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")]
50 char::{decode_utf16, REPLACEMENT_CHARACTER},
53 iter::{FromIterator, FusedIterator},
56 Bound::{Excluded, Included, Unbounded},
57 Add, AddAssign, Index, IndexMut, RangeBounds,
67 collections::CollectionAllocErr,
68 borrow::{Cow, ToOwned},
70 str::{self, from_boxed_utf8_unchecked, FromStr, Utf8Error, Chars},
74 /// A UTF-8 encoded, growable string.
76 /// The `String` type is the most common string type that has ownership over the
77 /// contents of the string. It has a close relationship with its borrowed
78 /// counterpart, the primitive [`str`].
80 /// [`str`]: ../../std/primitive.str.html
84 /// You can create a `String` from a literal string with [`String::from`]:
87 /// let hello = String::from("Hello, world!");
90 /// You can append a [`char`] to a `String` with the [`push`] method, and
91 /// append a [`&str`] with the [`push_str`] method:
94 /// let mut hello = String::from("Hello, ");
97 /// hello.push_str("orld!");
100 /// [`String::from`]: #method.from
101 /// [`char`]: ../../std/primitive.char.html
102 /// [`push`]: #method.push
103 /// [`push_str`]: #method.push_str
105 /// If you have a vector of UTF-8 bytes, you can create a `String` from it with
106 /// the [`from_utf8`] method:
109 /// // some bytes, in a vector
110 /// let sparkle_heart = vec![240, 159, 146, 150];
112 /// // We know these bytes are valid, so we'll use `unwrap()`.
113 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
115 /// assert_eq!("💖", sparkle_heart);
118 /// [`from_utf8`]: #method.from_utf8
122 /// `String`s are always valid UTF-8. This has a few implications, the first of
123 /// which is that if you need a non-UTF-8 string, consider [`OsString`]. It is
124 /// similar, but without the UTF-8 constraint. The second implication is that
125 /// you cannot index into a `String`:
127 /// ```compile_fail,E0277
130 /// println!("The first letter of s is {}", s[0]); // ERROR!!!
133 /// [`OsString`]: ../../std/ffi/struct.OsString.html
135 /// Indexing is intended to be a constant-time operation, but UTF-8 encoding
136 /// does not allow us to do this. Furthermore, it's not clear what sort of
137 /// thing the index should return: a byte, a codepoint, or a grapheme cluster.
138 /// The [`bytes`] and [`chars`] methods return iterators over the first
139 /// two, respectively.
141 /// [`bytes`]: #method.bytes
142 /// [`chars`]: #method.chars
146 /// `String`s implement [`Deref`]`<Target=str>`, and so inherit all of [`str`]'s
147 /// methods. In addition, this means that you can pass a `String` to a
148 /// function which takes a [`&str`] by using an ampersand (`&`):
151 /// fn takes_str(s: &str) { }
153 /// let s = String::from("Hello");
158 /// This will create a [`&str`] from the `String` and pass it in. This
159 /// conversion is very inexpensive, and so generally, functions will accept
160 /// [`&str`]s as arguments unless they need a `String` for some specific
163 /// In certain cases Rust doesn't have enough information to make this
164 /// conversion, known as [`Deref`] coercion. In the following example a string
165 /// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
166 /// `example_func` takes anything that implements the trait. In this case Rust
167 /// would need to make two implicit conversions, which Rust doesn't have the
168 /// means to do. For that reason, the following example will not compile.
170 /// ```compile_fail,E0277
171 /// trait TraitExample {}
173 /// impl<'a> TraitExample for &'a str {}
175 /// fn example_func<A: TraitExample>(example_arg: A) {}
178 /// let example_string = String::from("example_string");
179 /// example_func(&example_string);
183 /// There are two options that would work instead. The first would be to
184 /// change the line `example_func(&example_string);` to
185 /// `example_func(example_string.as_str());`, using the method [`as_str()`]
186 /// to explicitly extract the string slice containing the string. The second
187 /// way changes `example_func(&example_string);` to
188 /// `example_func(&*example_string);`. In this case we are dereferencing a
189 /// `String` to a [`str`][`&str`], then referencing the [`str`][`&str`] back to
190 /// [`&str`]. The second way is more idiomatic, however both work to do the
191 /// conversion explicitly rather than relying on the implicit conversion.
195 /// A `String` is made up of three components: a pointer to some bytes, a
196 /// length, and a capacity. The pointer points to an internal buffer `String`
197 /// uses to store its data. The length is the number of bytes currently stored
198 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
199 /// the length will always be less than or equal to the capacity.
201 /// This buffer is always stored on the heap.
203 /// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
209 /// let story = String::from("Once upon a time...");
211 /// let ptr = story.as_ptr();
212 /// let len = story.len();
213 /// let capacity = story.capacity();
215 /// // story has nineteen bytes
216 /// assert_eq!(19, len);
218 /// // Now that we have our parts, we throw the story away.
219 /// mem::forget(story);
221 /// // We can re-build a String out of ptr, len, and capacity. This is all
222 /// // unsafe because we are responsible for making sure the components are
224 /// let s = unsafe { String::from_raw_parts(ptr as *mut _, len, capacity) } ;
226 /// assert_eq!(String::from("Once upon a time..."), s);
229 /// [`as_ptr`]: #method.as_ptr
230 /// [`len`]: #method.len
231 /// [`capacity`]: #method.capacity
233 /// If a `String` has enough capacity, adding elements to it will not
234 /// re-allocate. For example, consider this program:
237 /// let mut s = String::new();
239 /// println!("{}", s.capacity());
242 /// s.push_str("hello");
243 /// println!("{}", s.capacity());
247 /// This will output the following:
258 /// At first, we have no memory allocated at all, but as we append to the
259 /// string, it increases its capacity appropriately. If we instead use the
260 /// [`with_capacity`] method to allocate the correct capacity initially:
263 /// let mut s = String::with_capacity(25);
265 /// println!("{}", s.capacity());
268 /// s.push_str("hello");
269 /// println!("{}", s.capacity());
273 /// [`with_capacity`]: #method.with_capacity
275 /// We end up with a different output:
286 /// Here, there's no need to allocate more memory inside the loop.
288 /// [`&str`]: ../../std/primitive.str.html
289 /// [`Deref`]: ../../std/ops/trait.Deref.html
290 /// [`as_str()`]: struct.String.html#method.as_str
291 #[derive(PartialOrd, Eq, Ord)]
292 #[stable(feature = "rust1", since = "1.0.0")]
297 /// A possible error value when converting a `String` from a UTF-8 byte vector.
299 /// This type is the error type for the [`from_utf8`] method on [`String`]. It
300 /// is designed in such a way to carefully avoid reallocations: the
301 /// [`into_bytes`] method will give back the byte vector that was used in the
302 /// conversion attempt.
