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::CollectionAllocErr;
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) {}
168 /// let example_string = String::from("example_string");
169 /// example_func(&example_string);
173 /// There are two options that would work instead. The first would be to
174 /// change the line `example_func(&example_string);` to
175 /// `example_func(example_string.as_str());`, using the method [`as_str()`]
176 /// to explicitly extract the string slice containing the string. The second
177 /// way changes `example_func(&example_string);` to
178 /// `example_func(&*example_string);`. In this case we are dereferencing a
179 /// `String` to a [`str`][`&str`], then referencing the [`str`][`&str`] back to
180 /// [`&str`]. The second way is more idiomatic, however both work to do the
181 /// conversion explicitly rather than relying on the implicit conversion.
185 /// A `String` is made up of three components: a pointer to some bytes, a
186 /// length, and a capacity. The pointer points to an internal buffer `String`
187 /// uses to store its data. The length is the number of bytes currently stored
188 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
189 /// the length will always be less than or equal to the capacity.
191 /// This buffer is always stored on the heap.
193 /// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
199 /// let story = String::from("Once upon a time...");
201 /// let ptr = story.as_ptr();
202 /// let len = story.len();
203 /// let capacity = story.capacity();
205 /// // story has nineteen bytes
206 /// assert_eq!(19, len);
208 /// // Now that we have our parts, we throw the story away.
209 /// mem::forget(story);
211 /// // We can re-build a String out of ptr, len, and capacity. This is all
212 /// // unsafe because we are responsible for making sure the components are
214 /// let s = unsafe { String::from_raw_parts(ptr as *mut _, len, capacity) } ;
216 /// assert_eq!(String::from("Once upon a time..."), s);
219 /// [`as_ptr`]: #method.as_ptr
220 /// [`len`]: #method.len
221 /// [`capacity`]: #method.capacity
223 /// If a `String` has enough capacity, adding elements to it will not
224 /// re-allocate. For example, consider this program:
227 /// let mut s = String::new();
229 /// println!("{}", s.capacity());
232 /// s.push_str("hello");
233 /// println!("{}", s.capacity());
237 /// This will output the following:
248 /// At first, we have no memory allocated at all, but as we append to the
249 /// string, it increases its capacity appropriately. If we instead use the
250 /// [`with_capacity`] method to allocate the correct capacity initially:
253 /// let mut s = String::with_capacity(25);
255 /// println!("{}", s.capacity());
258 /// s.push_str("hello");
259 /// println!("{}", s.capacity());
263 /// [`with_capacity`]: #method.with_capacity
265 /// We end up with a different output:
276 /// Here, there's no need to allocate more memory inside the loop.
278 /// [`&str`]: ../../std/primitive.str.html
279 /// [`Deref`]: ../../std/ops/trait.Deref.html
280 /// [`as_str()`]: struct.String.html#method.as_str
281 #[derive(PartialOrd, Eq, Ord)]
282 #[stable(feature = "rust1", since = "1.0.0")]
287 /// A possible error value when converting a `String` from a UTF-8 byte vector.
289 /// This type is the error type for the [`from_utf8`] method on [`String`]. It
290 /// is designed in such a way to carefully avoid reallocations: the
291 /// [`into_bytes`] method will give back the byte vector that was used in the
292 /// conversion attempt.
294 /// [`from_utf8`]: struct.String.html#method.from_utf8
295 /// [`String`]: struct.String.html
296 /// [`into_bytes`]: struct.FromUtf8Error.html#method.into_bytes
298 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
299 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
300 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
301 /// through the [`utf8_error`] method.
303 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
304 /// [`std::str`]: ../../std/str/index.html
305 /// [`u8`]: ../../std/primitive.u8.html
306 /// [`&str`]: ../../std/primitive.str.html
307 /// [`utf8_error`]: #method.utf8_error
314 /// // some invalid bytes, in a vector
315 /// let bytes = vec![0, 159];
317 /// let value = String::from_utf8(bytes);
319 /// assert!(value.is_err());
320 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
322 #[stable(feature = "rust1", since = "1.0.0")]
324 pub struct FromUtf8Error {
329 /// A possible error value when converting a `String` from a UTF-16 byte slice.
331 /// This type is the error type for the [`from_utf16`] method on [`String`].
333 /// [`from_utf16`]: struct.String.html#method.from_utf16
334 /// [`String`]: struct.String.html
341 /// // 𝄞mu<invalid>ic
342 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
343 /// 0xD800, 0x0069, 0x0063];
345 /// assert!(String::from_utf16(v).is_err());
347 #[stable(feature = "rust1", since = "1.0.0")]
349 pub struct FromUtf16Error(());
352 /// Creates a new empty `String`.
354 /// Given that the `String` is empty, this will not allocate any initial
355 /// buffer. While that means that this initial operation is very
356 /// inexpensive, it may cause excessive allocation later when you add
357 /// data. If you have an idea of how much data the `String` will hold,
358 /// consider the [`with_capacity`] method to prevent excessive
361 /// [`with_capacity`]: #method.with_capacity
368 /// let s = String::new();
371 #[stable(feature = "rust1", since = "1.0.0")]
372 #[rustc_const_unstable(feature = "const_string_new")]
373 pub const fn new() -> String {
374 String { vec: Vec::new() }
377 /// Creates a new empty `String` with a particular capacity.
379 /// `String`s have an internal buffer to hold their data. The capacity is
380 /// the length of that buffer, and can be queried with the [`capacity`]
381 /// method. This method creates an empty `String`, but one with an initial
382 /// buffer that can hold `capacity` bytes. This is useful when you may be
383 /// appending a bunch of data to the `String`, reducing the number of
384 /// reallocations it needs to do.
386 /// [`capacity`]: #method.capacity
388 /// If the given capacity is `0`, no allocation will occur, and this method
389 /// is identical to the [`new`] method.
391 /// [`new`]: #method.new
398 /// let mut s = String::with_capacity(10);
400 /// // The String contains no chars, even though it has capacity for more
401 /// assert_eq!(s.len(), 0);
403 /// // These are all done without reallocating...
404 /// let cap = s.capacity();
409 /// assert_eq!(s.capacity(), cap);
411 /// // ...but this may make the vector reallocate
415 #[stable(feature = "rust1", since = "1.0.0")]
416 pub fn with_capacity(capacity: usize) -> String {
417 String { vec: Vec::with_capacity(capacity) }
420 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
421 // required for this method definition, is not available. Since we don't
422 // require this method for testing purposes, I'll just stub it
423 // NB see the slice::hack module in slice.rs for more information
426 pub fn from_str(_: &str) -> String {
427 panic!("not available with cfg(test)");
430 /// Converts a vector of bytes to a `String`.
