1 //! A UTF-8–encoded, growable string.
3 //! This module contains the [`String`] type, the [`ToString`] trait for
4 //! converting to strings, and several error types that may result from
5 //! working with [`String`]s.
9 //! There are multiple ways to create a new [`String`] from a string literal:
12 //! let s = "Hello".to_string();
14 //! let s = String::from("world");
15 //! let s: String = "also this".into();
18 //! You can create a new [`String`] from an existing one by concatenating with
22 //! let s = "Hello".to_string();
24 //! let message = s + " world!";
27 //! If you have a vector of valid UTF-8 bytes, you can make a [`String`] out of
28 //! it. You can do the reverse too.
31 //! let sparkle_heart = vec![240, 159, 146, 150];
33 //! // We know these bytes are valid, so we'll use `unwrap()`.
34 //! let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
36 //! assert_eq!("💖", sparkle_heart);
38 //! let bytes = sparkle_heart.into_bytes();
40 //! assert_eq!(bytes, [240, 159, 146, 150]);
43 #![stable(feature = "rust1", since = "1.0.0")]
45 #[cfg(not(no_global_oom_handling))]
46 use core::char::{decode_utf16, REPLACEMENT_CHARACTER};
49 #[cfg(not(no_global_oom_handling))]
50 use core::iter::FromIterator;
51 use core::iter::{from_fn, FusedIterator};
52 #[cfg(not(no_global_oom_handling))]
54 #[cfg(not(no_global_oom_handling))]
55 use core::ops::AddAssign;
56 #[cfg(not(no_global_oom_handling))]
57 use core::ops::Bound::{Excluded, Included, Unbounded};
58 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
61 #[cfg(not(no_global_oom_handling))]
63 use core::str::pattern::Pattern;
65 #[cfg(not(no_global_oom_handling))]
66 use crate::borrow::{Cow, ToOwned};
67 use crate::boxed::Box;
68 use crate::collections::TryReserveError;
69 use crate::str::{self, Chars, Utf8Error};
70 #[cfg(not(no_global_oom_handling))]
71 use crate::str::{from_boxed_utf8_unchecked, FromStr};
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`].
82 /// You can create a `String` from [a literal string][`str`] with [`String::from`]:
84 /// [`String::from`]: From::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 /// [`push`]: String::push
101 /// [`push_str`]: String::push_str
103 /// If you have a vector of UTF-8 bytes, you can create a `String` from it with
104 /// the [`from_utf8`] method:
107 /// // some bytes, in a vector
108 /// let sparkle_heart = vec![240, 159, 146, 150];
110 /// // We know these bytes are valid, so we'll use `unwrap()`.
111 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
113 /// assert_eq!("💖", sparkle_heart);
116 /// [`from_utf8`]: String::from_utf8
120 /// `String`s are always valid UTF-8. This has a few implications, the first of
121 /// which is that if you need a non-UTF-8 string, consider [`OsString`]. It is
122 /// similar, but without the UTF-8 constraint. The second implication is that
123 /// you cannot index into a `String`:
125 /// ```compile_fail,E0277
128 /// println!("The first letter of s is {}", s[0]); // ERROR!!!
131 /// [`OsString`]: ../../std/ffi/struct.OsString.html
133 /// Indexing is intended to be a constant-time operation, but UTF-8 encoding
134 /// does not allow us to do this. Furthermore, it's not clear what sort of
135 /// thing the index should return: a byte, a codepoint, or a grapheme cluster.
136 /// The [`bytes`] and [`chars`] methods return iterators over the first
137 /// two, respectively.
139 /// [`bytes`]: str::bytes
140 /// [`chars`]: str::chars
144 /// `String`s implement [`Deref`]`<Target=str>`, and so inherit all of [`str`]'s
145 /// methods. In addition, this means that you can pass a `String` to a
146 /// function which takes a [`&str`] by using an ampersand (`&`):
149 /// fn takes_str(s: &str) { }
151 /// let s = String::from("Hello");
156 /// This will create a [`&str`] from the `String` and pass it in. This
157 /// conversion is very inexpensive, and so generally, functions will accept
158 /// [`&str`]s as arguments unless they need a `String` for some specific
161 /// In certain cases Rust doesn't have enough information to make this
162 /// conversion, known as [`Deref`] coercion. In the following example a string
163 /// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
164 /// `example_func` takes anything that implements the trait. In this case Rust
165 /// would need to make two implicit conversions, which Rust doesn't have the
166 /// means to do. For that reason, the following example will not compile.
168 /// ```compile_fail,E0277
169 /// trait TraitExample {}
171 /// impl<'a> TraitExample for &'a str {}
173 /// fn example_func<A: TraitExample>(example_arg: A) {}
175 /// let example_string = String::from("example_string");
176 /// example_func(&example_string);
179 /// There are two options that would work instead. The first would be to
180 /// change the line `example_func(&example_string);` to
181 /// `example_func(example_string.as_str());`, using the method [`as_str()`]
182 /// to explicitly extract the string slice containing the string. The second
183 /// way changes `example_func(&example_string);` to
184 /// `example_func(&*example_string);`. In this case we are dereferencing a
185 /// `String` to a [`str`][`&str`], then referencing the [`str`][`&str`] back to
186 /// [`&str`]. The second way is more idiomatic, however both work to do the
187 /// conversion explicitly rather than relying on the implicit conversion.
191 /// A `String` is made up of three components: a pointer to some bytes, a
192 /// length, and a capacity. The pointer points to an internal buffer `String`
193 /// uses to store its data. The length is the number of bytes currently stored
194 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
195 /// the length will always be less than or equal to the capacity.
197 /// This buffer is always stored on the heap.
199 /// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
205 /// let story = String::from("Once upon a time...");
207 // FIXME Update this when vec_into_raw_parts is stabilized
208 /// // Prevent automatically dropping the String's data
209 /// let mut story = mem::ManuallyDrop::new(story);
211 /// let ptr = story.as_mut_ptr();
212 /// let len = story.len();
213 /// let capacity = story.capacity();
215 /// // story has nineteen bytes
216 /// assert_eq!(19, len);
218 /// // We can re-build a String out of ptr, len, and capacity. This is all
219 /// // unsafe because we are responsible for making sure the components are
221 /// let s = unsafe { String::from_raw_parts(ptr, len, capacity) } ;
223 /// assert_eq!(String::from("Once upon a time..."), s);
226 /// [`as_ptr`]: str::as_ptr
227 /// [`len`]: String::len
228 /// [`capacity`]: String::capacity
230 /// If a `String` has enough capacity, adding elements to it will not
231 /// re-allocate. For example, consider this program:
234 /// let mut s = String::new();
236 /// println!("{}", s.capacity());
239 /// s.push_str("hello");
240 /// println!("{}", s.capacity());
244 /// This will output the following:
255 /// At first, we have no memory allocated at all, but as we append to the
256 /// string, it increases its capacity appropriately. If we instead use the
257 /// [`with_capacity`] method to allocate the correct capacity initially:
260 /// let mut s = String::with_capacity(25);
262 /// println!("{}", s.capacity());
265 /// s.push_str("hello");
266 /// println!("{}", s.capacity());
270 /// [`with_capacity`]: String::with_capacity
272 /// We end up with a different output:
283 /// Here, there's no need to allocate more memory inside the loop.
285 /// [`str`]: prim@str
286 /// [`&str`]: prim@str
287 /// [`Deref`]: core::ops::Deref
288 /// [`as_str()`]: String::as_str
289 #[derive(PartialOrd, Eq, Ord)]
290 #[cfg_attr(not(test), rustc_diagnostic_item = "string_type")]
291 #[stable(feature = "rust1", since = "1.0.0")]
296 /// A possible error value when converting a `String` from a UTF-8 byte vector.
298 /// This type is the error type for the [`from_utf8`] method on [`String`]. It
299 /// is designed in such a way to carefully avoid reallocations: the
300 /// [`into_bytes`] method will give back the byte vector that was used in the
301 /// conversion attempt.
303 /// [`from_utf8`]: String::from_utf8
304 /// [`into_bytes`]: FromUtf8Error::into_bytes
306 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
307 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
308 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
309 /// through the [`utf8_error`] method.
311 /// [`Utf8Error`]: core::str::Utf8Error
312 /// [`std::str`]: core::str
313 /// [`&str`]: prim@str
314 /// [`utf8_error`]: Self::utf8_error
321 /// // some invalid bytes, in a vector
322 /// let bytes = vec![0, 159];
324 /// let value = String::from_utf8(bytes);
326 /// assert!(value.is_err());
327 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
329 #[stable(feature = "rust1", since = "1.0.0")]
330 #[cfg_attr(not(no_global_oom_handling), derive(Clone))]
331 #[derive(Debug, PartialEq, Eq)]
332 pub struct FromUtf8Error {
337 /// A possible error value when converting a `String` from a UTF-16 byte slice.
