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 use core::char::{decode_utf16, REPLACEMENT_CHARACTER};
48 use core::iter::{FromIterator, FusedIterator};
49 use core::ops::Bound::{Excluded, Included, Unbounded};
50 use core::ops::{self, Add, AddAssign, Index, IndexMut, Range, RangeBounds};
52 use core::str::{lossy, pattern::Pattern};
54 use crate::borrow::{Cow, ToOwned};
55 use crate::boxed::Box;
56 use crate::collections::TryReserveError;
57 use crate::str::{self, from_boxed_utf8_unchecked, Chars, FromStr, Utf8Error};
60 /// A UTF-8–encoded, growable string.
62 /// The `String` type is the most common string type that has ownership over the
63 /// contents of the string. It has a close relationship with its borrowed
64 /// counterpart, the primitive [`str`].
68 /// You can create a `String` from [a literal string][`str`] with [`String::from`]:
70 /// [`String::from`]: From::from
73 /// let hello = String::from("Hello, world!");
76 /// You can append a [`char`] to a `String` with the [`push`] method, and
77 /// append a [`&str`] with the [`push_str`] method:
80 /// let mut hello = String::from("Hello, ");
83 /// hello.push_str("orld!");
86 /// [`push`]: String::push
87 /// [`push_str`]: String::push_str
89 /// If you have a vector of UTF-8 bytes, you can create a `String` from it with
90 /// the [`from_utf8`] method:
93 /// // some bytes, in a vector
94 /// let sparkle_heart = vec![240, 159, 146, 150];
96 /// // We know these bytes are valid, so we'll use `unwrap()`.
97 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
99 /// assert_eq!("💖", sparkle_heart);
102 /// [`from_utf8`]: String::from_utf8
106 /// `String`s are always valid UTF-8. This has a few implications, the first of
107 /// which is that if you need a non-UTF-8 string, consider [`OsString`]. It is
108 /// similar, but without the UTF-8 constraint. The second implication is that
109 /// you cannot index into a `String`:
111 /// ```compile_fail,E0277
114 /// println!("The first letter of s is {}", s[0]); // ERROR!!!
117 /// [`OsString`]: ../../std/ffi/struct.OsString.html
119 /// Indexing is intended to be a constant-time operation, but UTF-8 encoding
120 /// does not allow us to do this. Furthermore, it's not clear what sort of
121 /// thing the index should return: a byte, a codepoint, or a grapheme cluster.
122 /// The [`bytes`] and [`chars`] methods return iterators over the first
123 /// two, respectively.
125 /// [`bytes`]: str::bytes
126 /// [`chars`]: str::chars
130 /// `String`s implement [`Deref`]`<Target=str>`, and so inherit all of [`str`]'s
131 /// methods. In addition, this means that you can pass a `String` to a
132 /// function which takes a [`&str`] by using an ampersand (`&`):
135 /// fn takes_str(s: &str) { }
137 /// let s = String::from("Hello");
142 /// This will create a [`&str`] from the `String` and pass it in. This
143 /// conversion is very inexpensive, and so generally, functions will accept
144 /// [`&str`]s as arguments unless they need a `String` for some specific
147 /// In certain cases Rust doesn't have enough information to make this
148 /// conversion, known as [`Deref`] coercion. In the following example a string
149 /// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
150 /// `example_func` takes anything that implements the trait. In this case Rust
151 /// would need to make two implicit conversions, which Rust doesn't have the
152 /// means to do. For that reason, the following example will not compile.
154 /// ```compile_fail,E0277
155 /// trait TraitExample {}
157 /// impl<'a> TraitExample for &'a str {}
159 /// fn example_func<A: TraitExample>(example_arg: A) {}
161 /// let example_string = String::from("example_string");
162 /// example_func(&example_string);
165 /// There are two options that would work instead. The first would be to
166 /// change the line `example_func(&example_string);` to
167 /// `example_func(example_string.as_str());`, using the method [`as_str()`]
168 /// to explicitly extract the string slice containing the string. The second
169 /// way changes `example_func(&example_string);` to
170 /// `example_func(&*example_string);`. In this case we are dereferencing a
171 /// `String` to a [`str`][`&str`], then referencing the [`str`][`&str`] back to
172 /// [`&str`]. The second way is more idiomatic, however both work to do the
173 /// conversion explicitly rather than relying on the implicit conversion.
