1 //! A UTF-8–encoded, growable string.
3 //! This module contains the [`String`] type, the [`ToString`] trait for
4 //! converting to strings, and several error types that may result from
5 //! working with [`String`]s.
9 //! There are multiple ways to create a new [`String`] from a string literal:
12 //! let s = "Hello".to_string();
14 //! let s = String::from("world");
15 //! let s: String = "also this".into();
18 //! You can create a new [`String`] from an existing one by concatenating with
22 //! let s = "Hello".to_string();
24 //! let message = s + " world!";
27 //! If you have a vector of valid UTF-8 bytes, you can make a [`String`] out of
28 //! it. You can do the reverse too.
31 //! let sparkle_heart = vec![240, 159, 146, 150];
33 //! // We know these bytes are valid, so we'll use `unwrap()`.
34 //! let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
36 //! assert_eq!("💖", sparkle_heart);
38 //! let bytes = sparkle_heart.into_bytes();
40 //! assert_eq!(bytes, [240, 159, 146, 150]);
43 #![stable(feature = "rust1", since = "1.0.0")]
45 use core::char::{decode_utf16, REPLACEMENT_CHARACTER};
48 use core::iter::{FromIterator, FusedIterator};
49 use core::ops::Bound::{Excluded, Included, Unbounded};
50 use core::ops::{self, Add, AddAssign, Index, IndexMut, Range, RangeBounds};
52 use core::str::{lossy, pattern::Pattern};
54 use crate::borrow::{Cow, ToOwned};
55 use crate::boxed::Box;
56 use crate::collections::TryReserveError;
57 use crate::str::{self, from_boxed_utf8_unchecked, Chars, FromStr, Utf8Error};
60 /// A UTF-8–encoded, growable string.
62 /// The `String` type is the most common string type that has ownership over the
63 /// contents of the string. It has a close relationship with its borrowed
64 /// counterpart, the primitive [`str`].
68 /// You can create a `String` from [a literal string][`str`] with [`String::from`]:
70 /// [`String::from`]: From::from
73 /// let hello = String::from("Hello, world!");
76 /// You can append a [`char`] to a `String` with the [`push`] method, and
77 /// append a [`&str`] with the [`push_str`] method:
80 /// let mut hello = String::from("Hello, ");
83 /// hello.push_str("orld!");
86 /// [`push`]: String::push
87 /// [`push_str`]: String::push_str
89 /// If you have a vector of UTF-8 bytes, you can create a `String` from it with
90 /// the [`from_utf8`] method:
93 /// // some bytes, in a vector
94 /// let sparkle_heart = vec![240, 159, 146, 150];
96 /// // We know these bytes are valid, so we'll use `unwrap()`.
97 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
99 /// assert_eq!("💖", sparkle_heart);
102 /// [`from_utf8`]: String::from_utf8
106 /// `String`s are always valid UTF-8. This has a few implications, the first of
107 /// which is that if you need a non-UTF-8 string, consider [`OsString`]. It is
108 /// similar, but without the UTF-8 constraint. The second implication is that
109 /// you cannot index into a `String`:
111 /// ```compile_fail,E0277
114 /// println!("The first letter of s is {}", s[0]); // ERROR!!!
117 /// [`OsString`]: ../../std/ffi/struct.OsString.html
119 /// Indexing is intended to be a constant-time operation, but UTF-8 encoding
120 /// does not allow us to do this. Furthermore, it's not clear what sort of
121 /// thing the index should return: a byte, a codepoint, or a grapheme cluster.
122 /// The [`bytes`] and [`chars`] methods return iterators over the first
123 /// two, respectively.
125 /// [`bytes`]: str::bytes
126 /// [`chars`]: str::chars
130 /// `String`s implement [`Deref`]`<Target=str>`, and so inherit all of [`str`]'s
131 /// methods. In addition, this means that you can pass a `String` to a
132 /// function which takes a [`&str`] by using an ampersand (`&`):
135 /// fn takes_str(s: &str) { }
137 /// let s = String::from("Hello");
142 /// This will create a [`&str`] from the `String` and pass it in. This
143 /// conversion is very inexpensive, and so generally, functions will accept
144 /// [`&str`]s as arguments unless they need a `String` for some specific
147 /// In certain cases Rust doesn't have enough information to make this
148 /// conversion, known as [`Deref`] coercion. In the following example a string
149 /// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
150 /// `example_func` takes anything that implements the trait. In this case Rust
151 /// would need to make two implicit conversions, which Rust doesn't have the
152 /// means to do. For that reason, the following example will not compile.
154 /// ```compile_fail,E0277
155 /// trait TraitExample {}
157 /// impl<'a> TraitExample for &'a str {}
159 /// fn example_func<A: TraitExample>(example_arg: A) {}
161 /// let example_string = String::from("example_string");
162 /// example_func(&example_string);
165 /// There are two options that would work instead. The first would be to
166 /// change the line `example_func(&example_string);` to
167 /// `example_func(example_string.as_str());`, using the method [`as_str()`]
168 /// to explicitly extract the string slice containing the string. The second
169 /// way changes `example_func(&example_string);` to
170 /// `example_func(&*example_string);`. In this case we are dereferencing a
171 /// `String` to a [`str`][`&str`], then referencing the [`str`][`&str`] back to
172 /// [`&str`]. The second way is more idiomatic, however both work to do the
173 /// conversion explicitly rather than relying on the implicit conversion.
177 /// A `String` is made up of three components: a pointer to some bytes, a
178 /// length, and a capacity. The pointer points to an internal buffer `String`
179 /// uses to store its data. The length is the number of bytes currently stored
180 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
181 /// the length will always be less than or equal to the capacity.
183 /// This buffer is always stored on the heap.
185 /// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
191 /// let story = String::from("Once upon a time...");
193 // FIXME Update this when vec_into_raw_parts is stabilized
194 /// // Prevent automatically dropping the String's data
195 /// let mut story = mem::ManuallyDrop::new(story);
197 /// let ptr = story.as_mut_ptr();
198 /// let len = story.len();
199 /// let capacity = story.capacity();
201 /// // story has nineteen bytes
202 /// assert_eq!(19, len);
204 /// // We can re-build a String out of ptr, len, and capacity. This is all
205 /// // unsafe because we are responsible for making sure the components are
207 /// let s = unsafe { String::from_raw_parts(ptr, len, capacity) } ;
209 /// assert_eq!(String::from("Once upon a time..."), s);
212 /// [`as_ptr`]: str::as_ptr
213 /// [`len`]: String::len
214 /// [`capacity`]: String::capacity
216 /// If a `String` has enough capacity, adding elements to it will not
217 /// re-allocate. For example, consider this program:
220 /// let mut s = String::new();
222 /// println!("{}", s.capacity());
225 /// s.push_str("hello");
226 /// println!("{}", s.capacity());
230 /// This will output the following:
241 /// At first, we have no memory allocated at all, but as we append to the
242 /// string, it increases its capacity appropriately. If we instead use the
243 /// [`with_capacity`] method to allocate the correct capacity initially:
246 /// let mut s = String::with_capacity(25);
248 /// println!("{}", s.capacity());
251 /// s.push_str("hello");
252 /// println!("{}", s.capacity());
256 /// [`with_capacity`]: String::with_capacity
258 /// We end up with a different output:
269 /// Here, there's no need to allocate more memory inside the loop.