432 /// A string slice ([`&str`]) is made of bytes ([`u8`]), and a vector of bytes
433 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
434 /// two. Not all byte slices are valid `String`s, however: `String`
435 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
436 /// the bytes are valid UTF-8, and then does the conversion.
438 /// If you are sure that the byte slice is valid UTF-8, and you don't want
439 /// to incur the overhead of the validity check, there is an unsafe version
440 /// of this function, [`from_utf8_unchecked`], which has the same behavior
441 /// but skips the check.
443 /// This method will take care to not copy the vector, for efficiency's
446 /// If you need a [`&str`] instead of a `String`, consider
447 /// [`str::from_utf8`].
449 /// The inverse of this method is [`as_bytes`].
453 /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
454 /// provided bytes are not UTF-8. The vector you moved in is also included.
461 /// // some bytes, in a vector
462 /// let sparkle_heart = vec![240, 159, 146, 150];
464 /// // We know these bytes are valid, so we'll use `unwrap()`.
465 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
467 /// assert_eq!("💖", sparkle_heart);
473 /// // some invalid bytes, in a vector
474 /// let sparkle_heart = vec![0, 159, 146, 150];
476 /// assert!(String::from_utf8(sparkle_heart).is_err());
479 /// See the docs for [`FromUtf8Error`] for more details on what you can do
482 /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
483 /// [`&str`]: ../../std/primitive.str.html
484 /// [`u8`]: ../../std/primitive.u8.html
485 /// [`Vec<u8>`]: ../../std/vec/struct.Vec.html
486 /// [`str::from_utf8`]: ../../std/str/fn.from_utf8.html
487 /// [`as_bytes`]: struct.String.html#method.as_bytes
488 /// [`FromUtf8Error`]: struct.FromUtf8Error.html
489 /// [`Err`]: ../../stdresult/enum.Result.html#variant.Err
491 #[stable(feature = "rust1", since = "1.0.0")]
492 pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
493 match str::from_utf8(&vec) {
494 Ok(..) => Ok(String { vec }),
504 /// Converts a slice of bytes to a string, including invalid characters.
506 /// Strings are made of bytes ([`u8`]), and a slice of bytes
507 /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
508 /// between the two. Not all byte slices are valid strings, however: strings
509 /// are required to be valid UTF-8. During this conversion,
510 /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
511 /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: �
513 /// [`u8`]: ../../std/primitive.u8.html
514 /// [byteslice]: ../../std/primitive.slice.html
515 /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
517 /// If you are sure that the byte slice is valid UTF-8, and you don't want
518 /// to incur the overhead of the conversion, there is an unsafe version
519 /// of this function, [`from_utf8_unchecked`], which has the same behavior
520 /// but skips the checks.
522 /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
524 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
525 /// UTF-8, then we need to insert the replacement characters, which will
526 /// change the size of the string, and hence, require a `String`. But if
527 /// it's already valid UTF-8, we don't need a new allocation. This return
528 /// type allows us to handle both cases.
530 /// [`Cow<'a, str>`]: ../../std/borrow/enum.Cow.html
537 /// // some bytes, in a vector
538 /// let sparkle_heart = vec![240, 159, 146, 150];
540 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
542 /// assert_eq!("💖", sparkle_heart);
548 /// // some invalid bytes
549 /// let input = b"Hello \xF0\x90\x80World";
550 /// let output = String::from_utf8_lossy(input);
552 /// assert_eq!("Hello �World", output);
554 #[stable(feature = "rust1", since = "1.0.0")]
555 pub fn from_utf8_lossy<'a>(v: &'a [u8]) -> Cow<'a, str> {
556 let mut iter = lossy::Utf8Lossy::from_bytes(v).chunks();
558 let (first_valid, first_broken) = if let Some(chunk) = iter.next() {
559 let lossy::Utf8LossyChunk { valid, broken } = chunk;
560 if valid.len() == v.len() {
561 debug_assert!(broken.is_empty());
562 return Cow::Borrowed(valid);
566 return Cow::Borrowed("");
569 const REPLACEMENT: &str = "\u{FFFD}";
571 let mut res = String::with_capacity(v.len());
572 res.push_str(first_valid);
573 if !first_broken.is_empty() {
574 res.push_str(REPLACEMENT);
577 for lossy::Utf8LossyChunk { valid, broken } in iter {
579 if !broken.is_empty() {
580 res.push_str(REPLACEMENT);
587 /// Decode a UTF-16 encoded vector `v` into a `String`, returning [`Err`]
588 /// if `v` contains any invalid data.
590 /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
598 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
599 /// 0x0073, 0x0069, 0x0063];
600 /// assert_eq!(String::from("𝄞music"),
601 /// String::from_utf16(v).unwrap());
603 /// // 𝄞mu<invalid>ic
604 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
605 /// 0xD800, 0x0069, 0x0063];
606 /// assert!(String::from_utf16(v).is_err());
608 #[stable(feature = "rust1", since = "1.0.0")]
609 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
610 // This isn't done via collect::<Result<_, _>>() for performance reasons.
611 // FIXME: the function can be simplified again when #48994 is closed.
612 let mut ret = String::with_capacity(v.len());
613 for c in decode_utf16(v.iter().cloned()) {
617 return Err(FromUtf16Error(()));
623 /// Decode a UTF-16 encoded slice `v` into a `String`, replacing
624 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
626 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
627 /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
628 /// conversion requires a memory allocation.
630 /// [`from_utf8_lossy`]: #method.from_utf8_lossy
631 /// [`Cow<'a, str>`]: ../borrow/enum.Cow.html
632 /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
639 /// // 𝄞mus<invalid>ic<invalid>
640 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
641 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
644 /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
645 /// String::from_utf16_lossy(v));
648 #[stable(feature = "rust1", since = "1.0.0")]
649 pub fn from_utf16_lossy(v: &[u16]) -> String {
650 decode_utf16(v.iter().cloned()).map(|r| r.unwrap_or(REPLACEMENT_CHARACTER)).collect()
653 /// Creates a new `String` from a length, capacity, and pointer.
657 /// This is highly unsafe, due to the number of invariants that aren't
660 /// * The memory at `ptr` needs to have been previously allocated by the
661 /// same allocator the standard library uses.
662 /// * `length` needs to be less than or equal to `capacity`.
663 /// * `capacity` needs to be the correct value.
665 /// Violating these may cause problems like corrupting the allocator's
666 /// internal data structures.
