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 #[stable(feature = "rust1", since = "1.0.0")]
423 pub fn with_capacity(capacity
: usize) -> String
{
424 String { vec: Vec::with_capacity(capacity) }
427 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
428 // required for this method definition, is not available. Since we don't
429 // require this method for testing purposes, I'll just stub it
430 // NB see the slice::hack module in slice.rs for more information
433 pub fn from_str(_
: &str) -> String
{
434 panic
!("not available with cfg(test)");
437 /// Converts a vector of bytes to a `String`.
439 /// A string ([`String`]) is made of bytes ([`u8`]), and a vector of bytes
440 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
441 /// two. Not all byte slices are valid `String`s, however: `String`
442 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
443 /// the bytes are valid UTF-8, and then does the conversion.
445 /// If you are sure that the byte slice is valid UTF-8, and you don't want
446 /// to incur the overhead of the validity check, there is an unsafe version
447 /// of this function, [`from_utf8_unchecked`], which has the same behavior
448 /// but skips the check.
450 /// This method will take care to not copy the vector, for efficiency's
453 /// If you need a [`&str`] instead of a `String`, consider
454 /// [`str::from_utf8`].
456 /// The inverse of this method is [`into_bytes`].
460 /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
461 /// provided bytes are not UTF-8. The vector you moved in is also included.
468 /// // some bytes, in a vector
469 /// let sparkle_heart = vec![240, 159, 146, 150];
471 /// // We know these bytes are valid, so we'll use `unwrap()`.
472 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
474 /// assert_eq!("💖", sparkle_heart);
480 /// // some invalid bytes, in a vector
481 /// let sparkle_heart = vec![0, 159, 146, 150];
483 /// assert!(String::from_utf8(sparkle_heart).is_err());
486 /// See the docs for [`FromUtf8Error`] for more details on what you can do
489 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
490 /// [`Vec<u8>`]: crate::vec::Vec
491 /// [`&str`]: prim@str
492 /// [`into_bytes`]: String::into_bytes
494 #[stable(feature = "rust1", since = "1.0.0")]
495 pub fn from_utf8(vec
: Vec
<u8>) -> Result
<String
, FromUtf8Error
> {
496 match str::from_utf8(&vec
) {
497 Ok(..) => Ok(String { vec }
),
498 Err(e
) => Err(FromUtf8Error { bytes: vec, error: e }
),
502 /// Converts a slice of bytes to a string, including invalid characters.
504 /// Strings are made of bytes ([`u8`]), and a slice of bytes
505 /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
506 /// between the two. Not all byte slices are valid strings, however: strings
507 /// are required to be valid UTF-8. During this conversion,
508 /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
509 /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: �
511 /// [byteslice]: prim@slice
512 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
514 /// If you are sure that the byte slice is valid UTF-8, and you don't want
515 /// to incur the overhead of the conversion, there is an unsafe version
516 /// of this function, [`from_utf8_unchecked`], which has the same behavior
517 /// but skips the checks.
519 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
521 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
522 /// UTF-8, then we need to insert the replacement characters, which will
523 /// change the size of the string, and hence, require a `String`. But if
524 /// it's already valid UTF-8, we don't need a new allocation. This return
525 /// type allows us to handle both cases.
527 /// [`Cow<'a, str>`]: crate::borrow::Cow
534 /// // some bytes, in a vector
535 /// let sparkle_heart = vec![240, 159, 146, 150];
537 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
539 /// assert_eq!("💖", sparkle_heart);
545 /// // some invalid bytes
546 /// let input = b"Hello \xF0\x90\x80World";
547 /// let output = String::from_utf8_lossy(input);
549 /// assert_eq!("Hello �World", output);
551 #[cfg(not(no_global_oom_handling))]
552 #[stable(feature = "rust1", since = "1.0.0")]
553 pub fn from_utf8_lossy(v
: &[u8]) -> Cow
<'_
, str> {
554 let mut iter
= lossy
::Utf8Lossy
::from_bytes(v
).chunks();
556 let (first_valid
, first_broken
) = if let Some(chunk
) = iter
.next() {
557 let lossy
::Utf8LossyChunk { valid, broken }
= chunk
;
558 if valid
.len() == v
.len() {
559 debug_assert
!(broken
.is_empty());
560 return Cow
::Borrowed(valid
);
564 return Cow
::Borrowed("");
567 const REPLACEMENT
: &str = "\u{FFFD}";
569 let mut res
= String
::with_capacity(v
.len());
570 res
.push_str(first_valid
);
571 if !first_broken
.is_empty() {
572 res
.push_str(REPLACEMENT
);
575 for lossy
::Utf8LossyChunk { valid, broken }
in iter
{
577 if !broken
.is_empty() {
578 res
.push_str(REPLACEMENT
);
585 /// Decode a UTF-16–encoded vector `v` into a `String`, returning [`Err`]
586 /// if `v` contains any invalid data.
594 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
595 /// 0x0073, 0x0069, 0x0063];
596 /// assert_eq!(String::from("𝄞music"),
597 /// String::from_utf16(v).unwrap());
599 /// // 𝄞mu<invalid>ic
600 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
601 /// 0xD800, 0x0069, 0x0063];
602 /// assert!(String::from_utf16(v).is_err());
604 #[cfg(not(no_global_oom_handling))]
605 #[stable(feature = "rust1", since = "1.0.0")]
606 pub fn from_utf16(v
: &[u16]) -> Result
<String
, FromUtf16Error
> {
607 // This isn't done via collect::<Result<_, _>>() for performance reasons.
