1 //! A UTF-8βencoded, 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!("π", 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-8βencoded, 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!("π", sparkle_heart);
116 /// [`from_utf8`]: String::from_utf8
120 /// `String`s are always valid UTF-8. If you need a non-UTF-8 string, consider
121 /// [`OsString`]. It is similar, but without the UTF-8 constraint. Because UTF-8
122 /// is a variable width encoding, `String`s are typically smaller than an array of
123 /// the same `chars`:
128 /// // `s` is ASCII which represents each `char` as one byte
130 /// assert_eq!(s.len(), 5);
132 /// // A `char` array with the same contents would be longer because
133 /// // every `char` is four bytes
134 /// let s = ['h', 'e', 'l', 'l', 'o'];
135 /// let size: usize = s.into_iter().map(|c| mem::size_of_val(&c)).sum();
136 /// assert_eq!(size, 20);
138 /// // However, for non-ASCII strings, the difference will be smaller
139 /// // and sometimes they are the same
140 /// let s = "πππππ";
141 /// assert_eq!(s.len(), 20);
143 /// let s = ['π', 'π', 'π', 'π', 'π'];
144 /// let size: usize = s.into_iter().map(|c| mem::size_of_val(&c)).sum();
145 /// assert_eq!(size, 20);
148 /// This raises interesting questions as to how `s[i]` should work.
149 /// What should `i` be here? Several options include byte indices and
150 /// `char` indices but, because of UTF-8 encoding, only byte indices
151 /// would provide constant time indexing. Getting the `i`th `char`, for
152 /// example, is available using [`chars`]:
156 /// let third_character = s.chars().nth(2);
157 /// assert_eq!(third_character, Some('l'));
159 /// let s = "πππππ";
160 /// let third_character = s.chars().nth(2);
161 /// assert_eq!(third_character, Some('π'));
164 /// Next, what should `s[i]` return? Because indexing returns a reference
165 /// to underlying data it could be `&u8`, `&[u8]`, or something else similar.
166 /// Since we're only providing one index, `&u8` makes the most sense but that
167 /// might not be what the user expects and can be explicitly achieved with
171 /// // The first byte is 104 - the byte value of `'h'`
173 /// assert_eq!(s.as_bytes()[0], 104);
175 /// assert_eq!(s.as_bytes()[0], b'h');
177 /// // The first byte is 240 which isn't obviously useful
178 /// let s = "πππππ";
179 /// assert_eq!(s.as_bytes()[0], 240);
182 /// Due to these ambiguities/restrictions, indexing with a `usize` is simply
185 /// ```compile_fail,E0277
188 /// // The following will not compile!
189 /// println!("The first letter of s is {}", s[0]);
192 /// It is more clear, however, how `&s[i..j]` should work (that is,
193 /// indexing with a range). It should accept byte indices (to be constant-time)
194 /// and return a `&str` which is UTF-8 encoded. This is also called "string slicing".
195 /// Note this will panic if the byte indices provided are not character
196 /// boundaries - see [`is_char_boundary`] for more details. See the implementations
197 /// for [`SliceIndex<str>`] for more details on string slicing. For a non-panicking
198 /// version of string slicing, see [`get`].
200 /// [`OsString`]: ../../std/ffi/struct.OsString.html "ffi::OsString"
201 /// [`SliceIndex<str>`]: core::slice::SliceIndex
202 /// [`as_bytes()`]: str::as_bytes
203 /// [`get`]: str::get
204 /// [`is_char_boundary`]: str::is_char_boundary
206 /// The [`bytes`] and [`chars`] methods return iterators over the bytes and
207 /// codepoints of the string, respectively. To iterate over codepoints along
208 /// with byte indices, use [`char_indices`].
210 /// [`bytes`]: str::bytes
211 /// [`chars`]: str::chars
212 /// [`char_indices`]: str::char_indices
216 /// `String` implements <code>[Deref]<Target = [str]></code>, and so inherits all of [`str`]'s
217 /// methods. In addition, this means that you can pass a `String` to a
218 /// function which takes a [`&str`] by using an ampersand (`&`):
221 /// fn takes_str(s: &str) { }
223 /// let s = String::from("Hello");
228 /// This will create a [`&str`] from the `String` and pass it in. This
229 /// conversion is very inexpensive, and so generally, functions will accept
230 /// [`&str`]s as arguments unless they need a `String` for some specific
233 /// In certain cases Rust doesn't have enough information to make this
234 /// conversion, known as [`Deref`] coercion. In the following example a string
235 /// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
236 /// `example_func` takes anything that implements the trait. In this case Rust
237 /// would need to make two implicit conversions, which Rust doesn't have the
238 /// means to do. For that reason, the following example will not compile.
240 /// ```compile_fail,E0277
241 /// trait TraitExample {}
243 /// impl<'a> TraitExample for &'a str {}
245 /// fn example_func<A: TraitExample>(example_arg: A) {}
247 /// let example_string = String::from("example_string");
248 /// example_func(&example_string);
251 /// There are two options that would work instead. The first would be to
252 /// change the line `example_func(&example_string);` to
253 /// `example_func(example_string.as_str());`, using the method [`as_str()`]
254 /// to explicitly extract the string slice containing the string. The second
255 /// way changes `example_func(&example_string);` to
256 /// `example_func(&*example_string);`. In this case we are dereferencing a
257 /// `String` to a [`str`], then referencing the [`str`] back to
258 /// [`&str`]. The second way is more idiomatic, however both work to do the
259 /// conversion explicitly rather than relying on the implicit conversion.
263 /// A `String` is made up of three components: a pointer to some bytes, a
264 /// length, and a capacity. The pointer points to an internal buffer `String`
265 /// uses to store its data. The length is the number of bytes currently stored
266 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
267 /// the length will always be less than or equal to the capacity.
269 /// This buffer is always stored on the heap.
271 /// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
277 /// let story = String::from("Once upon a time...");
279 // FIXME Update this when vec_into_raw_parts is stabilized
280 /// // Prevent automatically dropping the String's data
281 /// let mut story = mem::ManuallyDrop::new(story);
283 /// let ptr = story.as_mut_ptr();
284 /// let len = story.len();
285 /// let capacity = story.capacity();
287 /// // story has nineteen bytes
288 /// assert_eq!(19, len);
290 /// // We can re-build a String out of ptr, len, and capacity. This is all
291 /// // unsafe because we are responsible for making sure the components are
293 /// let s = unsafe { String::from_raw_parts(ptr, len, capacity) } ;
295 /// assert_eq!(String::from("Once upon a time..."), s);
298 /// [`as_ptr`]: str::as_ptr
299 /// [`len`]: String::len
300 /// [`capacity`]: String::capacity
302 /// If a `String` has enough capacity, adding elements to it will not
303 /// re-allocate. For example, consider this program:
306 /// let mut s = String::new();
308 /// println!("{}", s.capacity());
311 /// s.push_str("hello");
312 /// println!("{}", s.capacity());
316 /// This will output the following:
327 /// At first, we have no memory allocated at all, but as we append to the
328 /// string, it increases its capacity appropriately. If we instead use the
329 /// [`with_capacity`] method to allocate the correct capacity initially:
332 /// let mut s = String::with_capacity(25);
334 /// println!("{}", s.capacity());
337 /// s.push_str("hello");
338 /// println!("{}", s.capacity());
342 /// [`with_capacity`]: String::with_capacity
344 /// We end up with a different output:
355 /// Here, there's no need to allocate more memory inside the loop.
357 /// [str]: prim@str "str"
358 /// [`str`]: prim@str "str"
359 /// [`&str`]: prim@str "&str"
360 /// [Deref]: core::ops::Deref "ops::Deref"
361 /// [`Deref`]: core::ops::Deref "ops::Deref"
362 /// [`as_str()`]: String::as_str
363 #[derive(PartialOrd, Eq, Ord)]
364 #[cfg_attr(not(test), rustc_diagnostic_item = "String")]
365 #[stable(feature = "rust1", since = "1.0.0")]
370 /// A possible error value when converting a `String` from a UTF-8 byte vector.
372 /// This type is the error type for the [`from_utf8`] method on [`String`]. It
373 /// is designed in such a way to carefully avoid reallocations: the
374 /// [`into_bytes`] method will give back the byte vector that was used in the
375 /// conversion attempt.
377 /// [`from_utf8`]: String::from_utf8
378 /// [`into_bytes`]: FromUtf8Error::into_bytes
380 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
381 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
382 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
383 /// through the [`utf8_error`] method.
385 /// [`Utf8Error`]: str::Utf8Error "std::str::Utf8Error"
386 /// [`std::str`]: core::str "std::str"
387 /// [`&str`]: prim@str "&str"
388 /// [`utf8_error`]: FromUtf8Error::utf8_error
395 /// // some invalid bytes, in a vector
396 /// let bytes = vec![0, 159];
398 /// let value = String::from_utf8(bytes);
400 /// assert!(value.is_err());
401 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
403 #[stable(feature = "rust1", since = "1.0.0")]
404 #[cfg_attr(not(no_global_oom_handling), derive(Clone))]
405 #[derive(Debug, PartialEq, Eq)]
406 pub struct FromUtf8Error {
411 /// A possible error value when converting a `String` from a UTF-16 byte slice.