668 /// The ownership of `ptr` is effectively transferred to the
669 /// `String` which may then deallocate, reallocate or change the
670 /// contents of memory pointed to by the pointer at will. Ensure
671 /// that nothing else uses the pointer after calling this
682 /// let s = String::from("hello");
683 /// let ptr = s.as_ptr();
684 /// let len = s.len();
685 /// let capacity = s.capacity();
689 /// let s = String::from_raw_parts(ptr as *mut _, len, capacity);
691 /// assert_eq!(String::from("hello"), s);
695 #[stable(feature = "rust1", since = "1.0.0")]
696 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
697 String { vec: Vec::from_raw_parts(buf, length, capacity) }
700 /// Converts a vector of bytes to a `String` without checking that the
701 /// string contains valid UTF-8.
703 /// See the safe version, [`from_utf8`], for more details.
705 /// [`from_utf8`]: struct.String.html#method.from_utf8
709 /// This function is unsafe because it does not check that the bytes passed
710 /// to it are valid UTF-8. If this constraint is violated, it may cause
711 /// memory unsafety issues with future users of the `String`, as the rest of
712 /// the standard library assumes that `String`s are valid UTF-8.
719 /// // some bytes, in a vector
720 /// let sparkle_heart = vec![240, 159, 146, 150];
722 /// let sparkle_heart = unsafe {
723 /// String::from_utf8_unchecked(sparkle_heart)
726 /// assert_eq!("💖", sparkle_heart);
729 #[stable(feature = "rust1", since = "1.0.0")]
730 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
731 String { vec: bytes }
734 /// Converts a `String` into a byte vector.
736 /// This consumes the `String`, so we do not need to copy its contents.
743 /// let s = String::from("hello");
744 /// let bytes = s.into_bytes();
746 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
749 #[stable(feature = "rust1", since = "1.0.0")]
750 pub fn into_bytes(self) -> Vec<u8> {
754 /// Extracts a string slice containing the entire `String`.
761 /// let s = String::from("foo");
763 /// assert_eq!("foo", s.as_str());
766 #[stable(feature = "string_as_str", since = "1.7.0")]
767 pub fn as_str(&self) -> &str {
771 /// Converts a `String` into a mutable string slice.
778 /// let mut s = String::from("foobar");
779 /// let s_mut_str = s.as_mut_str();
781 /// s_mut_str.make_ascii_uppercase();
783 /// assert_eq!("FOOBAR", s_mut_str);
786 #[stable(feature = "string_as_str", since = "1.7.0")]
787 pub fn as_mut_str(&mut self) -> &mut str {
791 /// Appends a given string slice onto the end of this `String`.
798 /// let mut s = String::from("foo");
800 /// s.push_str("bar");
802 /// assert_eq!("foobar", s);
805 #[stable(feature = "rust1", since = "1.0.0")]
806 pub fn push_str(&mut self, string: &str) {
807 self.vec.extend_from_slice(string.as_bytes())
810 /// Returns this `String`'s capacity, in bytes.
817 /// let s = String::with_capacity(10);
819 /// assert!(s.capacity() >= 10);
822 #[stable(feature = "rust1", since = "1.0.0")]
823 pub fn capacity(&self) -> usize {
827 /// Ensures that this `String`'s capacity is at least `additional` bytes
828 /// larger than its length.
830 /// The capacity may be increased by more than `additional` bytes if it
831 /// chooses, to prevent frequent reallocations.
833 /// If you do not want this "at least" behavior, see the [`reserve_exact`]
838 /// Panics if the new capacity overflows [`usize`].
840 /// [`reserve_exact`]: struct.String.html#method.reserve_exact
841 /// [`usize`]: ../../std/primitive.usize.html
848 /// let mut s = String::new();
852 /// assert!(s.capacity() >= 10);
855 /// This may not actually increase the capacity:
858 /// let mut s = String::with_capacity(10);
862 /// // s now has a length of 2 and a capacity of 10
863 /// assert_eq!(2, s.len());
864 /// assert_eq!(10, s.capacity());
866 /// // Since we already have an extra 8 capacity, calling this...
869 /// // ... doesn't actually increase.
870 /// assert_eq!(10, s.capacity());
873 #[stable(feature = "rust1", since = "1.0.0")]
874 pub fn reserve(&mut self, additional: usize) {
875 self.vec.reserve(additional)
878 /// Ensures that this `String`'s capacity is `additional` bytes
879 /// larger than its length.
881 /// Consider using the [`reserve`] method unless you absolutely know
882 /// better than the allocator.
884 /// [`reserve`]: #method.reserve
888 /// Panics if the new capacity overflows `usize`.
895 /// let mut s = String::new();
897 /// s.reserve_exact(10);
899 /// assert!(s.capacity() >= 10);
902 /// This may not actually increase the capacity:
905 /// let mut s = String::with_capacity(10);
909 /// // s now has a length of 2 and a capacity of 10
910 /// assert_eq!(2, s.len());
911 /// assert_eq!(10, s.capacity());
913 /// // Since we already have an extra 8 capacity, calling this...
914 /// s.reserve_exact(8);
916 /// // ... doesn't actually increase.
917 /// assert_eq!(10, s.capacity());
920 #[stable(feature = "rust1", since = "1.0.0")]
921 pub fn reserve_exact(&mut self, additional: usize) {
922 self.vec.reserve_exact(additional)
925 /// Tries to reserve capacity for at least `additional` more elements to be inserted
926 /// in the given `String`. The collection may reserve more space to avoid
927 /// frequent reallocations. After calling `reserve`, capacity will be
928 /// greater than or equal to `self.len() + additional`. Does nothing if
929 /// capacity is already sufficient.
933 /// If the capacity overflows, or the allocator reports a failure, then an error
939 /// #![feature(try_reserve)]
940 /// use std::collections::CollectionAllocErr;
942 /// fn process_data(data: &str) -> Result<String, CollectionAllocErr> {
943 /// let mut output = String::new();
945 /// // Pre-reserve the memory, exiting if we can't
946 /// output.try_reserve(data.len())?;
948 /// // Now we know this can't OOM in the middle of our complex work
949 /// output.push_str(data);
953 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
955 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
956 pub fn try_reserve(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
957 self.vec.try_reserve(additional)
960 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
961 /// be inserted in the given `String`. After calling `reserve_exact`,
962 /// capacity will be greater than or equal to `self.len() + additional`.
963 /// Does nothing if the capacity is already sufficient.
965 /// Note that the allocator may give the collection more space than it
966 /// requests. Therefore, capacity can not be relied upon to be precisely
967 /// minimal. Prefer `reserve` if future insertions are expected.