177 /// A `String` is made up of three components: a pointer to some bytes, a
178 /// length, and a capacity. The pointer points to an internal buffer `String`
179 /// uses to store its data. The length is the number of bytes currently stored
180 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
181 /// the length will always be less than or equal to the capacity.
183 /// This buffer is always stored on the heap.
185 /// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
191 /// let story = String::from("Once upon a time...");
193 // FIXME Update this when vec_into_raw_parts is stabilized
194 /// // Prevent automatically dropping the String's data
195 /// let mut story = mem::ManuallyDrop::new(story);
197 /// let ptr = story.as_mut_ptr();
198 /// let len = story.len();
199 /// let capacity = story.capacity();
201 /// // story has nineteen bytes
202 /// assert_eq!(19, len);
204 /// // We can re-build a String out of ptr, len, and capacity. This is all
205 /// // unsafe because we are responsible for making sure the components are
207 /// let s = unsafe { String::from_raw_parts(ptr, len, capacity) } ;
209 /// assert_eq!(String::from("Once upon a time..."), s);
212 /// [`as_ptr`]: str::as_ptr
213 /// [`len`]: String::len
214 /// [`capacity`]: String::capacity
216 /// If a `String` has enough capacity, adding elements to it will not
217 /// re-allocate. For example, consider this program:
220 /// let mut s = String::new();
222 /// println!("{}", s.capacity());
225 /// s.push_str("hello");
226 /// println!("{}", s.capacity());
230 /// This will output the following:
241 /// At first, we have no memory allocated at all, but as we append to the
242 /// string, it increases its capacity appropriately. If we instead use the
243 /// [`with_capacity`] method to allocate the correct capacity initially:
246 /// let mut s = String::with_capacity(25);
248 /// println!("{}", s.capacity());
251 /// s.push_str("hello");
252 /// println!("{}", s.capacity());
256 /// [`with_capacity`]: String::with_capacity
258 /// We end up with a different output:
269 /// Here, there's no need to allocate more memory inside the loop.
271 /// [`str`]: prim@str
272 /// [`&str`]: prim@str
273 /// [`Deref`]: core::ops::Deref
274 /// [`as_str()`]: String::as_str
275 #[derive(PartialOrd, Eq, Ord)]
276 #[cfg_attr(not(test), rustc_diagnostic_item = "string_type")]
277 #[stable(feature = "rust1", since = "1.0.0")]
282 /// A possible error value when converting a `String` from a UTF-8 byte vector.
284 /// This type is the error type for the [`from_utf8`] method on [`String`]. It
285 /// is designed in such a way to carefully avoid reallocations: the
286 /// [`into_bytes`] method will give back the byte vector that was used in the
287 /// conversion attempt.
289 /// [`from_utf8`]: String::from_utf8
290 /// [`into_bytes`]: FromUtf8Error::into_bytes
292 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
293 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
294 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
295 /// through the [`utf8_error`] method.
297 /// [`Utf8Error`]: core::str::Utf8Error
298 /// [`std::str`]: core::str
299 /// [`&str`]: prim@str
300 /// [`utf8_error`]: Self::utf8_error
307 /// // some invalid bytes, in a vector
308 /// let bytes = vec![0, 159];
310 /// let value = String::from_utf8(bytes);
312 /// assert!(value.is_err());
313 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
315 #[stable(feature = "rust1", since = "1.0.0")]
316 #[derive(Debug, Clone, PartialEq, Eq)]
317 pub struct FromUtf8Error {
322 /// A possible error value when converting a `String` from a UTF-16 byte slice.
324 /// This type is the error type for the [`from_utf16`] method on [`String`].