413 /// This type is the error type for the [`from_utf16`] method on [`String`].
415 /// [`from_utf16`]: String::from_utf16
421 /// // πmu<invalid>ic
422 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
423 /// 0xD800, 0x0069, 0x0063];
425 /// assert!(String::from_utf16(v).is_err());
427 #[stable(feature = "rust1", since = "1.0.0")]
429 pub struct FromUtf16Error(());
432 /// Creates a new empty `String`.
434 /// Given that the `String` is empty, this will not allocate any initial
435 /// buffer. While that means that this initial operation is very
436 /// inexpensive, it may cause excessive allocation later when you add
437 /// data. If you have an idea of how much data the `String` will hold,
438 /// consider the [`with_capacity`] method to prevent excessive
441 /// [`with_capacity`]: String::with_capacity
448 /// let s = String::new();
451 #[rustc_const_stable(feature = "const_string_new", since = "1.39.0")]
452 #[stable(feature = "rust1", since = "1.0.0")]
454 pub const fn new() -> String {
455 String { vec: Vec::new() }
458 /// Creates a new empty `String` with a particular capacity.
460 /// `String`s have an internal buffer to hold their data. The capacity is
461 /// the length of that buffer, and can be queried with the [`capacity`]
462 /// method. This method creates an empty `String`, but one with an initial
463 /// buffer that can hold `capacity` bytes. This is useful when you may be
464 /// appending a bunch of data to the `String`, reducing the number of
465 /// reallocations it needs to do.
467 /// [`capacity`]: String::capacity
469 /// If the given capacity is `0`, no allocation will occur, and this method
470 /// is identical to the [`new`] method.
472 /// [`new`]: String::new
479 /// let mut s = String::with_capacity(10);
481 /// // The String contains no chars, even though it has capacity for more
482 /// assert_eq!(s.len(), 0);
484 /// // These are all done without reallocating...
485 /// let cap = s.capacity();
490 /// assert_eq!(s.capacity(), cap);
492 /// // ...but this may make the string reallocate
495 #[cfg(not(no_global_oom_handling))]
497 #[stable(feature = "rust1", since = "1.0.0")]
499 pub fn with_capacity(capacity: usize) -> String {
500 String { vec: Vec::with_capacity(capacity) }
503 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
504 // required for this method definition, is not available. Since we don't
505 // require this method for testing purposes, I'll just stub it
506 // NB see the slice::hack module in slice.rs for more information
509 pub fn from_str(_: &str) -> String {
510 panic!("not available with cfg(test)");
513 /// Converts a vector of bytes to a `String`.
515 /// A string ([`String`]) is made of bytes ([`u8`]), and a vector of bytes
516 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
517 /// two. Not all byte slices are valid `String`s, however: `String`
518 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
519 /// the bytes are valid UTF-8, and then does the conversion.
521 /// If you are sure that the byte slice is valid UTF-8, and you don't want
522 /// to incur the overhead of the validity check, there is an unsafe version
523 /// of this function, [`from_utf8_unchecked`], which has the same behavior
524 /// but skips the check.
526 /// This method will take care to not copy the vector, for efficiency's
529 /// If you need a [`&str`] instead of a `String`, consider
530 /// [`str::from_utf8`].
532 /// The inverse of this method is [`into_bytes`].
536 /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
537 /// provided bytes are not UTF-8. The vector you moved in is also included.
544 /// // some bytes, in a vector
545 /// let sparkle_heart = vec![240, 159, 146, 150];
547 /// // We know these bytes are valid, so we'll use `unwrap()`.
548 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
550 /// assert_eq!("π", sparkle_heart);
556 /// // some invalid bytes, in a vector
557 /// let sparkle_heart = vec![0, 159, 146, 150];
559 /// assert!(String::from_utf8(sparkle_heart).is_err());
562 /// See the docs for [`FromUtf8Error`] for more details on what you can do
565 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
566 /// [`Vec<u8>`]: crate::vec::Vec "Vec"
567 /// [`&str`]: prim@str "&str"
568 /// [`into_bytes`]: String::into_bytes
570 #[stable(feature = "rust1", since = "1.0.0")]
571 pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
572 match str::from_utf8(&vec) {
573 Ok(..) => Ok(String { vec }),
574 Err(e) => Err(FromUtf8Error { bytes: vec, error: e }),
578 /// Converts a slice of bytes to a string, including invalid characters.
580 /// Strings are made of bytes ([`u8`]), and a slice of bytes
581 /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
582 /// between the two. Not all byte slices are valid strings, however: strings
583 /// are required to be valid UTF-8. During this conversion,
584 /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
585 /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: οΏ½
587 /// [byteslice]: prim@slice
588 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
590 /// If you are sure that the byte slice is valid UTF-8, and you don't want
591 /// to incur the overhead of the conversion, there is an unsafe version
592 /// of this function, [`from_utf8_unchecked`], which has the same behavior
593 /// but skips the checks.
595 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
597 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
598 /// UTF-8, then we need to insert the replacement characters, which will
599 /// change the size of the string, and hence, require a `String`. But if
600 /// it's already valid UTF-8, we don't need a new allocation. This return
601 /// type allows us to handle both cases.
603 /// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
610 /// // some bytes, in a vector
611 /// let sparkle_heart = vec![240, 159, 146, 150];
613 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
615 /// assert_eq!("π", sparkle_heart);
621 /// // some invalid bytes
622 /// let input = b"Hello \xF0\x90\x80World";
623 /// let output = String::from_utf8_lossy(input);
625 /// assert_eq!("Hello οΏ½World", output);
628 #[cfg(not(no_global_oom_handling))]
629 #[stable(feature = "rust1", since = "1.0.0")]
630 pub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, str> {
631 let mut iter = lossy::Utf8Lossy::from_bytes(v).chunks();
633 let first_valid = if let Some(chunk) = iter.next() {
634 let lossy::Utf8LossyChunk { valid, broken } = chunk;
635 if broken.is_empty() {
636 debug_assert_eq!(valid.len(), v.len());
637 return Cow::Borrowed(valid);
641 return Cow::Borrowed("");
644 const REPLACEMENT: &str = "\u{FFFD}";
646 let mut res = String::with_capacity(v.len());
647 res.push_str(first_valid);
648 res.push_str(REPLACEMENT);
650 for lossy::Utf8LossyChunk { valid, broken } in iter {
652 if !broken.is_empty() {
653 res.push_str(REPLACEMENT);
660 /// Decode a UTF-16βencoded vector `v` into a `String`, returning [`Err`]
661 /// if `v` contains any invalid data.
669 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
670 /// 0x0073, 0x0069, 0x0063];
671 /// assert_eq!(String::from("πmusic"),
672 /// String::from_utf16(v).unwrap());
674 /// // πmu<invalid>ic
675 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
676 /// 0xD800, 0x0069, 0x0063];
677 /// assert!(String::from_utf16(v).is_err());
679 #[cfg(not(no_global_oom_handling))]
680 #[stable(feature = "rust1", since = "1.0.0")]
681 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
682 // This isn't done via collect::<Result<_, _>>() for performance reasons.
683 // FIXME: the function can be simplified again when #48994 is closed.
684 let mut ret = String::with_capacity(v.len());
685 for c in decode_utf16(v.iter().cloned()) {
689 return Err(FromUtf16Error(()));
695 /// Decode a UTF-16βencoded slice `v` into a `String`, replacing
696 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
698 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
699 /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
700 /// conversion requires a memory allocation.
702 /// [`from_utf8_lossy`]: String::from_utf8_lossy
703 /// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
704 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
711 /// // πmus<invalid>ic<invalid>
712 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
713 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
716 /// assert_eq!(String::from("πmus\u{FFFD}ic\u{FFFD}"),
717 /// String::from_utf16_lossy(v));
719 #[cfg(not(no_global_oom_handling))]
722 #[stable(feature = "rust1", since = "1.0.0")]
723 pub fn from_utf16_lossy(v: &[u16]) -> String {
724 decode_utf16(v.iter().cloned()).map(|r| r.unwrap_or(REPLACEMENT_CHARACTER)).collect()
727 /// Decomposes a `String` into its raw components.
729 /// Returns the raw pointer to the underlying data, the length of
730 /// the string (in bytes), and the allocated capacity of the data
731 /// (in bytes). These are the same arguments in the same order as
732 /// the arguments to [`from_raw_parts`].
734 /// After calling this function, the caller is responsible for the
735 /// memory previously managed by the `String`. The only way to do
736 /// this is to convert the raw pointer, length, and capacity back
737 /// into a `String` with the [`from_raw_parts`] function, allowing
738 /// the destructor to perform the cleanup.