971 /// If the capacity overflows, or the allocator reports a failure, then an error
977 /// #![feature(try_reserve)]
978 /// use std::collections::CollectionAllocErr;
980 /// fn process_data(data: &str) -> Result<String, CollectionAllocErr> {
981 /// let mut output = String::new();
983 /// // Pre-reserve the memory, exiting if we can't
984 /// output.try_reserve(data.len())?;
986 /// // Now we know this can't OOM in the middle of our complex work
987 /// output.push_str(data);
991 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
993 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
994 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
995 self.vec.try_reserve_exact(additional)
998 /// Shrinks the capacity of this `String` to match its length.
1005 /// let mut s = String::from("foo");
1008 /// assert!(s.capacity() >= 100);
1010 /// s.shrink_to_fit();
1011 /// assert_eq!(3, s.capacity());
1014 #[stable(feature = "rust1", since = "1.0.0")]
1015 pub fn shrink_to_fit(&mut self) {
1016 self.vec.shrink_to_fit()
1019 /// Shrinks the capacity of this `String` with a lower bound.
1021 /// The capacity will remain at least as large as both the length
1022 /// and the supplied value.
1024 /// Panics if the current capacity is smaller than the supplied
1025 /// minimum capacity.
1030 /// #![feature(shrink_to)]
1031 /// let mut s = String::from("foo");
1034 /// assert!(s.capacity() >= 100);
1036 /// s.shrink_to(10);
1037 /// assert!(s.capacity() >= 10);
1039 /// assert!(s.capacity() >= 3);
1042 #[unstable(feature = "shrink_to", reason = "new API", issue="56431")]
1043 pub fn shrink_to(&mut self, min_capacity: usize) {
1044 self.vec.shrink_to(min_capacity)
1047 /// Appends the given [`char`] to the end of this `String`.
1049 /// [`char`]: ../../std/primitive.char.html
1056 /// let mut s = String::from("abc");
1062 /// assert_eq!("abc123", s);
1065 #[stable(feature = "rust1", since = "1.0.0")]
1066 pub fn push(&mut self, ch: char) {
1067 match ch.len_utf8() {
1068 1 => self.vec.push(ch as u8),
1069 _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
1073 /// Returns a byte slice of this `String`'s contents.
1075 /// The inverse of this method is [`from_utf8`].
1077 /// [`from_utf8`]: #method.from_utf8
1084 /// let s = String::from("hello");
1086 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
1089 #[stable(feature = "rust1", since = "1.0.0")]
1090 pub fn as_bytes(&self) -> &[u8] {
1094 /// Shortens this `String` to the specified length.
1096 /// If `new_len` is greater than the string's current length, this has no
1099 /// Note that this method has no effect on the allocated capacity
1104 /// Panics if `new_len` does not lie on a [`char`] boundary.
1106 /// [`char`]: ../../std/primitive.char.html
1113 /// let mut s = String::from("hello");
1117 /// assert_eq!("he", s);
1120 #[stable(feature = "rust1", since = "1.0.0")]
1121 pub fn truncate(&mut self, new_len: usize) {
1122 if new_len <= self.len() {
1123 assert!(self.is_char_boundary(new_len));
1124 self.vec.truncate(new_len)
1128 /// Removes the last character from the string buffer and returns it.
1130 /// Returns [`None`] if this `String` is empty.
1132 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1139 /// let mut s = String::from("foo");
1141 /// assert_eq!(s.pop(), Some('o'));
1142 /// assert_eq!(s.pop(), Some('o'));
1143 /// assert_eq!(s.pop(), Some('f'));
1145 /// assert_eq!(s.pop(), None);
1148 #[stable(feature = "rust1", since = "1.0.0")]
1149 pub fn pop(&mut self) -> Option<char> {
1150 let ch = self.chars().rev().next()?;
1151 let newlen = self.len() - ch.len_utf8();
1153 self.vec.set_len(newlen);
1158 /// Removes a [`char`] from this `String` at a byte position and returns it.
1160 /// This is an `O(n)` operation, as it requires copying every element in the
1165 /// Panics if `idx` is larger than or equal to the `String`'s length,
1166 /// or if it does not lie on a [`char`] boundary.
1168 /// [`char`]: ../../std/primitive.char.html
1175 /// let mut s = String::from("foo");
1177 /// assert_eq!(s.remove(0), 'f');
1178 /// assert_eq!(s.remove(1), 'o');
1179 /// assert_eq!(s.remove(0), 'o');
1182 #[stable(feature = "rust1", since = "1.0.0")]
1183 pub fn remove(&mut self, idx: usize) -> char {
1184 let ch = match self[idx..].chars().next() {
1186 None => panic!("cannot remove a char from the end of a string"),
1189 let next = idx + ch.len_utf8();
1190 let len = self.len();
1192 ptr::copy(self.vec.as_ptr().add(next),
1193 self.vec.as_mut_ptr().add(idx),
1195 self.vec.set_len(len - (next - idx));
1200 /// Retains only the characters specified by the predicate.
1202 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1203 /// This method operates in place and preserves the order of the retained
1209 /// let mut s = String::from("f_o_ob_ar");
1211 /// s.retain(|c| c != '_');
1213 /// assert_eq!(s, "foobar");
1216 #[stable(feature = "string_retain", since = "1.26.0")]
1217 pub fn retain<F>(&mut self, mut f: F)
1218 where F: FnMut(char) -> bool
1220 let len = self.len();
1221 let mut del_bytes = 0;
1226 self.get_unchecked(idx..len).chars().next().unwrap()
1228 let ch_len = ch.len_utf8();
1231 del_bytes += ch_len;
1232 } else if del_bytes > 0 {
1234 ptr::copy(self.vec.as_ptr().add(idx),
1235 self.vec.as_mut_ptr().add(idx - del_bytes),
1240 // Point idx to the next char
1245 unsafe { self.vec.set_len(len - del_bytes); }
1249 /// Inserts a character into this `String` at a byte position.
1251 /// This is an `O(n)` operation as it requires copying every element in the
1256 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1257 /// lie on a [`char`] boundary.