304 /// [`from_utf8`]: struct.String.html#method.from_utf8
305 /// [`String`]: struct.String.html
306 /// [`into_bytes`]: struct.FromUtf8Error.html#method.into_bytes
308 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
309 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
310 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
311 /// through the [`utf8_error`] method.
313 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
314 /// [`std::str`]: ../../std/str/index.html
315 /// [`u8`]: ../../std/primitive.u8.html
316 /// [`&str`]: ../../std/primitive.str.html
317 /// [`utf8_error`]: #method.utf8_error
324 /// // some invalid bytes, in a vector
325 /// let bytes = vec![0, 159];
327 /// let value = String::from_utf8(bytes);
329 /// assert!(value.is_err());
330 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
332 #[stable(feature = "rust1", since = "1.0.0")]
334 pub struct FromUtf8Error {
339 /// A possible error value when converting a `String` from a UTF-16 byte slice.
341 /// This type is the error type for the [`from_utf16`] method on [`String`].
343 /// [`from_utf16`]: struct.String.html#method.from_utf16
344 /// [`String`]: struct.String.html
351 /// // 𝄞mu<invalid>ic
352 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
353 /// 0xD800, 0x0069, 0x0063];
355 /// assert!(String::from_utf16(v).is_err());
357 #[stable(feature = "rust1", since = "1.0.0")]
359 pub struct FromUtf16Error(());
362 /// Creates a new empty `String`.
364 /// Given that the `String` is empty, this will not allocate any initial
365 /// buffer. While that means that this initial operation is very
366 /// inexpensive, it may cause excessive allocation later when you add
367 /// data. If you have an idea of how much data the `String` will hold,
368 /// consider the [`with_capacity`] method to prevent excessive
371 /// [`with_capacity`]: #method.with_capacity
378 /// let s = String::new();
381 #[stable(feature = "rust1", since = "1.0.0")]
382 #[rustc_const_unstable(feature = "const_string_new")]
383 pub const fn new() -> String {
384 String { vec: Vec::new() }
387 /// Creates a new empty `String` with a particular capacity.
389 /// `String`s have an internal buffer to hold their data. The capacity is
390 /// the length of that buffer, and can be queried with the [`capacity`]
391 /// method. This method creates an empty `String`, but one with an initial
392 /// buffer that can hold `capacity` bytes. This is useful when you may be
393 /// appending a bunch of data to the `String`, reducing the number of
394 /// reallocations it needs to do.
396 /// [`capacity`]: #method.capacity
398 /// If the given capacity is `0`, no allocation will occur, and this method
399 /// is identical to the [`new`] method.
401 /// [`new`]: #method.new
408 /// let mut s = String::with_capacity(10);
410 /// // The String contains no chars, even though it has capacity for more
411 /// assert_eq!(s.len(), 0);
413 /// // These are all done without reallocating...
414 /// let cap = s.capacity();
419 /// assert_eq!(s.capacity(), cap);
421 /// // ...but this may make the vector reallocate
425 #[stable(feature = "rust1", since = "1.0.0")]
426 pub fn with_capacity(capacity: usize) -> String {
427 String { vec: Vec::with_capacity(capacity) }
430 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
431 // required for this method definition, is not available. Since we don't
432 // require this method for testing purposes, I'll just stub it
433 // NB see the slice::hack module in slice.rs for more information
436 pub fn from_str(_: &str) -> String {
437 panic!("not available with cfg(test)");
440 /// Converts a vector of bytes to a `String`.
442 /// A string slice ([`&str`]) is made of bytes ([`u8`]), and a vector of bytes
443 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
444 /// two. Not all byte slices are valid `String`s, however: `String`
445 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
446 /// the bytes are valid UTF-8, and then does the conversion.
448 /// If you are sure that the byte slice is valid UTF-8, and you don't want
449 /// to incur the overhead of the validity check, there is an unsafe version
450 /// of this function, [`from_utf8_unchecked`], which has the same behavior
451 /// but skips the check.
453 /// This method will take care to not copy the vector, for efficiency's
456 /// If you need a [`&str`] instead of a `String`, consider
457 /// [`str::from_utf8`].
459 /// The inverse of this method is [`as_bytes`].
463 /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
464 /// provided bytes are not UTF-8. The vector you moved in is also included.
471 /// // some bytes, in a vector
472 /// let sparkle_heart = vec![240, 159, 146, 150];
474 /// // We know these bytes are valid, so we'll use `unwrap()`.
475 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
477 /// assert_eq!("💖", sparkle_heart);
483 /// // some invalid bytes, in a vector
484 /// let sparkle_heart = vec![0, 159, 146, 150];
486 /// assert!(String::from_utf8(sparkle_heart).is_err());
489 /// See the docs for [`FromUtf8Error`] for more details on what you can do
492 /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
493 /// [`&str`]: ../../std/primitive.str.html
494 /// [`u8`]: ../../std/primitive.u8.html
495 /// [`Vec<u8>`]: ../../std/vec/struct.Vec.html
496 /// [`str::from_utf8`]: ../../std/str/fn.from_utf8.html
497 /// [`as_bytes`]: struct.String.html#method.as_bytes
498 /// [`FromUtf8Error`]: struct.FromUtf8Error.html
499 /// [`Err`]: ../../stdresult/enum.Result.html#variant.Err
501 #[stable(feature = "rust1", since = "1.0.0")]
502 pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
503 match str::from_utf8(&vec) {
504 Ok(..) => Ok(String { vec }),
514 /// Converts a slice of bytes to a string, including invalid characters.
516 /// Strings are made of bytes ([`u8`]), and a slice of bytes
517 /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
518 /// between the two. Not all byte slices are valid strings, however: strings
519 /// are required to be valid UTF-8. During this conversion,
520 /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
521 /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: �
523 /// [`u8`]: ../../std/primitive.u8.html
524 /// [byteslice]: ../../std/primitive.slice.html
525 /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
527 /// If you are sure that the byte slice is valid UTF-8, and you don't want
528 /// to incur the overhead of the conversion, there is an unsafe version
529 /// of this function, [`from_utf8_unchecked`], which has the same behavior
530 /// but skips the checks.
532 /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
534 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
535 /// UTF-8, then we need to insert the replacement characters, which will
536 /// change the size of the string, and hence, require a `String`. But if
537 /// it's already valid UTF-8, we don't need a new allocation. This return
538 /// type allows us to handle both cases.