740 /// [`from_raw_parts`]: String::from_raw_parts
745 /// #![feature(vec_into_raw_parts)]
746 /// let s = String::from("hello");
748 /// let (ptr, len, cap) = s.into_raw_parts();
750 /// let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
751 /// assert_eq!(rebuilt, "hello");
753 #[must_use = "`self` will be dropped if the result is not used"]
754 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
755 pub fn into_raw_parts(self) -> (*mut u8, usize, usize) {
756 self.vec.into_raw_parts()
759 /// Creates a new `String` from a length, capacity, and pointer.
763 /// This is highly unsafe, due to the number of invariants that aren't
766 /// * The memory at `buf` needs to have been previously allocated by the
767 /// same allocator the standard library uses, with a required alignment of exactly 1.
768 /// * `length` needs to be less than or equal to `capacity`.
769 /// * `capacity` needs to be the correct value.
770 /// * The first `length` bytes at `buf` need to be valid UTF-8.
772 /// Violating these may cause problems like corrupting the allocator's
773 /// internal data structures.
775 /// The ownership of `buf` is effectively transferred to the
776 /// `String` which may then deallocate, reallocate or change the
777 /// contents of memory pointed to by the pointer at will. Ensure
778 /// that nothing else uses the pointer after calling this
789 /// let s = String::from("hello");
791 // FIXME Update this when vec_into_raw_parts is stabilized
792 /// // Prevent automatically dropping the String's data
793 /// let mut s = mem::ManuallyDrop::new(s);
795 /// let ptr = s.as_mut_ptr();
796 /// let len = s.len();
797 /// let capacity = s.capacity();
799 /// let s = String::from_raw_parts(ptr, len, capacity);
801 /// assert_eq!(String::from("hello"), s);
805 #[stable(feature = "rust1", since = "1.0.0")]
806 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
807 unsafe { String { vec: Vec::from_raw_parts(buf, length, capacity) } }
810 /// Converts a vector of bytes to a `String` without checking that the
811 /// string contains valid UTF-8.
813 /// See the safe version, [`from_utf8`], for more details.
815 /// [`from_utf8`]: String::from_utf8
819 /// This function is unsafe because it does not check that the bytes passed
820 /// to it are valid UTF-8. If this constraint is violated, it may cause
821 /// memory unsafety issues with future users of the `String`, as the rest of
822 /// the standard library assumes that `String`s are valid UTF-8.
829 /// // some bytes, in a vector
830 /// let sparkle_heart = vec![240, 159, 146, 150];
832 /// let sparkle_heart = unsafe {
833 /// String::from_utf8_unchecked(sparkle_heart)
836 /// assert_eq!("π", sparkle_heart);
840 #[stable(feature = "rust1", since = "1.0.0")]
841 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
842 String { vec: bytes }
845 /// Converts a `String` into a byte vector.
847 /// This consumes the `String`, so we do not need to copy its contents.
854 /// let s = String::from("hello");
855 /// let bytes = s.into_bytes();
857 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
860 #[must_use = "`self` will be dropped if the result is not used"]
861 #[stable(feature = "rust1", since = "1.0.0")]
862 pub fn into_bytes(self) -> Vec<u8> {
866 /// Extracts a string slice containing the entire `String`.
873 /// let s = String::from("foo");
875 /// assert_eq!("foo", s.as_str());
879 #[stable(feature = "string_as_str", since = "1.7.0")]
880 pub fn as_str(&self) -> &str {
884 /// Converts a `String` into a mutable string slice.
891 /// let mut s = String::from("foobar");
892 /// let s_mut_str = s.as_mut_str();
894 /// s_mut_str.make_ascii_uppercase();
896 /// assert_eq!("FOOBAR", s_mut_str);
900 #[stable(feature = "string_as_str", since = "1.7.0")]
901 pub fn as_mut_str(&mut self) -> &mut str {
905 /// Appends a given string slice onto the end of this `String`.
912 /// let mut s = String::from("foo");
914 /// s.push_str("bar");
916 /// assert_eq!("foobar", s);
918 #[cfg(not(no_global_oom_handling))]
920 #[stable(feature = "rust1", since = "1.0.0")]
921 pub fn push_str(&mut self, string: &str) {
922 self.vec.extend_from_slice(string.as_bytes())
925 /// Copies elements from `src` range to the end of the string.
929 /// Panics if the starting point or end point do not lie on a [`char`]
930 /// boundary, or if they're out of bounds.
935 /// #![feature(string_extend_from_within)]
936 /// let mut string = String::from("abcde");
938 /// string.extend_from_within(2..);
939 /// assert_eq!(string, "abcdecde");
941 /// string.extend_from_within(..2);
942 /// assert_eq!(string, "abcdecdeab");
944 /// string.extend_from_within(4..8);
945 /// assert_eq!(string, "abcdecdeabecde");
947 #[cfg(not(no_global_oom_handling))]
948 #[unstable(feature = "string_extend_from_within", issue = "none")]
949 pub fn extend_from_within<R>(&mut self, src: R)
951 R: RangeBounds<usize>,
953 let src @ Range { start, end } = slice::range(src, ..self.len());
955 assert!(self.is_char_boundary(start));
956 assert!(self.is_char_boundary(end));
958 self.vec.extend_from_within(src);
961 /// Returns this `String`'s capacity, in bytes.
968 /// let s = String::with_capacity(10);
970 /// assert!(s.capacity() >= 10);
974 #[stable(feature = "rust1", since = "1.0.0")]
975 pub fn capacity(&self) -> usize {
979 /// Ensures that this `String`'s capacity is at least `additional` bytes
980 /// larger than its length.
982 /// The capacity may be increased by more than `additional` bytes if it
983 /// chooses, to prevent frequent reallocations.
985 /// If you do not want this "at least" behavior, see the [`reserve_exact`]
990 /// Panics if the new capacity overflows [`usize`].
992 /// [`reserve_exact`]: String::reserve_exact
999 /// let mut s = String::new();
1003 /// assert!(s.capacity() >= 10);
1006 /// This might not actually increase the capacity:
1009 /// let mut s = String::with_capacity(10);
1013 /// // s now has a length of 2 and a capacity of 10
1014 /// assert_eq!(2, s.len());
1015 /// assert_eq!(10, s.capacity());
1017 /// // Since we already have an extra 8 capacity, calling this...
1020 /// // ... doesn't actually increase.
1021 /// assert_eq!(10, s.capacity());
1023 #[cfg(not(no_global_oom_handling))]
1025 #[stable(feature = "rust1", since = "1.0.0")]
1026 pub fn reserve(&mut self, additional: usize) {
1027 self.vec.reserve(additional)
1030 /// Ensures that this `String`'s capacity is `additional` bytes
1031 /// larger than its length.
1033 /// Consider using the [`reserve`] method unless you absolutely know
1034 /// better than the allocator.
1036 /// [`reserve`]: String::reserve
1040 /// Panics if the new capacity overflows `usize`.
1047 /// let mut s = String::new();
1049 /// s.reserve_exact(10);
1051 /// assert!(s.capacity() >= 10);
1054 /// This might not actually increase the capacity:
1057 /// let mut s = String::with_capacity(10);
1061 /// // s now has a length of 2 and a capacity of 10
1062 /// assert_eq!(2, s.len());
1063 /// assert_eq!(10, s.capacity());
1065 /// // Since we already have an extra 8 capacity, calling this...
1066 /// s.reserve_exact(8);
1068 /// // ... doesn't actually increase.
1069 /// assert_eq!(10, s.capacity());
1071 #[cfg(not(no_global_oom_handling))]
1073 #[stable(feature = "rust1", since = "1.0.0")]
1074 pub fn reserve_exact(&mut self, additional: usize) {
1075 self.vec.reserve_exact(additional)
1078 /// Tries to reserve capacity for at least `additional` more elements to be inserted
1079 /// in the given `String`. The collection may reserve more space to avoid
1080 /// frequent reallocations. After calling `reserve`, capacity will be
1081 /// greater than or equal to `self.len() + additional`. Does nothing if
1082 /// capacity is already sufficient.
1086 /// If the capacity overflows, or the allocator reports a failure, then an error
1092 /// use std::collections::TryReserveError;
1094 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
1095 /// let mut output = String::new();
1097 /// // Pre-reserve the memory, exiting if we can't
1098 /// output.try_reserve(data.len())?;
1100 /// // Now we know this can't OOM in the middle of our complex work
1101 /// output.push_str(data);
1105 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1107 #[stable(feature = "try_reserve", since = "1.57.0")]
1108 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
1109 self.vec.try_reserve(additional)
1112 /// Tries to reserve the minimum capacity for exactly `additional` more elements to
1113 /// be inserted in the given `String`. After calling `try_reserve_exact`,
1114 /// capacity will be greater than or equal to `self.len() + additional`.
1115 /// Does nothing if the capacity is already sufficient.
1117 /// Note that the allocator may give the collection more space than it
1118 /// requests. Therefore, capacity can not be relied upon to be precisely
1119 /// minimal. Prefer [`try_reserve`] if future insertions are expected.
