]'s
137 /// methods. In addition, this means that you can pass a `String` to a
138 /// function which takes a [`&str`] by using an ampersand (`&`):
141 /// fn takes_str(s: &str) { }
143 /// let s = String::from("Hello");
148 /// This will create a [`&str`] from the `String` and pass it in. This
149 /// conversion is very inexpensive, and so generally, functions will accept
150 /// [`&str`]s as arguments unless they need a `String` for some specific
153 /// In certain cases Rust doesn't have enough information to make this
154 /// conversion, known as [`Deref`] coercion. In the following example a string
155 /// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
156 /// `example_func` takes anything that implements the trait. In this case Rust
157 /// would need to make two implicit conversions, which Rust doesn't have the
158 /// means to do. For that reason, the following example will not compile.
160 /// ```compile_fail,E0277
161 /// trait TraitExample {}
163 /// impl<'a> TraitExample for &'a str {}
165 /// fn example_func<A: TraitExample>(example_arg: A) {}
167 /// let example_string = String::from("example_string");
168 /// example_func(&example_string);
171 /// There are two options that would work instead. The first would be to
172 /// change the line `example_func(&example_string);` to
173 /// `example_func(example_string.as_str());`, using the method [`as_str()`]
174 /// to explicitly extract the string slice containing the string. The second
175 /// way changes `example_func(&example_string);` to
176 /// `example_func(&*example_string);`. In this case we are dereferencing a
177 /// `String` to a [`str`][`&str`], then referencing the [`str`][`&str`] back to
178 /// [`&str`]. The second way is more idiomatic, however both work to do the
179 /// conversion explicitly rather than relying on the implicit conversion.
183 /// A `String` is made up of three components: a pointer to some bytes, a
184 /// length, and a capacity. The pointer points to an internal buffer `String`
185 /// uses to store its data. The length is the number of bytes currently stored
186 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
187 /// the length will always be less than or equal to the capacity.
189 /// This buffer is always stored on the heap.
191 /// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
197 /// let story = String::from("Once upon a time...");
199 // FIXME Update this when vec_into_raw_parts is stabilized
200 /// // Prevent automatically dropping the String's data
201 /// let mut story = mem::ManuallyDrop::new(story);
203 /// let ptr = story.as_mut_ptr();
204 /// let len = story.len();
205 /// let capacity = story.capacity();
207 /// // story has nineteen bytes
208 /// assert_eq!(19, len);
210 /// // We can re-build a String out of ptr, len, and capacity. This is all
211 /// // unsafe because we are responsible for making sure the components are
213 /// let s = unsafe { String::from_raw_parts(ptr, len, capacity) } ;
215 /// assert_eq!(String::from("Once upon a time..."), s);
218 /// [`as_ptr`]: #method.as_ptr
219 /// [`len`]: #method.len
220 /// [`capacity`]: #method.capacity
222 /// If a `String` has enough capacity, adding elements to it will not
223 /// re-allocate. For example, consider this program:
226 /// let mut s = String::new();
228 /// println!("{}", s.capacity());
231 /// s.push_str("hello");
232 /// println!("{}", s.capacity());
236 /// This will output the following:
247 /// At first, we have no memory allocated at all, but as we append to the
248 /// string, it increases its capacity appropriately. If we instead use the
249 /// [`with_capacity`] method to allocate the correct capacity initially:
252 /// let mut s = String::with_capacity(25);
254 /// println!("{}", s.capacity());
257 /// s.push_str("hello");
258 /// println!("{}", s.capacity());
262 /// [`with_capacity`]: #method.with_capacity
264 /// We end up with a different output:
275 /// Here, there's no need to allocate more memory inside the loop.
277 /// [`&str`]: ../../std/primitive.str.html
278 /// [`Deref`]: ../../std/ops/trait.Deref.html
279 /// [`as_str()`]: struct.String.html#method.as_str
280 #[derive(PartialOrd, Eq, Ord)]
281 #[stable(feature = "rust1", since = "1.0.0")]
286 /// A possible error value when converting a `String` from a UTF-8 byte vector.
288 /// This type is the error type for the [`from_utf8`] method on [`String`]. It
289 /// is designed in such a way to carefully avoid reallocations: the
290 /// [`into_bytes`] method will give back the byte vector that was used in the
291 /// conversion attempt.
293 /// [`from_utf8`]: struct.String.html#method.from_utf8
294 /// [`String`]: struct.String.html
295 /// [`into_bytes`]: struct.FromUtf8Error.html#method.into_bytes
297 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
298 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
299 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
300 /// through the [`utf8_error`] method.
302 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
303 /// [`std::str`]: ../../std/str/index.html
304 /// [`u8`]: ../../std/primitive.u8.html
305 /// [`&str`]: ../../std/primitive.str.html
306 /// [`utf8_error`]: #method.utf8_error
313 /// // some invalid bytes, in a vector
314 /// let bytes = vec![0, 159];
316 /// let value = String::from_utf8(bytes);
318 /// assert!(value.is_err());
319 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
321 #[stable(feature = "rust1", since = "1.0.0")]
323 pub struct FromUtf8Error {
328 /// A possible error value when converting a `String` from a UTF-16 byte slice.
330 /// This type is the error type for the [`from_utf16`] method on [`String`].
332 /// [`from_utf16`]: struct.String.html#method.from_utf16
333 /// [`String`]: struct.String.html
340 /// // 𝄞mu<invalid>ic
341 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
342 /// 0xD800, 0x0069, 0x0063];
344 /// assert!(String::from_utf16(v).is_err());
346 #[stable(feature = "rust1", since = "1.0.0")]
348 pub struct FromUtf16Error(());
351 /// Creates a new empty `String`.
353 /// Given that the `String` is empty, this will not allocate any initial
354 /// buffer. While that means that this initial operation is very
355 /// inexpensive, it may cause excessive allocation later when you add
356 /// data. If you have an idea of how much data the `String` will hold,
357 /// consider the [`with_capacity`] method to prevent excessive
360 /// [`with_capacity`]: #method.with_capacity
367 /// let s = String::new();
372 rustc_const_stable(feature = "const_string_new", since = "1.32.0"),
374 #[stable(feature = "rust1", since = "1.0.0")]
375 pub const fn new() -> String {
376 String { vec: Vec::new() }
379 /// Creates a new empty `String` with a particular capacity.
381 /// `String`s have an internal buffer to hold their data. The capacity is
382 /// the length of that buffer, and can be queried with the [`capacity`]
383 /// method. This method creates an empty `String`, but one with an initial
384 /// buffer that can hold `capacity` bytes. This is useful when you may be
385 /// appending a bunch of data to the `String`, reducing the number of
386 /// reallocations it needs to do.
388 /// [`capacity`]: #method.capacity
390 /// If the given capacity is `0`, no allocation will occur, and this method
391 /// is identical to the [`new`] method.