339 /// This type is the error type for the [`from_utf16`] method on [`String`].
341 /// [`from_utf16`]: String::from_utf16
347 /// // 𝄞mu<invalid>ic
348 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
349 /// 0xD800, 0x0069, 0x0063];
351 /// assert!(String::from_utf16(v).is_err());
353 #[stable(feature = "rust1", since = "1.0.0")]
355 pub struct FromUtf16Error(());
358 /// Creates a new empty `String`.
360 /// Given that the `String` is empty, this will not allocate any initial
361 /// buffer. While that means that this initial operation is very
362 /// inexpensive, it may cause excessive allocation later when you add
363 /// data. If you have an idea of how much data the `String` will hold,
364 /// consider the [`with_capacity`] method to prevent excessive
367 /// [`with_capacity`]: String::with_capacity
374 /// let s = String::new();
377 #[rustc_const_stable(feature = "const_string_new", since = "1.39.0")]
378 #[stable(feature = "rust1", since = "1.0.0")]
379 pub const fn new() -> String {
380 String { vec: Vec::new() }
383 /// Creates a new empty `String` with a particular capacity.
385 /// `String`s have an internal buffer to hold their data. The capacity is
386 /// the length of that buffer, and can be queried with the [`capacity`]
387 /// method. This method creates an empty `String`, but one with an initial
388 /// buffer that can hold `capacity` bytes. This is useful when you may be
389 /// appending a bunch of data to the `String`, reducing the number of
390 /// reallocations it needs to do.
392 /// [`capacity`]: String::capacity
394 /// If the given capacity is `0`, no allocation will occur, and this method
395 /// is identical to the [`new`] method.
397 /// [`new`]: String::new
404 /// let mut s = String::with_capacity(10);
406 /// // The String contains no chars, even though it has capacity for more
407 /// assert_eq!(s.len(), 0);
409 /// // These are all done without reallocating...
410 /// let cap = s.capacity();
415 /// assert_eq!(s.capacity(), cap);
417 /// // ...but this may make the string reallocate
420 #[cfg(not(no_global_oom_handling))]
422 #[doc(alias = "alloc")]
423 #[doc(alias = "malloc")]
424 #[stable(feature = "rust1", since = "1.0.0")]
425 pub fn with_capacity(capacity: usize) -> String {
426 String { vec: Vec::with_capacity(capacity) }
429 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
430 // required for this method definition, is not available. Since we don't
431 // require this method for testing purposes, I'll just stub it
432 // NB see the slice::hack module in slice.rs for more information
435 pub fn from_str(_: &str) -> String {
436 panic!("not available with cfg(test)");
439 /// Converts a vector of bytes to a `String`.
441 /// A string ([`String`]) is made of bytes ([`u8`]), and a vector of bytes
442 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
443 /// two. Not all byte slices are valid `String`s, however: `String`
444 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
445 /// the bytes are valid UTF-8, and then does the conversion.
447 /// If you are sure that the byte slice is valid UTF-8, and you don't want
448 /// to incur the overhead of the validity check, there is an unsafe version
449 /// of this function, [`from_utf8_unchecked`], which has the same behavior
450 /// but skips the check.
452 /// This method will take care to not copy the vector, for efficiency's
455 /// If you need a [`&str`] instead of a `String`, consider
456 /// [`str::from_utf8`].
458 /// The inverse of this method is [`into_bytes`].
462 /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
463 /// provided bytes are not UTF-8. The vector you moved in is also included.
470 /// // some bytes, in a vector
471 /// let sparkle_heart = vec![240, 159, 146, 150];
473 /// // We know these bytes are valid, so we'll use `unwrap()`.
474 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
476 /// assert_eq!("💖", sparkle_heart);
482 /// // some invalid bytes, in a vector
483 /// let sparkle_heart = vec![0, 159, 146, 150];
485 /// assert!(String::from_utf8(sparkle_heart).is_err());
488 /// See the docs for [`FromUtf8Error`] for more details on what you can do
491 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
492 /// [`Vec<u8>`]: crate::vec::Vec
493 /// [`&str`]: prim@str
494 /// [`into_bytes`]: String::into_bytes
496 #[stable(feature = "rust1", since = "1.0.0")]
497 pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
498 match str::from_utf8(&vec) {
499 Ok(..) => Ok(String { vec }),
500 Err(e) => Err(FromUtf8Error { bytes: vec, error: e }),
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 /// [byteslice]: prim@slice
514 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
516 /// If you are sure that the byte slice is valid UTF-8, and you don't want
517 /// to incur the overhead of the conversion, there is an unsafe version
518 /// of this function, [`from_utf8_unchecked`], which has the same behavior
519 /// but skips the checks.
521 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
523 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
524 /// UTF-8, then we need to insert the replacement characters, which will
525 /// change the size of the string, and hence, require a `String`. But if
526 /// it's already valid UTF-8, we don't need a new allocation. This return
527 /// type allows us to handle both cases.
529 /// [`Cow<'a, str>`]: crate::borrow::Cow
536 /// // some bytes, in a vector
537 /// let sparkle_heart = vec![240, 159, 146, 150];
539 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
541 /// assert_eq!("💖", sparkle_heart);
547 /// // some invalid bytes
548 /// let input = b"Hello \xF0\x90\x80World";
549 /// let output = String::from_utf8_lossy(input);
551 /// assert_eq!("Hello �World", output);
553 #[cfg(not(no_global_oom_handling))]
554 #[stable(feature = "rust1", since = "1.0.0")]
555 pub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, 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.
596 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
597 /// 0x0073, 0x0069, 0x0063];
598 /// assert_eq!(String::from("𝄞music"),
599 /// String::from_utf16(v).unwrap());
601 /// // 𝄞mu<invalid>ic
602 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
603 /// 0xD800, 0x0069, 0x0063];
604 /// assert!(String::from_utf16(v).is_err());
606 #[cfg(not(no_global_oom_handling))]
607 #[stable(feature = "rust1", since = "1.0.0")]
608 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
609 // This isn't done via collect::<Result<_, _>>() for performance reasons.
610 // FIXME: the function can be simplified again when #48994 is closed.
611 let mut ret = String::with_capacity(v.len());
612 for c in decode_utf16(v.iter().cloned()) {
616 return Err(FromUtf16Error(()));
622 /// Decode a UTF-16–encoded slice `v` into a `String`, replacing
623 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
625 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
626 /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
627 /// conversion requires a memory allocation.
629 /// [`from_utf8_lossy`]: String::from_utf8_lossy
630 /// [`Cow<'a, str>`]: crate::borrow::Cow
631 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
638 /// // 𝄞mus<invalid>ic<invalid>
639 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
640 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
643 /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
644 /// String::from_utf16_lossy(v));
646 #[cfg(not(no_global_oom_handling))]
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 /// Decomposes a `String` into its raw components.
655 /// Returns the raw pointer to the underlying data, the length of
656 /// the string (in bytes), and the allocated capacity of the data
657 /// (in bytes). These are the same arguments in the same order as
658 /// the arguments to [`from_raw_parts`].
660 /// After calling this function, the caller is responsible for the
661 /// memory previously managed by the `String`. The only way to do
662 /// this is to convert the raw pointer, length, and capacity back
663 /// into a `String` with the [`from_raw_parts`] function, allowing
664 /// the destructor to perform the cleanup.
666 /// [`from_raw_parts`]: String::from_raw_parts
671 /// #![feature(vec_into_raw_parts)]
672 /// let s = String::from("hello");
674 /// let (ptr, len, cap) = s.into_raw_parts();
676 /// let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
677 /// assert_eq!(rebuilt, "hello");
679 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
680 pub fn into_raw_parts(self) -> (*mut u8, usize, usize) {
681 self.vec.into_raw_parts()
684 /// Creates a new `String` from a length, capacity, and pointer.
688 /// This is highly unsafe, due to the number of invariants that aren't
691 /// * The memory at `buf` needs to have been previously allocated by the
692 /// same allocator the standard library uses, with a required alignment of exactly 1.
693 /// * `length` needs to be less than or equal to `capacity`.
694 /// * `capacity` needs to be the correct value.
695 /// * The first `length` bytes at `buf` need to be valid UTF-8.
697 /// Violating these may cause problems like corrupting the allocator's
698 /// internal data structures.