1121 /// [`try_reserve`]: String::try_reserve
1125 /// If the capacity overflows, or the allocator reports a failure, then an error
1131 /// use std::collections::TryReserveError;
1133 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
1134 /// let mut output = String::new();
1136 /// // Pre-reserve the memory, exiting if we can't
1137 /// output.try_reserve_exact(data.len())?;
1139 /// // Now we know this can't OOM in the middle of our complex work
1140 /// output.push_str(data);
1144 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1146 #[stable(feature = "try_reserve", since = "1.57.0")]
1147 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
1148 self.vec.try_reserve_exact(additional)
1151 /// Shrinks the capacity of this `String` to match its length.
1158 /// let mut s = String::from("foo");
1161 /// assert!(s.capacity() >= 100);
1163 /// s.shrink_to_fit();
1164 /// assert_eq!(3, s.capacity());
1166 #[cfg(not(no_global_oom_handling))]
1168 #[stable(feature = "rust1", since = "1.0.0")]
1169 pub fn shrink_to_fit(&mut self) {
1170 self.vec.shrink_to_fit()
1173 /// Shrinks the capacity of this `String` with a lower bound.
1175 /// The capacity will remain at least as large as both the length
1176 /// and the supplied value.
1178 /// If the current capacity is less than the lower limit, this is a no-op.
1183 /// let mut s = String::from("foo");
1186 /// assert!(s.capacity() >= 100);
1188 /// s.shrink_to(10);
1189 /// assert!(s.capacity() >= 10);
1191 /// assert!(s.capacity() >= 3);
1193 #[cfg(not(no_global_oom_handling))]
1195 #[stable(feature = "shrink_to", since = "1.56.0")]
1196 pub fn shrink_to(&mut self, min_capacity: usize) {
1197 self.vec.shrink_to(min_capacity)
1200 /// Appends the given [`char`] to the end of this `String`.
1207 /// let mut s = String::from("abc");
1213 /// assert_eq!("abc123", s);
1215 #[cfg(not(no_global_oom_handling))]
1217 #[stable(feature = "rust1", since = "1.0.0")]
1218 pub fn push(&mut self, ch: char) {
1219 match ch.len_utf8() {
1220 1 => self.vec.push(ch as u8),
1221 _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
1225 /// Returns a byte slice of this `String`'s contents.
1227 /// The inverse of this method is [`from_utf8`].
1229 /// [`from_utf8`]: String::from_utf8
1236 /// let s = String::from("hello");
1238 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
1242 #[stable(feature = "rust1", since = "1.0.0")]
1243 pub fn as_bytes(&self) -> &[u8] {
1247 /// Shortens this `String` to the specified length.
1249 /// If `new_len` is greater than the string's current length, this has no
1252 /// Note that this method has no effect on the allocated capacity
1257 /// Panics if `new_len` does not lie on a [`char`] boundary.
1264 /// let mut s = String::from("hello");
1268 /// assert_eq!("he", s);
1271 #[stable(feature = "rust1", since = "1.0.0")]
1272 pub fn truncate(&mut self, new_len: usize) {
1273 if new_len <= self.len() {
1274 assert!(self.is_char_boundary(new_len));
1275 self.vec.truncate(new_len)
1279 /// Removes the last character from the string buffer and returns it.
1281 /// Returns [`None`] if this `String` is empty.
1288 /// let mut s = String::from("foo");
1290 /// assert_eq!(s.pop(), Some('o'));
1291 /// assert_eq!(s.pop(), Some('o'));
1292 /// assert_eq!(s.pop(), Some('f'));
1294 /// assert_eq!(s.pop(), None);
1297 #[stable(feature = "rust1", since = "1.0.0")]
1298 pub fn pop(&mut self) -> Option<char> {
1299 let ch = self.chars().rev().next()?;
1300 let newlen = self.len() - ch.len_utf8();
1302 self.vec.set_len(newlen);
1307 /// Removes a [`char`] from this `String` at a byte position and returns it.
1309 /// This is an *O*(*n*) operation, as it requires copying every element in the
1314 /// Panics if `idx` is larger than or equal to the `String`'s length,
1315 /// or if it does not lie on a [`char`] boundary.
1322 /// let mut s = String::from("foo");
1324 /// assert_eq!(s.remove(0), 'f');
1325 /// assert_eq!(s.remove(1), 'o');
1326 /// assert_eq!(s.remove(0), 'o');
1329 #[stable(feature = "rust1", since = "1.0.0")]
1330 pub fn remove(&mut self, idx: usize) -> char {
1331 let ch = match self[idx..].chars().next() {
1333 None => panic!("cannot remove a char from the end of a string"),
1336 let next = idx + ch.len_utf8();
1337 let len = self.len();
1339 ptr::copy(self.vec.as_ptr().add(next), self.vec.as_mut_ptr().add(idx), len - next);
1340 self.vec.set_len(len - (next - idx));
1345 /// Remove all matches of pattern `pat` in the `String`.
1350 /// #![feature(string_remove_matches)]
1351 /// let mut s = String::from("Trees are not green, the sky is not blue.");
1352 /// s.remove_matches("not ");
1353 /// assert_eq!("Trees are green, the sky is blue.", s);
1356 /// Matches will be detected and removed iteratively, so in cases where
1357 /// patterns overlap, only the first pattern will be removed:
1360 /// #![feature(string_remove_matches)]
1361 /// let mut s = String::from("banana");
1362 /// s.remove_matches("ana");
1363 /// assert_eq!("bna", s);
1365 #[cfg(not(no_global_oom_handling))]
1366 #[unstable(feature = "string_remove_matches", reason = "new API", issue = "72826")]
1367 pub fn remove_matches<'a, P>(&'a mut self, pat: P)
1369 P: for<'x> Pattern<'x>,
1371 use core::str::pattern::Searcher;
1374 let mut searcher = pat.into_searcher(self);
1375 // Per Searcher::next:
1377 // A Match result needs to contain the whole matched pattern,
1378 // however Reject results may be split up into arbitrary many
1379 // adjacent fragments. Both ranges may have zero length.
1381 // In practice the implementation of Searcher::next_match tends to
1382 // be more efficient, so we use it here and do some work to invert
1383 // matches into rejections since that's what we want to copy below.
1385 let rejections: Vec<_> = from_fn(|| {
1386 let (start, end) = searcher.next_match()?;
1387 let prev_front = front;
1389 Some((prev_front, start))
1392 rejections.into_iter().chain(core::iter::once((front, self.len())))
1396 let ptr = self.vec.as_mut_ptr();
1398 for (start, end) in rejections {
1399 let count = end - start;
1401 // SAFETY: per Searcher::next:
1403 // The stream of Match and Reject values up to a Done will
1404 // contain index ranges that are adjacent, non-overlapping,
1405 // covering the whole haystack, and laying on utf8
1408 ptr::copy(ptr.add(start), ptr.add(len), count);
1415 self.vec.set_len(len);
1419 /// Retains only the characters specified by the predicate.
1421 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1422 /// This method operates in place, visiting each character exactly once in the
1423 /// original order, and preserves the order of the retained characters.
1428 /// let mut s = String::from("f_o_ob_ar");
1430 /// s.retain(|c| c != '_');
1432 /// assert_eq!(s, "foobar");
1435 /// Because the elements are visited exactly once in the original order,
1436 /// external state may be used to decide which elements to keep.
1439 /// let mut s = String::from("abcde");
1440 /// let keep = [false, true, true, false, true];
1441 /// let mut iter = keep.iter();
1442 /// s.retain(|_| *iter.next().unwrap());
1443 /// assert_eq!(s, "bce");
1446 #[stable(feature = "string_retain", since = "1.26.0")]
1447 pub fn retain<F>(&mut self, mut f: F)
1449 F: FnMut(char) -> bool,
1451 struct SetLenOnDrop<'a> {
1457 impl<'a> Drop for SetLenOnDrop<'a> {
1458 fn drop(&mut self) {
1459 let new_len = self.idx - self.del_bytes;
1460 debug_assert!(new_len <= self.s.len());
1461 unsafe { self.s.vec.set_len(new_len) };
1465 let len = self.len();
1466 let mut guard = SetLenOnDrop { s: self, idx: 0, del_bytes: 0 };
1468 while guard.idx < len {
1469 let ch = unsafe { guard.s.get_unchecked(guard.idx..len).chars().next().unwrap() };
1470 let ch_len = ch.len_utf8();
1473 guard.del_bytes += ch_len;
1474 } else if guard.del_bytes > 0 {
1477 guard.s.vec.as_ptr().add(guard.idx),
1478 guard.s.vec.as_mut_ptr().add(guard.idx - guard.del_bytes),
1484 // Point idx to the next char
1485 guard.idx += ch_len;
1491 /// Inserts a character into this `String` at a byte position.
1493 /// This is an *O*(*n*) operation as it requires copying every element in the
1498 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1499 /// lie on a [`char`] boundary.