540 /// [`Cow<'a, str>`]: ../../std/borrow/enum.Cow.html
547 /// // some bytes, in a vector
548 /// let sparkle_heart = vec![240, 159, 146, 150];
550 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
552 /// assert_eq!("💖", sparkle_heart);
558 /// // some invalid bytes
559 /// let input = b"Hello \xF0\x90\x80World";
560 /// let output = String::from_utf8_lossy(input);
562 /// assert_eq!("Hello �World", output);
564 #[stable(feature = "rust1", since = "1.0.0")]
565 pub fn from_utf8_lossy<'a>(v: &'a [u8]) -> Cow<'a, str> {
566 let mut iter = lossy::Utf8Lossy::from_bytes(v).chunks();
568 let (first_valid, first_broken) = if let Some(chunk) = iter.next() {
569 let lossy::Utf8LossyChunk { valid, broken } = chunk;
570 if valid.len() == v.len() {
571 debug_assert!(broken.is_empty());
572 return Cow::Borrowed(valid);
576 return Cow::Borrowed("");
579 const REPLACEMENT: &str = "\u{FFFD}";
581 let mut res = String::with_capacity(v.len());
582 res.push_str(first_valid);
583 if !first_broken.is_empty() {
584 res.push_str(REPLACEMENT);
587 for lossy::Utf8LossyChunk { valid, broken } in iter {
589 if !broken.is_empty() {
590 res.push_str(REPLACEMENT);
597 /// Decode a UTF-16 encoded vector `v` into a `String`, returning [`Err`]
598 /// if `v` contains any invalid data.
600 /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
608 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
609 /// 0x0073, 0x0069, 0x0063];
610 /// assert_eq!(String::from("𝄞music"),
611 /// String::from_utf16(v).unwrap());
613 /// // 𝄞mu<invalid>ic
614 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
615 /// 0xD800, 0x0069, 0x0063];
616 /// assert!(String::from_utf16(v).is_err());
618 #[stable(feature = "rust1", since = "1.0.0")]
619 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
620 // This isn't done via collect::<Result<_, _>>() for performance reasons.
621 // FIXME: the function can be simplified again when #48994 is closed.
622 let mut ret = String::with_capacity(v.len());
623 for c in decode_utf16(v.iter().cloned()) {
627 return Err(FromUtf16Error(()));
633 /// Decode a UTF-16 encoded slice `v` into a `String`, replacing
634 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
636 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
637 /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
638 /// conversion requires a memory allocation.
640 /// [`from_utf8_lossy`]: #method.from_utf8_lossy
641 /// [`Cow<'a, str>`]: ../borrow/enum.Cow.html
642 /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
649 /// // 𝄞mus<invalid>ic<invalid>
650 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
651 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
654 /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
655 /// String::from_utf16_lossy(v));
658 #[stable(feature = "rust1", since = "1.0.0")]
659 pub fn from_utf16_lossy(v: &[u16]) -> String {
660 decode_utf16(v.iter().cloned()).map(|r| r.unwrap_or(REPLACEMENT_CHARACTER)).collect()
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 `ptr` needs to have been previously allocated by the
671 /// same allocator the standard library uses.
672 /// * `length` needs to be less than or equal to `capacity`.
673 /// * `capacity` needs to be the correct value.
675 /// Violating these may cause problems like corrupting the allocator's
676 /// internal data structures.
678 /// The ownership of `ptr` is effectively transferred to the
679 /// `String` which may then deallocate, reallocate or change the
680 /// contents of memory pointed to by the pointer at will. Ensure
681 /// that nothing else uses the pointer after calling this
692 /// let s = String::from("hello");
693 /// let ptr = s.as_ptr();
694 /// let len = s.len();
695 /// let capacity = s.capacity();
699 /// let s = String::from_raw_parts(ptr as *mut _, len, capacity);
701 /// assert_eq!(String::from("hello"), s);
705 #[stable(feature = "rust1", since = "1.0.0")]
706 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
707 String { vec: Vec::from_raw_parts(buf, length, capacity) }
710 /// Converts a vector of bytes to a `String` without checking that the
711 /// string contains valid UTF-8.
713 /// See the safe version, [`from_utf8`], for more details.
715 /// [`from_utf8`]: struct.String.html#method.from_utf8
719 /// This function is unsafe because it does not check that the bytes passed
720 /// to it are valid UTF-8. If this constraint is violated, it may cause
721 /// memory unsafety issues with future users of the `String`, as the rest of
722 /// the standard library assumes that `String`s are valid UTF-8.
729 /// // some bytes, in a vector
730 /// let sparkle_heart = vec![240, 159, 146, 150];
732 /// let sparkle_heart = unsafe {
733 /// String::from_utf8_unchecked(sparkle_heart)
736 /// assert_eq!("💖", sparkle_heart);
739 #[stable(feature = "rust1", since = "1.0.0")]
740 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
741 String { vec: bytes }
744 /// Converts a `String` into a byte vector.
746 /// This consumes the `String`, so we do not need to copy its contents.
753 /// let s = String::from("hello");
754 /// let bytes = s.into_bytes();
756 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
759 #[stable(feature = "rust1", since = "1.0.0")]
760 pub fn into_bytes(self) -> Vec<u8> {
764 /// Extracts a string slice containing the entire `String`.
771 /// let s = String::from("foo");
773 /// assert_eq!("foo", s.as_str());
776 #[stable(feature = "string_as_str", since = "1.7.0")]
777 pub fn as_str(&self) -> &str {
781 /// Converts a `String` into a mutable string slice.
788 /// let mut s = String::from("foobar");
789 /// let s_mut_str = s.as_mut_str();
791 /// s_mut_str.make_ascii_uppercase();
793 /// assert_eq!("FOOBAR", s_mut_str);
796 #[stable(feature = "string_as_str", since = "1.7.0")]
797 pub fn as_mut_str(&mut self) -> &mut str {
801 /// Appends a given string slice onto the end of this `String`.
808 /// let mut s = String::from("foo");
810 /// s.push_str("bar");
812 /// assert_eq!("foobar", s);
815 #[stable(feature = "rust1", since = "1.0.0")]
816 pub fn push_str(&mut self, string: &str) {
817 self.vec.extend_from_slice(string.as_bytes())
820 /// Returns this `String`'s capacity, in bytes.
827 /// let s = String::with_capacity(10);
829 /// assert!(s.capacity() >= 10);
832 #[stable(feature = "rust1", since = "1.0.0")]
833 pub fn capacity(&self) -> usize {
837 /// Ensures that this `String`'s capacity is at least `additional` bytes
838 /// larger than its length.
840 /// The capacity may be increased by more than `additional` bytes if it
841 /// chooses, to prevent frequent reallocations.
843 /// If you do not want this "at least" behavior, see the [`reserve_exact`]
848 /// Panics if the new capacity overflows [`usize`].
850 /// [`reserve_exact`]: struct.String.html#method.reserve_exact
851 /// [`usize`]: ../../std/primitive.usize.html
858 /// let mut s = String::new();
862 /// assert!(s.capacity() >= 10);
865 /// This may not actually increase the capacity:
868 /// let mut s = String::with_capacity(10);
872 /// // s now has a length of 2 and a capacity of 10
873 /// assert_eq!(2, s.len());
874 /// assert_eq!(10, s.capacity());
876 /// // Since we already have an extra 8 capacity, calling this...
879 /// // ... doesn't actually increase.
880 /// assert_eq!(10, s.capacity());
883 #[stable(feature = "rust1", since = "1.0.0")]
884 pub fn reserve(&mut self, additional: usize) {
885 self.vec.reserve(additional)
888 /// Ensures that this `String`'s capacity is `additional` bytes
889 /// larger than its length.