700 /// The ownership of `buf` is effectively transferred to the
701 /// `String` which may then deallocate, reallocate or change the
702 /// contents of memory pointed to by the pointer at will. Ensure
703 /// that nothing else uses the pointer after calling this
714 /// let s = String::from("hello");
716 // FIXME Update this when vec_into_raw_parts is stabilized
717 /// // Prevent automatically dropping the String's data
718 /// let mut s = mem::ManuallyDrop::new(s);
720 /// let ptr = s.as_mut_ptr();
721 /// let len = s.len();
722 /// let capacity = s.capacity();
724 /// let s = String::from_raw_parts(ptr, len, capacity);
726 /// assert_eq!(String::from("hello"), s);
730 #[stable(feature = "rust1", since = "1.0.0")]
731 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
732 unsafe { String { vec: Vec::from_raw_parts(buf, length, capacity) } }
735 /// Converts a vector of bytes to a `String` without checking that the
736 /// string contains valid UTF-8.
738 /// See the safe version, [`from_utf8`], for more details.
740 /// [`from_utf8`]: String::from_utf8
744 /// This function is unsafe because it does not check that the bytes passed
745 /// to it are valid UTF-8. If this constraint is violated, it may cause
746 /// memory unsafety issues with future users of the `String`, as the rest of
747 /// the standard library assumes that `String`s are valid UTF-8.
754 /// // some bytes, in a vector
755 /// let sparkle_heart = vec![240, 159, 146, 150];
757 /// let sparkle_heart = unsafe {
758 /// String::from_utf8_unchecked(sparkle_heart)
761 /// assert_eq!("💖", sparkle_heart);
764 #[stable(feature = "rust1", since = "1.0.0")]
765 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
766 String { vec: bytes }
769 /// Converts a `String` into a byte vector.
771 /// This consumes the `String`, so we do not need to copy its contents.
778 /// let s = String::from("hello");
779 /// let bytes = s.into_bytes();
781 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
784 #[stable(feature = "rust1", since = "1.0.0")]
785 pub fn into_bytes(self) -> Vec<u8> {
789 /// Extracts a string slice containing the entire `String`.
796 /// let s = String::from("foo");
798 /// assert_eq!("foo", s.as_str());
801 #[stable(feature = "string_as_str", since = "1.7.0")]
802 pub fn as_str(&self) -> &str {
806 /// Converts a `String` into a mutable string slice.
813 /// let mut s = String::from("foobar");
814 /// let s_mut_str = s.as_mut_str();
816 /// s_mut_str.make_ascii_uppercase();
818 /// assert_eq!("FOOBAR", s_mut_str);
821 #[stable(feature = "string_as_str", since = "1.7.0")]
822 pub fn as_mut_str(&mut self) -> &mut str {
826 /// Appends a given string slice onto the end of this `String`.
833 /// let mut s = String::from("foo");
835 /// s.push_str("bar");
837 /// assert_eq!("foobar", s);
839 #[cfg(not(no_global_oom_handling))]
841 #[stable(feature = "rust1", since = "1.0.0")]
842 pub fn push_str(&mut self, string: &str) {
843 self.vec.extend_from_slice(string.as_bytes())
846 /// Copies elements from `src` range to the end of the string.
850 /// Panics if the starting point or end point do not lie on a [`char`]
851 /// boundary, or if they're out of bounds.
856 /// #![feature(string_extend_from_within)]
857 /// let mut string = String::from("abcde");
859 /// string.extend_from_within(2..);
860 /// assert_eq!(string, "abcdecde");
862 /// string.extend_from_within(..2);
863 /// assert_eq!(string, "abcdecdeab");
865 /// string.extend_from_within(4..8);
866 /// assert_eq!(string, "abcdecdeabecde");
868 #[cfg(not(no_global_oom_handling))]
869 #[unstable(feature = "string_extend_from_within", issue = "none")]
870 pub fn extend_from_within<R>(&mut self, src: R)
872 R: RangeBounds<usize>,
874 let src @ Range { start, end } = slice::range(src, ..self.len());
876 assert!(self.is_char_boundary(start));
877 assert!(self.is_char_boundary(end));
879 self.vec.extend_from_within(src);
882 /// Returns this `String`'s capacity, in bytes.
889 /// let s = String::with_capacity(10);
891 /// assert!(s.capacity() >= 10);
894 #[stable(feature = "rust1", since = "1.0.0")]
895 pub fn capacity(&self) -> usize {
899 /// Ensures that this `String`'s capacity is at least `additional` bytes
900 /// larger than its length.
902 /// The capacity may be increased by more than `additional` bytes if it
903 /// chooses, to prevent frequent reallocations.
905 /// If you do not want this "at least" behavior, see the [`reserve_exact`]
910 /// Panics if the new capacity overflows [`usize`].
912 /// [`reserve_exact`]: String::reserve_exact
919 /// let mut s = String::new();
923 /// assert!(s.capacity() >= 10);
926 /// This may not actually increase the capacity:
929 /// let mut s = String::with_capacity(10);
933 /// // s now has a length of 2 and a capacity of 10
934 /// assert_eq!(2, s.len());
935 /// assert_eq!(10, s.capacity());
937 /// // Since we already have an extra 8 capacity, calling this...
940 /// // ... doesn't actually increase.
941 /// assert_eq!(10, s.capacity());
943 #[cfg(not(no_global_oom_handling))]
945 #[stable(feature = "rust1", since = "1.0.0")]
946 pub fn reserve(&mut self, additional: usize) {
947 self.vec.reserve(additional)
950 /// Ensures that this `String`'s capacity is `additional` bytes
951 /// larger than its length.
953 /// Consider using the [`reserve`] method unless you absolutely know
954 /// better than the allocator.
956 /// [`reserve`]: String::reserve
960 /// Panics if the new capacity overflows `usize`.
967 /// let mut s = String::new();
969 /// s.reserve_exact(10);
971 /// assert!(s.capacity() >= 10);
974 /// This may not actually increase the capacity:
977 /// let mut s = String::with_capacity(10);
981 /// // s now has a length of 2 and a capacity of 10
982 /// assert_eq!(2, s.len());
983 /// assert_eq!(10, s.capacity());
985 /// // Since we already have an extra 8 capacity, calling this...
986 /// s.reserve_exact(8);
988 /// // ... doesn't actually increase.
989 /// assert_eq!(10, s.capacity());
991 #[cfg(not(no_global_oom_handling))]
993 #[stable(feature = "rust1", since = "1.0.0")]
994 pub fn reserve_exact(&mut self, additional: usize) {
995 self.vec.reserve_exact(additional)
998 /// Tries to reserve capacity for at least `additional` more elements to be inserted
999 /// in the given `String`. The collection may reserve more space to avoid
1000 /// frequent reallocations. After calling `reserve`, capacity will be
1001 /// greater than or equal to `self.len() + additional`. Does nothing if
1002 /// capacity is already sufficient.
1006 /// If the capacity overflows, or the allocator reports a failure, then an error
1012 /// #![feature(try_reserve)]
1013 /// use std::collections::TryReserveError;
1015 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
1016 /// let mut output = String::new();
1018 /// // Pre-reserve the memory, exiting if we can't
1019 /// output.try_reserve(data.len())?;
1021 /// // Now we know this can't OOM in the middle of our complex work
1022 /// output.push_str(data);
1026 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1028 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
1029 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
1030 self.vec.try_reserve(additional)
1033 /// Tries to reserve the minimum capacity for exactly `additional` more elements to
1034 /// be inserted in the given `String`. After calling `reserve_exact`,
1035 /// capacity will be greater than or equal to `self.len() + additional`.
1036 /// Does nothing if the capacity is already sufficient.
1038 /// Note that the allocator may give the collection more space than it
1039 /// requests. Therefore, capacity can not be relied upon to be precisely
1040 /// minimal. Prefer `reserve` if future insertions are expected.
1044 /// If the capacity overflows, or the allocator reports a failure, then an error
1050 /// #![feature(try_reserve)]
1051 /// use std::collections::TryReserveError;
1053 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
1054 /// let mut output = String::new();
1056 /// // Pre-reserve the memory, exiting if we can't
1057 /// output.try_reserve(data.len())?;
1059 /// // Now we know this can't OOM in the middle of our complex work
1060 /// output.push_str(data);
1064 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1066 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
1067 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
1068 self.vec.try_reserve_exact(additional)
1071 /// Shrinks the capacity of this `String` to match its length.
1078 /// let mut s = String::from("foo");
1081 /// assert!(s.capacity() >= 100);
1083 /// s.shrink_to_fit();
1084 /// assert_eq!(3, s.capacity());
1086 #[cfg(not(no_global_oom_handling))]
1088 #[stable(feature = "rust1", since = "1.0.0")]
1089 pub fn shrink_to_fit(&mut self) {
1090 self.vec.shrink_to_fit()
1093 /// Shrinks the capacity of this `String` with a lower bound.
1095 /// The capacity will remain at least as large as both the length
1096 /// and the supplied value.