271 /// [`str`]: prim@str
272 /// [`&str`]: prim@str
273 /// [`Deref`]: core::ops::Deref
274 /// [`as_str()`]: String::as_str
275 #[derive(PartialOrd, Eq, Ord)]
276 #[cfg_attr(not(test), rustc_diagnostic_item = "string_type")]
277 #[stable(feature = "rust1", since = "1.0.0")]
282 /// A possible error value when converting a `String` from a UTF-8 byte vector.
284 /// This type is the error type for the [`from_utf8`] method on [`String`]. It
285 /// is designed in such a way to carefully avoid reallocations: the
286 /// [`into_bytes`] method will give back the byte vector that was used in the
287 /// conversion attempt.
289 /// [`from_utf8`]: String::from_utf8
290 /// [`into_bytes`]: FromUtf8Error::into_bytes
292 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
293 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
294 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
295 /// through the [`utf8_error`] method.
297 /// [`Utf8Error`]: core::str::Utf8Error
298 /// [`std::str`]: core::str
299 /// [`&str`]: prim@str
300 /// [`utf8_error`]: Self::utf8_error
307 /// // some invalid bytes, in a vector
308 /// let bytes = vec![0, 159];
310 /// let value = String::from_utf8(bytes);
312 /// assert!(value.is_err());
313 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
315 #[stable(feature = "rust1", since = "1.0.0")]
316 #[derive(Debug, Clone, PartialEq, Eq)]
317 pub struct FromUtf8Error {
322 /// A possible error value when converting a `String` from a UTF-16 byte slice.
324 /// This type is the error type for the [`from_utf16`] method on [`String`].
326 /// [`from_utf16`]: String::from_utf16
332 /// // 𝄞mu<invalid>ic
333 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
334 /// 0xD800, 0x0069, 0x0063];
336 /// assert!(String::from_utf16(v).is_err());
338 #[stable(feature = "rust1", since = "1.0.0")]
340 pub struct FromUtf16Error(());
343 /// Creates a new empty `String`.
345 /// Given that the `String` is empty, this will not allocate any initial
346 /// buffer. While that means that this initial operation is very
347 /// inexpensive, it may cause excessive allocation later when you add
348 /// data. If you have an idea of how much data the `String` will hold,
349 /// consider the [`with_capacity`] method to prevent excessive
352 /// [`with_capacity`]: String::with_capacity
359 /// let s = String::new();
362 #[rustc_const_stable(feature = "const_string_new", since = "1.32.0")]
363 #[stable(feature = "rust1", since = "1.0.0")]
364 pub const fn new() -> String {
365 String { vec: Vec::new() }
368 /// Creates a new empty `String` with a particular capacity.
370 /// `String`s have an internal buffer to hold their data. The capacity is
371 /// the length of that buffer, and can be queried with the [`capacity`]
372 /// method. This method creates an empty `String`, but one with an initial
373 /// buffer that can hold `capacity` bytes. This is useful when you may be
374 /// appending a bunch of data to the `String`, reducing the number of
375 /// reallocations it needs to do.
377 /// [`capacity`]: String::capacity
379 /// If the given capacity is `0`, no allocation will occur, and this method
380 /// is identical to the [`new`] method.
382 /// [`new`]: String::new
389 /// let mut s = String::with_capacity(10);
391 /// // The String contains no chars, even though it has capacity for more
392 /// assert_eq!(s.len(), 0);
394 /// // These are all done without reallocating...
395 /// let cap = s.capacity();
400 /// assert_eq!(s.capacity(), cap);
402 /// // ...but this may make the string reallocate
406 #[stable(feature = "rust1", since = "1.0.0")]
407 pub fn with_capacity(capacity: usize) -> String {
408 String { vec: Vec::with_capacity(capacity) }
411 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
412 // required for this method definition, is not available. Since we don't
413 // require this method for testing purposes, I'll just stub it
414 // NB see the slice::hack module in slice.rs for more information
417 pub fn from_str(_: &str) -> String {
418 panic!("not available with cfg(test)");
421 /// Converts a vector of bytes to a `String`.
423 /// A string ([`String`]) is made of bytes ([`u8`]), and a vector of bytes
424 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
425 /// two. Not all byte slices are valid `String`s, however: `String`
426 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
427 /// the bytes are valid UTF-8, and then does the conversion.
429 /// If you are sure that the byte slice is valid UTF-8, and you don't want
430 /// to incur the overhead of the validity check, there is an unsafe version
431 /// of this function, [`from_utf8_unchecked`], which has the same behavior
432 /// but skips the check.
434 /// This method will take care to not copy the vector, for efficiency's
437 /// If you need a [`&str`] instead of a `String`, consider
438 /// [`str::from_utf8`].
440 /// The inverse of this method is [`into_bytes`].
444 /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
445 /// provided bytes are not UTF-8. The vector you moved in is also included.
452 /// // some bytes, in a vector
453 /// let sparkle_heart = vec![240, 159, 146, 150];
455 /// // We know these bytes are valid, so we'll use `unwrap()`.
456 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
458 /// assert_eq!("💖", sparkle_heart);
464 /// // some invalid bytes, in a vector
465 /// let sparkle_heart = vec![0, 159, 146, 150];
467 /// assert!(String::from_utf8(sparkle_heart).is_err());
470 /// See the docs for [`FromUtf8Error`] for more details on what you can do
473 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
474 /// [`Vec<u8>`]: crate::vec::Vec
475 /// [`&str`]: prim@str
476 /// [`into_bytes`]: String::into_bytes
478 #[stable(feature = "rust1", since = "1.0.0")]
479 pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
480 match str::from_utf8(&vec) {
481 Ok(..) => Ok(String { vec }),
482 Err(e) => Err(FromUtf8Error { bytes: vec, error: e }),
486 /// Converts a slice of bytes to a string, including invalid characters.
488 /// Strings are made of bytes ([`u8`]), and a slice of bytes
489 /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
490 /// between the two. Not all byte slices are valid strings, however: strings
491 /// are required to be valid UTF-8. During this conversion,
492 /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
493 /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: �
495 /// [byteslice]: ../../std/primitive.slice.html
496 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
498 /// If you are sure that the byte slice is valid UTF-8, and you don't want
499 /// to incur the overhead of the conversion, there is an unsafe version
500 /// of this function, [`from_utf8_unchecked`], which has the same behavior
501 /// but skips the checks.
503 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
505 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
506 /// UTF-8, then we need to insert the replacement characters, which will
507 /// change the size of the string, and hence, require a `String`. But if
508 /// it's already valid UTF-8, we don't need a new allocation. This return
509 /// type allows us to handle both cases.
511 /// [`Cow<'a, str>`]: crate::borrow::Cow
518 /// // some bytes, in a vector
519 /// let sparkle_heart = vec![240, 159, 146, 150];
521 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
523 /// assert_eq!("💖", sparkle_heart);
529 /// // some invalid bytes
530 /// let input = b"Hello \xF0\x90\x80World";
531 /// let output = String::from_utf8_lossy(input);
533 /// assert_eq!("Hello �World", output);
535 #[stable(feature = "rust1", since = "1.0.0")]
536 pub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, str> {
537 let mut iter = lossy::Utf8Lossy::from_bytes(v).chunks();
539 let (first_valid, first_broken) = if let Some(chunk) = iter.next() {
540 let lossy::Utf8LossyChunk { valid, broken } = chunk;
541 if valid.len() == v.len() {
542 debug_assert!(broken.is_empty());
543 return Cow::Borrowed(valid);
547 return Cow::Borrowed("");
550 const REPLACEMENT: &str = "\u{FFFD}";
552 let mut res = String::with_capacity(v.len());
553 res.push_str(first_valid);
554 if !first_broken.is_empty() {
555 res.push_str(REPLACEMENT);
558 for lossy::Utf8LossyChunk { valid, broken } in iter {
560 if !broken.is_empty() {
561 res.push_str(REPLACEMENT);
568 /// Decode a UTF-16–encoded vector `v` into a `String`, returning [`Err`]
569 /// if `v` contains any invalid data.