608 // FIXME: the function can be simplified again when #48994 is closed.
609 let mut ret
= String
::with_capacity(v
.len());
610 for c
in decode_utf16(v
.iter().cloned()) {
614 return Err(FromUtf16Error(()));
620 /// Decode a UTF-16–encoded slice `v` into a `String`, replacing
621 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
623 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
624 /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
625 /// conversion requires a memory allocation.
627 /// [`from_utf8_lossy`]: String::from_utf8_lossy
628 /// [`Cow<'a, str>`]: crate::borrow::Cow
629 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
636 /// // 𝄞mus<invalid>ic<invalid>
637 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
638 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
641 /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
642 /// String::from_utf16_lossy(v));
644 #[cfg(not(no_global_oom_handling))]
646 #[stable(feature = "rust1", since = "1.0.0")]
647 pub fn from_utf16_lossy(v
: &[u16]) -> String
{
648 decode_utf16(v
.iter().cloned()).map(|r
| r
.unwrap_or(REPLACEMENT_CHARACTER
)).collect()
651 /// Decomposes a `String` into its raw components.
653 /// Returns the raw pointer to the underlying data, the length of
654 /// the string (in bytes), and the allocated capacity of the data
655 /// (in bytes). These are the same arguments in the same order as
656 /// the arguments to [`from_raw_parts`].
658 /// After calling this function, the caller is responsible for the
659 /// memory previously managed by the `String`. The only way to do
660 /// this is to convert the raw pointer, length, and capacity back
661 /// into a `String` with the [`from_raw_parts`] function, allowing
662 /// the destructor to perform the cleanup.
664 /// [`from_raw_parts`]: String::from_raw_parts
669 /// #![feature(vec_into_raw_parts)]
670 /// let s = String::from("hello");
672 /// let (ptr, len, cap) = s.into_raw_parts();
674 /// let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
675 /// assert_eq!(rebuilt, "hello");
677 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
678 pub fn into_raw_parts(self) -> (*mut u8, usize, usize) {
679 self.vec
.into_raw_parts()
682 /// Creates a new `String` from a length, capacity, and pointer.
686 /// This is highly unsafe, due to the number of invariants that aren't
689 /// * The memory at `buf` needs to have been previously allocated by the
690 /// same allocator the standard library uses, with a required alignment of exactly 1.
691 /// * `length` needs to be less than or equal to `capacity`.
692 /// * `capacity` needs to be the correct value.
693 /// * The first `length` bytes at `buf` need to be valid UTF-8.
695 /// Violating these may cause problems like corrupting the allocator's
696 /// internal data structures.
698 /// The ownership of `buf` is effectively transferred to the
699 /// `String` which may then deallocate, reallocate or change the
700 /// contents of memory pointed to by the pointer at will. Ensure
701 /// that nothing else uses the pointer after calling this
712 /// let s = String::from("hello");
714 // FIXME Update this when vec_into_raw_parts is stabilized
715 /// // Prevent automatically dropping the String's data
716 /// let mut s = mem::ManuallyDrop::new(s);
718 /// let ptr = s.as_mut_ptr();
719 /// let len = s.len();
720 /// let capacity = s.capacity();
722 /// let s = String::from_raw_parts(ptr, len, capacity);
724 /// assert_eq!(String::from("hello"), s);
728 #[stable(feature = "rust1", since = "1.0.0")]
729 pub unsafe fn from_raw_parts(buf
: *mut u8, length
: usize, capacity
: usize) -> String
{
730 unsafe { String { vec: Vec::from_raw_parts(buf, length, capacity) }
}
733 /// Converts a vector of bytes to a `String` without checking that the
734 /// string contains valid UTF-8.
736 /// See the safe version, [`from_utf8`], for more details.
738 /// [`from_utf8`]: String::from_utf8
742 /// This function is unsafe because it does not check that the bytes passed
743 /// to it are valid UTF-8. If this constraint is violated, it may cause
744 /// memory unsafety issues with future users of the `String`, as the rest of
745 /// the standard library assumes that `String`s are valid UTF-8.
752 /// // some bytes, in a vector
753 /// let sparkle_heart = vec![240, 159, 146, 150];
755 /// let sparkle_heart = unsafe {
756 /// String::from_utf8_unchecked(sparkle_heart)
759 /// assert_eq!("💖", sparkle_heart);
762 #[stable(feature = "rust1", since = "1.0.0")]
763 pub unsafe fn from_utf8_unchecked(bytes
: Vec
<u8>) -> String
{
764 String { vec: bytes }
767 /// Converts a `String` into a byte vector.
769 /// This consumes the `String`, so we do not need to copy its contents.
776 /// let s = String::from("hello");
777 /// let bytes = s.into_bytes();
779 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
782 #[stable(feature = "rust1", since = "1.0.0")]
783 pub fn into_bytes(self) -> Vec
<u8> {
787 /// Extracts a string slice containing the entire `String`.