1098 /// If the current capacity is less than the lower limit, this is a no-op.
1103 /// #![feature(shrink_to)]
1104 /// let mut s = String::from("foo");
1107 /// assert!(s.capacity() >= 100);
1109 /// s.shrink_to(10);
1110 /// assert!(s.capacity() >= 10);
1112 /// assert!(s.capacity() >= 3);
1114 #[cfg(not(no_global_oom_handling))]
1116 #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")]
1117 pub fn shrink_to(&mut self, min_capacity: usize) {
1118 self.vec.shrink_to(min_capacity)
1121 /// Appends the given [`char`] to the end of this `String`.
1128 /// let mut s = String::from("abc");
1134 /// assert_eq!("abc123", s);
1136 #[cfg(not(no_global_oom_handling))]
1138 #[stable(feature = "rust1", since = "1.0.0")]
1139 pub fn push(&mut self, ch: char) {
1140 match ch.len_utf8() {
1141 1 => self.vec.push(ch as u8),
1142 _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
1146 /// Returns a byte slice of this `String`'s contents.
1148 /// The inverse of this method is [`from_utf8`].
1150 /// [`from_utf8`]: String::from_utf8
1157 /// let s = String::from("hello");
1159 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
1162 #[stable(feature = "rust1", since = "1.0.0")]
1163 pub fn as_bytes(&self) -> &[u8] {
1167 /// Shortens this `String` to the specified length.
1169 /// If `new_len` is greater than the string's current length, this has no
1172 /// Note that this method has no effect on the allocated capacity
1177 /// Panics if `new_len` does not lie on a [`char`] boundary.
1184 /// let mut s = String::from("hello");
1188 /// assert_eq!("he", s);
1191 #[stable(feature = "rust1", since = "1.0.0")]
1192 pub fn truncate(&mut self, new_len: usize) {
1193 if new_len <= self.len() {
1194 assert!(self.is_char_boundary(new_len));
1195 self.vec.truncate(new_len)
1199 /// Removes the last character from the string buffer and returns it.
1201 /// Returns [`None`] if this `String` is empty.
1208 /// let mut s = String::from("foo");
1210 /// assert_eq!(s.pop(), Some('o'));
1211 /// assert_eq!(s.pop(), Some('o'));
1212 /// assert_eq!(s.pop(), Some('f'));
1214 /// assert_eq!(s.pop(), None);
1217 #[stable(feature = "rust1", since = "1.0.0")]
1218 pub fn pop(&mut self) -> Option<char> {
1219 let ch = self.chars().rev().next()?;
1220 let newlen = self.len() - ch.len_utf8();
1222 self.vec.set_len(newlen);
1227 /// Removes a [`char`] from this `String` at a byte position and returns it.
1229 /// This is an *O*(*n*) operation, as it requires copying every element in the
1234 /// Panics if `idx` is larger than or equal to the `String`'s length,
1235 /// or if it does not lie on a [`char`] boundary.
1242 /// let mut s = String::from("foo");
1244 /// assert_eq!(s.remove(0), 'f');
1245 /// assert_eq!(s.remove(1), 'o');
1246 /// assert_eq!(s.remove(0), 'o');
1249 #[stable(feature = "rust1", since = "1.0.0")]
1250 pub fn remove(&mut self, idx: usize) -> char {
1251 let ch = match self[idx..].chars().next() {
1253 None => panic!("cannot remove a char from the end of a string"),
1256 let next = idx + ch.len_utf8();
1257 let len = self.len();
1259 ptr::copy(self.vec.as_ptr().add(next), self.vec.as_mut_ptr().add(idx), len - next);
1260 self.vec.set_len(len - (next - idx));
1265 /// Remove all matches of pattern `pat` in the `String`.
1270 /// #![feature(string_remove_matches)]
1271 /// let mut s = String::from("Trees are not green, the sky is not blue.");
1272 /// s.remove_matches("not ");
1273 /// assert_eq!("Trees are green, the sky is blue.", s);
1276 /// Matches will be detected and removed iteratively, so in cases where
1277 /// patterns overlap, only the first pattern will be removed:
1280 /// #![feature(string_remove_matches)]
1281 /// let mut s = String::from("banana");
1282 /// s.remove_matches("ana");
1283 /// assert_eq!("bna", s);
1285 #[cfg(not(no_global_oom_handling))]
1286 #[unstable(feature = "string_remove_matches", reason = "new API", issue = "72826")]
1287 pub fn remove_matches<'a, P>(&'a mut self, pat: P)
1289 P: for<'x> Pattern<'x>,
1291 use core::str::pattern::Searcher;
1294 let mut searcher = pat.into_searcher(self);
1295 // Per Searcher::next:
1297 // A Match result needs to contain the whole matched pattern,
1298 // however Reject results may be split up into arbitrary many
1299 // adjacent fragments. Both ranges may have zero length.
1301 // In practice the implementation of Searcher::next_match tends to
1302 // be more efficient, so we use it here and do some work to invert
1303 // matches into rejections since that's what we want to copy below.
1305 let rejections: Vec<_> = from_fn(|| {
1306 let (start, end) = searcher.next_match()?;
1307 let prev_front = front;
1309 Some((prev_front, start))
1312 rejections.into_iter().chain(core::iter::once((front, self.len())))
1316 let ptr = self.vec.as_mut_ptr();
1318 for (start, end) in rejections {
1319 let count = end - start;
1321 // SAFETY: per Searcher::next:
1323 // The stream of Match and Reject values up to a Done will
1324 // contain index ranges that are adjacent, non-overlapping,
1325 // covering the whole haystack, and laying on utf8
1328 ptr::copy(ptr.add(start), ptr.add(len), count);
1335 self.vec.set_len(len);
1339 /// Retains only the characters specified by the predicate.
1341 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1342 /// This method operates in place, visiting each character exactly once in the
1343 /// original order, and preserves the order of the retained characters.
1348 /// let mut s = String::from("f_o_ob_ar");
1350 /// s.retain(|c| c != '_');
1352 /// assert_eq!(s, "foobar");
1355 /// The exact order may be useful for tracking external state, like an index.
1358 /// let mut s = String::from("abcde");
1359 /// let keep = [false, true, true, false, true];
1361 /// s.retain(|_| (keep[i], i += 1).0);
1362 /// assert_eq!(s, "bce");
1365 #[stable(feature = "string_retain", since = "1.26.0")]
1366 pub fn retain<F>(&mut self, mut f: F)
1368 F: FnMut(char) -> bool,
1370 struct SetLenOnDrop<'a> {
1376 impl<'a> Drop for SetLenOnDrop<'a> {
1377 fn drop(&mut self) {
1378 let new_len = self.idx - self.del_bytes;
1379 debug_assert!(new_len <= self.s.len());
1380 unsafe { self.s.vec.set_len(new_len) };
1384 let len = self.len();
1385 let mut guard = SetLenOnDrop { s: self, idx: 0, del_bytes: 0 };
1387 while guard.idx < len {
1388 let ch = unsafe { guard.s.get_unchecked(guard.idx..len).chars().next().unwrap() };
1389 let ch_len = ch.len_utf8();
1392 guard.del_bytes += ch_len;
1393 } else if guard.del_bytes > 0 {
1396 guard.s.vec.as_ptr().add(guard.idx),
1397 guard.s.vec.as_mut_ptr().add(guard.idx - guard.del_bytes),
1403 // Point idx to the next char
1404 guard.idx += ch_len;
1410 /// Inserts a character into this `String` at a byte position.
1412 /// This is an *O*(*n*) operation as it requires copying every element in the
1417 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1418 /// lie on a [`char`] boundary.
1425 /// let mut s = String::with_capacity(3);
1427 /// s.insert(0, 'f');
1428 /// s.insert(1, 'o');
1429 /// s.insert(2, 'o');
1431 /// assert_eq!("foo", s);
1433 #[cfg(not(no_global_oom_handling))]
1435 #[stable(feature = "rust1", since = "1.0.0")]
1436 pub fn insert(&mut self, idx: usize, ch: char) {
1437 assert!(self.is_char_boundary(idx));
1438 let mut bits = [0; 4];
1439 let bits = ch.encode_utf8(&mut bits).as_bytes();
1442 self.insert_bytes(idx, bits);
1446 #[cfg(not(no_global_oom_handling))]
1447 unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1448 let len = self.len();
1449 let amt = bytes.len();
1450 self.vec.reserve(amt);
1453 ptr::copy(self.vec.as_ptr().add(idx), self.vec.as_mut_ptr().add(idx + amt), len - idx);
1454 ptr::copy_nonoverlapping(bytes.as_ptr(), self.vec.as_mut_ptr().add(idx), amt);
1455 self.vec.set_len(len + amt);
1459 /// Inserts a string slice into this `String` at a byte position.