1506 /// let mut s = String::with_capacity(3);
1508 /// s.insert(0, 'f');
1509 /// s.insert(1, 'o');
1510 /// s.insert(2, 'o');
1512 /// assert_eq!("foo", s);
1514 #[cfg(not(no_global_oom_handling))]
1516 #[stable(feature = "rust1", since = "1.0.0")]
1517 pub fn insert(&mut self, idx: usize, ch: char) {
1518 assert!(self.is_char_boundary(idx));
1519 let mut bits = [0; 4];
1520 let bits = ch.encode_utf8(&mut bits).as_bytes();
1523 self.insert_bytes(idx, bits);
1527 #[cfg(not(no_global_oom_handling))]
1528 unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1529 let len = self.len();
1530 let amt = bytes.len();
1531 self.vec.reserve(amt);
1534 ptr::copy(self.vec.as_ptr().add(idx), self.vec.as_mut_ptr().add(idx + amt), len - idx);
1535 ptr::copy_nonoverlapping(bytes.as_ptr(), self.vec.as_mut_ptr().add(idx), amt);
1536 self.vec.set_len(len + amt);
1540 /// Inserts a string slice into this `String` at a byte position.
1542 /// This is an *O*(*n*) operation as it requires copying every element in the
1547 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1548 /// lie on a [`char`] boundary.
1555 /// let mut s = String::from("bar");
1557 /// s.insert_str(0, "foo");
1559 /// assert_eq!("foobar", s);
1561 #[cfg(not(no_global_oom_handling))]
1563 #[stable(feature = "insert_str", since = "1.16.0")]
1564 pub fn insert_str(&mut self, idx: usize, string: &str) {
1565 assert!(self.is_char_boundary(idx));
1568 self.insert_bytes(idx, string.as_bytes());
1572 /// Returns a mutable reference to the contents of this `String`.
1576 /// This function is unsafe because the returned `&mut Vec` allows writing
1577 /// bytes which are not valid UTF-8. If this constraint is violated, using
1578 /// the original `String` after dropping the `&mut Vec` may violate memory
1579 /// safety, as the rest of the standard library assumes that `String`s are
1587 /// let mut s = String::from("hello");
1590 /// let vec = s.as_mut_vec();
1591 /// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1595 /// assert_eq!(s, "olleh");
1598 #[stable(feature = "rust1", since = "1.0.0")]
1599 pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1603 /// Returns the length of this `String`, in bytes, not [`char`]s or
1604 /// graphemes. In other words, it might not be what a human considers the
1605 /// length of the string.
1612 /// let a = String::from("foo");
1613 /// assert_eq!(a.len(), 3);
1615 /// let fancy_f = String::from("Ζoo");
1616 /// assert_eq!(fancy_f.len(), 4);
1617 /// assert_eq!(fancy_f.chars().count(), 3);
1621 #[stable(feature = "rust1", since = "1.0.0")]
1622 pub fn len(&self) -> usize {
1626 /// Returns `true` if this `String` has a length of zero, and `false` otherwise.
1633 /// let mut v = String::new();
1634 /// assert!(v.is_empty());
1637 /// assert!(!v.is_empty());
1641 #[stable(feature = "rust1", since = "1.0.0")]
1642 pub fn is_empty(&self) -> bool {
1646 /// Splits the string into two at the given byte index.
1648 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1649 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1650 /// boundary of a UTF-8 code point.
1652 /// Note that the capacity of `self` does not change.
1656 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1657 /// code point of the string.
1663 /// let mut hello = String::from("Hello, World!");
1664 /// let world = hello.split_off(7);
1665 /// assert_eq!(hello, "Hello, ");
1666 /// assert_eq!(world, "World!");
1669 #[cfg(not(no_global_oom_handling))]
1671 #[stable(feature = "string_split_off", since = "1.16.0")]
1672 #[must_use = "use `.truncate()` if you don't need the other half"]
1673 pub fn split_off(&mut self, at: usize) -> String {
1674 assert!(self.is_char_boundary(at));
1675 let other = self.vec.split_off(at);
1676 unsafe { String::from_utf8_unchecked(other) }
1679 /// Truncates this `String`, removing all contents.
1681 /// While this means the `String` will have a length of zero, it does not
1682 /// touch its capacity.
1689 /// let mut s = String::from("foo");
1693 /// assert!(s.is_empty());
1694 /// assert_eq!(0, s.len());
1695 /// assert_eq!(3, s.capacity());
1698 #[stable(feature = "rust1", since = "1.0.0")]
1699 pub fn clear(&mut self) {
1703 /// Removes the specified range from the string in bulk, returning all
1704 /// removed characters as an iterator.
1706 /// The returned iterator keeps a mutable borrow on the string to optimize
1707 /// its implementation.
1711 /// Panics if the starting point or end point do not lie on a [`char`]
1712 /// boundary, or if they're out of bounds.
1716 /// If the returned iterator goes out of scope without being dropped (due to
1717 /// [`core::mem::forget`], for example), the string may still contain a copy
1718 /// of any drained characters, or may have lost characters arbitrarily,
1719 /// including characters outside the range.
1726 /// let mut s = String::from("Ξ± is alpha, Ξ² is beta");
1727 /// let beta_offset = s.find('Ξ²').unwrap_or(s.len());
1729 /// // Remove the range up until the Ξ² from the string
1730 /// let t: String = s.drain(..beta_offset).collect();
1731 /// assert_eq!(t, "Ξ± is alpha, ");
1732 /// assert_eq!(s, "Ξ² is beta");
1734 /// // A full range clears the string, like `clear()` does
1736 /// assert_eq!(s, "");
1738 #[stable(feature = "drain", since = "1.6.0")]
1739 pub fn drain<R>(&mut self, range: R) -> Drain<'_>
1741 R: RangeBounds<usize>,
1745 // The String version of Drain does not have the memory safety issues
1746 // of the vector version. The data is just plain bytes.
1747 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1748 // the removal will not happen.
1749 let Range { start, end } = slice::range(range, ..self.len());
1750 assert!(self.is_char_boundary(start));
1751 assert!(self.is_char_boundary(end));
1753 // Take out two simultaneous borrows. The &mut String won't be accessed
1754 // until iteration is over, in Drop.
1755 let self_ptr = self as *mut _;
1756 // SAFETY: `slice::range` and `is_char_boundary` do the appropriate bounds checks.
1757 let chars_iter = unsafe { self.get_unchecked(start..end) }.chars();
1759 Drain { start, end, iter: chars_iter, string: self_ptr }
1762 /// Removes the specified range in the string,
1763 /// and replaces it with the given string.
1764 /// The given string doesn't need to be the same length as the range.
1768 /// Panics if the starting point or end point do not lie on a [`char`]
1769 /// boundary, or if they're out of bounds.
1776 /// let mut s = String::from("Ξ± is alpha, Ξ² is beta");
1777 /// let beta_offset = s.find('Ξ²').unwrap_or(s.len());
1779 /// // Replace the range up until the Ξ² from the string
1780 /// s.replace_range(..beta_offset, "Ξ is capital alpha; ");
1781 /// assert_eq!(s, "Ξ is capital alpha; Ξ² is beta");
1783 #[cfg(not(no_global_oom_handling))]
1784 #[stable(feature = "splice", since = "1.27.0")]
1785 pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
1787 R: RangeBounds<usize>,
1791 // Replace_range does not have the memory safety issues of a vector Splice.
1792 // of the vector version. The data is just plain bytes.
1794 // WARNING: Inlining this variable would be unsound (#81138)
1795 let start = range.start_bound();
1797 Included(&n) => assert!(self.is_char_boundary(n)),
1798 Excluded(&n) => assert!(self.is_char_boundary(n + 1)),
1801 // WARNING: Inlining this variable would be unsound (#81138)
1802 let end = range.end_bound();
1804 Included(&n) => assert!(self.is_char_boundary(n + 1)),
1805 Excluded(&n) => assert!(self.is_char_boundary(n)),
1809 // Using `range` again would be unsound (#81138)
1810 // We assume the bounds reported by `range` remain the same, but
1811 // an adversarial implementation could change between calls
1812 unsafe { self.as_mut_vec() }.splice((start, end), replace_with.bytes());
1815 /// Converts this `String` into a <code>[Box]<[str]></code>.
1817 /// This will drop any excess capacity.
1819 /// [str]: prim@str "str"
1826 /// let s = String::from("hello");
1828 /// let b = s.into_boxed_str();
1830 #[cfg(not(no_global_oom_handling))]
1831 #[stable(feature = "box_str", since = "1.4.0")]
1832 #[must_use = "`self` will be dropped if the result is not used"]
1834 pub fn into_boxed_str(self) -> Box<str> {
1835 let slice = self.vec.into_boxed_slice();
1836 unsafe { from_boxed_utf8_unchecked(slice) }
1840 impl FromUtf8Error {
1841 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1848 /// // some invalid bytes, in a vector
1849 /// let bytes = vec![0, 159];
1851 /// let value = String::from_utf8(bytes);
1853 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1856 #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
1857 pub fn as_bytes(&self) -> &[u8] {
1861 /// Returns the bytes that were attempted to convert to a `String`.
1863 /// This method is carefully constructed to avoid allocation. It will
1864 /// consume the error, moving out the bytes, so that a copy of the bytes
1865 /// does not need to be made.