326 /// [`from_utf16`]: String::from_utf16
332 /// // 𝄞mu<invalid>ic
333 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
334 /// 0xD800, 0x0069, 0x0063];
336 /// assert!(String::from_utf16(v).is_err());
338 #[stable(feature = "rust1", since = "1.0.0")]
340 pub struct FromUtf16Error(());
343 /// Creates a new empty `String`.
345 /// Given that the `String` is empty, this will not allocate any initial
346 /// buffer. While that means that this initial operation is very
347 /// inexpensive, it may cause excessive allocation later when you add
348 /// data. If you have an idea of how much data the `String` will hold,
349 /// consider the [`with_capacity`] method to prevent excessive
352 /// [`with_capacity`]: String::with_capacity
359 /// let s = String::new();
362 #[rustc_const_stable(feature = "const_string_new", since = "1.32.0")]
363 #[stable(feature = "rust1", since = "1.0.0")]
364 pub const fn new() -> String {
365 String { vec: Vec::new() }
368 /// Creates a new empty `String` with a particular capacity.
370 /// `String`s have an internal buffer to hold their data. The capacity is
371 /// the length of that buffer, and can be queried with the [`capacity`]
372 /// method. This method creates an empty `String`, but one with an initial
373 /// buffer that can hold `capacity` bytes. This is useful when you may be
374 /// appending a bunch of data to the `String`, reducing the number of
375 /// reallocations it needs to do.
377 /// [`capacity`]: String::capacity
379 /// If the given capacity is `0`, no allocation will occur, and this method
380 /// is identical to the [`new`] method.
382 /// [`new`]: String::new
389 /// let mut s = String::with_capacity(10);
391 /// // The String contains no chars, even though it has capacity for more
392 /// assert_eq!(s.len(), 0);
394 /// // These are all done without reallocating...
395 /// let cap = s.capacity();
400 /// assert_eq!(s.capacity(), cap);
402 /// // ...but this may make the string reallocate
406 #[doc(alias = "alloc")]
407 #[doc(alias = "malloc")]
408 #[stable(feature = "rust1", since = "1.0.0")]
409 pub fn with_capacity(capacity: usize) -> String {
410 String { vec: Vec::with_capacity(capacity) }
413 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
414 // required for this method definition, is not available. Since we don't
415 // require this method for testing purposes, I'll just stub it
416 // NB see the slice::hack module in slice.rs for more information
419 pub fn from_str(_: &str) -> String {
420 panic!("not available with cfg(test)");
423 /// Converts a vector of bytes to a `String`.
425 /// A string ([`String`]) is made of bytes ([`u8`]), and a vector of bytes
426 /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
427 /// two. Not all byte slices are valid `String`s, however: `String`
428 /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
429 /// the bytes are valid UTF-8, and then does the conversion.
431 /// If you are sure that the byte slice is valid UTF-8, and you don't want
432 /// to incur the overhead of the validity check, there is an unsafe version
433 /// of this function, [`from_utf8_unchecked`], which has the same behavior
434 /// but skips the check.
436 /// This method will take care to not copy the vector, for efficiency's
439 /// If you need a [`&str`] instead of a `String`, consider
440 /// [`str::from_utf8`].
442 /// The inverse of this method is [`into_bytes`].
446 /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
447 /// provided bytes are not UTF-8. The vector you moved in is also included.
454 /// // some bytes, in a vector
455 /// let sparkle_heart = vec![240, 159, 146, 150];
457 /// // We know these bytes are valid, so we'll use `unwrap()`.
458 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
460 /// assert_eq!("💖", sparkle_heart);
466 /// // some invalid bytes, in a vector
467 /// let sparkle_heart = vec![0, 159, 146, 150];
469 /// assert!(String::from_utf8(sparkle_heart).is_err());
472 /// See the docs for [`FromUtf8Error`] for more details on what you can do
475 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
476 /// [`Vec<u8>`]: crate::vec::Vec
477 /// [`&str`]: prim@str
478 /// [`into_bytes`]: String::into_bytes
480 #[stable(feature = "rust1", since = "1.0.0")]
481 pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
482 match str::from_utf8(&vec) {
483 Ok(..) => Ok(String { vec }),
484 Err(e) => Err(FromUtf8Error { bytes: vec, error: e }),
488 /// Converts a slice of bytes to a string, including invalid characters.