1461 /// This is an *O*(*n*) operation as it requires copying every element in the
1466 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1467 /// lie on a [`char`] boundary.
1474 /// let mut s = String::from("bar");
1476 /// s.insert_str(0, "foo");
1478 /// assert_eq!("foobar", s);
1480 #[cfg(not(no_global_oom_handling))]
1482 #[stable(feature = "insert_str", since = "1.16.0")]
1483 pub fn insert_str(&mut self, idx: usize, string: &str) {
1484 assert!(self.is_char_boundary(idx));
1487 self.insert_bytes(idx, string.as_bytes());
1491 /// Returns a mutable reference to the contents of this `String`.
1495 /// This function is unsafe because it does not check that the bytes passed
1496 /// to it are valid UTF-8. If this constraint is violated, it may cause
1497 /// memory unsafety issues with future users of the `String`, as the rest of
1498 /// the standard library assumes that `String`s are valid UTF-8.
1505 /// let mut s = String::from("hello");
1508 /// let vec = s.as_mut_vec();
1509 /// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1513 /// assert_eq!(s, "olleh");
1516 #[stable(feature = "rust1", since = "1.0.0")]
1517 pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1521 /// Returns the length of this `String`, in bytes, not [`char`]s or
1522 /// graphemes. In other words, it may not be what a human considers the
1523 /// length of the string.
1530 /// let a = String::from("foo");
1531 /// assert_eq!(a.len(), 3);
1533 /// let fancy_f = String::from("ƒoo");
1534 /// assert_eq!(fancy_f.len(), 4);
1535 /// assert_eq!(fancy_f.chars().count(), 3);
1537 #[doc(alias = "length")]
1539 #[stable(feature = "rust1", since = "1.0.0")]
1540 pub fn len(&self) -> usize {
1544 /// Returns `true` if this `String` has a length of zero, and `false` otherwise.
1551 /// let mut v = String::new();
1552 /// assert!(v.is_empty());
1555 /// assert!(!v.is_empty());
1558 #[stable(feature = "rust1", since = "1.0.0")]
1559 pub fn is_empty(&self) -> bool {
1563 /// Splits the string into two at the given byte index.
1565 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1566 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1567 /// boundary of a UTF-8 code point.
1569 /// Note that the capacity of `self` does not change.
1573 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1574 /// code point of the string.
1580 /// let mut hello = String::from("Hello, World!");
1581 /// let world = hello.split_off(7);
1582 /// assert_eq!(hello, "Hello, ");
1583 /// assert_eq!(world, "World!");
1586 #[cfg(not(no_global_oom_handling))]
1588 #[stable(feature = "string_split_off", since = "1.16.0")]
1589 #[must_use = "use `.truncate()` if you don't need the other half"]
1590 pub fn split_off(&mut self, at: usize) -> String {
1591 assert!(self.is_char_boundary(at));
1592 let other = self.vec.split_off(at);
1593 unsafe { String::from_utf8_unchecked(other) }
1596 /// Truncates this `String`, removing all contents.
1598 /// While this means the `String` will have a length of zero, it does not
1599 /// touch its capacity.
1606 /// let mut s = String::from("foo");
1610 /// assert!(s.is_empty());
1611 /// assert_eq!(0, s.len());
1612 /// assert_eq!(3, s.capacity());
1615 #[stable(feature = "rust1", since = "1.0.0")]
1616 pub fn clear(&mut self) {
1620 /// Creates a draining iterator that removes the specified range in the `String`
1621 /// and yields the removed `chars`.
1623 /// Note: The element range is removed even if the iterator is not
1624 /// consumed until the end.
1628 /// Panics if the starting point or end point do not lie on a [`char`]
1629 /// boundary, or if they're out of bounds.
1636 /// let mut s = String::from("α is alpha, β is beta");
1637 /// let beta_offset = s.find('β').unwrap_or(s.len());
1639 /// // Remove the range up until the β from the string
1640 /// let t: String = s.drain(..beta_offset).collect();
1641 /// assert_eq!(t, "α is alpha, ");
1642 /// assert_eq!(s, "β is beta");
1644 /// // A full range clears the string
1646 /// assert_eq!(s, "");
1648 #[stable(feature = "drain", since = "1.6.0")]
1649 pub fn drain<R>(&mut self, range: R) -> Drain<'_>
1651 R: RangeBounds<usize>,
1655 // The String version of Drain does not have the memory safety issues
1656 // of the vector version. The data is just plain bytes.
1657 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1658 // the removal will not happen.
1659 let Range { start, end } = slice::range(range, ..self.len());
1660 assert!(self.is_char_boundary(start));
1661 assert!(self.is_char_boundary(end));
1663 // Take out two simultaneous borrows. The &mut String won't be accessed
1664 // until iteration is over, in Drop.
1665 let self_ptr = self as *mut _;
1666 // SAFETY: `slice::range` and `is_char_boundary` do the appropriate bounds checks.
1667 let chars_iter = unsafe { self.get_unchecked(start..end) }.chars();
1669 Drain { start, end, iter: chars_iter, string: self_ptr }
1672 /// Removes the specified range in the string,
1673 /// and replaces it with the given string.
1674 /// The given string doesn't need to be the same length as the range.
1678 /// Panics if the starting point or end point do not lie on a [`char`]
1679 /// boundary, or if they're out of bounds.
1686 /// let mut s = String::from("α is alpha, β is beta");
1687 /// let beta_offset = s.find('β').unwrap_or(s.len());
1689 /// // Replace the range up until the β from the string
1690 /// s.replace_range(..beta_offset, "Α is capital alpha; ");
1691 /// assert_eq!(s, "Α is capital alpha; β is beta");
1693 #[cfg(not(no_global_oom_handling))]
1694 #[stable(feature = "splice", since = "1.27.0")]
1695 pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
1697 R: RangeBounds<usize>,
1701 // Replace_range does not have the memory safety issues of a vector Splice.
1702 // of the vector version. The data is just plain bytes.
1704 // WARNING: Inlining this variable would be unsound (#81138)
1705 let start = range.start_bound();
1707 Included(&n) => assert!(self.is_char_boundary(n)),
1708 Excluded(&n) => assert!(self.is_char_boundary(n + 1)),
1711 // WARNING: Inlining this variable would be unsound (#81138)
1712 let end = range.end_bound();
1714 Included(&n) => assert!(self.is_char_boundary(n + 1)),
1715 Excluded(&n) => assert!(self.is_char_boundary(n)),
1719 // Using `range` again would be unsound (#81138)
1720 // We assume the bounds reported by `range` remain the same, but
1721 // an adversarial implementation could change between calls
1722 unsafe { self.as_mut_vec() }.splice((start, end), replace_with.bytes());
1725 /// Converts this `String` into a [`Box`]`<`[`str`]`>`.
1727 /// This will drop any excess capacity.
1729 /// [`str`]: prim@str
1736 /// let s = String::from("hello");
1738 /// let b = s.into_boxed_str();
1740 #[cfg(not(no_global_oom_handling))]
1741 #[stable(feature = "box_str", since = "1.4.0")]
1743 pub fn into_boxed_str(self) -> Box<str> {
1744 let slice = self.vec.into_boxed_slice();
1745 unsafe { from_boxed_utf8_unchecked(slice) }
1749 impl FromUtf8Error {
1750 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1757 /// // some invalid bytes, in a vector
1758 /// let bytes = vec![0, 159];
1760 /// let value = String::from_utf8(bytes);
1762 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1764 #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
1765 pub fn as_bytes(&self) -> &[u8] {
1769 /// Returns the bytes that were attempted to convert to a `String`.
1771 /// This method is carefully constructed to avoid allocation. It will
1772 /// consume the error, moving out the bytes, so that a copy of the bytes
1773 /// does not need to be made.
1780 /// // some invalid bytes, in a vector
1781 /// let bytes = vec![0, 159];
1783 /// let value = String::from_utf8(bytes);
1785 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1787 #[stable(feature = "rust1", since = "1.0.0")]
1788 pub fn into_bytes(self) -> Vec<u8> {
1792 /// Fetch a `Utf8Error` to get more details about the conversion failure.