577 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
578 /// 0x0073, 0x0069, 0x0063];
579 /// assert_eq!(String::from("𝄞music"),
580 /// String::from_utf16(v).unwrap());
582 /// // 𝄞mu<invalid>ic
583 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
584 /// 0xD800, 0x0069, 0x0063];
585 /// assert!(String::from_utf16(v).is_err());
587 #[stable(feature = "rust1", since = "1.0.0")]
588 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
589 // This isn't done via collect::<Result<_, _>>() for performance reasons.
590 // FIXME: the function can be simplified again when #48994 is closed.
591 let mut ret = String::with_capacity(v.len());
592 for c in decode_utf16(v.iter().cloned()) {
596 return Err(FromUtf16Error(()));
602 /// Decode a UTF-16–encoded slice `v` into a `String`, replacing
603 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
605 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
606 /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
607 /// conversion requires a memory allocation.
609 /// [`from_utf8_lossy`]: String::from_utf8_lossy
610 /// [`Cow<'a, str>`]: crate::borrow::Cow
611 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
618 /// // 𝄞mus<invalid>ic<invalid>
619 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
620 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
623 /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
624 /// String::from_utf16_lossy(v));
627 #[stable(feature = "rust1", since = "1.0.0")]
628 pub fn from_utf16_lossy(v: &[u16]) -> String {
629 decode_utf16(v.iter().cloned()).map(|r| r.unwrap_or(REPLACEMENT_CHARACTER)).collect()
632 /// Decomposes a `String` into its raw components.
634 /// Returns the raw pointer to the underlying data, the length of
635 /// the string (in bytes), and the allocated capacity of the data
636 /// (in bytes). These are the same arguments in the same order as
637 /// the arguments to [`from_raw_parts`].
639 /// After calling this function, the caller is responsible for the
640 /// memory previously managed by the `String`. The only way to do
641 /// this is to convert the raw pointer, length, and capacity back
642 /// into a `String` with the [`from_raw_parts`] function, allowing
643 /// the destructor to perform the cleanup.
645 /// [`from_raw_parts`]: String::from_raw_parts
650 /// #![feature(vec_into_raw_parts)]
651 /// let s = String::from("hello");
653 /// let (ptr, len, cap) = s.into_raw_parts();
655 /// let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
656 /// assert_eq!(rebuilt, "hello");
658 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
659 pub fn into_raw_parts(self) -> (*mut u8, usize, usize) {
660 self.vec.into_raw_parts()
663 /// Creates a new `String` from a length, capacity, and pointer.
667 /// This is highly unsafe, due to the number of invariants that aren't
670 /// * The memory at `buf` needs to have been previously allocated by the
671 /// same allocator the standard library uses, with a required alignment of exactly 1.
672 /// * `length` needs to be less than or equal to `capacity`.
673 /// * `capacity` needs to be the correct value.
674 /// * The first `length` bytes at `buf` need to be valid UTF-8.
676 /// Violating these may cause problems like corrupting the allocator's
677 /// internal data structures.
679 /// The ownership of `buf` 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");
695 // FIXME Update this when vec_into_raw_parts is stabilized
696 /// // Prevent automatically dropping the String's data
697 /// let mut s = mem::ManuallyDrop::new(s);
699 /// let ptr = s.as_mut_ptr();
700 /// let len = s.len();
701 /// let capacity = s.capacity();
703 /// let s = String::from_raw_parts(ptr, len, capacity);
705 /// assert_eq!(String::from("hello"), s);
709 #[stable(feature = "rust1", since = "1.0.0")]
710 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
711 unsafe { String { vec: Vec::from_raw_parts(buf, length, capacity) } }
714 /// Converts a vector of bytes to a `String` without checking that the
715 /// string contains valid UTF-8.
717 /// See the safe version, [`from_utf8`], for more details.
719 /// [`from_utf8`]: String::from_utf8
723 /// This function is unsafe because it does not check that the bytes passed
724 /// to it are valid UTF-8. If this constraint is violated, it may cause
725 /// memory unsafety issues with future users of the `String`, as the rest of
726 /// the standard library assumes that `String`s are valid UTF-8.
733 /// // some bytes, in a vector
734 /// let sparkle_heart = vec![240, 159, 146, 150];
736 /// let sparkle_heart = unsafe {
737 /// String::from_utf8_unchecked(sparkle_heart)
740 /// assert_eq!("💖", sparkle_heart);
743 #[stable(feature = "rust1", since = "1.0.0")]
744 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
745 String { vec: bytes }
748 /// Converts a `String` into a byte vector.
750 /// This consumes the `String`, so we do not need to copy its contents.
757 /// let s = String::from("hello");
758 /// let bytes = s.into_bytes();
760 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
763 #[stable(feature = "rust1", since = "1.0.0")]
764 pub fn into_bytes(self) -> Vec<u8> {
768 /// Extracts a string slice containing the entire `String`.
775 /// let s = String::from("foo");
777 /// assert_eq!("foo", s.as_str());
780 #[stable(feature = "string_as_str", since = "1.7.0")]
781 pub fn as_str(&self) -> &str {
785 /// Converts a `String` into a mutable string slice.
792 /// let mut s = String::from("foobar");
793 /// let s_mut_str = s.as_mut_str();
795 /// s_mut_str.make_ascii_uppercase();
797 /// assert_eq!("FOOBAR", s_mut_str);
800 #[stable(feature = "string_as_str", since = "1.7.0")]
801 pub fn as_mut_str(&mut self) -> &mut str {
805 /// Appends a given string slice onto the end of this `String`.
812 /// let mut s = String::from("foo");
814 /// s.push_str("bar");
816 /// assert_eq!("foobar", s);
819 #[stable(feature = "rust1", since = "1.0.0")]
820 pub fn push_str(&mut self, string: &str) {
821 self.vec.extend_from_slice(string.as_bytes())
824 /// Returns this `String`'s capacity, in bytes.
831 /// let s = String::with_capacity(10);
833 /// assert!(s.capacity() >= 10);
836 #[stable(feature = "rust1", since = "1.0.0")]
837 pub fn capacity(&self) -> usize {
841 /// Ensures that this `String`'s capacity is at least `additional` bytes
842 /// larger than its length.
844 /// The capacity may be increased by more than `additional` bytes if it
845 /// chooses, to prevent frequent reallocations.
847 /// If you do not want this "at least" behavior, see the [`reserve_exact`]
852 /// Panics if the new capacity overflows [`usize`].
854 /// [`reserve_exact`]: String::reserve_exact
861 /// let mut s = String::new();
865 /// assert!(s.capacity() >= 10);
868 /// This may not actually increase the capacity:
871 /// let mut s = String::with_capacity(10);
875 /// // s now has a length of 2 and a capacity of 10
876 /// assert_eq!(2, s.len());
877 /// assert_eq!(10, s.capacity());
879 /// // Since we already have an extra 8 capacity, calling this...
882 /// // ... doesn't actually increase.