1259 /// [`char`]: ../../std/primitive.char.html
1266 /// let mut s = String::with_capacity(3);
1268 /// s.insert(0, 'f');
1269 /// s.insert(1, 'o');
1270 /// s.insert(2, 'o');
1272 /// assert_eq!("foo", s);
1275 #[stable(feature = "rust1", since = "1.0.0")]
1276 pub fn insert(&mut self, idx: usize, ch: char) {
1277 assert!(self.is_char_boundary(idx));
1278 let mut bits = [0; 4];
1279 let bits = ch.encode_utf8(&mut bits).as_bytes();
1282 self.insert_bytes(idx, bits);
1286 unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1287 let len = self.len();
1288 let amt = bytes.len();
1289 self.vec.reserve(amt);
1291 ptr::copy(self.vec.as_ptr().add(idx),
1292 self.vec.as_mut_ptr().add(idx + amt),
1294 ptr::copy(bytes.as_ptr(),
1295 self.vec.as_mut_ptr().add(idx),
1297 self.vec.set_len(len + amt);
1300 /// Inserts a string slice into this `String` at a byte position.
1302 /// This is an `O(n)` operation as it requires copying every element in the
1307 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1308 /// lie on a [`char`] boundary.
1310 /// [`char`]: ../../std/primitive.char.html
1317 /// let mut s = String::from("bar");
1319 /// s.insert_str(0, "foo");
1321 /// assert_eq!("foobar", s);
1324 #[stable(feature = "insert_str", since = "1.16.0")]
1325 pub fn insert_str(&mut self, idx: usize, string: &str) {
1326 assert!(self.is_char_boundary(idx));
1329 self.insert_bytes(idx, string.as_bytes());
1333 /// Returns a mutable reference to the contents of this `String`.
1337 /// This function is unsafe because it does not check that the bytes passed
1338 /// to it are valid UTF-8. If this constraint is violated, it may cause
1339 /// memory unsafety issues with future users of the `String`, as the rest of
1340 /// the standard library assumes that `String`s are valid UTF-8.
1347 /// let mut s = String::from("hello");
1350 /// let vec = s.as_mut_vec();
1351 /// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1355 /// assert_eq!(s, "olleh");
1358 #[stable(feature = "rust1", since = "1.0.0")]
1359 pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1363 /// Returns the length of this `String`, in bytes.
1370 /// let a = String::from("foo");
1372 /// assert_eq!(a.len(), 3);
1375 #[stable(feature = "rust1", since = "1.0.0")]
1376 pub fn len(&self) -> usize {
1380 /// Returns `true` if this `String` has a length of zero, and `false` otherwise.
1387 /// let mut v = String::new();
1388 /// assert!(v.is_empty());
1391 /// assert!(!v.is_empty());
1394 #[stable(feature = "rust1", since = "1.0.0")]
1395 pub fn is_empty(&self) -> bool {
1399 /// Splits the string into two at the given index.
1401 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1402 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1403 /// boundary of a UTF-8 code point.
1405 /// Note that the capacity of `self` does not change.
1409 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1410 /// code point of the string.
1416 /// let mut hello = String::from("Hello, World!");
1417 /// let world = hello.split_off(7);
1418 /// assert_eq!(hello, "Hello, ");
1419 /// assert_eq!(world, "World!");
1423 #[stable(feature = "string_split_off", since = "1.16.0")]
1424 pub fn split_off(&mut self, at: usize) -> String {
1425 assert!(self.is_char_boundary(at));
1426 let other = self.vec.split_off(at);
1427 unsafe { String::from_utf8_unchecked(other) }
1430 /// Truncates this `String`, removing all contents.
1432 /// While this means the `String` will have a length of zero, it does not
1433 /// touch its capacity.
1440 /// let mut s = String::from("foo");
1444 /// assert!(s.is_empty());
1445 /// assert_eq!(0, s.len());
1446 /// assert_eq!(3, s.capacity());
1449 #[stable(feature = "rust1", since = "1.0.0")]
1450 pub fn clear(&mut self) {
1454 /// Creates a draining iterator that removes the specified range in the `String`
1455 /// and yields the removed `chars`.
1457 /// Note: The element range is removed even if the iterator is not
1458 /// consumed until the end.
1462 /// Panics if the starting point or end point do not lie on a [`char`]
1463 /// boundary, or if they're out of bounds.
1465 /// [`char`]: ../../std/primitive.char.html
1472 /// let mut s = String::from("α is alpha, β is beta");
1473 /// let beta_offset = s.find('β').unwrap_or(s.len());
1475 /// // Remove the range up until the β from the string
1476 /// let t: String = s.drain(..beta_offset).collect();
1477 /// assert_eq!(t, "α is alpha, ");
1478 /// assert_eq!(s, "β is beta");
1480 /// // A full range clears the string
1482 /// assert_eq!(s, "");
1484 #[stable(feature = "drain", since = "1.6.0")]
1485 pub fn drain<R>(&mut self, range: R) -> Drain<'_>
1486 where R: RangeBounds<usize>
1490 // The String version of Drain does not have the memory safety issues
1491 // of the vector version. The data is just plain bytes.
1492 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1493 // the removal will not happen.
1494 let len = self.len();
1495 let start = match range.start_bound() {
1497 Excluded(&n) => n + 1,
1500 let end = match range.end_bound() {
1501 Included(&n) => n + 1,
1506 // Take out two simultaneous borrows. The &mut String won't be accessed
1507 // until iteration is over, in Drop.
1508 let self_ptr = self as *mut _;
1509 // slicing does the appropriate bounds checks
1510 let chars_iter = self[start..end].chars();
1520 /// Removes the specified range in the string,
1521 /// and replaces it with the given string.
1522 /// The given string doesn't need to be the same length as the range.
1526 /// Panics if the starting point or end point do not lie on a [`char`]
1527 /// boundary, or if they're out of bounds.
1529 /// [`char`]: ../../std/primitive.char.html
1530 /// [`Vec::splice`]: ../../std/vec/struct.Vec.html#method.splice
1537 /// let mut s = String::from("α is alpha, β is beta");
1538 /// let beta_offset = s.find('β').unwrap_or(s.len());
1540 /// // Replace the range up until the β from the string
1541 /// s.replace_range(..beta_offset, "Α is capital alpha; ");
1542 /// assert_eq!(s, "Α is capital alpha; β is beta");
1544 #[stable(feature = "splice", since = "1.27.0")]
1545 pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
1546 where 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)),
1566 }.splice(range, replace_with.bytes());
1569 /// Converts this `String` into a [`Box`]`<`[`str`]`>`.
1571 /// This will drop any excess capacity.