891 /// Consider using the [`reserve`] method unless you absolutely know
892 /// better than the allocator.
894 /// [`reserve`]: #method.reserve
898 /// Panics if the new capacity overflows `usize`.
905 /// let mut s = String::new();
907 /// s.reserve_exact(10);
909 /// assert!(s.capacity() >= 10);
912 /// This may not actually increase the capacity:
915 /// let mut s = String::with_capacity(10);
919 /// // s now has a length of 2 and a capacity of 10
920 /// assert_eq!(2, s.len());
921 /// assert_eq!(10, s.capacity());
923 /// // Since we already have an extra 8 capacity, calling this...
924 /// s.reserve_exact(8);
926 /// // ... doesn't actually increase.
927 /// assert_eq!(10, s.capacity());
930 #[stable(feature = "rust1", since = "1.0.0")]
931 pub fn reserve_exact(&mut self, additional: usize) {
932 self.vec.reserve_exact(additional)
935 /// Tries to reserve capacity for at least `additional` more elements to be inserted
936 /// in the given `String`. The collection may reserve more space to avoid
937 /// frequent reallocations. After calling `reserve`, capacity will be
938 /// greater than or equal to `self.len() + additional`. Does nothing if
939 /// capacity is already sufficient.
943 /// If the capacity overflows, or the allocator reports a failure, then an error
949 /// #![feature(try_reserve)]
950 /// use std::collections::CollectionAllocErr;
952 /// fn process_data(data: &str) -> Result<String, CollectionAllocErr> {
953 /// let mut output = String::new();
955 /// // Pre-reserve the memory, exiting if we can't
956 /// output.try_reserve(data.len())?;
958 /// // Now we know this can't OOM in the middle of our complex work
959 /// output.push_str(data);
963 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
965 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
966 pub fn try_reserve(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
967 self.vec.try_reserve(additional)
970 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
971 /// be inserted in the given `String`. After calling `reserve_exact`,
972 /// capacity will be greater than or equal to `self.len() + additional`.
973 /// Does nothing if the capacity is already sufficient.
975 /// Note that the allocator may give the collection more space than it
976 /// requests. Therefore capacity can not be relied upon to be precisely
977 /// minimal. Prefer `reserve` if future insertions are expected.
981 /// If the capacity overflows, or the allocator reports a failure, then an error
987 /// #![feature(try_reserve)]
988 /// use std::collections::CollectionAllocErr;
990 /// fn process_data(data: &str) -> Result<String, CollectionAllocErr> {
991 /// let mut output = String::new();
993 /// // Pre-reserve the memory, exiting if we can't
994 /// output.try_reserve(data.len())?;
996 /// // Now we know this can't OOM in the middle of our complex work
997 /// output.push_str(data);
1001 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1003 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
1004 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
1005 self.vec.try_reserve_exact(additional)
1008 /// Shrinks the capacity of this `String` to match its length.
1015 /// let mut s = String::from("foo");
1018 /// assert!(s.capacity() >= 100);
1020 /// s.shrink_to_fit();
1021 /// assert_eq!(3, s.capacity());
1024 #[stable(feature = "rust1", since = "1.0.0")]
1025 pub fn shrink_to_fit(&mut self) {
1026 self.vec.shrink_to_fit()
1029 /// Shrinks the capacity of this `String` with a lower bound.
1031 /// The capacity will remain at least as large as both the length
1032 /// and the supplied value.
1034 /// Panics if the current capacity is smaller than the supplied
1035 /// minimum capacity.
1040 /// #![feature(shrink_to)]
1041 /// let mut s = String::from("foo");
1044 /// assert!(s.capacity() >= 100);
1046 /// s.shrink_to(10);
1047 /// assert!(s.capacity() >= 10);
1049 /// assert!(s.capacity() >= 3);
1052 #[unstable(feature = "shrink_to", reason = "new API", issue="56431")]
1053 pub fn shrink_to(&mut self, min_capacity: usize) {
1054 self.vec.shrink_to(min_capacity)
1057 /// Appends the given [`char`] to the end of this `String`.
1059 /// [`char`]: ../../std/primitive.char.html
1066 /// let mut s = String::from("abc");
1072 /// assert_eq!("abc123", s);
1075 #[stable(feature = "rust1", since = "1.0.0")]
1076 pub fn push(&mut self, ch: char) {
1077 match ch.len_utf8() {
1078 1 => self.vec.push(ch as u8),
1079 _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
1083 /// Returns a byte slice of this `String`'s contents.
1085 /// The inverse of this method is [`from_utf8`].
1087 /// [`from_utf8`]: #method.from_utf8
1094 /// let s = String::from("hello");
1096 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
1099 #[stable(feature = "rust1", since = "1.0.0")]
1100 pub fn as_bytes(&self) -> &[u8] {
1104 /// Shortens this `String` to the specified length.
1106 /// If `new_len` is greater than the string's current length, this has no
1109 /// Note that this method has no effect on the allocated capacity
1114 /// Panics if `new_len` does not lie on a [`char`] boundary.
1116 /// [`char`]: ../../std/primitive.char.html
1123 /// let mut s = String::from("hello");
1127 /// assert_eq!("he", s);
1130 #[stable(feature = "rust1", since = "1.0.0")]
1131 pub fn truncate(&mut self, new_len: usize) {
1132 if new_len <= self.len() {
1133 assert!(self.is_char_boundary(new_len));
1134 self.vec.truncate(new_len)
1138 /// Removes the last character from the string buffer and returns it.
1140 /// Returns [`None`] if this `String` is empty.
1142 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1149 /// let mut s = String::from("foo");
1151 /// assert_eq!(s.pop(), Some('o'));
1152 /// assert_eq!(s.pop(), Some('o'));
1153 /// assert_eq!(s.pop(), Some('f'));
1155 /// assert_eq!(s.pop(), None);
1158 #[stable(feature = "rust1", since = "1.0.0")]
1159 pub fn pop(&mut self) -> Option<char> {
1160 let ch = self.chars().rev().next()?;
1161 let newlen = self.len() - ch.len_utf8();
1163 self.vec.set_len(newlen);
1168 /// Removes a [`char`] from this `String` at a byte position and returns it.
1170 /// This is an `O(n)` operation, as it requires copying every element in the
1175 /// Panics if `idx` is larger than or equal to the `String`'s length,
1176 /// or if it does not lie on a [`char`] boundary.
1178 /// [`char`]: ../../std/primitive.char.html
1185 /// let mut s = String::from("foo");
1187 /// assert_eq!(s.remove(0), 'f');
1188 /// assert_eq!(s.remove(1), 'o');
1189 /// assert_eq!(s.remove(0), 'o');
1192 #[stable(feature = "rust1", since = "1.0.0")]
1193 pub fn remove(&mut self, idx: usize) -> char {
1194 let ch = match self[idx..].chars().next() {
1196 None => panic!("cannot remove a char from the end of a string"),
1199 let next = idx + ch.len_utf8();
1200 let len = self.len();
1202 ptr::copy(self.vec.as_ptr().add(next),
1203 self.vec.as_mut_ptr().add(idx),
1205 self.vec.set_len(len - (next - idx));
1210 /// Retains only the characters specified by the predicate.