883 /// assert_eq!(10, s.capacity());
886 #[stable(feature = "rust1", since = "1.0.0")]
887 pub fn reserve(&mut self, additional: usize) {
888 self.vec.reserve(additional)
891 /// Ensures that this `String`'s capacity is `additional` bytes
892 /// larger than its length.
894 /// Consider using the [`reserve`] method unless you absolutely know
895 /// better than the allocator.
897 /// [`reserve`]: String::reserve
901 /// Panics if the new capacity overflows `usize`.
908 /// let mut s = String::new();
910 /// s.reserve_exact(10);
912 /// assert!(s.capacity() >= 10);
915 /// This may not actually increase the capacity:
918 /// let mut s = String::with_capacity(10);
922 /// // s now has a length of 2 and a capacity of 10
923 /// assert_eq!(2, s.len());
924 /// assert_eq!(10, s.capacity());
926 /// // Since we already have an extra 8 capacity, calling this...
927 /// s.reserve_exact(8);
929 /// // ... doesn't actually increase.
930 /// assert_eq!(10, s.capacity());
933 #[stable(feature = "rust1", since = "1.0.0")]
934 pub fn reserve_exact(&mut self, additional: usize) {
935 self.vec.reserve_exact(additional)
938 /// Tries to reserve capacity for at least `additional` more elements to be inserted
939 /// in the given `String`. The collection may reserve more space to avoid
940 /// frequent reallocations. After calling `reserve`, capacity will be
941 /// greater than or equal to `self.len() + additional`. Does nothing if
942 /// capacity is already sufficient.
946 /// If the capacity overflows, or the allocator reports a failure, then an error
952 /// #![feature(try_reserve)]
953 /// use std::collections::TryReserveError;
955 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
956 /// let mut output = String::new();
958 /// // Pre-reserve the memory, exiting if we can't
959 /// output.try_reserve(data.len())?;
961 /// // Now we know this can't OOM in the middle of our complex work
962 /// output.push_str(data);
966 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
968 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
969 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
970 self.vec.try_reserve(additional)
973 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
974 /// be inserted in the given `String`. After calling `reserve_exact`,
975 /// capacity will be greater than or equal to `self.len() + additional`.
976 /// Does nothing if the capacity is already sufficient.
978 /// Note that the allocator may give the collection more space than it
979 /// requests. Therefore, capacity can not be relied upon to be precisely
980 /// minimal. Prefer `reserve` if future insertions are expected.
984 /// If the capacity overflows, or the allocator reports a failure, then an error
990 /// #![feature(try_reserve)]
991 /// use std::collections::TryReserveError;
993 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
994 /// let mut output = String::new();
996 /// // Pre-reserve the memory, exiting if we can't
997 /// output.try_reserve(data.len())?;
999 /// // Now we know this can't OOM in the middle of our complex work
1000 /// output.push_str(data);
1004 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1006 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
1007 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
1008 self.vec.try_reserve_exact(additional)
1011 /// Shrinks the capacity of this `String` to match its length.
1018 /// let mut s = String::from("foo");
1021 /// assert!(s.capacity() >= 100);
1023 /// s.shrink_to_fit();
1024 /// assert_eq!(3, s.capacity());
1027 #[stable(feature = "rust1", since = "1.0.0")]
1028 pub fn shrink_to_fit(&mut self) {
1029 self.vec.shrink_to_fit()
1032 /// Shrinks the capacity of this `String` with a lower bound.
1034 /// The capacity will remain at least as large as both the length
1035 /// and the supplied value.
1037 /// Panics if the current capacity is smaller than the supplied
1038 /// minimum capacity.
1043 /// #![feature(shrink_to)]
1044 /// let mut s = String::from("foo");
1047 /// assert!(s.capacity() >= 100);
1049 /// s.shrink_to(10);
1050 /// assert!(s.capacity() >= 10);
1052 /// assert!(s.capacity() >= 3);
1055 #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")]
1056 pub fn shrink_to(&mut self, min_capacity: usize) {
1057 self.vec.shrink_to(min_capacity)
1060 /// Appends the given [`char`] to the end of this `String`.
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`]: String::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.
1122 /// let mut s = String::from("hello");
1126 /// assert_eq!("he", s);
1129 #[stable(feature = "rust1", since = "1.0.0")]
1130 pub fn truncate(&mut self, new_len: usize) {
1131 if new_len <= self.len() {
1132 assert!(self.is_char_boundary(new_len));
1133 self.vec.truncate(new_len)
1137 /// Removes the last character from the string buffer and returns it.
1139 /// Returns [`None`] if this `String` is empty.
1146 /// let mut s = String::from("foo");
1148 /// assert_eq!(s.pop(), Some('o'));
1149 /// assert_eq!(s.pop(), Some('o'));
1150 /// assert_eq!(s.pop(), Some('f'));
1152 /// assert_eq!(s.pop(), None);
1155 #[stable(feature = "rust1", since = "1.0.0")]
1156 pub fn pop(&mut self) -> Option<char> {
1157 let ch = self.chars().rev().next()?;
1158 let newlen = self.len() - ch.len_utf8();
1160 self.vec.set_len(newlen);
1165 /// Removes a [`char`] from this `String` at a byte position and returns it.
1167 /// This is an *O*(*n*) operation, as it requires copying every element in the
1172 /// Panics if `idx` is larger than or equal to the `String`'s length,
1173 /// or if it does not lie on a [`char`] boundary.
1180 /// let mut s = String::from("foo");
1182 /// assert_eq!(s.remove(0), 'f');
1183 /// assert_eq!(s.remove(1), 'o');
1184 /// assert_eq!(s.remove(0), 'o');
1187 #[stable(feature = "rust1", since = "1.0.0")]
1188 pub fn remove(&mut self, idx: usize) -> char {
1189 let ch = match self[idx..].chars().next() {
1191 None => panic!("cannot remove a char from the end of a string"),
1194 let next = idx + ch.len_utf8();
1195 let len = self.len();
1197 ptr::copy(self.vec.as_ptr().add(next), self.vec.as_mut_ptr().add(idx), len - next);
1198 self.vec.set_len(len - (next - idx));
1203 /// Retains only the characters specified by the predicate.
1205 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1206 /// This method operates in place, visiting each character exactly once in the
1207 /// original order, and preserves the order of the retained characters.
1212 /// let mut s = String::from("f_o_ob_ar");
1214 /// s.retain(|c| c != '_');
1216 /// assert_eq!(s, "foobar");
1219 /// The exact order may be useful for tracking external state, like an index.
1222 /// let mut s = String::from("abcde");
1223 /// let keep = [false, true, true, false, true];
1225 /// s.retain(|_| (keep[i], i += 1).0);
1226 /// assert_eq!(s, "bce");
1229 #[stable(feature = "string_retain", since = "1.26.0")]
1230 pub fn retain<F>(&mut self, mut f: F)
1232 F: FnMut(char) -> bool,
1234 let len = self.len();
1235 let mut del_bytes = 0;
1239 let ch = unsafe { self.get_unchecked(idx..len).chars().next().unwrap() };
1240 let ch_len = ch.len_utf8();
1243 del_bytes += ch_len;
1244 } else if del_bytes > 0 {
1247 self.vec.as_ptr().add(idx),
1248 self.vec.as_mut_ptr().add(idx - del_bytes),
1254 // Point idx to the next char
1260 self.vec.set_len(len - del_bytes);
1265 /// Inserts a character into this `String` at a byte position.