1794 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1795 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1796 /// an analogue to `FromUtf8Error`. See its documentation for more details
1799 /// [`std::str`]: core::str
1800 /// [`&str`]: prim@str
1807 /// // some invalid bytes, in a vector
1808 /// let bytes = vec![0, 159];
1810 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1812 /// // the first byte is invalid here
1813 /// assert_eq!(1, error.valid_up_to());
1815 #[stable(feature = "rust1", since = "1.0.0")]
1816 pub fn utf8_error(&self) -> Utf8Error {
1821 #[stable(feature = "rust1", since = "1.0.0")]
1822 impl fmt::Display for FromUtf8Error {
1823 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1824 fmt::Display::fmt(&self.error, f)
1828 #[stable(feature = "rust1", since = "1.0.0")]
1829 impl fmt::Display for FromUtf16Error {
1830 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1831 fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
1835 #[cfg(not(no_global_oom_handling))]
1836 #[stable(feature = "rust1", since = "1.0.0")]
1837 impl Clone for String {
1838 fn clone(&self) -> Self {
1839 String { vec: self.vec.clone() }
1842 fn clone_from(&mut self, source: &Self) {
1843 self.vec.clone_from(&source.vec);
1847 #[cfg(not(no_global_oom_handling))]
1848 #[stable(feature = "rust1", since = "1.0.0")]
1849 impl FromIterator<char> for String {
1850 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
1851 let mut buf = String::new();
1857 #[cfg(not(no_global_oom_handling))]
1858 #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
1859 impl<'a> FromIterator<&'a char> for String {
1860 fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
1861 let mut buf = String::new();
1867 #[cfg(not(no_global_oom_handling))]
1868 #[stable(feature = "rust1", since = "1.0.0")]
1869 impl<'a> FromIterator<&'a str> for String {
1870 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
1871 let mut buf = String::new();
1877 #[cfg(not(no_global_oom_handling))]
1878 #[stable(feature = "extend_string", since = "1.4.0")]
1879 impl FromIterator<String> for String {
1880 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
1881 let mut iterator = iter.into_iter();
1883 // Because we're iterating over `String`s, we can avoid at least
1884 // one allocation by getting the first string from the iterator
1885 // and appending to it all the subsequent strings.
1886 match iterator.next() {
1887 None => String::new(),
1889 buf.extend(iterator);
1896 #[cfg(not(no_global_oom_handling))]
1897 #[stable(feature = "box_str2", since = "1.45.0")]
1898 impl FromIterator<Box<str>> for String {
1899 fn from_iter<I: IntoIterator<Item = Box<str>>>(iter: I) -> String {
1900 let mut buf = String::new();
1906 #[cfg(not(no_global_oom_handling))]
1907 #[stable(feature = "herd_cows", since = "1.19.0")]
1908 impl<'a> FromIterator<Cow<'a, str>> for String {
1909 fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
1910 let mut iterator = iter.into_iter();
1912 // Because we're iterating over CoWs, we can (potentially) avoid at least
1913 // one allocation by getting the first item and appending to it all the
1914 // subsequent items.
1915 match iterator.next() {
1916 None => String::new(),
1918 let mut buf = cow.into_owned();
1919 buf.extend(iterator);
1926 #[cfg(not(no_global_oom_handling))]
1927 #[stable(feature = "rust1", since = "1.0.0")]
1928 impl Extend<char> for String {
1929 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
1930 let iterator = iter.into_iter();
1931 let (lower_bound, _) = iterator.size_hint();
1932 self.reserve(lower_bound);
1933 iterator.for_each(move |c| self.push(c));
1937 fn extend_one(&mut self, c: char) {
1942 fn extend_reserve(&mut self, additional: usize) {
1943 self.reserve(additional);
1947 #[cfg(not(no_global_oom_handling))]
1948 #[stable(feature = "extend_ref", since = "1.2.0")]
1949 impl<'a> Extend<&'a char> for String {
1950 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
1951 self.extend(iter.into_iter().cloned());
1955 fn extend_one(&mut self, &c: &'a char) {
1960 fn extend_reserve(&mut self, additional: usize) {
1961 self.reserve(additional);
1965 #[cfg(not(no_global_oom_handling))]
1966 #[stable(feature = "rust1", since = "1.0.0")]
1967 impl<'a> Extend<&'a str> for String {
1968 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
1969 iter.into_iter().for_each(move |s| self.push_str(s));
1973 fn extend_one(&mut self, s: &'a str) {
1978 #[cfg(not(no_global_oom_handling))]
1979 #[stable(feature = "box_str2", since = "1.45.0")]
1980 impl Extend<Box<str>> for String {
1981 fn extend<I: IntoIterator<Item = Box<str>>>(&mut self, iter: I) {
1982 iter.into_iter().for_each(move |s| self.push_str(&s));
1986 #[cfg(not(no_global_oom_handling))]
1987 #[stable(feature = "extend_string", since = "1.4.0")]
1988 impl Extend<String> for String {
1989 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
1990 iter.into_iter().for_each(move |s| self.push_str(&s));
1994 fn extend_one(&mut self, s: String) {
1999 #[cfg(not(no_global_oom_handling))]
2000 #[stable(feature = "herd_cows", since = "1.19.0")]
2001 impl<'a> Extend<Cow<'a, str>> for String {
2002 fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
2003 iter.into_iter().for_each(move |s| self.push_str(&s));
2007 fn extend_one(&mut self, s: Cow<'a, str>) {
2012 /// A convenience impl that delegates to the impl for `&str`.
2017 /// assert_eq!(String::from("Hello world").find("world"), Some(6));
2020 feature = "pattern",
2021 reason = "API not fully fleshed out and ready to be stabilized",
2024 impl<'a, 'b> Pattern<'a> for &'b String {
2025 type Searcher = <&'b str as Pattern<'a>>::Searcher;
2027 fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
2028 self[..].into_searcher(haystack)
2032 fn is_contained_in(self, haystack: &'a str) -> bool {
2033 self[..].is_contained_in(haystack)
2037 fn is_prefix_of(self, haystack: &'a str) -> bool {
2038 self[..].is_prefix_of(haystack)
2042 fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str> {
2043 self[..].strip_prefix_of(haystack)
2047 fn is_suffix_of(self, haystack: &'a str) -> bool {
2048 self[..].is_suffix_of(haystack)
2052 fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str> {
2053 self[..].strip_suffix_of(haystack)
2057 #[stable(feature = "rust1", since = "1.0.0")]
2058 impl PartialEq for String {
2060 fn eq(&self, other: &String) -> bool {
2061 PartialEq::eq(&self[..], &other[..])
2064 fn ne(&self, other: &String) -> bool {
2065 PartialEq::ne(&self[..], &other[..])
2069 macro_rules! impl_eq {
2070 ($lhs:ty, $rhs: ty) => {
2071 #[stable(feature = "rust1", since = "1.0.0")]
2072 #[allow(unused_lifetimes)]
2073 impl<'a, 'b> PartialEq<$rhs> for $lhs {
2075 fn eq(&self, other: &$rhs) -> bool {
2076 PartialEq::eq(&self[..], &other[..])
2079 fn ne(&self, other: &$rhs) -> bool {
2080 PartialEq::ne(&self[..], &other[..])
2084 #[stable(feature = "rust1", since = "1.0.0")]
2085 #[allow(unused_lifetimes)]
2086 impl<'a, 'b> PartialEq<$lhs> for $rhs {
2088 fn eq(&self, other: &$lhs) -> bool {
2089 PartialEq::eq(&self[..], &other[..])
2092 fn ne(&self, other: &$lhs) -> bool {
2093 PartialEq::ne(&self[..], &other[..])
2099 impl_eq! { String, str }
2100 impl_eq! { String, &'a str }
2101 #[cfg(not(no_global_oom_handling))]
2102 impl_eq! { Cow<'a, str>, str }
2103 #[cfg(not(no_global_oom_handling))]
2104 impl_eq! { Cow<'a, str>, &'b str }
2105 #[cfg(not(no_global_oom_handling))]
2106 impl_eq! { Cow<'a, str>, String }
2108 #[stable(feature = "rust1", since = "1.0.0")]
2109 impl Default for String {
2110 /// Creates an empty `String`.
2112 fn default() -> String {
2117 #[stable(feature = "rust1", since = "1.0.0")]
2118 impl fmt::Display for String {
2120 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2121 fmt::Display::fmt(&**self, f)
2125 #[stable(feature = "rust1", since = "1.0.0")]
2126 impl fmt::Debug for String {
2128 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2129 fmt::Debug::fmt(&**self, f)
2133 #[stable(feature = "rust1", since = "1.0.0")]
2134 impl hash::Hash for String {
2136 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
2137 (**self).hash(hasher)
2141 /// Implements the `+` operator for concatenating two strings.
2143 /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
2144 /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
2145 /// every operation, which would lead to *O*(*n*^2) running time when building an *n*-byte string by
2146 /// repeated concatenation.
2148 /// The string on the right-hand side is only borrowed; its contents are copied into the returned
2153 /// Concatenating two `String`s takes the first by value and borrows the second:
2156 /// let a = String::from("hello");
2157 /// let b = String::from(" world");
2159 /// // `a` is moved and can no longer be used here.