794 /// let s = String::from("foo");
796 /// assert_eq!("foo", s.as_str());
799 #[stable(feature = "string_as_str", since = "1.7.0")]
800 pub fn as_str(&self) -> &str {
804 /// Converts a `String` into a mutable string slice.
811 /// let mut s = String::from("foobar");
812 /// let s_mut_str = s.as_mut_str();
814 /// s_mut_str.make_ascii_uppercase();
816 /// assert_eq!("FOOBAR", s_mut_str);
819 #[stable(feature = "string_as_str", since = "1.7.0")]
820 pub fn as_mut_str(&mut self) -> &mut str {
824 /// Appends a given string slice onto the end of this `String`.
831 /// let mut s = String::from("foo");
833 /// s.push_str("bar");
835 /// assert_eq!("foobar", s);
837 #[cfg(not(no_global_oom_handling))]
839 #[stable(feature = "rust1", since = "1.0.0")]
840 pub fn push_str(&mut self, string
: &str) {
841 self.vec
.extend_from_slice(string
.as_bytes())
844 /// Copies elements from `src` range to the end of the string.
848 /// Panics if the starting point or end point do not lie on a [`char`]
849 /// boundary, or if they're out of bounds.
854 /// #![feature(string_extend_from_within)]
855 /// let mut string = String::from("abcde");
857 /// string.extend_from_within(2..);
858 /// assert_eq!(string, "abcdecde");
860 /// string.extend_from_within(..2);
861 /// assert_eq!(string, "abcdecdeab");
863 /// string.extend_from_within(4..8);
864 /// assert_eq!(string, "abcdecdeabecde");
866 #[cfg(not(no_global_oom_handling))]
867 #[unstable(feature = "string_extend_from_within", issue = "none")]
868 pub fn extend_from_within
<R
>(&mut self, src
: R
)
870 R
: RangeBounds
<usize>,
872 let src @ Range { start, end }
= slice
::range(src
, ..self.len());
874 assert
!(self.is_char_boundary(start
));
875 assert
!(self.is_char_boundary(end
));
877 self.vec
.extend_from_within(src
);
880 /// Returns this `String`'s capacity, in bytes.
887 /// let s = String::with_capacity(10);
889 /// assert!(s.capacity() >= 10);
892 #[stable(feature = "rust1", since = "1.0.0")]
893 pub fn capacity(&self) -> usize {
897 /// Ensures that this `String`'s capacity is at least `additional` bytes
898 /// larger than its length.
900 /// The capacity may be increased by more than `additional` bytes if it
901 /// chooses, to prevent frequent reallocations.
903 /// If you do not want this "at least" behavior, see the [`reserve_exact`]
908 /// Panics if the new capacity overflows [`usize`].
910 /// [`reserve_exact`]: String::reserve_exact
917 /// let mut s = String::new();
921 /// assert!(s.capacity() >= 10);
924 /// This might not actually increase the capacity:
927 /// let mut s = String::with_capacity(10);
931 /// // s now has a length of 2 and a capacity of 10
932 /// assert_eq!(2, s.len());
933 /// assert_eq!(10, s.capacity());
935 /// // Since we already have an extra 8 capacity, calling this...
938 /// // ... doesn't actually increase.
939 /// assert_eq!(10, s.capacity());
941 #[cfg(not(no_global_oom_handling))]
943 #[stable(feature = "rust1", since = "1.0.0")]
944 pub fn reserve(&mut self, additional
: usize) {
945 self.vec
.reserve(additional
)
948 /// Ensures that this `String`'s capacity is `additional` bytes
949 /// larger than its length.
951 /// Consider using the [`reserve`] method unless you absolutely know
952 /// better than the allocator.
954 /// [`reserve`]: String::reserve
958 /// Panics if the new capacity overflows `usize`.
965 /// let mut s = String::new();
967 /// s.reserve_exact(10);
969 /// assert!(s.capacity() >= 10);
972 /// This might not actually increase the capacity:
975 /// let mut s = String::with_capacity(10);
979 /// // s now has a length of 2 and a capacity of 10
980 /// assert_eq!(2, s.len());
981 /// assert_eq!(10, s.capacity());
983 /// // Since we already have an extra 8 capacity, calling this...
984 /// s.reserve_exact(8);
986 /// // ... doesn't actually increase.
987 /// assert_eq!(10, s.capacity());
989 #[cfg(not(no_global_oom_handling))]
991 #[stable(feature = "rust1", since = "1.0.0")]
992 pub fn reserve_exact(&mut self, additional
: usize) {
993 self.vec
.reserve_exact(additional
)
996 /// Tries to reserve capacity for at least `additional` more elements to be inserted
997 /// in the given `String`. The collection may reserve more space to avoid
998 /// frequent reallocations. After calling `reserve`, capacity will be
999 /// greater than or equal to `self.len() + additional`. Does nothing if
1000 /// capacity is already sufficient.
1004 /// If the capacity overflows, or the allocator reports a failure, then an error
1010 /// #![feature(try_reserve)]
1011 /// use std::collections::TryReserveError;
1013 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
1014 /// let mut output = String::new();
1016 /// // Pre-reserve the memory, exiting if we can't
1017 /// output.try_reserve(data.len())?;
1019 /// // Now we know this can't OOM in the middle of our complex work
1020 /// output.push_str(data);
1024 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1026 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
1027 pub fn try_reserve(&mut self, additional
: usize) -> Result
<(), TryReserveError
> {
1028 self.vec
.try_reserve(additional
)
1031 /// Tries to reserve the minimum capacity for exactly `additional` more elements to
1032 /// be inserted in the given `String`. After calling `reserve_exact`,
1033 /// capacity will be greater than or equal to `self.len() + additional`.