393 /// [`new`]: #method.new
400 /// let mut s = String::with_capacity(10);
402 /// // The String contains no chars, even though it has capacity for more
403 /// assert_eq!(s.len(), 0);
405 /// // These are all done without reallocating...
406 /// let cap = s.capacity();
411 /// assert_eq!(s.capacity(), cap);
413 /// // ...but this may make the vector reallocate
417 #[stable(feature = "rust1", since = "1.0.0")]
418 pub fn with_capacity(capacity: usize) -> String {
419 String { vec: Vec::with_capacity(capacity) }
422 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
423 // required for this method definition, is not available. Since we don't
424 // require this method for testing purposes, I'll just stub it
425 // NB see the slice::hack module in slice.rs for more information
428 pub fn from_str(_: &str) -> String {
429 panic!("not available with cfg(test)");
432 /// Converts a vector of bytes to a `String`.
434 /// A string ([`String`]) is made of bytes ([`u8`]), and a vector of bytes
435 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
436 /// two. Not all byte slices are valid `String`s, however: `String`
437 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
438 /// the bytes are valid UTF-8, and then does the conversion.
440 /// If you are sure that the byte slice is valid UTF-8, and you don't want
441 /// to incur the overhead of the validity check, there is an unsafe version
442 /// of this function, [`from_utf8_unchecked`], which has the same behavior
443 /// but skips the check.
445 /// This method will take care to not copy the vector, for efficiency's
448 /// If you need a [`&str`] instead of a `String`, consider
449 /// [`str::from_utf8`].
451 /// The inverse of this method is [`into_bytes`].
455 /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
456 /// provided bytes are not UTF-8. The vector you moved in is also included.
463 /// // some bytes, in a vector
464 /// let sparkle_heart = vec![240, 159, 146, 150];
466 /// // We know these bytes are valid, so we'll use `unwrap()`.
467 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
469 /// assert_eq!("💖", sparkle_heart);
475 /// // some invalid bytes, in a vector
476 /// let sparkle_heart = vec![0, 159, 146, 150];
478 /// assert!(String::from_utf8(sparkle_heart).is_err());
481 /// See the docs for [`FromUtf8Error`] for more details on what you can do
484 /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
485 /// [`String`]: struct.String.html
486 /// [`u8`]: ../../std/primitive.u8.html
487 /// [`Vec<u8>`]: ../../std/vec/struct.Vec.html
488 /// [`str::from_utf8`]: ../../std/str/fn.from_utf8.html
489 /// [`into_bytes`]: struct.String.html#method.into_bytes
490 /// [`FromUtf8Error`]: struct.FromUtf8Error.html
491 /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
493 #[stable(feature = "rust1", since = "1.0.0")]
494 pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
495 match str::from_utf8(&vec) {
496 Ok(..) => Ok(String { vec }),
506 /// Converts a slice of bytes to a string, including invalid characters.
508 /// Strings are made of bytes ([`u8`]), and a slice of bytes
509 /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
510 /// between the two. Not all byte slices are valid strings, however: strings
511 /// are required to be valid UTF-8. During this conversion,
512 /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
513 /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: �
515 /// [`u8`]: ../../std/primitive.u8.html
516 /// [byteslice]: ../../std/primitive.slice.html
517 /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
519 /// If you are sure that the byte slice is valid UTF-8, and you don't want
520 /// to incur the overhead of the conversion, there is an unsafe version
521 /// of this function, [`from_utf8_unchecked`], which has the same behavior
522 /// but skips the checks.
524 /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
526 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
527 /// UTF-8, then we need to insert the replacement characters, which will
528 /// change the size of the string, and hence, require a `String`. But if
529 /// it's already valid UTF-8, we don't need a new allocation. This return
530 /// type allows us to handle both cases.
532 /// [`Cow<'a, str>`]: ../../std/borrow/enum.Cow.html
539 /// // some bytes, in a vector
540 /// let sparkle_heart = vec![240, 159, 146, 150];
542 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
544 /// assert_eq!("💖", sparkle_heart);
550 /// // some invalid bytes
551 /// let input = b"Hello \xF0\x90\x80World";
552 /// let output = String::from_utf8_lossy(input);
554 /// assert_eq!("Hello �World", output);
556 #[stable(feature = "rust1", since = "1.0.0")]
557 pub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, str> {
558 let mut iter = lossy::Utf8Lossy::from_bytes(v).chunks();
560 let (first_valid, first_broken) = if let Some(chunk) = iter.next() {
561 let lossy::Utf8LossyChunk { valid, broken } = chunk;
562 if valid.len() == v.len() {
563 debug_assert!(broken.is_empty());
564 return Cow::Borrowed(valid);
568 return Cow::Borrowed("");
571 const REPLACEMENT: &str = "\u{FFFD}";
573 let mut res = String::with_capacity(v.len());
574 res.push_str(first_valid);
575 if !first_broken.is_empty() {
576 res.push_str(REPLACEMENT);
579 for lossy::Utf8LossyChunk { valid, broken } in iter {
581 if !broken.is_empty() {
582 res.push_str(REPLACEMENT);
589 /// Decode a UTF-16 encoded vector `v` into a `String`, returning [`Err`]
590 /// if `v` contains any invalid data.
592 /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
600 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
601 /// 0x0073, 0x0069, 0x0063];
602 /// assert_eq!(String::from("𝄞music"),
603 /// String::from_utf16(v).unwrap());
605 /// // 𝄞mu<invalid>ic
606 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
607 /// 0xD800, 0x0069, 0x0063];
608 /// assert!(String::from_utf16(v).is_err());
610 #[stable(feature = "rust1", since = "1.0.0")]
611 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
612 // This isn't done via collect::<Result<_, _>>() for performance reasons.
613 // FIXME: the function can be simplified again when #48994 is closed.
614 let mut ret = String::with_capacity(v.len());
615 for c in decode_utf16(v.iter().cloned()) {
619 return Err(FromUtf16Error(()));
625 /// Decode a UTF-16 encoded slice `v` into a `String`, replacing
626 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
628 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
629 /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
630 /// conversion requires a memory allocation.
632 /// [`from_utf8_lossy`]: #method.from_utf8_lossy
633 /// [`Cow<'a, str>`]: ../borrow/enum.Cow.html
634 /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
641 /// // 𝄞mus<invalid>ic<invalid>
642 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
643 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
646 /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
647 /// String::from_utf16_lossy(v));
650 #[stable(feature = "rust1", since = "1.0.0")]
651 pub fn from_utf16_lossy(v: &[u16]) -> String {
652 decode_utf16(v.iter().cloned()).map(|r| r.unwrap_or(REPLACEMENT_CHARACTER)).collect()
655 /// Decomposes a `String` into its raw components.
657 /// Returns the raw pointer to the underlying data, the length of
658 /// the string (in bytes), and the allocated capacity of the data
659 /// (in bytes). These are the same arguments in the same order as
660 /// the arguments to [`from_raw_parts`].