490 /// Strings are made of bytes ([`u8`]), and a slice of bytes
491 /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
492 /// between the two. Not all byte slices are valid strings, however: strings
493 /// are required to be valid UTF-8. During this conversion,
494 /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
495 /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: �
497 /// [byteslice]: ../../std/primitive.slice.html
498 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
500 /// If you are sure that the byte slice is valid UTF-8, and you don't want
501 /// to incur the overhead of the conversion, there is an unsafe version
502 /// of this function, [`from_utf8_unchecked`], which has the same behavior
503 /// but skips the checks.
505 /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
507 /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
508 /// UTF-8, then we need to insert the replacement characters, which will
509 /// change the size of the string, and hence, require a `String`. But if
510 /// it's already valid UTF-8, we don't need a new allocation. This return
511 /// type allows us to handle both cases.
513 /// [`Cow<'a, str>`]: crate::borrow::Cow
520 /// // some bytes, in a vector
521 /// let sparkle_heart = vec![240, 159, 146, 150];
523 /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
525 /// assert_eq!("💖", sparkle_heart);
531 /// // some invalid bytes
532 /// let input = b"Hello \xF0\x90\x80World";
533 /// let output = String::from_utf8_lossy(input);
535 /// assert_eq!("Hello �World", output);
537 #[stable(feature = "rust1", since = "1.0.0")]
538 pub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, str> {
539 let mut iter = lossy::Utf8Lossy::from_bytes(v).chunks();
541 let (first_valid, first_broken) = if let Some(chunk) = iter.next() {
542 let lossy::Utf8LossyChunk { valid, broken } = chunk;
543 if valid.len() == v.len() {
544 debug_assert!(broken.is_empty());
545 return Cow::Borrowed(valid);
549 return Cow::Borrowed("");
552 const REPLACEMENT: &str = "\u{FFFD}";
554 let mut res = String::with_capacity(v.len());
555 res.push_str(first_valid);
556 if !first_broken.is_empty() {
557 res.push_str(REPLACEMENT);
560 for lossy::Utf8LossyChunk { valid, broken } in iter {
562 if !broken.is_empty() {
563 res.push_str(REPLACEMENT);
570 /// Decode a UTF-16–encoded vector `v` into a `String`, returning [`Err`]
571 /// if `v` contains any invalid data.
579 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
580 /// 0x0073, 0x0069, 0x0063];
581 /// assert_eq!(String::from("𝄞music"),
582 /// String::from_utf16(v).unwrap());
584 /// // 𝄞mu<invalid>ic
585 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
586 /// 0xD800, 0x0069, 0x0063];
587 /// assert!(String::from_utf16(v).is_err());
589 #[stable(feature = "rust1", since = "1.0.0")]
590 pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
591 // This isn't done via collect::<Result<_, _>>() for performance reasons.
592 // FIXME: the function can be simplified again when #48994 is closed.
593 let mut ret = String::with_capacity(v.len());
594 for c in decode_utf16(v.iter().cloned()) {
598 return Err(FromUtf16Error(()));
604 /// Decode a UTF-16–encoded slice `v` into a `String`, replacing
605 /// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
607 /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
608 /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
609 /// conversion requires a memory allocation.
611 /// [`from_utf8_lossy`]: String::from_utf8_lossy
612 /// [`Cow<'a, str>`]: crate::borrow::Cow
613 /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
620 /// // 𝄞mus<invalid>ic<invalid>
621 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
622 /// 0x0073, 0xDD1E, 0x0069, 0x0063,
625 /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
626 /// String::from_utf16_lossy(v));
629 #[stable(feature = "rust1", since = "1.0.0")]
630 pub fn from_utf16_lossy(v: &[u16]) -> String {
631 decode_utf16(v.iter().cloned()).map(|r| r.unwrap_or(REPLACEMENT_CHARACTER)).collect()
634 /// Decomposes a `String` into its raw components.