1034 /// Does nothing if the capacity is already sufficient.
1036 /// Note that the allocator may give the collection more space than it
1037 /// requests. Therefore, capacity can not be relied upon to be precisely
1038 /// minimal. Prefer [`reserve`] if future insertions are expected.
1040 /// [`reserve`]: String::reserve
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 /// let mut s = String::from("foo");
1106 /// assert!(s.capacity() >= 100);
1108 /// s.shrink_to(10);
1109 /// assert!(s.capacity() >= 10);
1111 /// assert!(s.capacity() >= 3);
1113 #[cfg(not(no_global_oom_handling))]
1115 #[stable(feature = "shrink_to", since = "1.56.0")]
1116 pub fn shrink_to(&mut self, min_capacity
: usize) {
1117 self.vec
.shrink_to(min_capacity
)
1120 /// Appends the given [`char`] to the end of this `String`.
1127 /// let mut s = String::from("abc");
1133 /// assert_eq!("abc123", s);
1135 #[cfg(not(no_global_oom_handling))]
1137 #[stable(feature = "rust1", since = "1.0.0")]
1138 pub fn push(&mut self, ch
: char) {
1139 match ch
.len_utf8() {
1140 1 => self.vec
.push(ch
as u8),
1141 _
=> self.vec
.extend_from_slice(ch
.encode_utf8(&mut [0; 4]).as_bytes()),
1145 /// Returns a byte slice of this `String`'s contents.
1147 /// The inverse of this method is [`from_utf8`].
1149 /// [`from_utf8`]: String::from_utf8
1156 /// let s = String::from("hello");
1158 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
1161 #[stable(feature = "rust1", since = "1.0.0")]
1162 pub fn as_bytes(&self) -> &[u8] {
1166 /// Shortens this `String` to the specified length.
1168 /// If `new_len` is greater than the string's current length, this has no
1171 /// Note that this method has no effect on the allocated capacity
1176 /// Panics if `new_len` does not lie on a [`char`] boundary.
1183 /// let mut s = String::from("hello");
1187 /// assert_eq!("he", s);
1190 #[stable(feature = "rust1", since = "1.0.0")]
1191 pub fn truncate(&mut self, new_len
: usize) {
1192 if new_len
<= self.len() {
1193 assert
!(self.is_char_boundary(new_len
));
1194 self.vec
.truncate(new_len
)
1198 /// Removes the last character from the string buffer and returns it.
1200 /// Returns [`None`] if this `String` is empty.
1207 /// let mut s = String::from("foo");
1209 /// assert_eq!(s.pop(), Some('o'));
1210 /// assert_eq!(s.pop(), Some('o'));
1211 /// assert_eq!(s.pop(), Some('f'));
1213 /// assert_eq!(s.pop(), None);
1216 #[stable(feature = "rust1", since = "1.0.0")]
1217 pub fn pop(&mut self) -> Option
<char> {
1218 let ch
= self.chars().rev().next()?
;
1219 let newlen
= self.len() - ch
.len_utf8();
1221 self.vec
.set_len(newlen
);
1226 /// Removes a [`char`] from this `String` at a byte position and returns it.
1228 /// This is an *O*(*n*) operation, as it requires copying every element in the
1233 /// Panics if `idx` is larger than or equal to the `String`'s length,
1234 /// or if it does not lie on a [`char`] boundary.
1241 /// let mut s = String::from("foo");
1243 /// assert_eq!(s.remove(0), 'f');
1244 /// assert_eq!(s.remove(1), 'o');
1245 /// assert_eq!(s.remove(0), 'o');
1248 #[stable(feature = "rust1", since = "1.0.0")]
1249 pub fn remove(&mut self, idx
: usize) -> char {
1250 let ch
= match self[idx
..].chars().next() {
1252 None
=> panic
!("cannot remove a char from the end of a string"),
1255 let next
= idx
+ ch
.len_utf8();
1256 let len
= self.len();
1258 ptr
::copy(self.vec
.as_ptr().add(next
), self.vec
.as_mut_ptr().add(idx
), len
- next
);
1259 self.vec
.set_len(len
- (next
- idx
));
1264 /// Remove all matches of pattern `pat` in the `String`.
1269 /// #![feature(string_remove_matches)]
1270 /// let mut s = String::from("Trees are not green, the sky is not blue.");
1271 /// s.remove_matches("not ");
1272 /// assert_eq!("Trees are green, the sky is blue.", s);
1275 /// Matches will be detected and removed iteratively, so in cases where
1276 /// patterns overlap, only the first pattern will be removed:
1279 /// #![feature(string_remove_matches)]
1280 /// let mut s = String::from("banana");
1281 /// s.remove_matches("ana");
1282 /// assert_eq!("bna", s);
1284 #[cfg(not(no_global_oom_handling))]
1285 #[unstable(feature = "string_remove_matches", reason = "new API", issue = "72826")]
1286 pub fn remove_matches
<'a
, P
>(&'a
mut self, pat
: P
)
1288 P
: for<'x
> Pattern
<'x
>,
1290 use core
::str::pattern
::Searcher
;
1293 let mut searcher
= pat
.into_searcher(self);
1294 // Per Searcher::next:
1296 // A Match result needs to contain the whole matched pattern,
1297 // however Reject results may be split up into arbitrary many
1298 // adjacent fragments. Both ranges may have zero length.