1872 /// // some invalid bytes, in a vector
1873 /// let bytes = vec![0, 159];
1875 /// let value = String::from_utf8(bytes);
1877 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1879 #[must_use = "`self` will be dropped if the result is not used"]
1880 #[stable(feature = "rust1", since = "1.0.0")]
1881 pub fn into_bytes(self) -> Vec<u8> {
1885 /// Fetch a `Utf8Error` to get more details about the conversion failure.
1887 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1888 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1889 /// an analogue to `FromUtf8Error`. See its documentation for more details
1892 /// [`std::str`]: core::str "std::str"
1893 /// [`&str`]: prim@str "&str"
1900 /// // some invalid bytes, in a vector
1901 /// let bytes = vec![0, 159];
1903 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1905 /// // the first byte is invalid here
1906 /// assert_eq!(1, error.valid_up_to());
1909 #[stable(feature = "rust1", since = "1.0.0")]
1910 pub fn utf8_error(&self) -> Utf8Error {
1915 #[stable(feature = "rust1", since = "1.0.0")]
1916 impl fmt::Display for FromUtf8Error {
1917 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1918 fmt::Display::fmt(&self.error, f)
1922 #[stable(feature = "rust1", since = "1.0.0")]
1923 impl fmt::Display for FromUtf16Error {
1924 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1925 fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
1929 #[cfg(not(no_global_oom_handling))]
1930 #[stable(feature = "rust1", since = "1.0.0")]
1931 impl Clone for String {
1932 fn clone(&self) -> Self {
1933 String { vec: self.vec.clone() }
1936 fn clone_from(&mut self, source: &Self) {
1937 self.vec.clone_from(&source.vec);
1941 #[cfg(not(no_global_oom_handling))]
1942 #[stable(feature = "rust1", since = "1.0.0")]
1943 impl FromIterator<char> for String {
1944 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
1945 let mut buf = String::new();
1951 #[cfg(not(no_global_oom_handling))]
1952 #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
1953 impl<'a> FromIterator<&'a char> for String {
1954 fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
1955 let mut buf = String::new();
1961 #[cfg(not(no_global_oom_handling))]
1962 #[stable(feature = "rust1", since = "1.0.0")]
1963 impl<'a> FromIterator<&'a str> for String {
1964 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
1965 let mut buf = String::new();
1971 #[cfg(not(no_global_oom_handling))]
1972 #[stable(feature = "extend_string", since = "1.4.0")]
1973 impl FromIterator<String> for String {
1974 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
1975 let mut iterator = iter.into_iter();
1977 // Because we're iterating over `String`s, we can avoid at least
1978 // one allocation by getting the first string from the iterator
1979 // and appending to it all the subsequent strings.
1980 match iterator.next() {
1981 None => String::new(),
1983 buf.extend(iterator);
1990 #[cfg(not(no_global_oom_handling))]
1991 #[stable(feature = "box_str2", since = "1.45.0")]
1992 impl FromIterator<Box<str>> for String {
1993 fn from_iter<I: IntoIterator<Item = Box<str>>>(iter: I) -> String {
1994 let mut buf = String::new();
2000 #[cfg(not(no_global_oom_handling))]
2001 #[stable(feature = "herd_cows", since = "1.19.0")]
2002 impl<'a> FromIterator<Cow<'a, str>> for String {
2003 fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
2004 let mut iterator = iter.into_iter();
2006 // Because we're iterating over CoWs, we can (potentially) avoid at least
2007 // one allocation by getting the first item and appending to it all the
2008 // subsequent items.
2009 match iterator.next() {
2010 None => String::new(),
2012 let mut buf = cow.into_owned();
2013 buf.extend(iterator);
2020 #[cfg(not(no_global_oom_handling))]
2021 #[stable(feature = "rust1", since = "1.0.0")]
2022 impl Extend<char> for String {
2023 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
2024 let iterator = iter.into_iter();
2025 let (lower_bound, _) = iterator.size_hint();
2026 self.reserve(lower_bound);
2027 iterator.for_each(move |c| self.push(c));
2031 fn extend_one(&mut self, c: char) {
2036 fn extend_reserve(&mut self, additional: usize) {
2037 self.reserve(additional);
2041 #[cfg(not(no_global_oom_handling))]
2042 #[stable(feature = "extend_ref", since = "1.2.0")]
2043 impl<'a> Extend<&'a char> for String {
2044 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
2045 self.extend(iter.into_iter().cloned());
2049 fn extend_one(&mut self, &c: &'a char) {
2054 fn extend_reserve(&mut self, additional: usize) {
2055 self.reserve(additional);
2059 #[cfg(not(no_global_oom_handling))]
2060 #[stable(feature = "rust1", since = "1.0.0")]
2061 impl<'a> Extend<&'a str> for String {
2062 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
2063 iter.into_iter().for_each(move |s| self.push_str(s));
2067 fn extend_one(&mut self, s: &'a str) {
2072 #[cfg(not(no_global_oom_handling))]
2073 #[stable(feature = "box_str2", since = "1.45.0")]
2074 impl Extend<Box<str>> for String {
2075 fn extend<I: IntoIterator<Item = Box<str>>>(&mut self, iter: I) {
2076 iter.into_iter().for_each(move |s| self.push_str(&s));
2080 #[cfg(not(no_global_oom_handling))]
2081 #[stable(feature = "extend_string", since = "1.4.0")]
2082 impl Extend<String> for String {
2083 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
2084 iter.into_iter().for_each(move |s| self.push_str(&s));
2088 fn extend_one(&mut self, s: String) {
2093 #[cfg(not(no_global_oom_handling))]
2094 #[stable(feature = "herd_cows", since = "1.19.0")]
2095 impl<'a> Extend<Cow<'a, str>> for String {
2096 fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
2097 iter.into_iter().for_each(move |s| self.push_str(&s));
2101 fn extend_one(&mut self, s: Cow<'a, str>) {
2106 /// A convenience impl that delegates to the impl for `&str`.
2111 /// assert_eq!(String::from("Hello world").find("world"), Some(6));
2114 feature = "pattern",
2115 reason = "API not fully fleshed out and ready to be stabilized",
2118 impl<'a, 'b> Pattern<'a> for &'b String {
2119 type Searcher = <&'b str as Pattern<'a>>::Searcher;
2121 fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
2122 self[..].into_searcher(haystack)
2126 fn is_contained_in(self, haystack: &'a str) -> bool {
2127 self[..].is_contained_in(haystack)
2131 fn is_prefix_of(self, haystack: &'a str) -> bool {
2132 self[..].is_prefix_of(haystack)
2136 fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str> {
2137 self[..].strip_prefix_of(haystack)
2141 fn is_suffix_of(self, haystack: &'a str) -> bool {
2142 self[..].is_suffix_of(haystack)
2146 fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str> {
2147 self[..].strip_suffix_of(haystack)
2151 #[stable(feature = "rust1", since = "1.0.0")]
2152 impl PartialEq for String {
2154 fn eq(&self, other: &String) -> bool {
2155 PartialEq::eq(&self[..], &other[..])
2158 fn ne(&self, other: &String) -> bool {
2159 PartialEq::ne(&self[..], &other[..])
2163 macro_rules! impl_eq {
2164 ($lhs:ty, $rhs: ty) => {
2165 #[stable(feature = "rust1", since = "1.0.0")]
2166 #[allow(unused_lifetimes)]
2167 impl<'a, 'b> PartialEq<$rhs> for $lhs {
2169 fn eq(&self, other: &$rhs) -> bool {
2170 PartialEq::eq(&self[..], &other[..])
2173 fn ne(&self, other: &$rhs) -> bool {
2174 PartialEq::ne(&self[..], &other[..])
2178 #[stable(feature = "rust1", since = "1.0.0")]
2179 #[allow(unused_lifetimes)]
2180 impl<'a, 'b> PartialEq<$lhs> for $rhs {
2182 fn eq(&self, other: &$lhs) -> bool {
2183 PartialEq::eq(&self[..], &other[..])
2186 fn ne(&self, other: &$lhs) -> bool {
2187 PartialEq::ne(&self[..], &other[..])
2193 impl_eq! { String, str }
2194 impl_eq! { String, &'a str }
2195 #[cfg(not(no_global_oom_handling))]
2196 impl_eq! { Cow<'a, str>, str }
2197 #[cfg(not(no_global_oom_handling))]
2198 impl_eq! { Cow<'a, str>, &'b str }
2199 #[cfg(not(no_global_oom_handling))]
2200 impl_eq! { Cow<'a, str>, String }
2202 #[stable(feature = "rust1", since = "1.0.0")]
2203 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
2204 impl const Default for String {
2205 /// Creates an empty `String`.