662 /// After calling this function, the caller is responsible for the
663 /// memory previously managed by the `String`. The only way to do
664 /// this is to convert the raw pointer, length, and capacity back
665 /// into a `String` with the [`from_raw_parts`] function, allowing
666 /// the destructor to perform the cleanup.
668 /// [`from_raw_parts`]: #method.from_raw_parts
673 /// #![feature(vec_into_raw_parts)]
674 /// let s = String::from("hello");
676 /// let (ptr, len, cap) = s.into_raw_parts();
678 /// let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
679 /// assert_eq!(rebuilt, "hello");
681 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
682 pub fn into_raw_parts(self) -> (*mut u8, usize, usize) {
683 self.vec.into_raw_parts()
686 /// Creates a new `String` from a length, capacity, and pointer.
690 /// This is highly unsafe, due to the number of invariants that aren't
693 /// * The memory at `ptr` needs to have been previously allocated by the
694 /// same allocator the standard library uses, with a required alignment of exactly 1.
695 /// * `length` needs to be less than or equal to `capacity`.
696 /// * `capacity` needs to be the correct value.
698 /// Violating these may cause problems like corrupting the allocator's
699 /// internal data structures.
701 /// The ownership of `ptr` is effectively transferred to the
702 /// `String` which may then deallocate, reallocate or change the
703 /// contents of memory pointed to by the pointer at will. Ensure
704 /// that nothing else uses the pointer after calling this
715 /// let s = String::from("hello");
717 // FIXME Update this when vec_into_raw_parts is stabilized
718 /// // Prevent automatically dropping the String's data
719 /// let mut s = mem::ManuallyDrop::new(s);
721 /// let ptr = s.as_mut_ptr();
722 /// let len = s.len();
723 /// let capacity = s.capacity();
725 /// let s = String::from_raw_parts(ptr, len, capacity);
727 /// assert_eq!(String::from("hello"), s);
731 #[stable(feature = "rust1", since = "1.0.0")]
732 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
733 String { vec: Vec::from_raw_parts(buf, length, capacity) }
736 /// Converts a vector of bytes to a `String` without checking that the
737 /// string contains valid UTF-8.
739 /// See the safe version, [`from_utf8`], for more details.
741 /// [`from_utf8`]: struct.String.html#method.from_utf8
745 /// This function is unsafe because it does not check that the bytes passed
746 /// to it are valid UTF-8. If this constraint is violated, it may cause
747 /// memory unsafety issues with future users of the `String`, as the rest of
748 /// the standard library assumes that `String`s are valid UTF-8.
755 /// // some bytes, in a vector
756 /// let sparkle_heart = vec![240, 159, 146, 150];
758 /// let sparkle_heart = unsafe {
759 /// String::from_utf8_unchecked(sparkle_heart)
762 /// assert_eq!("💖", sparkle_heart);
765 #[stable(feature = "rust1", since = "1.0.0")]
766 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
767 String { vec: bytes }
770 /// Converts a `String` into a byte vector.
772 /// This consumes the `String`, so we do not need to copy its contents.
779 /// let s = String::from("hello");
780 /// let bytes = s.into_bytes();
782 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
785 #[stable(feature = "rust1", since = "1.0.0")]
786 pub fn into_bytes(self) -> Vec<u8> {
790 /// Extracts a string slice containing the entire `String`.
797 /// let s = String::from("foo");
799 /// assert_eq!("foo", s.as_str());
802 #[stable(feature = "string_as_str", since = "1.7.0")]
803 pub fn as_str(&self) -> &str {
807 /// Converts a `String` into a mutable string slice.
814 /// let mut s = String::from("foobar");
815 /// let s_mut_str = s.as_mut_str();
817 /// s_mut_str.make_ascii_uppercase();
819 /// assert_eq!("FOOBAR", s_mut_str);
822 #[stable(feature = "string_as_str", since = "1.7.0")]
823 pub fn as_mut_str(&mut self) -> &mut str {
827 /// Appends a given string slice onto the end of this `String`.
834 /// let mut s = String::from("foo");
836 /// s.push_str("bar");
838 /// assert_eq!("foobar", s);
841 #[stable(feature = "rust1", since = "1.0.0")]
842 pub fn push_str(&mut self, string: &str) {
843 self.vec.extend_from_slice(string.as_bytes())
846 /// Returns this `String`'s capacity, in bytes.
853 /// let s = String::with_capacity(10);
855 /// assert!(s.capacity() >= 10);
858 #[stable(feature = "rust1", since = "1.0.0")]
859 pub fn capacity(&self) -> usize {
863 /// Ensures that this `String`'s capacity is at least `additional` bytes
864 /// larger than its length.
866 /// The capacity may be increased by more than `additional` bytes if it
867 /// chooses, to prevent frequent reallocations.
869 /// If you do not want this "at least" behavior, see the [`reserve_exact`]
874 /// Panics if the new capacity overflows [`usize`].
876 /// [`reserve_exact`]: struct.String.html#method.reserve_exact
877 /// [`usize`]: ../../std/primitive.usize.html
884 /// let mut s = String::new();
888 /// assert!(s.capacity() >= 10);
891 /// This may not actually increase the capacity:
894 /// let mut s = String::with_capacity(10);
898 /// // s now has a length of 2 and a capacity of 10
899 /// assert_eq!(2, s.len());
900 /// assert_eq!(10, s.capacity());
902 /// // Since we already have an extra 8 capacity, calling this...
905 /// // ... doesn't actually increase.
906 /// assert_eq!(10, s.capacity());
909 #[stable(feature = "rust1", since = "1.0.0")]
910 pub fn reserve(&mut self, additional: usize) {
911 self.vec.reserve(additional)
914 /// Ensures that this `String`'s capacity is `additional` bytes
915 /// larger than its length.
917 /// Consider using the [`reserve`] method unless you absolutely know
918 /// better than the allocator.
920 /// [`reserve`]: #method.reserve
924 /// Panics if the new capacity overflows `usize`.
931 /// let mut s = String::new();
933 /// s.reserve_exact(10);
935 /// assert!(s.capacity() >= 10);
938 /// This may not actually increase the capacity:
941 /// let mut s = String::with_capacity(10);
945 /// // s now has a length of 2 and a capacity of 10
946 /// assert_eq!(2, s.len());
947 /// assert_eq!(10, s.capacity());
949 /// // Since we already have an extra 8 capacity, calling this...
950 /// s.reserve_exact(8);
952 /// // ... doesn't actually increase.
953 /// assert_eq!(10, s.capacity());
956 #[stable(feature = "rust1", since = "1.0.0")]
957 pub fn reserve_exact(&mut self, additional: usize) {
958 self.vec.reserve_exact(additional)
961 /// Tries to reserve capacity for at least `additional` more elements to be inserted
962 /// in the given `String`. The collection may reserve more space to avoid
963 /// frequent reallocations. After calling `reserve`, capacity will be
964 /// greater than or equal to `self.len() + additional`. Does nothing if
965 /// capacity is already sufficient.