1267 /// This is an *O*(*n*) operation as it requires copying every element in the
1272 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1273 /// lie on a [`char`] boundary.
1280 /// let mut s = String::with_capacity(3);
1282 /// s.insert(0, 'f');
1283 /// s.insert(1, 'o');
1284 /// s.insert(2, 'o');
1286 /// assert_eq!("foo", s);
1289 #[stable(feature = "rust1", since = "1.0.0")]
1290 pub fn insert(&mut self, idx: usize, ch: char) {
1291 assert!(self.is_char_boundary(idx));
1292 let mut bits = [0; 4];
1293 let bits = ch.encode_utf8(&mut bits).as_bytes();
1296 self.insert_bytes(idx, bits);
1300 unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1301 let len = self.len();
1302 let amt = bytes.len();
1303 self.vec.reserve(amt);
1306 ptr::copy(self.vec.as_ptr().add(idx), self.vec.as_mut_ptr().add(idx + amt), len - idx);
1307 ptr::copy(bytes.as_ptr(), self.vec.as_mut_ptr().add(idx), amt);
1308 self.vec.set_len(len + amt);
1312 /// Inserts a string slice into this `String` at a byte position.
1314 /// This is an *O*(*n*) operation as it requires copying every element in the
1319 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1320 /// lie on a [`char`] boundary.
1327 /// let mut s = String::from("bar");
1329 /// s.insert_str(0, "foo");
1331 /// assert_eq!("foobar", s);
1334 #[stable(feature = "insert_str", since = "1.16.0")]
1335 pub fn insert_str(&mut self, idx: usize, string: &str) {
1336 assert!(self.is_char_boundary(idx));
1339 self.insert_bytes(idx, string.as_bytes());
1343 /// Returns a mutable reference to the contents of this `String`.
1347 /// This function is unsafe because it does not check that the bytes passed
1348 /// to it are valid UTF-8. If this constraint is violated, it may cause
1349 /// memory unsafety issues with future users of the `String`, as the rest of
1350 /// the standard library assumes that `String`s are valid UTF-8.
1357 /// let mut s = String::from("hello");
1360 /// let vec = s.as_mut_vec();
1361 /// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1365 /// assert_eq!(s, "olleh");
1368 #[stable(feature = "rust1", since = "1.0.0")]
1369 pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1373 /// Returns the length of this `String`, in bytes, not [`char`]s or
1374 /// graphemes. In other words, it may not be what a human considers the
1375 /// length of the string.
1382 /// let a = String::from("foo");
1383 /// assert_eq!(a.len(), 3);
1385 /// let fancy_f = String::from("ƒoo");
1386 /// assert_eq!(fancy_f.len(), 4);
1387 /// assert_eq!(fancy_f.chars().count(), 3);
1390 #[stable(feature = "rust1", since = "1.0.0")]
1391 pub fn len(&self) -> usize {
1395 /// Returns `true` if this `String` has a length of zero, and `false` otherwise.
1402 /// let mut v = String::new();
1403 /// assert!(v.is_empty());
1406 /// assert!(!v.is_empty());
1409 #[stable(feature = "rust1", since = "1.0.0")]
1410 pub fn is_empty(&self) -> bool {
1414 /// Splits the string into two at the given index.
1416 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1417 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1418 /// boundary of a UTF-8 code point.
1420 /// Note that the capacity of `self` does not change.
1424 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1425 /// code point of the string.
1431 /// let mut hello = String::from("Hello, World!");
1432 /// let world = hello.split_off(7);
1433 /// assert_eq!(hello, "Hello, ");
1434 /// assert_eq!(world, "World!");
1438 #[stable(feature = "string_split_off", since = "1.16.0")]
1439 #[must_use = "use `.truncate()` if you don't need the other half"]
1440 pub fn split_off(&mut self, at: usize) -> String {
1441 assert!(self.is_char_boundary(at));
1442 let other = self.vec.split_off(at);
1443 unsafe { String::from_utf8_unchecked(other) }
1446 /// Truncates this `String`, removing all contents.
1448 /// While this means the `String` will have a length of zero, it does not
1449 /// touch its capacity.
1456 /// let mut s = String::from("foo");
1460 /// assert!(s.is_empty());
1461 /// assert_eq!(0, s.len());
1462 /// assert_eq!(3, s.capacity());
1465 #[stable(feature = "rust1", since = "1.0.0")]
1466 pub fn clear(&mut self) {
1470 /// Creates a draining iterator that removes the specified range in the `String`
1471 /// and yields the removed `chars`.
1473 /// Note: The element range is removed even if the iterator is not
1474 /// consumed until the end.
1478 /// Panics if the starting point or end point do not lie on a [`char`]
1479 /// boundary, or if they're out of bounds.
1486 /// let mut s = String::from("α is alpha, β is beta");
1487 /// let beta_offset = s.find('β').unwrap_or(s.len());
1489 /// // Remove the range up until the β from the string
1490 /// let t: String = s.drain(..beta_offset).collect();
1491 /// assert_eq!(t, "α is alpha, ");
1492 /// assert_eq!(s, "β is beta");
1494 /// // A full range clears the string
1496 /// assert_eq!(s, "");
1498 #[stable(feature = "drain", since = "1.6.0")]
1499 pub fn drain<R>(&mut self, range: R) -> Drain<'_>
1501 R: RangeBounds<usize>,
1505 // The String version of Drain does not have the memory safety issues
1506 // of the vector version. The data is just plain bytes.
1507 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1508 // the removal will not happen.
1509 let Range { start, end } = range.assert_len(self.len());
1510 assert!(self.is_char_boundary(start));
1511 assert!(self.is_char_boundary(end));
1513 // Take out two simultaneous borrows. The &mut String won't be accessed
1514 // until iteration is over, in Drop.
1515 let self_ptr = self as *mut _;
1516 // SAFETY: `assert_len` and `is_char_boundary` do the appropriate bounds checks.
1517 let chars_iter = unsafe { self.get_unchecked(start..end) }.chars();
1519 Drain { start, end, iter: chars_iter, string: self_ptr }
1522 /// Removes the specified range in the string,
1523 /// and replaces it with the given string.
1524 /// The given string doesn't need to be the same length as the range.
1528 /// Panics if the starting point or end point do not lie on a [`char`]
1529 /// boundary, or if they're out of bounds.
1536 /// let mut s = String::from("α is alpha, β is beta");
1537 /// let beta_offset = s.find('β').unwrap_or(s.len());
1539 /// // Replace the range up until the β from the string
1540 /// s.replace_range(..beta_offset, "Α is capital alpha; ");
1541 /// assert_eq!(s, "Α is capital alpha; β is beta");
1543 #[stable(feature = "splice", since = "1.27.0")]
1544 pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
1546 R: RangeBounds<usize>,
1550 // Replace_range does not have the memory safety issues of a vector Splice.
1551 // of the vector version. The data is just plain bytes.
1553 match range.start_bound() {
1554 Included(&n) => assert!(self.is_char_boundary(n)),
1555 Excluded(&n) => assert!(self.is_char_boundary(n + 1)),
1558 match range.end_bound() {
1559 Included(&n) => assert!(self.is_char_boundary(n + 1)),
1560 Excluded(&n) => assert!(self.is_char_boundary(n)),
1564 unsafe { self.as_mut_vec() }.splice(range, replace_with.bytes());
1567 /// Converts this `String` into a [`Box`]`<`[`str`]`>`.
1569 /// This will drop any excess capacity.