1300 // In practice the implementation of Searcher::next_match tends to
1301 // be more efficient, so we use it here and do some work to invert
1302 // matches into rejections since that's what we want to copy below.
1304 let rejections
: Vec
<_
> = from_fn(|| {
1305 let (start
, end
) = searcher
.next_match()?
;
1306 let prev_front
= front
;
1308 Some((prev_front
, start
))
1311 rejections
.into_iter().chain(core
::iter
::once((front
, self.len())))
1315 let ptr
= self.vec
.as_mut_ptr();
1317 for (start
, end
) in rejections
{
1318 let count
= end
- start
;
1320 // SAFETY: per Searcher::next:
1322 // The stream of Match and Reject values up to a Done will
1323 // contain index ranges that are adjacent, non-overlapping,
1324 // covering the whole haystack, and laying on utf8
1327 ptr
::copy(ptr
.add(start
), ptr
.add(len
), count
);
1334 self.vec
.set_len(len
);
1338 /// Retains only the characters specified by the predicate.
1340 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1341 /// This method operates in place, visiting each character exactly once in the
1342 /// original order, and preserves the order of the retained characters.
1347 /// let mut s = String::from("f_o_ob_ar");
1349 /// s.retain(|c| c != '_');
1351 /// assert_eq!(s, "foobar");
1354 /// Because the elements are visited exactly once in the original order,
1355 /// external state may be used to decide which elements to keep.
1358 /// let mut s = String::from("abcde");
1359 /// let keep = [false, true, true, false, true];
1360 /// let mut iter = keep.iter();
1361 /// s.retain(|_| *iter.next().unwrap());
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 might 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);
1538 #[stable(feature = "rust1", since = "1.0.0")]
1539 pub fn len(&self) -> usize {
1543 /// Returns `true` if this `String` has a length of zero, and `false` otherwise.
1550 /// let mut v = String::new();
1551 /// assert!(v.is_empty());
1554 /// assert!(!v.is_empty());
1557 #[stable(feature = "rust1", since = "1.0.0")]
1558 pub fn is_empty(&self) -> bool
{
1562 /// Splits the string into two at the given byte index.
1564 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1565 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1566 /// boundary of a UTF-8 code point.
1568 /// Note that the capacity of `self` does not change.
1572 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1573 /// code point of the string.
1579 /// let mut hello = String::from("Hello, World!");
1580 /// let world = hello.split_off(7);
1581 /// assert_eq!(hello, "Hello, ");
1582 /// assert_eq!(world, "World!");
1585 #[cfg(not(no_global_oom_handling))]
1587 #[stable(feature = "string_split_off", since = "1.16.0")]
1588 #[must_use = "use `.truncate()` if you don't need the other half"]
1589 pub fn split_off(&mut self, at
: usize) -> String
{
1590 assert
!(self.is_char_boundary(at
));
1591 let other
= self.vec
.split_off(at
);
1592 unsafe { String::from_utf8_unchecked(other) }
1595 /// Truncates this `String`, removing all contents.
1597 /// While this means the `String` will have a length of zero, it does not
1598 /// touch its capacity.
1605 /// let mut s = String::from("foo");
1609 /// assert!(s.is_empty());
1610 /// assert_eq!(0, s.len());
1611 /// assert_eq!(3, s.capacity());
1614 #[stable(feature = "rust1", since = "1.0.0")]
1615 pub fn clear(&mut self) {
1619 /// Creates a draining iterator that removes the specified range in the `String`
1620 /// and yields the removed `chars`.
1622 /// Note: The element range is removed even if the iterator is not
1623 /// consumed until the end.
1627 /// Panics if the starting point or end point do not lie on a [`char`]
1628 /// boundary, or if they're out of bounds.
1635 /// let mut s = String::from("α is alpha, β is beta");
1636 /// let beta_offset = s.find('β').unwrap_or(s.len());
1638 /// // Remove the range up until the β from the string
1639 /// let t: String = s.drain(..beta_offset).collect();
1640 /// assert_eq!(t, "α is alpha, ");
1641 /// assert_eq!(s, "β is beta");
1643 /// // A full range clears the string
1645 /// assert_eq!(s, "");
1647 #[stable(feature = "drain", since = "1.6.0")]
1648 pub fn drain
<R
>(&mut self, range
: R
) -> Drain
<'_
>
1650 R
: RangeBounds
<usize>,
1654 // The String version of Drain does not have the memory safety issues
1655 // of the vector version. The data is just plain bytes.
1656 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1657 // the removal will not happen.
1658 let Range { start, end }
= slice
::range(range
, ..self.len());
1659 assert
!(self.is_char_boundary(start
));
1660 assert
!(self.is_char_boundary(end
));
1662 // Take out two simultaneous borrows. The &mut String won't be accessed
1663 // until iteration is over, in Drop.