1212 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1213 /// This method operates in place and preserves the order of the retained
1219 /// let mut s = String::from("f_o_ob_ar");
1221 /// s.retain(|c| c != '_');
1223 /// assert_eq!(s, "foobar");
1226 #[stable(feature = "string_retain", since = "1.26.0")]
1227 pub fn retain<F>(&mut self, mut f: F)
1228 where F: FnMut(char) -> bool
1230 let len = self.len();
1231 let mut del_bytes = 0;
1236 self.get_unchecked(idx..len).chars().next().unwrap()
1238 let ch_len = ch.len_utf8();
1241 del_bytes += ch_len;
1242 } else if del_bytes > 0 {
1244 ptr::copy(self.vec.as_ptr().add(idx),
1245 self.vec.as_mut_ptr().add(idx - del_bytes),
1250 // Point idx to the next char
1255 unsafe { self.vec.set_len(len - del_bytes); }
1259 /// Inserts a character into this `String` at a byte position.
1261 /// This is an `O(n)` operation as it requires copying every element in the
1266 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1267 /// lie on a [`char`] boundary.
1269 /// [`char`]: ../../std/primitive.char.html
1276 /// let mut s = String::with_capacity(3);
1278 /// s.insert(0, 'f');
1279 /// s.insert(1, 'o');
1280 /// s.insert(2, 'o');
1282 /// assert_eq!("foo", s);
1285 #[stable(feature = "rust1", since = "1.0.0")]
1286 pub fn insert(&mut self, idx: usize, ch: char) {
1287 assert!(self.is_char_boundary(idx));
1288 let mut bits = [0; 4];
1289 let bits = ch.encode_utf8(&mut bits).as_bytes();
1292 self.insert_bytes(idx, bits);
1296 unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1297 let len = self.len();
1298 let amt = bytes.len();
1299 self.vec.reserve(amt);
1301 ptr::copy(self.vec.as_ptr().add(idx),
1302 self.vec.as_mut_ptr().add(idx + amt),
1304 ptr::copy(bytes.as_ptr(),
1305 self.vec.as_mut_ptr().add(idx),
1307 self.vec.set_len(len + amt);
1310 /// Inserts a string slice into this `String` at a byte position.
1312 /// This is an `O(n)` operation as it requires copying every element in the
1317 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1318 /// lie on a [`char`] boundary.
1320 /// [`char`]: ../../std/primitive.char.html
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.
1380 /// let a = String::from("foo");
1382 /// assert_eq!(a.len(), 3);
1385 #[stable(feature = "rust1", since = "1.0.0")]
1386 pub fn len(&self) -> usize {
1390 /// Returns `true` if this `String` has a length of zero.
1392 /// Returns `false` otherwise.
1399 /// let mut v = String::new();
1400 /// assert!(v.is_empty());
1403 /// assert!(!v.is_empty());
1406 #[stable(feature = "rust1", since = "1.0.0")]
1407 pub fn is_empty(&self) -> bool {
1411 /// Splits the string into two at the given index.
1413 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1414 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1415 /// boundary of a UTF-8 code point.
1417 /// Note that the capacity of `self` does not change.
1421 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1422 /// code point of the string.
1428 /// let mut hello = String::from("Hello, World!");
1429 /// let world = hello.split_off(7);
1430 /// assert_eq!(hello, "Hello, ");
1431 /// assert_eq!(world, "World!");
1435 #[stable(feature = "string_split_off", since = "1.16.0")]
1436 pub fn split_off(&mut self, at: usize) -> String {
1437 assert!(self.is_char_boundary(at));
1438 let other = self.vec.split_off(at);
1439 unsafe { String::from_utf8_unchecked(other) }
1442 /// Truncates this `String`, removing all contents.
1444 /// While this means the `String` will have a length of zero, it does not
1445 /// touch its capacity.
1452 /// let mut s = String::from("foo");
1456 /// assert!(s.is_empty());
1457 /// assert_eq!(0, s.len());
1458 /// assert_eq!(3, s.capacity());
1461 #[stable(feature = "rust1", since = "1.0.0")]
1462 pub fn clear(&mut self) {
1466 /// Creates a draining iterator that removes the specified range in the `String`
1467 /// and yields the removed `chars`.
1469 /// Note: The element range is removed even if the iterator is not
1470 /// consumed until the end.
1474 /// Panics if the starting point or end point do not lie on a [`char`]
1475 /// boundary, or if they're out of bounds.
1477 /// [`char`]: ../../std/primitive.char.html
1484 /// let mut s = String::from("α is alpha, β is beta");
1485 /// let beta_offset = s.find('β').unwrap_or(s.len());
1487 /// // Remove the range up until the β from the string
1488 /// let t: String = s.drain(..beta_offset).collect();
1489 /// assert_eq!(t, "α is alpha, ");
1490 /// assert_eq!(s, "β is beta");
1492 /// // A full range clears the string
1494 /// assert_eq!(s, "");
1496 #[stable(feature = "drain", since = "1.6.0")]
1497 pub fn drain<R>(&mut self, range: R) -> Drain
1498 where R: RangeBounds<usize>
1502 // The String version of Drain does not have the memory safety issues
1503 // of the vector version. The data is just plain bytes.
1504 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1505 // the removal will not happen.
1506 let len = self.len();
1507 let start = match range.start_bound() {
1509 Excluded(&n) => n + 1,
1512 let end = match range.end_bound() {
1513 Included(&n) => n + 1,
1518 // Take out two simultaneous borrows. The &mut String won't be accessed
1519 // until iteration is over, in Drop.
1520 let self_ptr = self as *mut _;
1521 // slicing does the appropriate bounds checks
1522 let chars_iter = self[start..end].chars();
1532 /// Removes the specified range in the string,
1533 /// and replaces it with the given string.
1534 /// The given string doesn't need to be the same length as the range.
1538 /// Panics if the starting point or end point do not lie on a [`char`]
1539 /// boundary, or if they're out of bounds.
1541 /// [`char`]: ../../std/primitive.char.html
1542 /// [`Vec::splice`]: ../../std/vec/struct.Vec.html#method.splice
1549 /// let mut s = String::from("α is alpha, β is beta");
1550 /// let beta_offset = s.find('β').unwrap_or(s.len());
1552 /// // Replace the range up until the β from the string
1553 /// s.replace_range(..beta_offset, "Α is capital alpha; ");
1554 /// assert_eq!(s, "Α is capital alpha; β is beta");
1556 #[stable(feature = "splice", since = "1.27.0")]
1557 pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
1558 where R: RangeBounds<usize>
1562 // Replace_range does not have the memory safety issues of a vector Splice.