2162 /// If you want to keep using the first `String`, you can clone it and append to the clone instead:
2165 /// let a = String::from("hello");
2166 /// let b = String::from(" world");
2167 /// let c = a.clone() + &b;
2168 /// // `a` is still valid here.
2171 /// Concatenating `&str` slices can be done by converting the first to a `String`:
2174 /// let a = "hello";
2175 /// let b = " world";
2176 /// let c = a.to_string() + b;
2178 #[cfg(not(no_global_oom_handling))]
2179 #[stable(feature = "rust1", since = "1.0.0")]
2180 impl Add<&str> for String {
2181 type Output = String;
2184 fn add(mut self, other: &str) -> String {
2185 self.push_str(other);
2190 /// Implements the `+=` operator for appending to a `String`.
2192 /// This has the same behavior as the [`push_str`][String::push_str] method.
2193 #[cfg(not(no_global_oom_handling))]
2194 #[stable(feature = "stringaddassign", since = "1.12.0")]
2195 impl AddAssign<&str> for String {
2197 fn add_assign(&mut self, other: &str) {
2198 self.push_str(other);
2202 #[stable(feature = "rust1", since = "1.0.0")]
2203 impl ops::Index<ops::Range<usize>> for String {
2207 fn index(&self, index: ops::Range<usize>) -> &str {
2211 #[stable(feature = "rust1", since = "1.0.0")]
2212 impl ops::Index<ops::RangeTo<usize>> for String {
2216 fn index(&self, index: ops::RangeTo<usize>) -> &str {
2220 #[stable(feature = "rust1", since = "1.0.0")]
2221 impl ops::Index<ops::RangeFrom<usize>> for String {
2225 fn index(&self, index: ops::RangeFrom<usize>) -> &str {
2229 #[stable(feature = "rust1", since = "1.0.0")]
2230 impl ops::Index<ops::RangeFull> for String {
2234 fn index(&self, _index: ops::RangeFull) -> &str {
2235 unsafe { str::from_utf8_unchecked(&self.vec) }
2238 #[stable(feature = "inclusive_range", since = "1.26.0")]
2239 impl ops::Index<ops::RangeInclusive<usize>> for String {
2243 fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
2244 Index::index(&**self, index)
2247 #[stable(feature = "inclusive_range", since = "1.26.0")]
2248 impl ops::Index<ops::RangeToInclusive<usize>> for String {
2252 fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
2253 Index::index(&**self, index)
2257 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2258 impl ops::IndexMut<ops::Range<usize>> for String {
2260 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
2261 &mut self[..][index]
2264 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2265 impl ops::IndexMut<ops::RangeTo<usize>> for String {
2267 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
2268 &mut self[..][index]
2271 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2272 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
2274 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
2275 &mut self[..][index]
2278 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2279 impl ops::IndexMut<ops::RangeFull> for String {
2281 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
2282 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2285 #[stable(feature = "inclusive_range", since = "1.26.0")]
2286 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
2288 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
2289 IndexMut::index_mut(&mut **self, index)
2292 #[stable(feature = "inclusive_range", since = "1.26.0")]
2293 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
2295 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
2296 IndexMut::index_mut(&mut **self, index)
2300 #[stable(feature = "rust1", since = "1.0.0")]
2301 impl ops::Deref for String {
2305 fn deref(&self) -> &str {
2306 unsafe { str::from_utf8_unchecked(&self.vec) }
2310 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2311 impl ops::DerefMut for String {
2313 fn deref_mut(&mut self) -> &mut str {
2314 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2318 /// A type alias for [`Infallible`].
2320 /// This alias exists for backwards compatibility, and may be eventually deprecated.
2322 /// [`Infallible`]: core::convert::Infallible
2323 #[stable(feature = "str_parse_error", since = "1.5.0")]
2324 pub type ParseError = core::convert::Infallible;
2326 #[cfg(not(no_global_oom_handling))]
2327 #[stable(feature = "rust1", since = "1.0.0")]
2328 impl FromStr for String {
2329 type Err = core::convert::Infallible;
2331 fn from_str(s: &str) -> Result<String, Self::Err> {
2336 /// A trait for converting a value to a `String`.
2338 /// This trait is automatically implemented for any type which implements the
2339 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
2340 /// [`Display`] should be implemented instead, and you get the `ToString`
2341 /// implementation for free.
2343 /// [`Display`]: fmt::Display
2344 #[cfg_attr(not(test), rustc_diagnostic_item = "ToString")]
2345 #[stable(feature = "rust1", since = "1.0.0")]
2346 pub trait ToString {
2347 /// Converts the given value to a `String`.
2355 /// let five = String::from("5");
2357 /// assert_eq!(five, i.to_string());
2359 #[rustc_conversion_suggestion]
2360 #[stable(feature = "rust1", since = "1.0.0")]
2361 fn to_string(&self) -> String;
2366 /// In this implementation, the `to_string` method panics
2367 /// if the `Display` implementation returns an error.
2368 /// This indicates an incorrect `Display` implementation
2369 /// since `fmt::Write for String` never returns an error itself.
2370 #[cfg(not(no_global_oom_handling))]
2371 #[stable(feature = "rust1", since = "1.0.0")]
2372 impl<T: fmt::Display + ?Sized> ToString for T {
2373 // A common guideline is to not inline generic functions. However,
2374 // removing `#[inline]` from this method causes non-negligible regressions.
2375 // See <https://github.com/rust-lang/rust/pull/74852>, the last attempt
2376 // to try to remove it.
2378 default fn to_string(&self) -> String {
2379 let mut buf = String::new();
2380 let mut formatter = core::fmt::Formatter::new(&mut buf);
2381 // Bypass format_args!() to avoid write_str with zero-length strs
2382 fmt::Display::fmt(self, &mut formatter)
2383 .expect("a Display implementation returned an error unexpectedly");
2388 #[cfg(not(no_global_oom_handling))]
2389 #[stable(feature = "char_to_string_specialization", since = "1.46.0")]
2390 impl ToString for char {
2392 fn to_string(&self) -> String {
2393 String::from(self.encode_utf8(&mut [0; 4]))
2397 #[cfg(not(no_global_oom_handling))]
2398 #[stable(feature = "u8_to_string_specialization", since = "1.54.0")]
2399 impl ToString for u8 {
2401 fn to_string(&self) -> String {
2402 let mut buf = String::with_capacity(3);
2406 buf.push((b'0' + n / 100) as char);
2409 buf.push((b'0' + n / 10) as char);
2412 buf.push((b'0' + n) as char);
2417 #[cfg(not(no_global_oom_handling))]
2418 #[stable(feature = "i8_to_string_specialization", since = "1.54.0")]
2419 impl ToString for i8 {
2421 fn to_string(&self) -> String {
2422 let mut buf = String::with_capacity(4);
2423 if self.is_negative() {
2426 let mut n = self.unsigned_abs();
2432 buf.push((b'0' + n / 10) as char);
2435 buf.push((b'0' + n) as char);
2440 #[cfg(not(no_global_oom_handling))]
2441 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
2442 impl ToString for str {
2444 fn to_string(&self) -> String {
2449 #[cfg(not(no_global_oom_handling))]
2450 #[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
2451 impl ToString for Cow<'_, str> {
2453 fn to_string(&self) -> String {
2458 #[cfg(not(no_global_oom_handling))]
2459 #[stable(feature = "string_to_string_specialization", since = "1.17.0")]
2460 impl ToString for String {
2462 fn to_string(&self) -> String {
2467 #[stable(feature = "rust1", since = "1.0.0")]
2468 impl AsRef<str> for String {
2470 fn as_ref(&self) -> &str {
2475 #[stable(feature = "string_as_mut", since = "1.43.0")]
2476 impl AsMut<str> for String {
2478 fn as_mut(&mut self) -> &mut str {
2483 #[stable(feature = "rust1", since = "1.0.0")]
2484 impl AsRef<[u8]> for String {
2486 fn as_ref(&self) -> &[u8] {
2491 #[cfg(not(no_global_oom_handling))]
2492 #[stable(feature = "rust1", since = "1.0.0")]
2493 impl From<&str> for String {
2494 /// Converts a `&str` into a [`String`].
2496 /// The result is allocated on the heap.
2498 fn from(s: &str) -> String {
2503 #[cfg(not(no_global_oom_handling))]
2504 #[stable(feature = "from_mut_str_for_string", since = "1.44.0")]
2505 impl From<&mut str> for String {
2506 /// Converts a `&mut str` into a [`String`].
2508 /// The result is allocated on the heap.
2510 fn from(s: &mut str) -> String {
2515 #[cfg(not(no_global_oom_handling))]
2516 #[stable(feature = "from_ref_string", since = "1.35.0")]
2517 impl From<&String> for String {
2518 /// Converts a `&String` into a [`String`].