1664 let self_ptr
= self as *mut _
;
1665 // SAFETY: `slice::range` and `is_char_boundary` do the appropriate bounds checks.
1666 let chars_iter
= unsafe { self.get_unchecked(start..end) }
.chars();
1668 Drain { start, end, iter: chars_iter, string: self_ptr }
1671 /// Removes the specified range in the string,
1672 /// and replaces it with the given string.
1673 /// The given string doesn't need to be the same length as the range.
1677 /// Panics if the starting point or end point do not lie on a [`char`]
1678 /// boundary, or if they're out of bounds.
1685 /// let mut s = String::from("α is alpha, β is beta");
1686 /// let beta_offset = s.find('β').unwrap_or(s.len());
1688 /// // Replace the range up until the β from the string
1689 /// s.replace_range(..beta_offset, "Α is capital alpha; ");
1690 /// assert_eq!(s, "Α is capital alpha; β is beta");
1692 #[cfg(not(no_global_oom_handling))]
1693 #[stable(feature = "splice", since = "1.27.0")]
1694 pub fn replace_range
<R
>(&mut self, range
: R
, replace_with
: &str)
1696 R
: RangeBounds
<usize>,
1700 // Replace_range does not have the memory safety issues of a vector Splice.
1701 // of the vector version. The data is just plain bytes.
1703 // WARNING: Inlining this variable would be unsound (#81138)
1704 let start
= range
.start_bound();
1706 Included(&n
) => assert
!(self.is_char_boundary(n
)),
1707 Excluded(&n
) => assert
!(self.is_char_boundary(n
+ 1)),
1710 // WARNING: Inlining this variable would be unsound (#81138)
1711 let end
= range
.end_bound();
1713 Included(&n
) => assert
!(self.is_char_boundary(n
+ 1)),
1714 Excluded(&n
) => assert
!(self.is_char_boundary(n
)),
1718 // Using `range` again would be unsound (#81138)
1719 // We assume the bounds reported by `range` remain the same, but
1720 // an adversarial implementation could change between calls
1721 unsafe { self.as_mut_vec() }
.splice((start
, end
), replace_with
.bytes());
1724 /// Converts this `String` into a [`Box`]`<`[`str`]`>`.
1726 /// This will drop any excess capacity.
1728 /// [`str`]: prim@str
1735 /// let s = String::from("hello");
1737 /// let b = s.into_boxed_str();
1739 #[cfg(not(no_global_oom_handling))]
1740 #[stable(feature = "box_str", since = "1.4.0")]
1742 pub fn into_boxed_str(self) -> Box
<str> {
1743 let slice
= self.vec
.into_boxed_slice();
1744 unsafe { from_boxed_utf8_unchecked(slice) }
1748 impl FromUtf8Error
{
1749 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1756 /// // some invalid bytes, in a vector
1757 /// let bytes = vec![0, 159];
1759 /// let value = String::from_utf8(bytes);
1761 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1763 #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
1764 pub fn as_bytes(&self) -> &[u8] {
1768 /// Returns the bytes that were attempted to convert to a `String`.
1770 /// This method is carefully constructed to avoid allocation. It will
1771 /// consume the error, moving out the bytes, so that a copy of the bytes
1772 /// does not need to be made.
1779 /// // some invalid bytes, in a vector
1780 /// let bytes = vec![0, 159];
1782 /// let value = String::from_utf8(bytes);
1784 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1786 #[stable(feature = "rust1", since = "1.0.0")]
1787 pub fn into_bytes(self) -> Vec
<u8> {
1791 /// Fetch a `Utf8Error` to get more details about the conversion failure.
1793 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1794 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1795 /// an analogue to `FromUtf8Error`. See its documentation for more details
1798 /// [`std::str`]: core::str
1799 /// [`&str`]: prim@str
1806 /// // some invalid bytes, in a vector
1807 /// let bytes = vec![0, 159];
1809 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1811 /// // the first byte is invalid here
1812 /// assert_eq!(1, error.valid_up_to());
1814 #[stable(feature = "rust1", since = "1.0.0")]
1815 pub fn utf8_error(&self) -> Utf8Error
{
1820 #[stable(feature = "rust1", since = "1.0.0")]
1821 impl fmt
::Display
for FromUtf8Error
{
1822 fn fmt(&self, f
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
1823 fmt
::Display
::fmt(&self.error
, f
)
1827 #[stable(feature = "rust1", since = "1.0.0")]
1828 impl fmt
::Display
for FromUtf16Error
{
1829 fn fmt(&self, f
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
1830 fmt
::Display
::fmt("invalid utf-16: lone surrogate found", f
)
1834 #[cfg(not(no_global_oom_handling))]
1835 #[stable(feature = "rust1", since = "1.0.0")]
1836 impl Clone
for String
{
1837 fn clone(&self) -> Self {
1838 String { vec: self.vec.clone() }
1841 fn clone_from(&mut self, source
: &Self) {
1842 self.vec
.clone_from(&source
.vec
);
1846 #[cfg(not(no_global_oom_handling))]
1847 #[stable(feature = "rust1", since = "1.0.0")]
1848 impl FromIterator
<char> for String
{
1849 fn from_iter
<I
: IntoIterator
<Item
= char>>(iter
: I
) -> String
{
1850 let mut buf
= String
::new();
1856 #[cfg(not(no_global_oom_handling))]
1857 #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
1858 impl<'a
> FromIterator
<&'a
char> for String
{
1859 fn from_iter
<I
: IntoIterator
<Item
= &'a
char>>(iter
: I
) -> String
{
1860 let mut buf
= String
::new();
1866 #[cfg(not(no_global_oom_handling))]
1867 #[stable(feature = "rust1", since = "1.0.0")]
1868 impl<'a
> FromIterator
<&'a
str> for String
{
1869 fn from_iter
<I
: IntoIterator
<Item
= &'a
str>>(iter
: I
) -> String
{
1870 let mut buf
= String
::new();
1876 #[cfg(not(no_global_oom_handling))]
1877 #[stable(feature = "extend_string", since = "1.4.0")]
1878 impl FromIterator
<String
> for String
{
1879 fn from_iter
<I
: IntoIterator
<Item
= String
>>(iter
: I
) -> String
{
1880 let mut iterator
= iter
.into_iter();
1882 // Because we're iterating over `String`s, we can avoid at least
1883 // one allocation by getting the first string from the iterator
1884 // and appending to it all the subsequent strings.