1563 // of the vector version. The data is just plain bytes.
1565 match range.start_bound() {
1566 Included(&n) => assert!(self.is_char_boundary(n)),
1567 Excluded(&n) => assert!(self.is_char_boundary(n + 1)),
1570 match range.end_bound() {
1571 Included(&n) => assert!(self.is_char_boundary(n + 1)),
1572 Excluded(&n) => assert!(self.is_char_boundary(n)),
1578 }.splice(range, replace_with.bytes());
1581 /// Converts this `String` into a [`Box`]`<`[`str`]`>`.
1583 /// This will drop any excess capacity.
1585 /// [`Box`]: ../../std/boxed/struct.Box.html
1586 /// [`str`]: ../../std/primitive.str.html
1593 /// let s = String::from("hello");
1595 /// let b = s.into_boxed_str();
1597 #[stable(feature = "box_str", since = "1.4.0")]
1599 pub fn into_boxed_str(self) -> Box<str> {
1600 let slice = self.vec.into_boxed_slice();
1601 unsafe { from_boxed_utf8_unchecked(slice) }
1605 impl FromUtf8Error {
1606 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1613 /// // some invalid bytes, in a vector
1614 /// let bytes = vec![0, 159];
1616 /// let value = String::from_utf8(bytes);
1618 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1620 #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
1621 pub fn as_bytes(&self) -> &[u8] {
1625 /// Returns the bytes that were attempted to convert to a `String`.
1627 /// This method is carefully constructed to avoid allocation. It will
1628 /// consume the error, moving out the bytes, so that a copy of the bytes
1629 /// does not need to be made.
1636 /// // some invalid bytes, in a vector
1637 /// let bytes = vec![0, 159];
1639 /// let value = String::from_utf8(bytes);
1641 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1643 #[stable(feature = "rust1", since = "1.0.0")]
1644 pub fn into_bytes(self) -> Vec<u8> {
1648 /// Fetch a `Utf8Error` to get more details about the conversion failure.
1650 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1651 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1652 /// an analogue to `FromUtf8Error`. See its documentation for more details
1655 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
1656 /// [`std::str`]: ../../std/str/index.html
1657 /// [`u8`]: ../../std/primitive.u8.html
1658 /// [`&str`]: ../../std/primitive.str.html
1665 /// // some invalid bytes, in a vector
1666 /// let bytes = vec![0, 159];
1668 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1670 /// // the first byte is invalid here
1671 /// assert_eq!(1, error.valid_up_to());
1673 #[stable(feature = "rust1", since = "1.0.0")]
1674 pub fn utf8_error(&self) -> Utf8Error {
1679 #[stable(feature = "rust1", since = "1.0.0")]
1680 impl fmt::Display for FromUtf8Error {
1681 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1682 fmt::Display::fmt(&self.error, f)
1686 #[stable(feature = "rust1", since = "1.0.0")]
1687 impl fmt::Display for FromUtf16Error {
1688 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1689 fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
1693 #[stable(feature = "rust1", since = "1.0.0")]
1694 impl Clone for String {
1695 fn clone(&self) -> Self {
1696 String { vec: self.vec.clone() }
1699 fn clone_from(&mut self, source: &Self) {
1700 self.vec.clone_from(&source.vec);
1704 #[stable(feature = "rust1", since = "1.0.0")]
1705 impl FromIterator<char> for String {
1706 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
1707 let mut buf = String::new();
1713 #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
1714 impl<'a> FromIterator<&'a char> for String {
1715 fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
1716 let mut buf = String::new();
1722 #[stable(feature = "rust1", since = "1.0.0")]
1723 impl<'a> FromIterator<&'a str> for String {
1724 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
1725 let mut buf = String::new();
1731 #[stable(feature = "extend_string", since = "1.4.0")]
1732 impl FromIterator<String> for String {
1733 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
1734 let mut iterator = iter.into_iter();
1736 // Because we're iterating over `String`s, we can avoid at least
1737 // one allocation by getting the first string from the iterator
1738 // and appending to it all the subsequent strings.
1739 match iterator.next() {
1740 None => String::new(),
1742 buf.extend(iterator);
1749 #[stable(feature = "herd_cows", since = "1.19.0")]
1750 impl<'a> FromIterator<Cow<'a, str>> for String {
1751 fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
1752 let mut iterator = iter.into_iter();
1754 // Because we're iterating over CoWs, we can (potentially) avoid at least
1755 // one allocation by getting the first item and appending to it all the
1756 // subsequent items.
1757 match iterator.next() {
1758 None => String::new(),
1760 let mut buf = cow.into_owned();
1761 buf.extend(iterator);
1768 #[stable(feature = "rust1", since = "1.0.0")]
1769 impl Extend<char> for String {
1770 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
1771 let iterator = iter.into_iter();
1772 let (lower_bound, _) = iterator.size_hint();
1773 self.reserve(lower_bound);
1774 iterator.for_each(move |c| self.push(c));
1778 #[stable(feature = "extend_ref", since = "1.2.0")]
1779 impl<'a> Extend<&'a char> for String {
1780 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
1781 self.extend(iter.into_iter().cloned());
1785 #[stable(feature = "rust1", since = "1.0.0")]
1786 impl<'a> Extend<&'a str> for String {
1787 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
1788 iter.into_iter().for_each(move |s| self.push_str(s));
1792 #[stable(feature = "extend_string", since = "1.4.0")]
1793 impl Extend<String> for String {
1794 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
1795 iter.into_iter().for_each(move |s| self.push_str(&s));
1799 #[stable(feature = "herd_cows", since = "1.19.0")]
1800 impl<'a> Extend<Cow<'a, str>> for String {
1801 fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
1802 iter.into_iter().for_each(move |s| self.push_str(&s));
1806 /// A convenience impl that delegates to the impl for `&str`
1807 #[unstable(feature = "pattern",
1808 reason = "API not fully fleshed out and ready to be stabilized",
1810 impl<'a, 'b> Pattern<'a> for &'b String {
1811 type Searcher = <&'b str as Pattern<'a>>::Searcher;
1813 fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
1814 self[..].into_searcher(haystack)
1818 fn is_contained_in(self, haystack: &'a str) -> bool {
1819 self[..].is_contained_in(haystack)
1823 fn is_prefix_of(self, haystack: &'a str) -> bool {
1824 self[..].is_prefix_of(haystack)
1828 #[stable(feature = "rust1", since = "1.0.0")]
1829 impl PartialEq for String {
1831 fn eq(&self, other: &String) -> bool {
1832 PartialEq::eq(&self[..], &other[..])
1835 fn ne(&self, other: &String) -> bool {
1836 PartialEq::ne(&self[..], &other[..])
1840 macro_rules! impl_eq {
1841 ($lhs:ty, $rhs: ty) => {
1842 #[stable(feature = "rust1", since = "1.0.0")]
1843 impl<'a, 'b> PartialEq<$rhs> for $lhs {
1845 fn eq(&self, other: &$rhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1847 fn ne(&self, other: &$rhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1850 #[stable(feature = "rust1", since = "1.0.0")]
1851 impl<'a, 'b> PartialEq<$lhs> for $rhs {
1853 fn eq(&self, other: &$lhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1855 fn ne(&self, other: &$lhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1861 impl_eq! { String, str }
1862 impl_eq! { String, &'a str }
1863 impl_eq! { Cow<'a, str>, str }
1864 impl_eq! { Cow<'a, str>, &'b str }
1865 impl_eq! { Cow<'a, str>, String }
1867 #[stable(feature = "rust1", since = "1.0.0")]
1868 impl Default for String {
1869 /// Creates an empty `String`.