1571 /// [`str`]: prim@str
1578 /// let s = String::from("hello");
1580 /// let b = s.into_boxed_str();
1582 #[stable(feature = "box_str", since = "1.4.0")]
1584 pub fn into_boxed_str(self) -> Box<str> {
1585 let slice = self.vec.into_boxed_slice();
1586 unsafe { from_boxed_utf8_unchecked(slice) }
1590 impl FromUtf8Error {
1591 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1598 /// // some invalid bytes, in a vector
1599 /// let bytes = vec![0, 159];
1601 /// let value = String::from_utf8(bytes);
1603 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1605 #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
1606 pub fn as_bytes(&self) -> &[u8] {
1610 /// Returns the bytes that were attempted to convert to a `String`.
1612 /// This method is carefully constructed to avoid allocation. It will
1613 /// consume the error, moving out the bytes, so that a copy of the bytes
1614 /// does not need to be made.
1621 /// // some invalid bytes, in a vector
1622 /// let bytes = vec![0, 159];
1624 /// let value = String::from_utf8(bytes);
1626 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1628 #[stable(feature = "rust1", since = "1.0.0")]
1629 pub fn into_bytes(self) -> Vec<u8> {
1633 /// Fetch a `Utf8Error` to get more details about the conversion failure.
1635 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1636 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1637 /// an analogue to `FromUtf8Error`. See its documentation for more details
1640 /// [`std::str`]: core::str
1641 /// [`&str`]: prim@str
1648 /// // some invalid bytes, in a vector
1649 /// let bytes = vec![0, 159];
1651 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1653 /// // the first byte is invalid here
1654 /// assert_eq!(1, error.valid_up_to());
1656 #[stable(feature = "rust1", since = "1.0.0")]
1657 pub fn utf8_error(&self) -> Utf8Error {
1662 #[stable(feature = "rust1", since = "1.0.0")]
1663 impl fmt::Display for FromUtf8Error {
1664 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1665 fmt::Display::fmt(&self.error, f)
1669 #[stable(feature = "rust1", since = "1.0.0")]
1670 impl fmt::Display for FromUtf16Error {
1671 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1672 fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
1676 #[stable(feature = "rust1", since = "1.0.0")]
1677 impl Clone for String {
1678 fn clone(&self) -> Self {
1679 String { vec: self.vec.clone() }
1682 fn clone_from(&mut self, source: &Self) {
1683 self.vec.clone_from(&source.vec);
1687 #[stable(feature = "rust1", since = "1.0.0")]
1688 impl FromIterator<char> for String {
1689 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
1690 let mut buf = String::new();
1696 #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
1697 impl<'a> FromIterator<&'a char> for String {
1698 fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
1699 let mut buf = String::new();
1705 #[stable(feature = "rust1", since = "1.0.0")]
1706 impl<'a> FromIterator<&'a str> for String {
1707 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
1708 let mut buf = String::new();
1714 #[stable(feature = "extend_string", since = "1.4.0")]
1715 impl FromIterator<String> for String {
1716 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
1717 let mut iterator = iter.into_iter();
1719 // Because we're iterating over `String`s, we can avoid at least
1720 // one allocation by getting the first string from the iterator
1721 // and appending to it all the subsequent strings.
1722 match iterator.next() {
1723 None => String::new(),
1725 buf.extend(iterator);
1732 #[stable(feature = "box_str2", since = "1.45.0")]
1733 impl FromIterator<Box<str>> for String {
1734 fn from_iter<I: IntoIterator<Item = Box<str>>>(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 iterator = iter.into_iter();
1746 // Because we're iterating over CoWs, we can (potentially) avoid at least
1747 // one allocation by getting the first item and appending to it all the
1748 // subsequent items.
1749 match iterator.next() {
1750 None => String::new(),
1752 let mut buf = cow.into_owned();
1753 buf.extend(iterator);
1760 #[stable(feature = "rust1", since = "1.0.0")]
1761 impl Extend<char> for String {
1762 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
1763 let iterator = iter.into_iter();
1764 let (lower_bound, _) = iterator.size_hint();
1765 self.reserve(lower_bound);
1766 iterator.for_each(move |c| self.push(c));
1770 fn extend_one(&mut self, c: char) {
1775 fn extend_reserve(&mut self, additional: usize) {
1776 self.reserve(additional);
1780 #[stable(feature = "extend_ref", since = "1.2.0")]
1781 impl<'a> Extend<&'a char> for String {
1782 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
1783 self.extend(iter.into_iter().cloned());
1787 fn extend_one(&mut self, &c: &'a char) {
1792 fn extend_reserve(&mut self, additional: usize) {
1793 self.reserve(additional);
1797 #[stable(feature = "rust1", since = "1.0.0")]
1798 impl<'a> Extend<&'a str> for String {
1799 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
1800 iter.into_iter().for_each(move |s| self.push_str(s));
1804 fn extend_one(&mut self, s: &'a str) {
1809 #[stable(feature = "box_str2", since = "1.45.0")]
1810 impl Extend<Box<str>> for String {
1811 fn extend<I: IntoIterator<Item = Box<str>>>(&mut self, iter: I) {
1812 iter.into_iter().for_each(move |s| self.push_str(&s));
1816 #[stable(feature = "extend_string", since = "1.4.0")]
1817 impl Extend<String> for String {
1818 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
1819 iter.into_iter().for_each(move |s| self.push_str(&s));
1823 fn extend_one(&mut self, s: String) {
1828 #[stable(feature = "herd_cows", since = "1.19.0")]
1829 impl<'a> Extend<Cow<'a, str>> for String {
1830 fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
1831 iter.into_iter().for_each(move |s| self.push_str(&s));
1835 fn extend_one(&mut self, s: Cow<'a, str>) {
1840 /// A convenience impl that delegates to the impl for `&str`.
1845 /// assert_eq!(String::from("Hello world").find("world"), Some(6));
1848 feature = "pattern",
1849 reason = "API not fully fleshed out and ready to be stabilized",
1852 impl<'a, 'b> Pattern<'a> for &'b String {
1853 type Searcher = <&'b str as Pattern<'a>>::Searcher;
1855 fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
1856 self[..].into_searcher(haystack)
1860 fn is_contained_in(self, haystack: &'a str) -> bool {
1861 self[..].is_contained_in(haystack)
1865 fn is_prefix_of(self, haystack: &'a str) -> bool {
1866 self[..].is_prefix_of(haystack)
1870 fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str> {
1871 self[..].strip_prefix_of(haystack)
1875 fn is_suffix_of(self, haystack: &'a str) -> bool {
1876 self[..].is_suffix_of(haystack)
1880 fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str> {
1881 self[..].strip_suffix_of(haystack)
1885 #[stable(feature = "rust1", since = "1.0.0")]
1886 impl PartialEq for String {
1888 fn eq(&self, other: &String) -> bool {
1889 PartialEq::eq(&self[..], &other[..])
1892 fn ne(&self, other: &String) -> bool {
1893 PartialEq::ne(&self[..], &other[..])
1897 macro_rules! impl_eq {
1898 ($lhs:ty, $rhs: ty) => {
1899 #[stable(feature = "rust1", since = "1.0.0")]
1900 #[allow(unused_lifetimes)]
1901 impl<'a, 'b> PartialEq<$rhs> for $lhs {
1903 fn eq(&self, other: &$rhs) -> bool {
1904 PartialEq::eq(&self[..], &other[..])
1907 fn ne(&self, other: &$rhs) -> bool {
1908 PartialEq::ne(&self[..], &other[..])
1912 #[stable(feature = "rust1", since = "1.0.0")]
1913 #[allow(unused_lifetimes)]
1914 impl<'a, 'b> PartialEq<$lhs> for $rhs {
1916 fn eq(&self, other: &$lhs) -> bool {
1917 PartialEq::eq(&self[..], &other[..])
1920 fn ne(&self, other: &$lhs) -> bool {
1921 PartialEq::ne(&self[..], &other[..])
1927 impl_eq! { String, str }
1928 impl_eq! { String, &'a str }
1929 impl_eq! { Cow<'a, str>, str }
1930 impl_eq! { Cow<'a, str>, &'b str }
1931 impl_eq! { Cow<'a, str>, String }
1933 #[stable(feature = "rust1", since = "1.0.0")]
1934 impl Default for String {
1935 /// Creates an empty `String`.