2207 fn default() -> String {
2212 #[stable(feature = "rust1", since = "1.0.0")]
2213 impl fmt::Display for String {
2215 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2216 fmt::Display::fmt(&**self, f)
2220 #[stable(feature = "rust1", since = "1.0.0")]
2221 impl fmt::Debug for String {
2223 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2224 fmt::Debug::fmt(&**self, f)
2228 #[stable(feature = "rust1", since = "1.0.0")]
2229 impl hash::Hash for String {
2231 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
2232 (**self).hash(hasher)
2236 /// Implements the `+` operator for concatenating two strings.
2238 /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
2239 /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
2240 /// every operation, which would lead to *O*(*n*^2) running time when building an *n*-byte string by
2241 /// repeated concatenation.
2243 /// The string on the right-hand side is only borrowed; its contents are copied into the returned
2248 /// Concatenating two `String`s takes the first by value and borrows the second:
2251 /// let a = String::from("hello");
2252 /// let b = String::from(" world");
2254 /// // `a` is moved and can no longer be used here.
2257 /// If you want to keep using the first `String`, you can clone it and append to the clone instead:
2260 /// let a = String::from("hello");
2261 /// let b = String::from(" world");
2262 /// let c = a.clone() + &b;
2263 /// // `a` is still valid here.
2266 /// Concatenating `&str` slices can be done by converting the first to a `String`:
2269 /// let a = "hello";
2270 /// let b = " world";
2271 /// let c = a.to_string() + b;
2273 #[cfg(not(no_global_oom_handling))]
2274 #[stable(feature = "rust1", since = "1.0.0")]
2275 impl Add<&str> for String {
2276 type Output = String;
2279 fn add(mut self, other: &str) -> String {
2280 self.push_str(other);
2285 /// Implements the `+=` operator for appending to a `String`.
2287 /// This has the same behavior as the [`push_str`][String::push_str] method.
2288 #[cfg(not(no_global_oom_handling))]
2289 #[stable(feature = "stringaddassign", since = "1.12.0")]
2290 impl AddAssign<&str> for String {
2292 fn add_assign(&mut self, other: &str) {
2293 self.push_str(other);
2297 #[stable(feature = "rust1", since = "1.0.0")]
2298 impl ops::Index<ops::Range<usize>> for String {
2302 fn index(&self, index: ops::Range<usize>) -> &str {
2306 #[stable(feature = "rust1", since = "1.0.0")]
2307 impl ops::Index<ops::RangeTo<usize>> for String {
2311 fn index(&self, index: ops::RangeTo<usize>) -> &str {
2315 #[stable(feature = "rust1", since = "1.0.0")]
2316 impl ops::Index<ops::RangeFrom<usize>> for String {
2320 fn index(&self, index: ops::RangeFrom<usize>) -> &str {
2324 #[stable(feature = "rust1", since = "1.0.0")]
2325 impl ops::Index<ops::RangeFull> for String {
2329 fn index(&self, _index: ops::RangeFull) -> &str {
2330 unsafe { str::from_utf8_unchecked(&self.vec) }
2333 #[stable(feature = "inclusive_range", since = "1.26.0")]
2334 impl ops::Index<ops::RangeInclusive<usize>> for String {
2338 fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
2339 Index::index(&**self, index)
2342 #[stable(feature = "inclusive_range", since = "1.26.0")]
2343 impl ops::Index<ops::RangeToInclusive<usize>> for String {
2347 fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
2348 Index::index(&**self, index)
2352 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2353 impl ops::IndexMut<ops::Range<usize>> for String {
2355 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
2356 &mut self[..][index]
2359 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2360 impl ops::IndexMut<ops::RangeTo<usize>> for String {
2362 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
2363 &mut self[..][index]
2366 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2367 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
2369 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
2370 &mut self[..][index]
2373 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2374 impl ops::IndexMut<ops::RangeFull> for String {
2376 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
2377 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2380 #[stable(feature = "inclusive_range", since = "1.26.0")]
2381 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
2383 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
2384 IndexMut::index_mut(&mut **self, index)
2387 #[stable(feature = "inclusive_range", since = "1.26.0")]
2388 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
2390 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
2391 IndexMut::index_mut(&mut **self, index)
2395 #[stable(feature = "rust1", since = "1.0.0")]
2396 impl ops::Deref for String {
2400 fn deref(&self) -> &str {
2401 unsafe { str::from_utf8_unchecked(&self.vec) }
2405 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2406 impl ops::DerefMut for String {
2408 fn deref_mut(&mut self) -> &mut str {
2409 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2413 /// A type alias for [`Infallible`].
2415 /// This alias exists for backwards compatibility, and may be eventually deprecated.
2417 /// [`Infallible`]: core::convert::Infallible "convert::Infallible"
2418 #[stable(feature = "str_parse_error", since = "1.5.0")]
2419 pub type ParseError = core::convert::Infallible;
2421 #[cfg(not(no_global_oom_handling))]
2422 #[stable(feature = "rust1", since = "1.0.0")]
2423 impl FromStr for String {
2424 type Err = core::convert::Infallible;
2426 fn from_str(s: &str) -> Result<String, Self::Err> {
2431 /// A trait for converting a value to a `String`.
2433 /// This trait is automatically implemented for any type which implements the
2434 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
2435 /// [`Display`] should be implemented instead, and you get the `ToString`
2436 /// implementation for free.
2438 /// [`Display`]: fmt::Display
2439 #[cfg_attr(not(test), rustc_diagnostic_item = "ToString")]
2440 #[stable(feature = "rust1", since = "1.0.0")]
2441 pub trait ToString {
2442 /// Converts the given value to a `String`.
2450 /// let five = String::from("5");
2452 /// assert_eq!(five, i.to_string());
2454 #[rustc_conversion_suggestion]
2455 #[stable(feature = "rust1", since = "1.0.0")]
2456 fn to_string(&self) -> String;
2461 /// In this implementation, the `to_string` method panics
2462 /// if the `Display` implementation returns an error.
2463 /// This indicates an incorrect `Display` implementation
2464 /// since `fmt::Write for String` never returns an error itself.
2465 #[cfg(not(no_global_oom_handling))]
2466 #[stable(feature = "rust1", since = "1.0.0")]
2467 impl<T: fmt::Display + ?Sized> ToString for T {
2468 // A common guideline is to not inline generic functions. However,
2469 // removing `#[inline]` from this method causes non-negligible regressions.
2470 // See <https://github.com/rust-lang/rust/pull/74852>, the last attempt
2471 // to try to remove it.
2473 default fn to_string(&self) -> String {
2474 let mut buf = String::new();
2475 let mut formatter = core::fmt::Formatter::new(&mut buf);
2476 // Bypass format_args!() to avoid write_str with zero-length strs
2477 fmt::Display::fmt(self, &mut formatter)
2478 .expect("a Display implementation returned an error unexpectedly");
2483 #[cfg(not(no_global_oom_handling))]
2484 #[stable(feature = "char_to_string_specialization", since = "1.46.0")]
2485 impl ToString for char {
2487 fn to_string(&self) -> String {
2488 String::from(self.encode_utf8(&mut [0; 4]))
2492 #[cfg(not(no_global_oom_handling))]
2493 #[stable(feature = "u8_to_string_specialization", since = "1.54.0")]
2494 impl ToString for u8 {
2496 fn to_string(&self) -> String {
2497 let mut buf = String::with_capacity(3);
2501 buf.push((b'0' + n / 100) as char);
2504 buf.push((b'0' + n / 10) as char);
2507 buf.push((b'0' + n) as char);
2512 #[cfg(not(no_global_oom_handling))]
2513 #[stable(feature = "i8_to_string_specialization", since = "1.54.0")]
2514 impl ToString for i8 {
2516 fn to_string(&self) -> String {
2517 let mut buf = String::with_capacity(4);
2518 if self.is_negative() {
2521 let mut n = self.unsigned_abs();
2527 buf.push((b'0' + n / 10) as char);
2530 buf.push((b'0' + n) as char);
2535 #[cfg(not(no_global_oom_handling))]
2536 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
2537 impl ToString for str {
2539 fn to_string(&self) -> String {
2544 #[cfg(not(no_global_oom_handling))]
2545 #[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
2546 impl ToString for Cow<'_, str> {
2548 fn to_string(&self) -> String {
2553 #[cfg(not(no_global_oom_handling))]
2554 #[stable(feature = "string_to_string_specialization", since = "1.17.0")]
2555 impl ToString for String {
2557 fn to_string(&self) -> String {
2562 #[stable(feature = "rust1", since = "1.0.0")]
2563 impl AsRef<str> for String {
2565 fn as_ref(&self) -> &str {
2570 #[stable(feature = "string_as_mut", since = "1.43.0")]
2571 impl AsMut<str> for String {
2573 fn as_mut(&mut self) -> &mut str {
2578 #[stable(feature = "rust1", since = "1.0.0")]
2579 impl AsRef<[u8]> for String {
2581 fn as_ref(&self) -> &[u8] {
2586 #[cfg(not(no_global_oom_handling))]
2587 #[stable(feature = "rust1", since = "1.0.0")]
2588 impl From<&str> for String {
2589 /// Converts a `&str` into a [`String`].
2591 /// The result is allocated on the heap.