1871 fn default() -> String {
1876 #[stable(feature = "rust1", since = "1.0.0")]
1877 impl fmt::Display for String {
1879 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1880 fmt::Display::fmt(&**self, f)
1884 #[stable(feature = "rust1", since = "1.0.0")]
1885 impl fmt::Debug for String {
1887 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1888 fmt::Debug::fmt(&**self, f)
1892 #[stable(feature = "rust1", since = "1.0.0")]
1893 impl hash::Hash for String {
1895 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
1896 (**self).hash(hasher)
1900 /// Implements the `+` operator for concatenating two strings.
1902 /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
1903 /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
1904 /// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by
1905 /// repeated concatenation.
1907 /// The string on the right-hand side is only borrowed; its contents are copied into the returned
1912 /// Concatenating two `String`s takes the first by value and borrows the second:
1915 /// let a = String::from("hello");
1916 /// let b = String::from(" world");
1918 /// // `a` is moved and can no longer be used here.
1921 /// If you want to keep using the first `String`, you can clone it and append to the clone instead:
1924 /// let a = String::from("hello");
1925 /// let b = String::from(" world");
1926 /// let c = a.clone() + &b;
1927 /// // `a` is still valid here.
1930 /// Concatenating `&str` slices can be done by converting the first to a `String`:
1933 /// let a = "hello";
1934 /// let b = " world";
1935 /// let c = a.to_string() + b;
1937 #[stable(feature = "rust1", since = "1.0.0")]
1938 impl<'a> Add<&'a str> for String {
1939 type Output = String;
1942 fn add(mut self, other: &str) -> String {
1943 self.push_str(other);
1948 /// Implements the `+=` operator for appending to a `String`.
1950 /// This has the same behavior as the [`push_str`][String::push_str] method.
1951 #[stable(feature = "stringaddassign", since = "1.12.0")]
1952 impl<'a> AddAssign<&'a str> for String {
1954 fn add_assign(&mut self, other: &str) {
1955 self.push_str(other);
1959 #[stable(feature = "rust1", since = "1.0.0")]
1960 impl ops::Index<ops::Range<usize>> for String {
1964 fn index(&self, index: ops::Range<usize>) -> &str {
1968 #[stable(feature = "rust1", since = "1.0.0")]
1969 impl ops::Index<ops::RangeTo<usize>> for String {
1973 fn index(&self, index: ops::RangeTo<usize>) -> &str {
1977 #[stable(feature = "rust1", since = "1.0.0")]
1978 impl ops::Index<ops::RangeFrom<usize>> for String {
1982 fn index(&self, index: ops::RangeFrom<usize>) -> &str {
1986 #[stable(feature = "rust1", since = "1.0.0")]
1987 impl ops::Index<ops::RangeFull> for String {
1991 fn index(&self, _index: ops::RangeFull) -> &str {
1992 unsafe { str::from_utf8_unchecked(&self.vec) }
1995 #[stable(feature = "inclusive_range", since = "1.26.0")]
1996 impl ops::Index<ops::RangeInclusive<usize>> for String {
2000 fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
2001 Index::index(&**self, index)
2004 #[stable(feature = "inclusive_range", since = "1.26.0")]
2005 impl ops::Index<ops::RangeToInclusive<usize>> for String {
2009 fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
2010 Index::index(&**self, index)
2014 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2015 impl ops::IndexMut<ops::Range<usize>> for String {
2017 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
2018 &mut self[..][index]
2021 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2022 impl ops::IndexMut<ops::RangeTo<usize>> for String {
2024 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
2025 &mut self[..][index]
2028 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2029 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
2031 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
2032 &mut self[..][index]
2035 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2036 impl ops::IndexMut<ops::RangeFull> for String {
2038 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
2039 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2042 #[stable(feature = "inclusive_range", since = "1.26.0")]
2043 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
2045 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
2046 IndexMut::index_mut(&mut **self, index)
2049 #[stable(feature = "inclusive_range", since = "1.26.0")]
2050 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
2052 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
2053 IndexMut::index_mut(&mut **self, index)
2057 #[stable(feature = "rust1", since = "1.0.0")]
2058 impl ops::Deref for String {
2062 fn deref(&self) -> &str {
2063 unsafe { str::from_utf8_unchecked(&self.vec) }
2067 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2068 impl ops::DerefMut for String {
2070 fn deref_mut(&mut self) -> &mut str {
2071 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2075 /// An error when parsing a `String`.
2077 /// This `enum` is slightly awkward: it will never actually exist. This error is
2078 /// part of the type signature of the implementation of [`FromStr`] on
2079 /// [`String`]. The return type of [`from_str`], requires that an error be
2080 /// defined, but, given that a [`String`] can always be made into a new
2081 /// [`String`] without error, this type will never actually be returned. As
2082 /// such, it is only here to satisfy said signature, and is useless otherwise.
2084 /// [`FromStr`]: ../../std/str/trait.FromStr.html
2085 /// [`String`]: struct.String.html
2086 /// [`from_str`]: ../../std/str/trait.FromStr.html#tymethod.from_str
2087 #[stable(feature = "str_parse_error", since = "1.5.0")]
2089 pub enum ParseError {}
2091 #[stable(feature = "rust1", since = "1.0.0")]
2092 impl FromStr for String {
2093 type Err = ParseError;
2095 fn from_str(s: &str) -> Result<String, ParseError> {
2100 #[stable(feature = "str_parse_error", since = "1.5.0")]
2101 impl Clone for ParseError {
2102 fn clone(&self) -> ParseError {
2107 #[stable(feature = "str_parse_error", since = "1.5.0")]
2108 impl fmt::Debug for ParseError {
2109 fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
2114 #[stable(feature = "str_parse_error2", since = "1.8.0")]
2115 impl fmt::Display for ParseError {
2116 fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
2121 #[stable(feature = "str_parse_error", since = "1.5.0")]
2122 impl PartialEq for ParseError {
2123 fn eq(&self, _: &ParseError) -> bool {
2128 #[stable(feature = "str_parse_error", since = "1.5.0")]
2129 impl Eq for ParseError {}
2131 /// A trait for converting a value to a `String`.