1885 match iterator
.next() {
1886 None
=> String
::new(),
1888 buf
.extend(iterator
);
1895 #[cfg(not(no_global_oom_handling))]
1896 #[stable(feature = "box_str2", since = "1.45.0")]
1897 impl FromIterator
<Box
<str>> for String
{
1898 fn from_iter
<I
: IntoIterator
<Item
= Box
<str>>>(iter
: I
) -> String
{
1899 let mut buf
= String
::new();
1905 #[cfg(not(no_global_oom_handling))]
1906 #[stable(feature = "herd_cows", since = "1.19.0")]
1907 impl<'a
> FromIterator
<Cow
<'a
, str>> for String
{
1908 fn from_iter
<I
: IntoIterator
<Item
= Cow
<'a
, str>>>(iter
: I
) -> String
{
1909 let mut iterator
= iter
.into_iter();
1911 // Because we're iterating over CoWs, we can (potentially) avoid at least
1912 // one allocation by getting the first item and appending to it all the
1913 // subsequent items.
1914 match iterator
.next() {
1915 None
=> String
::new(),
1917 let mut buf
= cow
.into_owned();
1918 buf
.extend(iterator
);
1925 #[cfg(not(no_global_oom_handling))]
1926 #[stable(feature = "rust1", since = "1.0.0")]
1927 impl Extend
<char> for String
{
1928 fn extend
<I
: IntoIterator
<Item
= char>>(&mut self, iter
: I
) {
1929 let iterator
= iter
.into_iter();
1930 let (lower_bound
, _
) = iterator
.size_hint();
1931 self.reserve(lower_bound
);
1932 iterator
.for_each(move |c
| self.push(c
));
1936 fn extend_one(&mut self, c
: char) {
1941 fn extend_reserve(&mut self, additional
: usize) {
1942 self.reserve(additional
);
1946 #[cfg(not(no_global_oom_handling))]
1947 #[stable(feature = "extend_ref", since = "1.2.0")]
1948 impl<'a
> Extend
<&'a
char> for String
{
1949 fn extend
<I
: IntoIterator
<Item
= &'a
char>>(&mut self, iter
: I
) {
1950 self.extend(iter
.into_iter().cloned());
1954 fn extend_one(&mut self, &c
: &'a
char) {
1959 fn extend_reserve(&mut self, additional
: usize) {
1960 self.reserve(additional
);
1964 #[cfg(not(no_global_oom_handling))]
1965 #[stable(feature = "rust1", since = "1.0.0")]
1966 impl<'a
> Extend
<&'a
str> for String
{
1967 fn extend
<I
: IntoIterator
<Item
= &'a
str>>(&mut self, iter
: I
) {
1968 iter
.into_iter().for_each(move |s
| self.push_str(s
));
1972 fn extend_one(&mut self, s
: &'a
str) {
1977 #[cfg(not(no_global_oom_handling))]
1978 #[stable(feature = "box_str2", since = "1.45.0")]
1979 impl Extend
<Box
<str>> for String
{
1980 fn extend
<I
: IntoIterator
<Item
= Box
<str>>>(&mut self, iter
: I
) {
1981 iter
.into_iter().for_each(move |s
| self.push_str(&s
));
1985 #[cfg(not(no_global_oom_handling))]
1986 #[stable(feature = "extend_string", since = "1.4.0")]
1987 impl Extend
<String
> for String
{
1988 fn extend
<I
: IntoIterator
<Item
= String
>>(&mut self, iter
: I
) {
1989 iter
.into_iter().for_each(move |s
| self.push_str(&s
));
1993 fn extend_one(&mut self, s
: String
) {
1998 #[cfg(not(no_global_oom_handling))]
1999 #[stable(feature = "herd_cows", since = "1.19.0")]
2000 impl<'a
> Extend
<Cow
<'a
, str>> for String
{
2001 fn extend
<I
: IntoIterator
<Item
= Cow
<'a
, str>>>(&mut self, iter
: I
) {
2002 iter
.into_iter().for_each(move |s
| self.push_str(&s
));
2006 fn extend_one(&mut self, s
: Cow
<'a
, str>) {
2011 /// A convenience impl that delegates to the impl for `&str`.