1573 /// [`Box`]: ../../std/boxed/struct.Box.html
1574 /// [`str`]: ../../std/primitive.str.html
1581 /// let s = String::from("hello");
1583 /// let b = s.into_boxed_str();
1585 #[stable(feature = "box_str", since = "1.4.0")]
1587 pub fn into_boxed_str(self) -> Box<str> {
1588 let slice = self.vec.into_boxed_slice();
1589 unsafe { from_boxed_utf8_unchecked(slice) }
1593 impl FromUtf8Error {
1594 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1601 /// // some invalid bytes, in a vector
1602 /// let bytes = vec![0, 159];
1604 /// let value = String::from_utf8(bytes);
1606 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1608 #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
1609 pub fn as_bytes(&self) -> &[u8] {
1613 /// Returns the bytes that were attempted to convert to a `String`.
1615 /// This method is carefully constructed to avoid allocation. It will
1616 /// consume the error, moving out the bytes, so that a copy of the bytes
1617 /// does not need to be made.
1624 /// // some invalid bytes, in a vector
1625 /// let bytes = vec![0, 159];
1627 /// let value = String::from_utf8(bytes);
1629 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1631 #[stable(feature = "rust1", since = "1.0.0")]
1632 pub fn into_bytes(self) -> Vec<u8> {
1636 /// Fetch a `Utf8Error` to get more details about the conversion failure.
1638 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1639 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1640 /// an analogue to `FromUtf8Error`. See its documentation for more details
1643 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
1644 /// [`std::str`]: ../../std/str/index.html
1645 /// [`u8`]: ../../std/primitive.u8.html
1646 /// [`&str`]: ../../std/primitive.str.html
1653 /// // some invalid bytes, in a vector
1654 /// let bytes = vec![0, 159];
1656 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1658 /// // the first byte is invalid here
1659 /// assert_eq!(1, error.valid_up_to());
1661 #[stable(feature = "rust1", since = "1.0.0")]
1662 pub fn utf8_error(&self) -> Utf8Error {
1667 #[stable(feature = "rust1", since = "1.0.0")]
1668 impl fmt::Display for FromUtf8Error {
1669 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1670 fmt::Display::fmt(&self.error, f)
1674 #[stable(feature = "rust1", since = "1.0.0")]
1675 impl fmt::Display for FromUtf16Error {
1676 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1677 fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
1681 #[stable(feature = "rust1", since = "1.0.0")]
1682 impl Clone for String {
1683 fn clone(&self) -> Self {
1684 String { vec: self.vec.clone() }
1687 fn clone_from(&mut self, source: &Self) {
1688 self.vec.clone_from(&source.vec);
1692 #[stable(feature = "rust1", since = "1.0.0")]
1693 impl FromIterator<char> for String {
1694 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
1695 let mut buf = String::new();
1701 #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
1702 impl<'a> FromIterator<&'a char> for String {
1703 fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
1704 let mut buf = String::new();
1710 #[stable(feature = "rust1", since = "1.0.0")]
1711 impl<'a> FromIterator<&'a str> for String {
1712 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
1713 let mut buf = String::new();
1719 #[stable(feature = "extend_string", since = "1.4.0")]
1720 impl FromIterator<String> for String {
1721 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
1722 let mut iterator = iter.into_iter();
1724 // Because we're iterating over `String`s, we can avoid at least
1725 // one allocation by getting the first string from the iterator
1726 // and appending to it all the subsequent strings.
1727 match iterator.next() {
1728 None => String::new(),
1730 buf.extend(iterator);
1737 #[stable(feature = "herd_cows", since = "1.19.0")]
1738 impl<'a> FromIterator<Cow<'a, str>> for String {
1739 fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
1740 let mut iterator = iter.into_iter();
1742 // Because we're iterating over CoWs, we can (potentially) avoid at least
1743 // one allocation by getting the first item and appending to it all the
1744 // subsequent items.
1745 match iterator.next() {
1746 None => String::new(),
1748 let mut buf = cow.into_owned();
1749 buf.extend(iterator);
1756 #[stable(feature = "rust1", since = "1.0.0")]
1757 impl Extend<char> for String {
1758 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
1759 let iterator = iter.into_iter();
1760 let (lower_bound, _) = iterator.size_hint();
1761 self.reserve(lower_bound);
1762 iterator.for_each(move |c| self.push(c));
1766 #[stable(feature = "extend_ref", since = "1.2.0")]
1767 impl<'a> Extend<&'a char> for String {
1768 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
1769 self.extend(iter.into_iter().cloned());
1773 #[stable(feature = "rust1", since = "1.0.0")]
1774 impl<'a> Extend<&'a str> for String {
1775 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
1776 iter.into_iter().for_each(move |s| self.push_str(s));
1780 #[stable(feature = "extend_string", since = "1.4.0")]
1781 impl Extend<String> for String {
1782 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
1783 iter.into_iter().for_each(move |s| self.push_str(&s));
1787 #[stable(feature = "herd_cows", since = "1.19.0")]
1788 impl<'a> Extend<Cow<'a, str>> for String {
1789 fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
1790 iter.into_iter().for_each(move |s| self.push_str(&s));
1794 /// A convenience impl that delegates to the impl for `&str`
1795 #[unstable(feature = "pattern",
1796 reason = "API not fully fleshed out and ready to be stabilized",
1798 impl<'a, 'b> Pattern<'a> for &'b String {
1799 type Searcher = <&'b str as Pattern<'a>>::Searcher;
1801 fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
1802 self[..].into_searcher(haystack)
1806 fn is_contained_in(self, haystack: &'a str) -> bool {
1807 self[..].is_contained_in(haystack)
1811 fn is_prefix_of(self, haystack: &'a str) -> bool {
1812 self[..].is_prefix_of(haystack)
1816 #[stable(feature = "rust1", since = "1.0.0")]
1817 impl PartialEq for String {
1819 fn eq(&self, other: &String) -> bool {
1820 PartialEq::eq(&self[..], &other[..])
1823 fn ne(&self, other: &String) -> bool {
1824 PartialEq::ne(&self[..], &other[..])
1828 macro_rules! impl_eq {
1829 ($lhs:ty, $rhs: ty) => {
1830 #[stable(feature = "rust1", since = "1.0.0")]
1831 impl<'a, 'b> PartialEq<$rhs> for $lhs {
1833 fn eq(&self, other: &$rhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1835 fn ne(&self, other: &$rhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1838 #[stable(feature = "rust1", since = "1.0.0")]
1839 impl<'a, 'b> PartialEq<$lhs> for $rhs {
1841 fn eq(&self, other: &$lhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1843 fn ne(&self, other: &$lhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1849 impl_eq! { String, str }
1850 impl_eq! { String, &'a str }
1851 impl_eq! { Cow<'a, str>, str }
1852 impl_eq! { Cow<'a, str>, &'b str }
1853 impl_eq! { Cow<'a, str>, String }
1855 #[stable(feature = "rust1", since = "1.0.0")]
1856 impl Default for String {
1857 /// Creates an empty `String`.