636 /// Returns the raw pointer to the underlying data, the length of
637 /// the string (in bytes), and the allocated capacity of the data
638 /// (in bytes). These are the same arguments in the same order as
639 /// the arguments to [`from_raw_parts`].
641 /// After calling this function, the caller is responsible for the
642 /// memory previously managed by the `String`. The only way to do
643 /// this is to convert the raw pointer, length, and capacity back
644 /// into a `String` with the [`from_raw_parts`] function, allowing
645 /// the destructor to perform the cleanup.
647 /// [`from_raw_parts`]: String::from_raw_parts
652 /// #![feature(vec_into_raw_parts)]
653 /// let s = String::from("hello");
655 /// let (ptr, len, cap) = s.into_raw_parts();
657 /// let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
658 /// assert_eq!(rebuilt, "hello");
660 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
661 pub fn into_raw_parts(self) -> (*mut u8, usize, usize) {
662 self.vec.into_raw_parts()
665 /// Creates a new `String` from a length, capacity, and pointer.
669 /// This is highly unsafe, due to the number of invariants that aren't
672 /// * The memory at `buf` needs to have been previously allocated by the
673 /// same allocator the standard library uses, with a required alignment of exactly 1.
674 /// * `length` needs to be less than or equal to `capacity`.
675 /// * `capacity` needs to be the correct value.
676 /// * The first `length` bytes at `buf` need to be valid UTF-8.
678 /// Violating these may cause problems like corrupting the allocator's
679 /// internal data structures.
681 /// The ownership of `buf` is effectively transferred to the
682 /// `String` which may then deallocate, reallocate or change the
683 /// contents of memory pointed to by the pointer at will. Ensure
684 /// that nothing else uses the pointer after calling this
695 /// let s = String::from("hello");
697 // FIXME Update this when vec_into_raw_parts is stabilized
698 /// // Prevent automatically dropping the String's data
699 /// let mut s = mem::ManuallyDrop::new(s);
701 /// let ptr = s.as_mut_ptr();
702 /// let len = s.len();
703 /// let capacity = s.capacity();
705 /// let s = String::from_raw_parts(ptr, len, capacity);
707 /// assert_eq!(String::from("hello"), s);
711 #[stable(feature = "rust1", since = "1.0.0")]
712 pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
713 unsafe { String { vec: Vec::from_raw_parts(buf, length, capacity) } }
716 /// Converts a vector of bytes to a `String` without checking that the
717 /// string contains valid UTF-8.
719 /// See the safe version, [`from_utf8`], for more details.
721 /// [`from_utf8`]: String::from_utf8
725 /// This function is unsafe because it does not check that the bytes passed
726 /// to it are valid UTF-8. If this constraint is violated, it may cause
727 /// memory unsafety issues with future users of the `String`, as the rest of
728 /// the standard library assumes that `String`s are valid UTF-8.
735 /// // some bytes, in a vector
736 /// let sparkle_heart = vec![240, 159, 146, 150];
738 /// let sparkle_heart = unsafe {
739 /// String::from_utf8_unchecked(sparkle_heart)
742 /// assert_eq!("💖", sparkle_heart);
745 #[stable(feature = "rust1", since = "1.0.0")]
746 pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
747 String { vec: bytes }
750 /// Converts a `String` into a byte vector.
752 /// This consumes the `String`, so we do not need to copy its contents.
759 /// let s = String::from("hello");
760 /// let bytes = s.into_bytes();
762 /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
765 #[stable(feature = "rust1", since = "1.0.0")]
766 pub fn into_bytes(self) -> Vec<u8> {
770 /// Extracts a string slice containing the entire `String`.
777 /// let s = String::from("foo");
779 /// assert_eq!("foo", s.as_str());
782 #[stable(feature = "string_as_str", since = "1.7.0")]
783 pub fn as_str(&self) -> &str {
787 /// Converts a `String` into a mutable string slice.
794 /// let mut s = String::from("foobar");
795 /// let s_mut_str = s.as_mut_str();
797 /// s_mut_str.make_ascii_uppercase();
799 /// assert_eq!("FOOBAR", s_mut_str);
802 #[stable(feature = "string_as_str", since = "1.7.0")]
803 pub fn as_mut_str(&mut self) -> &mut str {
807 /// Appends a given string slice onto the end of this `String`.