969 /// If the capacity overflows, or the allocator reports a failure, then an error
975 /// #![feature(try_reserve)]
976 /// use std::collections::TryReserveError;
978 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
979 /// let mut output = String::new();
981 /// // Pre-reserve the memory, exiting if we can't
982 /// output.try_reserve(data.len())?;
984 /// // Now we know this can't OOM in the middle of our complex work
985 /// output.push_str(data);
989 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
991 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
992 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
993 self.vec.try_reserve(additional)
996 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
997 /// be inserted in the given `String`. After calling `reserve_exact`,
998 /// capacity will be greater than or equal to `self.len() + additional`.
999 /// Does nothing if the capacity is already sufficient.
1001 /// Note that the allocator may give the collection more space than it
1002 /// requests. Therefore, capacity can not be relied upon to be precisely
1003 /// minimal. Prefer `reserve` if future insertions are expected.
1007 /// If the capacity overflows, or the allocator reports a failure, then an error
1013 /// #![feature(try_reserve)]
1014 /// use std::collections::TryReserveError;
1016 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
1017 /// let mut output = String::new();
1019 /// // Pre-reserve the memory, exiting if we can't
1020 /// output.try_reserve(data.len())?;
1022 /// // Now we know this can't OOM in the middle of our complex work
1023 /// output.push_str(data);
1027 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1029 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
1030 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
1031 self.vec.try_reserve_exact(additional)
1034 /// Shrinks the capacity of this `String` to match its length.
1041 /// let mut s = String::from("foo");
1044 /// assert!(s.capacity() >= 100);
1046 /// s.shrink_to_fit();
1047 /// assert_eq!(3, s.capacity());
1050 #[stable(feature = "rust1", since = "1.0.0")]
1051 pub fn shrink_to_fit(&mut self) {
1052 self.vec.shrink_to_fit()
1055 /// Shrinks the capacity of this `String` with a lower bound.
1057 /// The capacity will remain at least as large as both the length
1058 /// and the supplied value.
1060 /// Panics if the current capacity is smaller than the supplied
1061 /// minimum capacity.
1066 /// #![feature(shrink_to)]
1067 /// let mut s = String::from("foo");
1070 /// assert!(s.capacity() >= 100);
1072 /// s.shrink_to(10);
1073 /// assert!(s.capacity() >= 10);
1075 /// assert!(s.capacity() >= 3);
1078 #[unstable(feature = "shrink_to", reason = "new API", issue="56431")]
1079 pub fn shrink_to(&mut self, min_capacity: usize) {
1080 self.vec.shrink_to(min_capacity)
1083 /// Appends the given [`char`] to the end of this `String`.
1085 /// [`char`]: ../../std/primitive.char.html
1092 /// let mut s = String::from("abc");
1098 /// assert_eq!("abc123", s);
1101 #[stable(feature = "rust1", since = "1.0.0")]
1102 pub fn push(&mut self, ch: char) {
1103 match ch.len_utf8() {
1104 1 => self.vec.push(ch as u8),
1105 _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
1109 /// Returns a byte slice of this `String`'s contents.
1111 /// The inverse of this method is [`from_utf8`].
1113 /// [`from_utf8`]: #method.from_utf8
1120 /// let s = String::from("hello");
1122 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
1125 #[stable(feature = "rust1", since = "1.0.0")]
1126 pub fn as_bytes(&self) -> &[u8] {
1130 /// Shortens this `String` to the specified length.
1132 /// If `new_len` is greater than the string's current length, this has no
1135 /// Note that this method has no effect on the allocated capacity
1140 /// Panics if `new_len` does not lie on a [`char`] boundary.
1142 /// [`char`]: ../../std/primitive.char.html
1149 /// let mut s = String::from("hello");
1153 /// assert_eq!("he", s);
1156 #[stable(feature = "rust1", since = "1.0.0")]
1157 pub fn truncate(&mut self, new_len: usize) {
1158 if new_len <= self.len() {
1159 assert!(self.is_char_boundary(new_len));
1160 self.vec.truncate(new_len)
1164 /// Removes the last character from the string buffer and returns it.
1166 /// Returns [`None`] if this `String` is empty.
1168 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1175 /// let mut s = String::from("foo");
1177 /// assert_eq!(s.pop(), Some('o'));
1178 /// assert_eq!(s.pop(), Some('o'));
1179 /// assert_eq!(s.pop(), Some('f'));
1181 /// assert_eq!(s.pop(), None);
1184 #[stable(feature = "rust1", since = "1.0.0")]
1185 pub fn pop(&mut self) -> Option<char> {
1186 let ch = self.chars().rev().next()?;
1187 let newlen = self.len() - ch.len_utf8();
1189 self.vec.set_len(newlen);
1194 /// Removes a [`char`] from this `String` at a byte position and returns it.
1196 /// This is an `O(n)` operation, as it requires copying every element in the
1201 /// Panics if `idx` is larger than or equal to the `String`'s length,
1202 /// or if it does not lie on a [`char`] boundary.
1204 /// [`char`]: ../../std/primitive.char.html
1211 /// let mut s = String::from("foo");
1213 /// assert_eq!(s.remove(0), 'f');
1214 /// assert_eq!(s.remove(1), 'o');
1215 /// assert_eq!(s.remove(0), 'o');
1218 #[stable(feature = "rust1", since = "1.0.0")]
1219 pub fn remove(&mut self, idx: usize) -> char {
1220 let ch = match self[idx..].chars().next() {
1222 None => panic!("cannot remove a char from the end of a string"),
1225 let next = idx + ch.len_utf8();
1226 let len = self.len();
1228 ptr::copy(self.vec.as_ptr().add(next),
1229 self.vec.as_mut_ptr().add(idx),
1231 self.vec.set_len(len - (next - idx));
1236 /// Retains only the characters specified by the predicate.
1238 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1239 /// This method operates in place, visiting each character exactly once in the
1240 /// original order, and preserves the order of the retained characters.
1245 /// let mut s = String::from("f_o_ob_ar");
1247 /// s.retain(|c| c != '_');
1249 /// assert_eq!(s, "foobar");
1252 /// The exact order may be useful for tracking external state, like an index.
1255 /// let mut s = String::from("abcde");
1256 /// let keep = [false, true, true, false, true];
1258 /// s.retain(|_| (keep[i], i += 1).0);
1259 /// assert_eq!(s, "bce");
1262 #[stable(feature = "string_retain", since = "1.26.0")]
1263 pub fn retain<F>(&mut self, mut f: F)
1264 where F: FnMut(char) -> bool
1266 let len = self.len();
1267 let mut del_bytes = 0;
1272 self.get_unchecked(idx..len).chars().next().unwrap()
1274 let ch_len = ch.len_utf8();
1277 del_bytes += ch_len;
1278 } else if del_bytes > 0 {
1280 ptr::copy(self.vec.as_ptr().add(idx),
1281 self.vec.as_mut_ptr().add(idx - del_bytes),
1286 // Point idx to the next char
1291 unsafe { self.vec.set_len(len - del_bytes); }
1295 /// Inserts a character into this `String` at a byte position.