1859 fn default() -> String {
1864 #[stable(feature = "rust1", since = "1.0.0")]
1865 impl fmt::Display for String {
1867 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1868 fmt::Display::fmt(&**self, f)
1872 #[stable(feature = "rust1", since = "1.0.0")]
1873 impl fmt::Debug for String {
1875 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1876 fmt::Debug::fmt(&**self, f)
1880 #[stable(feature = "rust1", since = "1.0.0")]
1881 impl hash::Hash for String {
1883 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
1884 (**self).hash(hasher)
1888 /// Implements the `+` operator for concatenating two strings.
1890 /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
1891 /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
1892 /// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by
1893 /// repeated concatenation.
1895 /// The string on the right-hand side is only borrowed; its contents are copied into the returned
1900 /// Concatenating two `String`s takes the first by value and borrows the second:
1903 /// let a = String::from("hello");
1904 /// let b = String::from(" world");
1906 /// // `a` is moved and can no longer be used here.
1909 /// If you want to keep using the first `String`, you can clone it and append to the clone instead:
1912 /// let a = String::from("hello");
1913 /// let b = String::from(" world");
1914 /// let c = a.clone() + &b;
1915 /// // `a` is still valid here.
1918 /// Concatenating `&str` slices can be done by converting the first to a `String`:
1921 /// let a = "hello";
1922 /// let b = " world";
1923 /// let c = a.to_string() + b;
1925 #[stable(feature = "rust1", since = "1.0.0")]
1926 impl Add<&str> for String {
1927 type Output = String;
1930 fn add(mut self, other: &str) -> String {
1931 self.push_str(other);
1936 /// Implements the `+=` operator for appending to a `String`.
1938 /// This has the same behavior as the [`push_str`][String::push_str] method.
1939 #[stable(feature = "stringaddassign", since = "1.12.0")]
1940 impl AddAssign<&str> for String {
1942 fn add_assign(&mut self, other: &str) {
1943 self.push_str(other);
1947 #[stable(feature = "rust1", since = "1.0.0")]
1948 impl ops::Index<ops::Range<usize>> for String {
1952 fn index(&self, index: ops::Range<usize>) -> &str {
1956 #[stable(feature = "rust1", since = "1.0.0")]
1957 impl ops::Index<ops::RangeTo<usize>> for String {
1961 fn index(&self, index: ops::RangeTo<usize>) -> &str {
1965 #[stable(feature = "rust1", since = "1.0.0")]
1966 impl ops::Index<ops::RangeFrom<usize>> for String {
1970 fn index(&self, index: ops::RangeFrom<usize>) -> &str {
1974 #[stable(feature = "rust1", since = "1.0.0")]
1975 impl ops::Index<ops::RangeFull> for String {
1979 fn index(&self, _index: ops::RangeFull) -> &str {
1980 unsafe { str::from_utf8_unchecked(&self.vec) }
1983 #[stable(feature = "inclusive_range", since = "1.26.0")]
1984 impl ops::Index<ops::RangeInclusive<usize>> for String {
1988 fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
1989 Index::index(&**self, index)
1992 #[stable(feature = "inclusive_range", since = "1.26.0")]
1993 impl ops::Index<ops::RangeToInclusive<usize>> for String {
1997 fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
1998 Index::index(&**self, index)
2002 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2003 impl ops::IndexMut<ops::Range<usize>> for String {
2005 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
2006 &mut self[..][index]
2009 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2010 impl ops::IndexMut<ops::RangeTo<usize>> for String {
2012 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
2013 &mut self[..][index]
2016 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2017 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
2019 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
2020 &mut self[..][index]
2023 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2024 impl ops::IndexMut<ops::RangeFull> for String {
2026 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
2027 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2030 #[stable(feature = "inclusive_range", since = "1.26.0")]
2031 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
2033 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
2034 IndexMut::index_mut(&mut **self, index)
2037 #[stable(feature = "inclusive_range", since = "1.26.0")]
2038 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
2040 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
2041 IndexMut::index_mut(&mut **self, index)
2045 #[stable(feature = "rust1", since = "1.0.0")]
2046 impl ops::Deref for String {
2050 fn deref(&self) -> &str {
2051 unsafe { str::from_utf8_unchecked(&self.vec) }
2055 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2056 impl ops::DerefMut for String {
2058 fn deref_mut(&mut self) -> &mut str {
2059 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2063 /// An error when parsing a `String`.
2065 /// This `enum` is slightly awkward: it will never actually exist. This error is
2066 /// part of the type signature of the implementation of [`FromStr`] on
2067 /// [`String`]. The return type of [`from_str`], requires that an error be
2068 /// defined, but, given that a [`String`] can always be made into a new
2069 /// [`String`] without error, this type will never actually be returned. As
2070 /// such, it is only here to satisfy said signature, and is useless otherwise.
2072 /// [`FromStr`]: ../../std/str/trait.FromStr.html
2073 /// [`String`]: struct.String.html
2074 /// [`from_str`]: ../../std/str/trait.FromStr.html#tymethod.from_str
2075 #[stable(feature = "str_parse_error", since = "1.5.0")]
2077 pub enum ParseError {}
2079 #[stable(feature = "rust1", since = "1.0.0")]
2080 impl FromStr for String {
2081 type Err = ParseError;
2083 fn from_str(s: &str) -> Result<String, ParseError> {
2088 #[stable(feature = "str_parse_error", since = "1.5.0")]
2089 impl Clone for ParseError {
2090 fn clone(&self) -> ParseError {
2095 #[stable(feature = "str_parse_error", since = "1.5.0")]
2096 impl fmt::Debug for ParseError {
2097 fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result {
2102 #[stable(feature = "str_parse_error2", since = "1.8.0")]
2103 impl fmt::Display for ParseError {
2104 fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result {
2109 #[stable(feature = "str_parse_error", since = "1.5.0")]
2110 impl PartialEq for ParseError {
2111 fn eq(&self, _: &ParseError) -> bool {
2116 #[stable(feature = "str_parse_error", since = "1.5.0")]
2117 impl Eq for ParseError {}
2119 /// A trait for converting a value to a `String`.
2121 /// This trait is automatically implemented for any type which implements the
2122 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
2123 /// [`Display`] should be implemented instead, and you get the `ToString`
2124 /// implementation for free.
2126 /// [`Display`]: ../../std/fmt/trait.Display.html
2127 #[stable(feature = "rust1", since = "1.0.0")]
2128 pub trait ToString {
2129 /// Converts the given value to a `String`.