2133 /// This trait is automatically implemented for any type which implements the
2134 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
2135 /// [`Display`] should be implemented instead, and you get the `ToString`
2136 /// implementation for free.
2138 /// [`Display`]: ../../std/fmt/trait.Display.html
2139 #[stable(feature = "rust1", since = "1.0.0")]
2140 pub trait ToString {
2141 /// Converts the given value to a `String`.
2149 /// let five = String::from("5");
2151 /// assert_eq!(five, i.to_string());
2153 #[rustc_conversion_suggestion]
2154 #[stable(feature = "rust1", since = "1.0.0")]
2155 fn to_string(&self) -> String;
2160 /// In this implementation, the `to_string` method panics
2161 /// if the `Display` implementation returns an error.
2162 /// This indicates an incorrect `Display` implementation
2163 /// since `fmt::Write for String` never returns an error itself.
2164 #[stable(feature = "rust1", since = "1.0.0")]
2165 impl<T: fmt::Display + ?Sized> ToString for T {
2167 default fn to_string(&self) -> String {
2169 let mut buf = String::new();
2170 buf.write_fmt(format_args!("{}", self))
2171 .expect("a Display implementation returned an error unexpectedly");
2172 buf.shrink_to_fit();
2177 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
2178 impl ToString for str {
2180 fn to_string(&self) -> String {
2185 #[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
2186 impl<'a> ToString for Cow<'a, str> {
2188 fn to_string(&self) -> String {
2193 #[stable(feature = "string_to_string_specialization", since = "1.17.0")]
2194 impl ToString for String {
2196 fn to_string(&self) -> String {
2201 #[stable(feature = "rust1", since = "1.0.0")]
2202 impl AsRef<str> for String {
2204 fn as_ref(&self) -> &str {
2209 #[stable(feature = "rust1", since = "1.0.0")]
2210 impl AsRef<[u8]> for String {
2212 fn as_ref(&self) -> &[u8] {
2217 #[stable(feature = "rust1", since = "1.0.0")]
2218 impl<'a> From<&'a str> for String {
2220 fn from(s: &'a str) -> String {
2225 // note: test pulls in libstd, which causes errors here
2227 #[stable(feature = "string_from_box", since = "1.18.0")]
2228 impl From<Box<str>> for String {
2229 /// Converts the given boxed `str` slice to a `String`.
2230 /// It is notable that the `str` slice is owned.
2237 /// let s1: String = String::from("hello world");
2238 /// let s2: Box<str> = s1.into_boxed_str();
2239 /// let s3: String = String::from(s2);
2241 /// assert_eq!("hello world", s3)
2243 fn from(s: Box<str>) -> String {
2248 #[stable(feature = "box_from_str", since = "1.20.0")]
2249 impl From<String> for Box<str> {
2250 /// Converts the given `String` to a boxed `str` slice that is owned.
2257 /// let s1: String = String::from("hello world");
2258 /// let s2: Box<str> = Box::from(s1);
2259 /// let s3: String = String::from(s2);
2261 /// assert_eq!("hello world", s3)
2263 fn from(s: String) -> Box<str> {
2268 #[stable(feature = "string_from_cow_str", since = "1.14.0")]
2269 impl<'a> From<Cow<'a, str>> for String {
2270 fn from(s: Cow<'a, str>) -> String {
2275 #[stable(feature = "rust1", since = "1.0.0")]
2276 impl<'a> From<&'a str> for Cow<'a, str> {
2278 fn from(s: &'a str) -> Cow<'a, str> {
2283 #[stable(feature = "rust1", since = "1.0.0")]
2284 impl<'a> From<String> for Cow<'a, str> {
2286 fn from(s: String) -> Cow<'a, str> {
2291 #[stable(feature = "cow_from_string_ref", since = "1.28.0")]
2292 impl<'a> From<&'a String> for Cow<'a, str> {
2294 fn from(s: &'a String) -> Cow<'a, str> {
2295 Cow::Borrowed(s.as_str())
2299 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2300 impl<'a> FromIterator<char> for Cow<'a, str> {
2301 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
2302 Cow::Owned(FromIterator::from_iter(it))
2306 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2307 impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
2308 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
2309 Cow::Owned(FromIterator::from_iter(it))
2313 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2314 impl<'a> FromIterator<String> for Cow<'a, str> {
2315 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
2316 Cow::Owned(FromIterator::from_iter(it))
2320 #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
2321 impl From<String> for Vec<u8> {
2322 /// Converts the given `String` to a vector `Vec` that holds values of type `u8`.
2329 /// let s1 = String::from("hello world");
2330 /// let v1 = Vec::from(s1);
2333 /// println!("{}", b);
2336 fn from(string: String) -> Vec<u8> {
2341 #[stable(feature = "rust1", since = "1.0.0")]
2342 impl fmt::Write for String {
2344 fn write_str(&mut self, s: &str) -> fmt::Result {
2350 fn write_char(&mut self, c: char) -> fmt::Result {
2356 /// A draining iterator for `String`.
2358 /// This struct is created by the [`drain`] method on [`String`]. See its
2359 /// documentation for more.
2361 /// [`drain`]: struct.String.html#method.drain
2362 /// [`String`]: struct.String.html
2363 #[stable(feature = "drain", since = "1.6.0")]
2364 pub struct Drain<'a> {
2365 /// Will be used as &'a mut String in the destructor
2366 string: *mut String,
2367 /// Start of part to remove
2369 /// End of part to remove
2371 /// Current remaining range to remove
2375 #[stable(feature = "collection_debug", since = "1.17.0")]
2376 impl<'a> fmt::Debug for Drain<'a> {
2377 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2378 f.pad("Drain { .. }")
2382 #[stable(feature = "drain", since = "1.6.0")]
2383 unsafe impl<'a> Sync for Drain<'a> {}
2384 #[stable(feature = "drain", since = "1.6.0")]
2385 unsafe impl<'a> Send for Drain<'a> {}
2387 #[stable(feature = "drain", since = "1.6.0")]
2388 impl<'a> Drop for Drain<'a> {
2389 fn drop(&mut self) {
2391 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
2392 // panic code being inserted again.
2393 let self_vec = (*self.string).as_mut_vec();
2394 if self.start <= self.end && self.end <= self_vec.len() {
2395 self_vec.drain(self.start..self.end);
2401 #[stable(feature = "drain", since = "1.6.0")]
2402 impl<'a> Iterator for Drain<'a> {
2406 fn next(&mut self) -> Option<char> {
2410 fn size_hint(&self) -> (usize, Option<usize>) {
2411 self.iter.size_hint()
2415 #[stable(feature = "drain", since = "1.6.0")]
2416 impl<'a> DoubleEndedIterator for Drain<'a> {
2418 fn next_back(&mut self) -> Option<char> {
2419 self.iter.next_back()
2423 #[stable(feature = "fused", since = "1.26.0")]
2424 impl<'a> FusedIterator for Drain<'a> {}