1297 /// This is an `O(n)` operation as it requires copying every element in the
1302 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1303 /// lie on a [`char`] boundary.
1305 /// [`char`]: ../../std/primitive.char.html
1312 /// let mut s = String::with_capacity(3);
1314 /// s.insert(0, 'f');
1315 /// s.insert(1, 'o');
1316 /// s.insert(2, 'o');
1318 /// assert_eq!("foo", s);
1321 #[stable(feature = "rust1", since = "1.0.0")]
1322 pub fn insert(&mut self, idx: usize, ch: char) {
1323 assert!(self.is_char_boundary(idx));
1324 let mut bits = [0; 4];
1325 let bits = ch.encode_utf8(&mut bits).as_bytes();
1328 self.insert_bytes(idx, bits);
1332 unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1333 let len = self.len();
1334 let amt = bytes.len();
1335 self.vec.reserve(amt);
1337 ptr::copy(self.vec.as_ptr().add(idx),
1338 self.vec.as_mut_ptr().add(idx + amt),
1340 ptr::copy(bytes.as_ptr(),
1341 self.vec.as_mut_ptr().add(idx),
1343 self.vec.set_len(len + amt);
1346 /// Inserts a string slice into this `String` at a byte position.
1348 /// This is an `O(n)` operation as it requires copying every element in the
1353 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1354 /// lie on a [`char`] boundary.
1356 /// [`char`]: ../../std/primitive.char.html
1363 /// let mut s = String::from("bar");
1365 /// s.insert_str(0, "foo");
1367 /// assert_eq!("foobar", s);
1370 #[stable(feature = "insert_str", since = "1.16.0")]
1371 pub fn insert_str(&mut self, idx: usize, string: &str) {
1372 assert!(self.is_char_boundary(idx));
1375 self.insert_bytes(idx, string.as_bytes());
1379 /// Returns a mutable reference to the contents of this `String`.
1383 /// This function is unsafe because it does not check that the bytes passed
1384 /// to it are valid UTF-8. If this constraint is violated, it may cause
1385 /// memory unsafety issues with future users of the `String`, as the rest of
1386 /// the standard library assumes that `String`s are valid UTF-8.
1393 /// let mut s = String::from("hello");
1396 /// let vec = s.as_mut_vec();
1397 /// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1401 /// assert_eq!(s, "olleh");
1404 #[stable(feature = "rust1", since = "1.0.0")]
1405 pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1409 /// Returns the length of this `String`, in bytes, not [`char`]s or
1410 /// graphemes. In other words, it may not be what a human considers the
1411 /// length of the string.
1418 /// let a = String::from("foo");
1419 /// assert_eq!(a.len(), 3);
1421 /// let fancy_f = String::from("ƒoo");
1422 /// assert_eq!(fancy_f.len(), 4);
1423 /// assert_eq!(fancy_f.chars().count(), 3);
1426 #[stable(feature = "rust1", since = "1.0.0")]
1427 pub fn len(&self) -> usize {
1431 /// Returns `true` if this `String` has a length of zero, and `false` otherwise.
1438 /// let mut v = String::new();
1439 /// assert!(v.is_empty());
1442 /// assert!(!v.is_empty());
1445 #[stable(feature = "rust1", since = "1.0.0")]
1446 pub fn is_empty(&self) -> bool {
1450 /// Splits the string into two at the given index.
1452 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1453 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1454 /// boundary of a UTF-8 code point.
1456 /// Note that the capacity of `self` does not change.
1460 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1461 /// code point of the string.
1467 /// let mut hello = String::from("Hello, World!");
1468 /// let world = hello.split_off(7);
1469 /// assert_eq!(hello, "Hello, ");
1470 /// assert_eq!(world, "World!");
1474 #[stable(feature = "string_split_off", since = "1.16.0")]
1475 pub fn split_off(&mut self, at: usize) -> String {
1476 assert!(self.is_char_boundary(at));
1477 let other = self.vec.split_off(at);
1478 unsafe { String::from_utf8_unchecked(other) }
1481 /// Truncates this `String`, removing all contents.
1483 /// While this means the `String` will have a length of zero, it does not
1484 /// touch its capacity.
1491 /// let mut s = String::from("foo");
1495 /// assert!(s.is_empty());
1496 /// assert_eq!(0, s.len());
1497 /// assert_eq!(3, s.capacity());
1500 #[stable(feature = "rust1", since = "1.0.0")]
1501 pub fn clear(&mut self) {
1505 /// Creates a draining iterator that removes the specified range in the `String`
1506 /// and yields the removed `chars`.
1508 /// Note: The element range is removed even if the iterator is not
1509 /// consumed until the end.
1513 /// Panics if the starting point or end point do not lie on a [`char`]
1514 /// boundary, or if they're out of bounds.
1516 /// [`char`]: ../../std/primitive.char.html
1523 /// let mut s = String::from("α is alpha, β is beta");
1524 /// let beta_offset = s.find('β').unwrap_or(s.len());
1526 /// // Remove the range up until the β from the string
1527 /// let t: String = s.drain(..beta_offset).collect();
1528 /// assert_eq!(t, "α is alpha, ");
1529 /// assert_eq!(s, "β is beta");
1531 /// // A full range clears the string
1533 /// assert_eq!(s, "");
1535 #[stable(feature = "drain", since = "1.6.0")]
1536 pub fn drain<R>(&mut self, range: R) -> Drain<'_>
1537 where R: RangeBounds<usize>
1541 // The String version of Drain does not have the memory safety issues
1542 // of the vector version. The data is just plain bytes.
1543 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1544 // the removal will not happen.
1545 let len = self.len();
1546 let start = match range.start_bound() {
1548 Excluded(&n) => n + 1,
1551 let end = match range.end_bound() {
1552 Included(&n) => n + 1,
1557 // Take out two simultaneous borrows. The &mut String won't be accessed
1558 // until iteration is over, in Drop.
1559 let self_ptr = self as *mut _;
1560 // slicing does the appropriate bounds checks
1561 let chars_iter = self[start..end].chars();
1571 /// Removes the specified range in the string,
1572 /// and replaces it with the given string.
1573 /// The given string doesn't need to be the same length as the range.
1577 /// Panics if the starting point or end point do not lie on a [`char`]
1578 /// boundary, or if they're out of bounds.