2137 /// let five = String::from("5");
2139 /// assert_eq!(five, i.to_string());
2141 #[rustc_conversion_suggestion]
2142 #[stable(feature = "rust1", since = "1.0.0")]
2143 fn to_string(&self) -> String;
2148 /// In this implementation, the `to_string` method panics
2149 /// if the `Display` implementation returns an error.
2150 /// This indicates an incorrect `Display` implementation
2151 /// since `fmt::Write for String` never returns an error itself.
2152 #[stable(feature = "rust1", since = "1.0.0")]
2153 impl<T: fmt::Display + ?Sized> ToString for T {
2155 default fn to_string(&self) -> String {
2157 let mut buf = String::new();
2158 buf.write_fmt(format_args!("{}", self))
2159 .expect("a Display implementation returned an error unexpectedly");
2160 buf.shrink_to_fit();
2165 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
2166 impl ToString for str {
2168 fn to_string(&self) -> String {
2173 #[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
2174 impl ToString for Cow<'_, str> {
2176 fn to_string(&self) -> String {
2181 #[stable(feature = "string_to_string_specialization", since = "1.17.0")]
2182 impl ToString for String {
2184 fn to_string(&self) -> String {
2189 #[stable(feature = "rust1", since = "1.0.0")]
2190 impl AsRef<str> for String {
2192 fn as_ref(&self) -> &str {
2197 #[stable(feature = "rust1", since = "1.0.0")]
2198 impl AsRef<[u8]> for String {
2200 fn as_ref(&self) -> &[u8] {
2205 #[stable(feature = "rust1", since = "1.0.0")]
2206 impl<'a> From<&'a str> for String {
2208 fn from(s: &'a str) -> String {
2213 // note: test pulls in libstd, which causes errors here
2215 #[stable(feature = "string_from_box", since = "1.18.0")]
2216 impl From<Box<str>> for String {
2217 /// Converts the given boxed `str` slice to a `String`.
2218 /// It is notable that the `str` slice is owned.
2225 /// let s1: String = String::from("hello world");
2226 /// let s2: Box<str> = s1.into_boxed_str();
2227 /// let s3: String = String::from(s2);
2229 /// assert_eq!("hello world", s3)
2231 fn from(s: Box<str>) -> String {
2236 #[stable(feature = "box_from_str", since = "1.20.0")]
2237 impl From<String> for Box<str> {
2238 /// Converts the given `String` to a boxed `str` slice that is owned.
2245 /// let s1: String = String::from("hello world");
2246 /// let s2: Box<str> = Box::from(s1);
2247 /// let s3: String = String::from(s2);
2249 /// assert_eq!("hello world", s3)
2251 fn from(s: String) -> Box<str> {
2256 #[stable(feature = "string_from_cow_str", since = "1.14.0")]
2257 impl<'a> From<Cow<'a, str>> for String {
2258 fn from(s: Cow<'a, str>) -> String {
2263 #[stable(feature = "rust1", since = "1.0.0")]
2264 impl<'a> From<&'a str> for Cow<'a, str> {
2266 fn from(s: &'a str) -> Cow<'a, str> {
2271 #[stable(feature = "rust1", since = "1.0.0")]
2272 impl<'a> From<String> for Cow<'a, str> {
2274 fn from(s: String) -> Cow<'a, str> {
2279 #[stable(feature = "cow_from_string_ref", since = "1.28.0")]
2280 impl<'a> From<&'a String> for Cow<'a, str> {
2282 fn from(s: &'a String) -> Cow<'a, str> {
2283 Cow::Borrowed(s.as_str())
2287 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2288 impl<'a> FromIterator<char> for Cow<'a, str> {
2289 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
2290 Cow::Owned(FromIterator::from_iter(it))
2294 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2295 impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
2296 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
2297 Cow::Owned(FromIterator::from_iter(it))
2301 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2302 impl<'a> FromIterator<String> for Cow<'a, str> {
2303 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
2304 Cow::Owned(FromIterator::from_iter(it))
2308 #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
2309 impl From<String> for Vec<u8> {
2310 /// Converts the given `String` to a vector `Vec` that holds values of type `u8`.
2317 /// let s1 = String::from("hello world");
2318 /// let v1 = Vec::from(s1);
2321 /// println!("{}", b);
2324 fn from(string: String) -> Vec<u8> {
2329 #[stable(feature = "rust1", since = "1.0.0")]
2330 impl fmt::Write for String {
2332 fn write_str(&mut self, s: &str) -> fmt::Result {
2338 fn write_char(&mut self, c: char) -> fmt::Result {
2344 /// A draining iterator for `String`.
2346 /// This struct is created by the [`drain`] method on [`String`]. See its
2347 /// documentation for more.
2349 /// [`drain`]: struct.String.html#method.drain
2350 /// [`String`]: struct.String.html
2351 #[stable(feature = "drain", since = "1.6.0")]
2352 pub struct Drain<'a> {
2353 /// Will be used as &'a mut String in the destructor
2354 string: *mut String,
2355 /// Start of part to remove
2357 /// End of part to remove
2359 /// Current remaining range to remove
2363 #[stable(feature = "collection_debug", since = "1.17.0")]
2364 impl fmt::Debug for Drain<'_> {
2365 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2366 f.pad("Drain { .. }")
2370 #[stable(feature = "drain", since = "1.6.0")]
2371 unsafe impl Sync for Drain<'_> {}
2372 #[stable(feature = "drain", since = "1.6.0")]
2373 unsafe impl Send for Drain<'_> {}
2375 #[stable(feature = "drain", since = "1.6.0")]
2376 impl Drop for Drain<'_> {
2377 fn drop(&mut self) {
2379 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
2380 // panic code being inserted again.
2381 let self_vec = (*self.string).as_mut_vec();
2382 if self.start <= self.end && self.end <= self_vec.len() {
2383 self_vec.drain(self.start..self.end);
2389 #[stable(feature = "drain", since = "1.6.0")]
2390 impl Iterator for Drain<'_> {
2394 fn next(&mut self) -> Option<char> {
2398 fn size_hint(&self) -> (usize, Option<usize>) {
2399 self.iter.size_hint()
2403 #[stable(feature = "drain", since = "1.6.0")]
2404 impl DoubleEndedIterator for Drain<'_> {
2406 fn next_back(&mut self) -> Option<char> {
2407 self.iter.next_back()
2411 #[stable(feature = "fused", since = "1.26.0")]
2412 impl FusedIterator for Drain<'_> {}