2520 /// This clones `s` and returns the clone.
2522 fn from(s: &String) -> String {
2527 // note: test pulls in libstd, which causes errors here
2529 #[stable(feature = "string_from_box", since = "1.18.0")]
2530 impl From<Box<str>> for String {
2531 /// Converts the given boxed `str` slice to a [`String`].
2532 /// It is notable that the `str` slice is owned.
2539 /// let s1: String = String::from("hello world");
2540 /// let s2: Box<str> = s1.into_boxed_str();
2541 /// let s3: String = String::from(s2);
2543 /// assert_eq!("hello world", s3)
2545 fn from(s: Box<str>) -> String {
2550 #[cfg(not(no_global_oom_handling))]
2551 #[stable(feature = "box_from_str", since = "1.20.0")]
2552 impl From<String> for Box<str> {
2553 /// Converts the given [`String`] to a boxed `str` slice that is owned.
2560 /// let s1: String = String::from("hello world");
2561 /// let s2: Box<str> = Box::from(s1);
2562 /// let s3: String = String::from(s2);
2564 /// assert_eq!("hello world", s3)
2566 fn from(s: String) -> Box<str> {
2571 #[cfg(not(no_global_oom_handling))]
2572 #[stable(feature = "string_from_cow_str", since = "1.14.0")]
2573 impl<'a> From<Cow<'a, str>> for String {
2574 /// Converts a clone-on-write string to an owned
2575 /// instance of [`String`].
2577 /// This extracts the owned string,
2578 /// clones the string if it is not already owned.
2583 /// # use std::borrow::Cow;
2584 /// // If the string is not owned...
2585 /// let cow: Cow<str> = Cow::Borrowed("eggplant");
2586 /// // It will allocate on the heap and copy the string.
2587 /// let owned: String = String::from(cow);
2588 /// assert_eq!(&owned[..], "eggplant");
2590 fn from(s: Cow<'a, str>) -> String {
2595 #[cfg(not(no_global_oom_handling))]
2596 #[stable(feature = "rust1", since = "1.0.0")]
2597 impl<'a> From<&'a str> for Cow<'a, str> {
2598 /// Converts a string slice into a [`Borrowed`] variant.
2599 /// No heap allocation is performed, and the string
2605 /// # use std::borrow::Cow;
2606 /// assert_eq!(Cow::from("eggplant"), Cow::Borrowed("eggplant"));
2609 /// [`Borrowed`]: crate::borrow::Cow::Borrowed
2611 fn from(s: &'a str) -> Cow<'a, str> {
2616 #[cfg(not(no_global_oom_handling))]
2617 #[stable(feature = "rust1", since = "1.0.0")]
2618 impl<'a> From<String> for Cow<'a, str> {
2619 /// Converts a [`String`] into an [`Owned`] variant.
2620 /// No heap allocation is performed, and the string
2626 /// # use std::borrow::Cow;
2627 /// let s = "eggplant".to_string();
2628 /// let s2 = "eggplant".to_string();
2629 /// assert_eq!(Cow::from(s), Cow::<'static, str>::Owned(s2));
2632 /// [`Owned`]: crate::borrow::Cow::Owned
2634 fn from(s: String) -> Cow<'a, str> {
2639 #[cfg(not(no_global_oom_handling))]
2640 #[stable(feature = "cow_from_string_ref", since = "1.28.0")]
2641 impl<'a> From<&'a String> for Cow<'a, str> {
2642 /// Converts a [`String`] reference into a [`Borrowed`] variant.
2643 /// No heap allocation is performed, and the string
2649 /// # use std::borrow::Cow;
2650 /// let s = "eggplant".to_string();
2651 /// assert_eq!(Cow::from(&s), Cow::Borrowed("eggplant"));
2654 /// [`Borrowed`]: crate::borrow::Cow::Borrowed
2656 fn from(s: &'a String) -> Cow<'a, str> {
2657 Cow::Borrowed(s.as_str())
2661 #[cfg(not(no_global_oom_handling))]
2662 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2663 impl<'a> FromIterator<char> for Cow<'a, str> {
2664 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
2665 Cow::Owned(FromIterator::from_iter(it))
2669 #[cfg(not(no_global_oom_handling))]
2670 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2671 impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
2672 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
2673 Cow::Owned(FromIterator::from_iter(it))
2677 #[cfg(not(no_global_oom_handling))]
2678 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2679 impl<'a> FromIterator<String> for Cow<'a, str> {
2680 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
2681 Cow::Owned(FromIterator::from_iter(it))
2685 #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
2686 impl From<String> for Vec<u8> {
2687 /// Converts the given [`String`] to a vector [`Vec`] that holds values of type [`u8`].
2694 /// let s1 = String::from("hello world");
2695 /// let v1 = Vec::from(s1);
2698 /// println!("{}", b);
2701 fn from(string: String) -> Vec<u8> {
2706 #[cfg(not(no_global_oom_handling))]
2707 #[stable(feature = "rust1", since = "1.0.0")]
2708 impl fmt::Write for String {
2710 fn write_str(&mut self, s: &str) -> fmt::Result {
2716 fn write_char(&mut self, c: char) -> fmt::Result {
2722 /// A draining iterator for `String`.
2724 /// This struct is created by the [`drain`] method on [`String`]. See its
2725 /// documentation for more.
2727 /// [`drain`]: String::drain
2728 #[stable(feature = "drain", since = "1.6.0")]
2729 pub struct Drain<'a> {
2730 /// Will be used as &'a mut String in the destructor
2731 string: *mut String,
2732 /// Start of part to remove
2734 /// End of part to remove
2736 /// Current remaining range to remove
2740 #[stable(feature = "collection_debug", since = "1.17.0")]
2741 impl fmt::Debug for Drain<'_> {
2742 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2743 f.debug_tuple("Drain").field(&self.as_str()).finish()
2747 #[stable(feature = "drain", since = "1.6.0")]
2748 unsafe impl Sync for Drain<'_> {}
2749 #[stable(feature = "drain", since = "1.6.0")]
2750 unsafe impl Send for Drain<'_> {}
2752 #[stable(feature = "drain", since = "1.6.0")]
2753 impl Drop for Drain<'_> {
2754 fn drop(&mut self) {
2756 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
2757 // panic code being inserted again.
2758 let self_vec = (*self.string).as_mut_vec();
2759 if self.start <= self.end && self.end <= self_vec.len() {
2760 self_vec.drain(self.start..self.end);
2766 impl<'a> Drain<'a> {
2767 /// Returns the remaining (sub)string of this iterator as a slice.
2772 /// #![feature(string_drain_as_str)]
2773 /// let mut s = String::from("abc");
2774 /// let mut drain = s.drain(..);
2775 /// assert_eq!(drain.as_str(), "abc");
2776 /// let _ = drain.next().unwrap();
2777 /// assert_eq!(drain.as_str(), "bc");
2779 #[unstable(feature = "string_drain_as_str", issue = "76905")] // Note: uncomment AsRef impls below when stabilizing.
2780 pub fn as_str(&self) -> &str {
2785 // Uncomment when stabilizing `string_drain_as_str`.
2786 // #[unstable(feature = "string_drain_as_str", issue = "76905")]
2787 // impl<'a> AsRef<str> for Drain<'a> {
2788 // fn as_ref(&self) -> &str {
2793 // #[unstable(feature = "string_drain_as_str", issue = "76905")]
2794 // impl<'a> AsRef<[u8]> for Drain<'a> {
2795 // fn as_ref(&self) -> &[u8] {
2796 // self.as_str().as_bytes()
2800 #[stable(feature = "drain", since = "1.6.0")]
2801 impl Iterator for Drain<'_> {
2805 fn next(&mut self) -> Option<char> {
2809 fn size_hint(&self) -> (usize, Option<usize>) {
2810 self.iter.size_hint()
2814 fn last(mut self) -> Option<char> {
2819 #[stable(feature = "drain", since = "1.6.0")]
2820 impl DoubleEndedIterator for Drain<'_> {
2822 fn next_back(&mut self) -> Option<char> {
2823 self.iter.next_back()
2827 #[stable(feature = "fused", since = "1.26.0")]
2828 impl FusedIterator for Drain<'_> {}
2830 #[cfg(not(no_global_oom_handling))]
2831 #[stable(feature = "from_char_for_string", since = "1.46.0")]
2832 impl From<char> for String {
2833 /// Allocates an owned [`String`] from a single character.
2837 /// let c: char = 'a';
2838 /// let s: String = String::from(c);
2839 /// assert_eq!("a", &s[..]);
2842 fn from(c: char) -> Self {