2593 fn from(s: &str) -> String {
2598 #[cfg(not(no_global_oom_handling))]
2599 #[stable(feature = "from_mut_str_for_string", since = "1.44.0")]
2600 impl From<&mut str> for String {
2601 /// Converts a `&mut str` into a [`String`].
2603 /// The result is allocated on the heap.
2605 fn from(s: &mut str) -> String {
2610 #[cfg(not(no_global_oom_handling))]
2611 #[stable(feature = "from_ref_string", since = "1.35.0")]
2612 impl From<&String> for String {
2613 /// Converts a `&String` into a [`String`].
2615 /// This clones `s` and returns the clone.
2617 fn from(s: &String) -> String {
2622 // note: test pulls in libstd, which causes errors here
2624 #[stable(feature = "string_from_box", since = "1.18.0")]
2625 impl From<Box<str>> for String {
2626 /// Converts the given boxed `str` slice to a [`String`].
2627 /// It is notable that the `str` slice is owned.
2634 /// let s1: String = String::from("hello world");
2635 /// let s2: Box<str> = s1.into_boxed_str();
2636 /// let s3: String = String::from(s2);
2638 /// assert_eq!("hello world", s3)
2640 fn from(s: Box<str>) -> String {
2645 #[cfg(not(no_global_oom_handling))]
2646 #[stable(feature = "box_from_str", since = "1.20.0")]
2647 impl From<String> for Box<str> {
2648 /// Converts the given [`String`] to a boxed `str` slice that is owned.
2655 /// let s1: String = String::from("hello world");
2656 /// let s2: Box<str> = Box::from(s1);
2657 /// let s3: String = String::from(s2);
2659 /// assert_eq!("hello world", s3)
2661 fn from(s: String) -> Box<str> {
2666 #[cfg(not(no_global_oom_handling))]
2667 #[stable(feature = "string_from_cow_str", since = "1.14.0")]
2668 impl<'a> From<Cow<'a, str>> for String {
2669 /// Converts a clone-on-write string to an owned
2670 /// instance of [`String`].
2672 /// This extracts the owned string,
2673 /// clones the string if it is not already owned.
2678 /// # use std::borrow::Cow;
2679 /// // If the string is not owned...
2680 /// let cow: Cow<str> = Cow::Borrowed("eggplant");
2681 /// // It will allocate on the heap and copy the string.
2682 /// let owned: String = String::from(cow);
2683 /// assert_eq!(&owned[..], "eggplant");
2685 fn from(s: Cow<'a, str>) -> String {
2690 #[cfg(not(no_global_oom_handling))]
2691 #[stable(feature = "rust1", since = "1.0.0")]
2692 impl<'a> From<&'a str> for Cow<'a, str> {
2693 /// Converts a string slice into a [`Borrowed`] variant.
2694 /// No heap allocation is performed, and the string
2700 /// # use std::borrow::Cow;
2701 /// assert_eq!(Cow::from("eggplant"), Cow::Borrowed("eggplant"));
2704 /// [`Borrowed`]: crate::borrow::Cow::Borrowed "borrow::Cow::Borrowed"
2706 fn from(s: &'a str) -> Cow<'a, str> {
2711 #[cfg(not(no_global_oom_handling))]
2712 #[stable(feature = "rust1", since = "1.0.0")]
2713 impl<'a> From<String> for Cow<'a, str> {
2714 /// Converts a [`String`] into an [`Owned`] variant.
2715 /// No heap allocation is performed, and the string
2721 /// # use std::borrow::Cow;
2722 /// let s = "eggplant".to_string();
2723 /// let s2 = "eggplant".to_string();
2724 /// assert_eq!(Cow::from(s), Cow::<'static, str>::Owned(s2));
2727 /// [`Owned`]: crate::borrow::Cow::Owned "borrow::Cow::Owned"
2729 fn from(s: String) -> Cow<'a, str> {
2734 #[cfg(not(no_global_oom_handling))]
2735 #[stable(feature = "cow_from_string_ref", since = "1.28.0")]
2736 impl<'a> From<&'a String> for Cow<'a, str> {
2737 /// Converts a [`String`] reference into a [`Borrowed`] variant.
2738 /// No heap allocation is performed, and the string
2744 /// # use std::borrow::Cow;
2745 /// let s = "eggplant".to_string();
2746 /// assert_eq!(Cow::from(&s), Cow::Borrowed("eggplant"));
2749 /// [`Borrowed`]: crate::borrow::Cow::Borrowed "borrow::Cow::Borrowed"
2751 fn from(s: &'a String) -> Cow<'a, str> {
2752 Cow::Borrowed(s.as_str())
2756 #[cfg(not(no_global_oom_handling))]
2757 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2758 impl<'a> FromIterator<char> for Cow<'a, str> {
2759 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
2760 Cow::Owned(FromIterator::from_iter(it))
2764 #[cfg(not(no_global_oom_handling))]
2765 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2766 impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
2767 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
2768 Cow::Owned(FromIterator::from_iter(it))
2772 #[cfg(not(no_global_oom_handling))]
2773 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2774 impl<'a> FromIterator<String> for Cow<'a, str> {
2775 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
2776 Cow::Owned(FromIterator::from_iter(it))
2780 #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
2781 impl From<String> for Vec<u8> {
2782 /// Converts the given [`String`] to a vector [`Vec`] that holds values of type [`u8`].
2789 /// let s1 = String::from("hello world");
2790 /// let v1 = Vec::from(s1);
2793 /// println!("{b}");
2796 fn from(string: String) -> Vec<u8> {
2801 #[cfg(not(no_global_oom_handling))]
2802 #[stable(feature = "rust1", since = "1.0.0")]
2803 impl fmt::Write for String {
2805 fn write_str(&mut self, s: &str) -> fmt::Result {
2811 fn write_char(&mut self, c: char) -> fmt::Result {
2817 /// A draining iterator for `String`.
2819 /// This struct is created by the [`drain`] method on [`String`]. See its
2820 /// documentation for more.
2822 /// [`drain`]: String::drain
2823 #[stable(feature = "drain", since = "1.6.0")]
2824 pub struct Drain<'a> {
2825 /// Will be used as &'a mut String in the destructor
2826 string: *mut String,
2827 /// Start of part to remove
2829 /// End of part to remove
2831 /// Current remaining range to remove
2835 #[stable(feature = "collection_debug", since = "1.17.0")]
2836 impl fmt::Debug for Drain<'_> {
2837 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2838 f.debug_tuple("Drain").field(&self.as_str()).finish()
2842 #[stable(feature = "drain", since = "1.6.0")]
2843 unsafe impl Sync for Drain<'_> {}
2844 #[stable(feature = "drain", since = "1.6.0")]
2845 unsafe impl Send for Drain<'_> {}
2847 #[stable(feature = "drain", since = "1.6.0")]
2848 impl Drop for Drain<'_> {
2849 fn drop(&mut self) {
2851 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
2852 // panic code being inserted again.
2853 let self_vec = (*self.string).as_mut_vec();
2854 if self.start <= self.end && self.end <= self_vec.len() {
2855 self_vec.drain(self.start..self.end);
2861 impl<'a> Drain<'a> {
2862 /// Returns the remaining (sub)string of this iterator as a slice.
2867 /// let mut s = String::from("abc");
2868 /// let mut drain = s.drain(..);
2869 /// assert_eq!(drain.as_str(), "abc");
2870 /// let _ = drain.next().unwrap();
2871 /// assert_eq!(drain.as_str(), "bc");
2874 #[stable(feature = "string_drain_as_str", since = "1.55.0")]
2875 pub fn as_str(&self) -> &str {
2880 #[stable(feature = "string_drain_as_str", since = "1.55.0")]
2881 impl<'a> AsRef<str> for Drain<'a> {
2882 fn as_ref(&self) -> &str {
2887 #[stable(feature = "string_drain_as_str", since = "1.55.0")]
2888 impl<'a> AsRef<[u8]> for Drain<'a> {
2889 fn as_ref(&self) -> &[u8] {
2890 self.as_str().as_bytes()
2894 #[stable(feature = "drain", since = "1.6.0")]
2895 impl Iterator for Drain<'_> {
2899 fn next(&mut self) -> Option<char> {
2903 fn size_hint(&self) -> (usize, Option<usize>) {
2904 self.iter.size_hint()
2908 fn last(mut self) -> Option<char> {
2913 #[stable(feature = "drain", since = "1.6.0")]
2914 impl DoubleEndedIterator for Drain<'_> {
2916 fn next_back(&mut self) -> Option<char> {
2917 self.iter.next_back()
2921 #[stable(feature = "fused", since = "1.26.0")]
2922 impl FusedIterator for Drain<'_> {}
2924 #[cfg(not(no_global_oom_handling))]
2925 #[stable(feature = "from_char_for_string", since = "1.46.0")]
2926 impl From<char> for String {
2927 /// Allocates an owned [`String`] from a single character.
2931 /// let c: char = 'a';
2932 /// let s: String = String::from(c);
2933 /// assert_eq!("a", &s[..]);
2936 fn from(c: char) -> Self {