1580 /// [`char`]: ../../std/primitive.char.html
1581 /// [`Vec::splice`]: ../../std/vec/struct.Vec.html#method.splice
1588 /// let mut s = String::from("α is alpha, β is beta");
1589 /// let beta_offset = s.find('β').unwrap_or(s.len());
1591 /// // Replace the range up until the β from the string
1592 /// s.replace_range(..beta_offset, "Α is capital alpha; ");
1593 /// assert_eq!(s, "Α is capital alpha; β is beta");
1595 #[stable(feature = "splice", since = "1.27.0")]
1596 pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
1597 where R: RangeBounds<usize>
1601 // Replace_range does not have the memory safety issues of a vector Splice.
1602 // of the vector version. The data is just plain bytes.
1604 match range.start_bound() {
1605 Included(&n) => assert!(self.is_char_boundary(n)),
1606 Excluded(&n) => assert!(self.is_char_boundary(n + 1)),
1609 match range.end_bound() {
1610 Included(&n) => assert!(self.is_char_boundary(n + 1)),
1611 Excluded(&n) => assert!(self.is_char_boundary(n)),
1617 }.splice(range, replace_with.bytes());
1620 /// Converts this `String` into a [`Box`]`<`[`str`]`>`.
1622 /// This will drop any excess capacity.
1624 /// [`Box`]: ../../std/boxed/struct.Box.html
1625 /// [`str`]: ../../std/primitive.str.html
1632 /// let s = String::from("hello");
1634 /// let b = s.into_boxed_str();
1636 #[stable(feature = "box_str", since = "1.4.0")]
1638 pub fn into_boxed_str(self) -> Box<str> {
1639 let slice = self.vec.into_boxed_slice();
1640 unsafe { from_boxed_utf8_unchecked(slice) }
1644 impl FromUtf8Error {
1645 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1652 /// // some invalid bytes, in a vector
1653 /// let bytes = vec![0, 159];
1655 /// let value = String::from_utf8(bytes);
1657 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1659 #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
1660 pub fn as_bytes(&self) -> &[u8] {
1664 /// Returns the bytes that were attempted to convert to a `String`.
1666 /// This method is carefully constructed to avoid allocation. It will
1667 /// consume the error, moving out the bytes, so that a copy of the bytes
1668 /// does not need to be made.
1675 /// // some invalid bytes, in a vector
1676 /// let bytes = vec![0, 159];
1678 /// let value = String::from_utf8(bytes);
1680 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1682 #[stable(feature = "rust1", since = "1.0.0")]
1683 pub fn into_bytes(self) -> Vec<u8> {
1687 /// Fetch a `Utf8Error` to get more details about the conversion failure.
1689 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1690 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1691 /// an analogue to `FromUtf8Error`. See its documentation for more details
1694 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
1695 /// [`std::str`]: ../../std/str/index.html
1696 /// [`u8`]: ../../std/primitive.u8.html
1697 /// [`&str`]: ../../std/primitive.str.html
1704 /// // some invalid bytes, in a vector
1705 /// let bytes = vec![0, 159];
1707 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1709 /// // the first byte is invalid here
1710 /// assert_eq!(1, error.valid_up_to());
1712 #[stable(feature = "rust1", since = "1.0.0")]
1713 pub fn utf8_error(&self) -> Utf8Error {
1718 #[stable(feature = "rust1", since = "1.0.0")]
1719 impl fmt::Display for FromUtf8Error {
1720 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1721 fmt::Display::fmt(&self.error, f)
1725 #[stable(feature = "rust1", since = "1.0.0")]
1726 impl fmt::Display for FromUtf16Error {
1727 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1728 fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
1732 #[stable(feature = "rust1", since = "1.0.0")]
1733 impl Clone for String {
1734 fn clone(&self) -> Self {
1735 String { vec: self.vec.clone() }
1738 fn clone_from(&mut self, source: &Self) {
1739 self.vec.clone_from(&source.vec);
1743 #[stable(feature = "rust1", since = "1.0.0")]
1744 impl FromIterator<char> for String {
1745 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
1746 let mut buf = String::new();
1752 #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
1753 impl<'a> FromIterator<&'a char> for String {
1754 fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
1755 let mut buf = String::new();
1761 #[stable(feature = "rust1", since = "1.0.0")]
1762 impl<'a> FromIterator<&'a str> for String {
1763 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
1764 let mut buf = String::new();
1770 #[stable(feature = "extend_string", since = "1.4.0")]
1771 impl FromIterator<String> for String {
1772 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
1773 let mut iterator = iter.into_iter();
1775 // Because we're iterating over `String`s, we can avoid at least
1776 // one allocation by getting the first string from the iterator
1777 // and appending to it all the subsequent strings.
1778 match iterator.next() {
1779 None => String::new(),
1781 buf.extend(iterator);
1788 #[stable(feature = "herd_cows", since = "1.19.0")]
1789 impl<'a> FromIterator<Cow<'a, str>> for String {
1790 fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
1791 let mut iterator = iter.into_iter();
1793 // Because we're iterating over CoWs, we can (potentially) avoid at least
1794 // one allocation by getting the first item and appending to it all the
1795 // subsequent items.
1796 match iterator.next() {
1797 None => String::new(),
1799 let mut buf = cow.into_owned();
1800 buf.extend(iterator);
1807 #[stable(feature = "rust1", since = "1.0.0")]
1808 impl Extend<char> for String {
1809 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
1810 let iterator = iter.into_iter();
1811 let (lower_bound, _) = iterator.size_hint();
1812 self.reserve(lower_bound);
1813 iterator.for_each(move |c| self.push(c));
1817 #[stable(feature = "extend_ref", since = "1.2.0")]
1818 impl<'a> Extend<&'a char> for String {
1819 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
1820 self.extend(iter.into_iter().cloned());
1824 #[stable(feature = "rust1", since = "1.0.0")]
1825 impl<'a> Extend<&'a str> for String {
1826 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
1827 iter.into_iter().for_each(move |s| self.push_str(s));
1831 #[stable(feature = "extend_string", since = "1.4.0")]
1832 impl Extend<String> for String {
1833 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
1834 iter.into_iter().for_each(move |s| self.push_str(&s));
1838 #[stable(feature = "herd_cows", since = "1.19.0")]
1839 impl<'a> Extend<Cow<'a, str>> for String {
1840 fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
1841 iter.into_iter().for_each(move |s| self.push_str(&s));
1845 /// A convenience impl that delegates to the impl for `&str`
1846 #[unstable(feature = "pattern",
1847 reason = "API not fully fleshed out and ready to be stabilized",
1849 impl<'a, 'b> Pattern<'a> for &'b String {
1850 type Searcher = <&'b str as Pattern<'a>>::Searcher;
1852 fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
1853 self[..].into_searcher(haystack)
1857 fn is_contained_in(self, haystack: &'a str) -> bool {
1858 self[..].is_contained_in(haystack)
1862 fn is_prefix_of(self, haystack: &'a str) -> bool {
1863 self[..].is_prefix_of(haystack)
1867 #[stable(feature = "rust1", since = "1.0.0")]