1937 fn default() -> String {
1942 #[stable(feature = "rust1", since = "1.0.0")]
1943 impl fmt::Display for String {
1945 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1946 fmt::Display::fmt(&**self, f)
1950 #[stable(feature = "rust1", since = "1.0.0")]
1951 impl fmt::Debug for String {
1953 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1954 fmt::Debug::fmt(&**self, f)
1958 #[stable(feature = "rust1", since = "1.0.0")]
1959 impl hash::Hash for String {
1961 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
1962 (**self).hash(hasher)
1966 /// Implements the `+` operator for concatenating two strings.
1968 /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
1969 /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
1970 /// every operation, which would lead to *O*(*n*^2) running time when building an *n*-byte string by
1971 /// repeated concatenation.
1973 /// The string on the right-hand side is only borrowed; its contents are copied into the returned
1978 /// Concatenating two `String`s takes the first by value and borrows the second:
1981 /// let a = String::from("hello");
1982 /// let b = String::from(" world");
1984 /// // `a` is moved and can no longer be used here.
1987 /// If you want to keep using the first `String`, you can clone it and append to the clone instead:
1990 /// let a = String::from("hello");
1991 /// let b = String::from(" world");
1992 /// let c = a.clone() + &b;
1993 /// // `a` is still valid here.
1996 /// Concatenating `&str` slices can be done by converting the first to a `String`:
1999 /// let a = "hello";
2000 /// let b = " world";
2001 /// let c = a.to_string() + b;
2003 #[stable(feature = "rust1", since = "1.0.0")]
2004 impl Add<&str> for String {
2005 type Output = String;
2008 fn add(mut self, other: &str) -> String {
2009 self.push_str(other);
2014 /// Implements the `+=` operator for appending to a `String`.
2016 /// This has the same behavior as the [`push_str`][String::push_str] method.
2017 #[stable(feature = "stringaddassign", since = "1.12.0")]
2018 impl AddAssign<&str> for String {
2020 fn add_assign(&mut self, other: &str) {
2021 self.push_str(other);
2025 #[stable(feature = "rust1", since = "1.0.0")]
2026 impl ops::Index<ops::Range<usize>> for String {
2030 fn index(&self, index: ops::Range<usize>) -> &str {
2034 #[stable(feature = "rust1", since = "1.0.0")]
2035 impl ops::Index<ops::RangeTo<usize>> for String {
2039 fn index(&self, index: ops::RangeTo<usize>) -> &str {
2043 #[stable(feature = "rust1", since = "1.0.0")]
2044 impl ops::Index<ops::RangeFrom<usize>> for String {
2048 fn index(&self, index: ops::RangeFrom<usize>) -> &str {
2052 #[stable(feature = "rust1", since = "1.0.0")]
2053 impl ops::Index<ops::RangeFull> for String {
2057 fn index(&self, _index: ops::RangeFull) -> &str {
2058 unsafe { str::from_utf8_unchecked(&self.vec) }
2061 #[stable(feature = "inclusive_range", since = "1.26.0")]
2062 impl ops::Index<ops::RangeInclusive<usize>> for String {
2066 fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
2067 Index::index(&**self, index)
2070 #[stable(feature = "inclusive_range", since = "1.26.0")]
2071 impl ops::Index<ops::RangeToInclusive<usize>> for String {
2075 fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
2076 Index::index(&**self, index)
2080 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2081 impl ops::IndexMut<ops::Range<usize>> for String {
2083 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
2084 &mut self[..][index]
2087 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2088 impl ops::IndexMut<ops::RangeTo<usize>> for String {
2090 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
2091 &mut self[..][index]
2094 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2095 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
2097 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
2098 &mut self[..][index]
2101 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2102 impl ops::IndexMut<ops::RangeFull> for String {
2104 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
2105 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2108 #[stable(feature = "inclusive_range", since = "1.26.0")]
2109 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
2111 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
2112 IndexMut::index_mut(&mut **self, index)
2115 #[stable(feature = "inclusive_range", since = "1.26.0")]
2116 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
2118 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
2119 IndexMut::index_mut(&mut **self, index)
2123 #[stable(feature = "rust1", since = "1.0.0")]
2124 impl ops::Deref for String {
2128 fn deref(&self) -> &str {
2129 unsafe { str::from_utf8_unchecked(&self.vec) }
2133 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2134 impl ops::DerefMut for String {
2136 fn deref_mut(&mut self) -> &mut str {
2137 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2141 /// A type alias for [`Infallible`].
2143 /// This alias exists for backwards compatibility, and may be eventually deprecated.
2145 /// [`Infallible`]: core::convert::Infallible
2146 #[stable(feature = "str_parse_error", since = "1.5.0")]
2147 pub type ParseError = core::convert::Infallible;
2149 #[stable(feature = "rust1", since = "1.0.0")]
2150 impl FromStr for String {
2151 type Err = core::convert::Infallible;
2153 fn from_str(s: &str) -> Result<String, Self::Err> {
2158 /// A trait for converting a value to a `String`.
2160 /// This trait is automatically implemented for any type which implements the
2161 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
2162 /// [`Display`] should be implemented instead, and you get the `ToString`
2163 /// implementation for free.
2165 /// [`Display`]: fmt::Display
2166 #[stable(feature = "rust1", since = "1.0.0")]
2167 pub trait ToString {
2168 /// Converts the given value to a `String`.
2176 /// let five = String::from("5");
2178 /// assert_eq!(five, i.to_string());
2180 #[rustc_conversion_suggestion]
2181 #[stable(feature = "rust1", since = "1.0.0")]
2182 fn to_string(&self) -> String;
2187 /// In this implementation, the `to_string` method panics
2188 /// if the `Display` implementation returns an error.
2189 /// This indicates an incorrect `Display` implementation
2190 /// since `fmt::Write for String` never returns an error itself.
2191 #[stable(feature = "rust1", since = "1.0.0")]
2192 impl<T: fmt::Display + ?Sized> ToString for T {
2193 // A common guideline is to not inline generic functions. However,
2194 // removing `#[inline]` from this method causes non-negligible regressions.
2195 // See <https://github.com/rust-lang/rust/pull/74852>, the last attempt
2196 // to try to remove it.