2016 /// assert_eq!(String::from("Hello world").find("world"), Some(6));
2019 feature
= "pattern",
2020 reason
= "API not fully fleshed out and ready to be stabilized",
2023 impl<'a
, 'b
> Pattern
<'a
> for &'b String
{
2024 type Searcher
= <&'b
str as Pattern
<'a
>>::Searcher
;
2026 fn into_searcher(self, haystack
: &'a
str) -> <&'b
str as Pattern
<'a
>>::Searcher
{
2027 self[..].into_searcher(haystack
)
2031 fn is_contained_in(self, haystack
: &'a
str) -> bool
{
2032 self[..].is_contained_in(haystack
)
2036 fn is_prefix_of(self, haystack
: &'a
str) -> bool
{
2037 self[..].is_prefix_of(haystack
)
2041 fn strip_prefix_of(self, haystack
: &'a
str) -> Option
<&'a
str> {
2042 self[..].strip_prefix_of(haystack
)
2046 fn is_suffix_of(self, haystack
: &'a
str) -> bool
{
2047 self[..].is_suffix_of(haystack
)
2051 fn strip_suffix_of(self, haystack
: &'a
str) -> Option
<&'a
str> {
2052 self[..].strip_suffix_of(haystack
)
2056 #[stable(feature = "rust1", since = "1.0.0")]
2057 impl PartialEq
for String
{
2059 fn eq(&self, other
: &String
) -> bool
{
2060 PartialEq
::eq(&self[..], &other
[..])
2063 fn ne(&self, other
: &String
) -> bool
{
2064 PartialEq
::ne(&self[..], &other
[..])
2068 macro_rules
! impl_eq
{
2069 ($lhs
:ty
, $rhs
: ty
) => {
2070 #[stable(feature = "rust1", since = "1.0.0")]
2071 #[allow(unused_lifetimes)]
2072 impl<'a
, 'b
> PartialEq
<$rhs
> for $lhs
{
2074 fn eq(&self, other
: &$rhs
) -> bool
{
2075 PartialEq
::eq(&self[..], &other
[..])
2078 fn ne(&self, other
: &$rhs
) -> bool
{
2079 PartialEq
::ne(&self[..], &other
[..])
2083 #[stable(feature = "rust1", since = "1.0.0")]
2084 #[allow(unused_lifetimes)]
2085 impl<'a
, 'b
> PartialEq
<$lhs
> for $rhs
{
2087 fn eq(&self, other
: &$lhs
) -> bool
{
2088 PartialEq
::eq(&self[..], &other
[..])
2091 fn ne(&self, other
: &$lhs
) -> bool
{
2092 PartialEq
::ne(&self[..], &other
[..])
2098 impl_eq
! { String, str }
2099 impl_eq
! { String, &'a str }
2100 #[cfg(not(no_global_oom_handling))]
2101 impl_eq
! { Cow<'a, str>, str }
2102 #[cfg(not(no_global_oom_handling))]
2103 impl_eq
! { Cow<'a, str>, &'b str }
2104 #[cfg(not(no_global_oom_handling))]
2105 impl_eq
! { Cow<'a, str>, String }
2107 #[stable(feature = "rust1", since = "1.0.0")]
2108 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
2109 impl const 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 /// let mut s = String::from("abc");
2773 /// let mut drain = s.drain(..);
2774 /// assert_eq!(drain.as_str(), "abc");
2775 /// let _ = drain.next().unwrap();
2776 /// assert_eq!(drain.as_str(), "bc");
2778 #[stable(feature = "string_drain_as_str", since = "1.55.0")]
2779 pub fn as_str(&self) -> &str {
2784 #[stable(feature = "string_drain_as_str", since = "1.55.0")]
2785 impl<'a
> AsRef
<str> for Drain
<'a
> {
2786 fn as_ref(&self) -> &str {
2791 #[stable(feature = "string_drain_as_str", since = "1.55.0")]
2792 impl<'a
> AsRef
<[u8]> for Drain
<'a
> {
2793 fn as_ref(&self) -> &[u8] {
2794 self.as_str().as_bytes()
2798 #[stable(feature = "drain", since = "1.6.0")]
2799 impl Iterator
for Drain
<'_
> {
2803 fn next(&mut self) -> Option
<char> {
2807 fn size_hint(&self) -> (usize, Option
<usize>) {
2808 self.iter
.size_hint()
2812 fn last(mut self) -> Option
<char> {
2817 #[stable(feature = "drain", since = "1.6.0")]
2818 impl DoubleEndedIterator
for Drain
<'_
> {
2820 fn next_back(&mut self) -> Option
<char> {
2821 self.iter
.next_back()
2825 #[stable(feature = "fused", since = "1.26.0")]
2826 impl FusedIterator
for Drain
<'_
> {}
2828 #[cfg(not(no_global_oom_handling))]
2829 #[stable(feature = "from_char_for_string", since = "1.46.0")]
2830 impl From
<char> for String
{
2831 /// Allocates an owned [`String`] from a single character.
2835 /// let c: char = 'a';
2836 /// let s: String = String::from(c);
2837 /// assert_eq!("a", &s[..]);
2840 fn from(c
: char) -> Self {