1868 impl PartialEq for String {
1870 fn eq(&self, other: &String) -> bool {
1871 PartialEq::eq(&self[..], &other[..])
1874 fn ne(&self, other: &String) -> bool {
1875 PartialEq::ne(&self[..], &other[..])
1879 macro_rules! impl_eq {
1880 ($lhs:ty, $rhs: ty) => {
1881 #[stable(feature = "rust1", since = "1.0.0")]
1882 #[allow(unused_lifetimes)]
1883 impl<'a, 'b> PartialEq<$rhs> for $lhs {
1885 fn eq(&self, other: &$rhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1887 fn ne(&self, other: &$rhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1890 #[stable(feature = "rust1", since = "1.0.0")]
1891 #[allow(unused_lifetimes)]
1892 impl<'a, 'b> PartialEq<$lhs> for $rhs {
1894 fn eq(&self, other: &$lhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1896 fn ne(&self, other: &$lhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1902 impl_eq! { String, str }
1903 impl_eq! { String, &'a str }
1904 impl_eq! { Cow<'a, str>, str }
1905 impl_eq! { Cow<'a, str>, &'b str }
1906 impl_eq! { Cow<'a, str>, String }
1908 #[stable(feature = "rust1", since = "1.0.0")]
1909 impl Default for String {
1910 /// Creates an empty `String`.
1912 fn default() -> String {
1917 #[stable(feature = "rust1", since = "1.0.0")]
1918 impl fmt::Display for String {
1920 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1921 fmt::Display::fmt(&**self, f)
1925 #[stable(feature = "rust1", since = "1.0.0")]
1926 impl fmt::Debug for String {
1928 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1929 fmt::Debug::fmt(&**self, f)
1933 #[stable(feature = "rust1", since = "1.0.0")]
1934 impl hash::Hash for String {
1936 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
1937 (**self).hash(hasher)
1941 /// Implements the `+` operator for concatenating two strings.
1943 /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
1944 /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
1945 /// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by
1946 /// repeated concatenation.
1948 /// The string on the right-hand side is only borrowed; its contents are copied into the returned
1953 /// Concatenating two `String`s takes the first by value and borrows the second:
1956 /// let a = String::from("hello");
1957 /// let b = String::from(" world");
1959 /// // `a` is moved and can no longer be used here.
1962 /// If you want to keep using the first `String`, you can clone it and append to the clone instead:
1965 /// let a = String::from("hello");
1966 /// let b = String::from(" world");
1967 /// let c = a.clone() + &b;
1968 /// // `a` is still valid here.
1971 /// Concatenating `&str` slices can be done by converting the first to a `String`:
1974 /// let a = "hello";
1975 /// let b = " world";
1976 /// let c = a.to_string() + b;
1978 #[stable(feature = "rust1", since = "1.0.0")]
1979 impl Add<&str> for String {
1980 type Output = String;
1983 fn add(mut self, other: &str) -> String {
1984 self.push_str(other);
1989 /// Implements the `+=` operator for appending to a `String`.
1991 /// This has the same behavior as the [`push_str`][String::push_str] method.
1992 #[stable(feature = "stringaddassign", since = "1.12.0")]
1993 impl AddAssign<&str> for String {
1995 fn add_assign(&mut self, other: &str) {
1996 self.push_str(other);
2000 #[stable(feature = "rust1", since = "1.0.0")]
2001 impl ops::Index<ops::Range<usize>> for String {
2005 fn index(&self, index: ops::Range<usize>) -> &str {
2009 #[stable(feature = "rust1", since = "1.0.0")]
2010 impl ops::Index<ops::RangeTo<usize>> for String {
2014 fn index(&self, index: ops::RangeTo<usize>) -> &str {
2018 #[stable(feature = "rust1", since = "1.0.0")]
2019 impl ops::Index<ops::RangeFrom<usize>> for String {
2023 fn index(&self, index: ops::RangeFrom<usize>) -> &str {
2027 #[stable(feature = "rust1", since = "1.0.0")]
2028 impl ops::Index<ops::RangeFull> for String {
2032 fn index(&self, _index: ops::RangeFull) -> &str {
2033 unsafe { str::from_utf8_unchecked(&self.vec) }
2036 #[stable(feature = "inclusive_range", since = "1.26.0")]
2037 impl ops::Index<ops::RangeInclusive<usize>> for String {
2041 fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
2042 Index::index(&**self, index)
2045 #[stable(feature = "inclusive_range", since = "1.26.0")]
2046 impl ops::Index<ops::RangeToInclusive<usize>> for String {
2050 fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
2051 Index::index(&**self, index)
2055 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2056 impl ops::IndexMut<ops::Range<usize>> for String {
2058 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
2059 &mut self[..][index]
2062 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2063 impl ops::IndexMut<ops::RangeTo<usize>> for String {
2065 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
2066 &mut self[..][index]
2069 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2070 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
2072 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
2073 &mut self[..][index]
2076 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2077 impl ops::IndexMut<ops::RangeFull> for String {
2079 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
2080 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2083 #[stable(feature = "inclusive_range", since = "1.26.0")]
2084 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
2086 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
2087 IndexMut::index_mut(&mut **self, index)
2090 #[stable(feature = "inclusive_range", since = "1.26.0")]
2091 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
2093 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
2094 IndexMut::index_mut(&mut **self, index)
2098 #[stable(feature = "rust1", since = "1.0.0")]
2099 impl ops::Deref for String {
2103 fn deref(&self) -> &str {
2104 unsafe { str::from_utf8_unchecked(&self.vec) }
2108 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2109 impl ops::DerefMut for String {
2111 fn deref_mut(&mut self) -> &mut str {
2112 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2116 /// An error when parsing a `String`.
2118 /// This `enum` is slightly awkward: it will never actually exist. This error is
2119 /// part of the type signature of the implementation of [`FromStr`] on
2120 /// [`String`]. The return type of [`from_str`], requires that an error be
2121 /// defined, but, given that a [`String`] can always be made into a new
2122 /// [`String`] without error, this type will never actually be returned. As
2123 /// such, it is only here to satisfy said signature, and is useless otherwise.
2125 /// [`FromStr`]: ../../std/str/trait.FromStr.html
2126 /// [`String`]: struct.String.html
2127 /// [`from_str`]: ../../std/str/trait.FromStr.html#tymethod.from_str
2128 #[stable(feature = "str_parse_error", since = "1.5.0")]
2129 pub type ParseError = core::convert::Infallible;
2131 #[stable(feature = "rust1", since = "1.0.0")]
2132 impl FromStr for String {
2133 type Err = core::convert::Infallible;
2135 fn from_str(s: &str) -> Result<String, ParseError> {
2141 /// A trait for converting a value to a `String`.
2143 /// This trait is automatically implemented for any type which implements the
2144 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
2145 /// [`Display`] should be implemented instead, and you get the `ToString`
2146 /// implementation for free.