2198 default fn to_string(&self) -> String {
2200 let mut buf = String::new();
2201 buf.write_fmt(format_args!("{}", self))
2202 .expect("a Display implementation returned an error unexpectedly");
2207 #[stable(feature = "char_to_string_specialization", since = "1.46.0")]
2208 impl ToString for char {
2210 fn to_string(&self) -> String {
2211 String::from(self.encode_utf8(&mut [0; 4]))
2215 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
2216 impl ToString for str {
2218 fn to_string(&self) -> String {
2223 #[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
2224 impl ToString for Cow<'_, str> {
2226 fn to_string(&self) -> String {
2231 #[stable(feature = "string_to_string_specialization", since = "1.17.0")]
2232 impl ToString for String {
2234 fn to_string(&self) -> String {
2239 #[stable(feature = "rust1", since = "1.0.0")]
2240 impl AsRef<str> for String {
2242 fn as_ref(&self) -> &str {
2247 #[stable(feature = "string_as_mut", since = "1.43.0")]
2248 impl AsMut<str> for String {
2250 fn as_mut(&mut self) -> &mut str {
2255 #[stable(feature = "rust1", since = "1.0.0")]
2256 impl AsRef<[u8]> for String {
2258 fn as_ref(&self) -> &[u8] {
2263 #[stable(feature = "rust1", since = "1.0.0")]
2264 impl From<&str> for String {
2266 fn from(s: &str) -> String {
2271 #[stable(feature = "from_mut_str_for_string", since = "1.44.0")]
2272 impl From<&mut str> for String {
2273 /// Converts a `&mut str` into a `String`.
2275 /// The result is allocated on the heap.
2277 fn from(s: &mut str) -> String {
2282 #[stable(feature = "from_ref_string", since = "1.35.0")]
2283 impl From<&String> for String {
2285 fn from(s: &String) -> String {
2290 // note: test pulls in libstd, which causes errors here
2292 #[stable(feature = "string_from_box", since = "1.18.0")]
2293 impl From<Box<str>> for String {
2294 /// Converts the given boxed `str` slice to a `String`.
2295 /// It is notable that the `str` slice is owned.
2302 /// let s1: String = String::from("hello world");
2303 /// let s2: Box<str> = s1.into_boxed_str();
2304 /// let s3: String = String::from(s2);
2306 /// assert_eq!("hello world", s3)
2308 fn from(s: Box<str>) -> String {
2313 #[stable(feature = "box_from_str", since = "1.20.0")]
2314 impl From<String> for Box<str> {
2315 /// Converts the given `String` to a boxed `str` slice that is owned.
2322 /// let s1: String = String::from("hello world");
2323 /// let s2: Box<str> = Box::from(s1);
2324 /// let s3: String = String::from(s2);
2326 /// assert_eq!("hello world", s3)
2328 fn from(s: String) -> Box<str> {
2333 #[stable(feature = "string_from_cow_str", since = "1.14.0")]
2334 impl<'a> From<Cow<'a, str>> for String {
2335 fn from(s: Cow<'a, str>) -> String {
2340 #[stable(feature = "rust1", since = "1.0.0")]
2341 impl<'a> From<&'a str> for Cow<'a, str> {
2343 fn from(s: &'a str) -> Cow<'a, str> {
2348 #[stable(feature = "rust1", since = "1.0.0")]
2349 impl<'a> From<String> for Cow<'a, str> {
2351 fn from(s: String) -> Cow<'a, str> {
2356 #[stable(feature = "cow_from_string_ref", since = "1.28.0")]
2357 impl<'a> From<&'a String> for Cow<'a, str> {
2359 fn from(s: &'a String) -> Cow<'a, str> {
2360 Cow::Borrowed(s.as_str())
2364 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2365 impl<'a> FromIterator<char> for Cow<'a, str> {
2366 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
2367 Cow::Owned(FromIterator::from_iter(it))
2371 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2372 impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
2373 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
2374 Cow::Owned(FromIterator::from_iter(it))
2378 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2379 impl<'a> FromIterator<String> for Cow<'a, str> {
2380 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
2381 Cow::Owned(FromIterator::from_iter(it))
2385 #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
2386 impl From<String> for Vec<u8> {
2387 /// Converts the given `String` to a vector `Vec` that holds values of type `u8`.
2394 /// let s1 = String::from("hello world");
2395 /// let v1 = Vec::from(s1);
2398 /// println!("{}", b);
2401 fn from(string: String) -> Vec<u8> {
2406 #[stable(feature = "rust1", since = "1.0.0")]
2407 impl fmt::Write for String {
2409 fn write_str(&mut self, s: &str) -> fmt::Result {
2415 fn write_char(&mut self, c: char) -> fmt::Result {
2421 /// A draining iterator for `String`.
2423 /// This struct is created by the [`drain`] method on [`String`]. See its
2424 /// documentation for more.
2426 /// [`drain`]: String::drain
2427 #[stable(feature = "drain", since = "1.6.0")]
2428 pub struct Drain<'a> {
2429 /// Will be used as &'a mut String in the destructor
2430 string: *mut String,
2431 /// Start of part to remove
2433 /// End of part to remove
2435 /// Current remaining range to remove
2439 #[stable(feature = "collection_debug", since = "1.17.0")]
2440 impl fmt::Debug for Drain<'_> {
2441 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2442 f.debug_tuple("Drain").field(&self.as_str()).finish()
2446 #[stable(feature = "drain", since = "1.6.0")]
2447 unsafe impl Sync for Drain<'_> {}
2448 #[stable(feature = "drain", since = "1.6.0")]
2449 unsafe impl Send for Drain<'_> {}
2451 #[stable(feature = "drain", since = "1.6.0")]
2452 impl Drop for Drain<'_> {
2453 fn drop(&mut self) {
2455 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
2456 // panic code being inserted again.
2457 let self_vec = (*self.string).as_mut_vec();
2458 if self.start <= self.end && self.end <= self_vec.len() {
2459 self_vec.drain(self.start..self.end);
2465 impl<'a> Drain<'a> {
2466 /// Returns the remaining (sub)string of this iterator as a slice.
2471 /// #![feature(string_drain_as_str)]
2472 /// let mut s = String::from("abc");
2473 /// let mut drain = s.drain(..);
2474 /// assert_eq!(drain.as_str(), "abc");
2475 /// let _ = drain.next().unwrap();
2476 /// assert_eq!(drain.as_str(), "bc");
2478 #[unstable(feature = "string_drain_as_str", issue = "76905")] // Note: uncomment AsRef impls below when stabilizing.
2479 pub fn as_str(&self) -> &str {
2484 // Uncomment when stabilizing `string_drain_as_str`.
2485 // #[unstable(feature = "string_drain_as_str", issue = "76905")]
2486 // impl<'a> AsRef<str> for Drain<'a> {
2487 // fn as_ref(&self) -> &str {
2492 // #[unstable(feature = "string_drain_as_str", issue = "76905")]
2493 // impl<'a> AsRef<[u8]> for Drain<'a> {
2494 // fn as_ref(&self) -> &[u8] {
2495 // self.as_str().as_bytes()
2499 #[stable(feature = "drain", since = "1.6.0")]
2500 impl Iterator for Drain<'_> {
2504 fn next(&mut self) -> Option<char> {
2508 fn size_hint(&self) -> (usize, Option<usize>) {
2509 self.iter.size_hint()
2513 fn last(mut self) -> Option<char> {
2518 #[stable(feature = "drain", since = "1.6.0")]
2519 impl DoubleEndedIterator for Drain<'_> {
2521 fn next_back(&mut self) -> Option<char> {
2522 self.iter.next_back()
2526 #[stable(feature = "fused", since = "1.26.0")]
2527 impl FusedIterator for Drain<'_> {}
2529 #[stable(feature = "from_char_for_string", since = "1.46.0")]
2530 impl From<char> for String {
2532 fn from(c: char) -> Self {