2148 /// [`Display`]: ../../std/fmt/trait.Display.html
2149 #[stable(feature = "rust1", since = "1.0.0")]
2150 pub trait ToString {
2151 /// Converts the given value to a `String`.
2159 /// let five = String::from("5");
2161 /// assert_eq!(five, i.to_string());
2163 #[rustc_conversion_suggestion]
2164 #[stable(feature = "rust1", since = "1.0.0")]
2165 fn to_string(&self) -> String;
2170 /// In this implementation, the `to_string` method panics
2171 /// if the `Display` implementation returns an error.
2172 /// This indicates an incorrect `Display` implementation
2173 /// since `fmt::Write for String` never returns an error itself.
2174 #[stable(feature = "rust1", since = "1.0.0")]
2175 impl<T: fmt::Display + ?Sized> ToString for T {
2177 default fn to_string(&self) -> String {
2179 let mut buf = String::new();
2180 buf.write_fmt(format_args!("{}", self))
2181 .expect("a Display implementation returned an error unexpectedly");
2182 buf.shrink_to_fit();
2187 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
2188 impl ToString for str {
2190 fn to_string(&self) -> String {
2195 #[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
2196 impl ToString for Cow<'_, str> {
2198 fn to_string(&self) -> String {
2203 #[stable(feature = "string_to_string_specialization", since = "1.17.0")]
2204 impl ToString for String {
2206 fn to_string(&self) -> String {
2211 #[stable(feature = "rust1", since = "1.0.0")]
2212 impl AsRef<str> for String {
2214 fn as_ref(&self) -> &str {
2219 #[stable(feature = "rust1", since = "1.0.0")]
2220 impl AsRef<[u8]> for String {
2222 fn as_ref(&self) -> &[u8] {
2227 #[stable(feature = "rust1", since = "1.0.0")]
2228 impl From<&str> for String {
2230 fn from(s: &str) -> String {
2235 #[stable(feature = "from_ref_string", since = "1.35.0")]
2236 impl From<&String> for String {
2238 fn from(s: &String) -> String {
2243 // note: test pulls in libstd, which causes errors here
2245 #[stable(feature = "string_from_box", since = "1.18.0")]
2246 impl From<Box<str>> for String {
2247 /// Converts the given boxed `str` slice to a `String`.
2248 /// It is notable that the `str` slice is owned.
2255 /// let s1: String = String::from("hello world");
2256 /// let s2: Box<str> = s1.into_boxed_str();
2257 /// let s3: String = String::from(s2);
2259 /// assert_eq!("hello world", s3)
2261 fn from(s: Box<str>) -> String {
2266 #[stable(feature = "box_from_str", since = "1.20.0")]
2267 impl From<String> for Box<str> {
2268 /// Converts the given `String` to a boxed `str` slice that is owned.
2275 /// let s1: String = String::from("hello world");
2276 /// let s2: Box<str> = Box::from(s1);
2277 /// let s3: String = String::from(s2);
2279 /// assert_eq!("hello world", s3)
2281 fn from(s: String) -> Box<str> {
2286 #[stable(feature = "string_from_cow_str", since = "1.14.0")]
2287 impl<'a> From<Cow<'a, str>> for String {
2288 fn from(s: Cow<'a, str>) -> String {
2293 #[stable(feature = "rust1", since = "1.0.0")]
2294 impl<'a> From<&'a str> for Cow<'a, str> {
2296 fn from(s: &'a str) -> Cow<'a, str> {
2301 #[stable(feature = "rust1", since = "1.0.0")]
2302 impl<'a> From<String> for Cow<'a, str> {
2304 fn from(s: String) -> Cow<'a, str> {
2309 #[stable(feature = "cow_from_string_ref", since = "1.28.0")]
2310 impl<'a> From<&'a String> for Cow<'a, str> {
2312 fn from(s: &'a String) -> Cow<'a, str> {
2313 Cow::Borrowed(s.as_str())
2317 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2318 impl<'a> FromIterator<char> for Cow<'a, str> {
2319 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
2320 Cow::Owned(FromIterator::from_iter(it))
2324 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2325 impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
2326 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
2327 Cow::Owned(FromIterator::from_iter(it))
2331 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2332 impl<'a> FromIterator<String> for Cow<'a, str> {
2333 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
2334 Cow::Owned(FromIterator::from_iter(it))
2338 #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
2339 impl From<String> for Vec<u8> {
2340 /// Converts the given `String` to a vector `Vec` that holds values of type `u8`.
2347 /// let s1 = String::from("hello world");
2348 /// let v1 = Vec::from(s1);
2351 /// println!("{}", b);
2354 fn from(string: String) -> Vec<u8> {
2359 #[stable(feature = "rust1", since = "1.0.0")]
2360 impl fmt::Write for String {
2362 fn write_str(&mut self, s: &str) -> fmt::Result {
2368 fn write_char(&mut self, c: char) -> fmt::Result {
2374 /// A draining iterator for `String`.
2376 /// This struct is created by the [`drain`] method on [`String`]. See its
2377 /// documentation for more.
2379 /// [`drain`]: struct.String.html#method.drain
2380 /// [`String`]: struct.String.html
2381 #[stable(feature = "drain", since = "1.6.0")]
2382 pub struct Drain<'a> {
2383 /// Will be used as &'a mut String in the destructor
2384 string: *mut String,
2385 /// Start of part to remove
2387 /// End of part to remove
2389 /// Current remaining range to remove
2393 #[stable(feature = "collection_debug", since = "1.17.0")]
2394 impl fmt::Debug for Drain<'_> {
2395 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2396 f.pad("Drain { .. }")
2400 #[stable(feature = "drain", since = "1.6.0")]
2401 unsafe impl Sync for Drain<'_> {}
2402 #[stable(feature = "drain", since = "1.6.0")]
2403 unsafe impl Send for Drain<'_> {}
2405 #[stable(feature = "drain", since = "1.6.0")]
2406 impl Drop for Drain<'_> {
2407 fn drop(&mut self) {
2409 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
2410 // panic code being inserted again.
2411 let self_vec = (*self.string).as_mut_vec();
2412 if self.start <= self.end && self.end <= self_vec.len() {
2413 self_vec.drain(self.start..self.end);
2419 #[stable(feature = "drain", since = "1.6.0")]
2420 impl Iterator for Drain<'_> {
2424 fn next(&mut self) -> Option<char> {
2428 fn size_hint(&self) -> (usize, Option<usize>) {
2429 self.iter.size_hint()
2433 fn last(mut self) -> Option<char> {
2438 #[stable(feature = "drain", since = "1.6.0")]
2439 impl DoubleEndedIterator for Drain<'_> {
2441 fn next_back(&mut self) -> Option<char> {
2442 self.iter.next_back()
2446 #[stable(feature = "fused", since = "1.26.0")]
2447 impl FusedIterator for Drain<'_> {}