814 /// let mut s = String::from("foo");
816 /// s.push_str("bar");
818 /// assert_eq!("foobar", s);
821 #[stable(feature = "rust1", since = "1.0.0")]
822 pub fn push_str(&mut self, string: &str) {
823 self.vec.extend_from_slice(string.as_bytes())
826 /// Returns this `String`'s capacity, in bytes.
833 /// let s = String::with_capacity(10);
835 /// assert!(s.capacity() >= 10);
838 #[stable(feature = "rust1", since = "1.0.0")]
839 pub fn capacity(&self) -> usize {
843 /// Ensures that this `String`'s capacity is at least `additional` bytes
844 /// larger than its length.
846 /// The capacity may be increased by more than `additional` bytes if it
847 /// chooses, to prevent frequent reallocations.
849 /// If you do not want this "at least" behavior, see the [`reserve_exact`]
854 /// Panics if the new capacity overflows [`usize`].
856 /// [`reserve_exact`]: String::reserve_exact
863 /// let mut s = String::new();
867 /// assert!(s.capacity() >= 10);
870 /// This may not actually increase the capacity:
873 /// let mut s = String::with_capacity(10);
877 /// // s now has a length of 2 and a capacity of 10
878 /// assert_eq!(2, s.len());
879 /// assert_eq!(10, s.capacity());
881 /// // Since we already have an extra 8 capacity, calling this...
884 /// // ... doesn't actually increase.
885 /// assert_eq!(10, s.capacity());
888 #[stable(feature = "rust1", since = "1.0.0")]
889 pub fn reserve(&mut self, additional: usize) {
890 self.vec.reserve(additional)
893 /// Ensures that this `String`'s capacity is `additional` bytes
894 /// larger than its length.
896 /// Consider using the [`reserve`] method unless you absolutely know
897 /// better than the allocator.
899 /// [`reserve`]: String::reserve
903 /// Panics if the new capacity overflows `usize`.
910 /// let mut s = String::new();
912 /// s.reserve_exact(10);
914 /// assert!(s.capacity() >= 10);
917 /// This may not actually increase the capacity:
920 /// let mut s = String::with_capacity(10);
924 /// // s now has a length of 2 and a capacity of 10
925 /// assert_eq!(2, s.len());
926 /// assert_eq!(10, s.capacity());
928 /// // Since we already have an extra 8 capacity, calling this...
929 /// s.reserve_exact(8);
931 /// // ... doesn't actually increase.
932 /// assert_eq!(10, s.capacity());
935 #[stable(feature = "rust1", since = "1.0.0")]
936 pub fn reserve_exact(&mut self, additional: usize) {
937 self.vec.reserve_exact(additional)
940 /// Tries to reserve capacity for at least `additional` more elements to be inserted
941 /// in the given `String`. The collection may reserve more space to avoid
942 /// frequent reallocations. After calling `reserve`, capacity will be
943 /// greater than or equal to `self.len() + additional`. Does nothing if
944 /// capacity is already sufficient.
948 /// If the capacity overflows, or the allocator reports a failure, then an error
954 /// #![feature(try_reserve)]
955 /// use std::collections::TryReserveError;
957 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
958 /// let mut output = String::new();
960 /// // Pre-reserve the memory, exiting if we can't
961 /// output.try_reserve(data.len())?;
963 /// // Now we know this can't OOM in the middle of our complex work
964 /// output.push_str(data);
968 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
970 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
971 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
972 self.vec.try_reserve(additional)
975 /// Tries to reserve the minimum capacity for exactly `additional` more elements to
976 /// be inserted in the given `String`. After calling `reserve_exact`,
977 /// capacity will be greater than or equal to `self.len() + additional`.
978 /// Does nothing if the capacity is already sufficient.
980 /// Note that the allocator may give the collection more space than it
981 /// requests. Therefore, capacity can not be relied upon to be precisely
982 /// minimal. Prefer `reserve` if future insertions are expected.
986 /// If the capacity overflows, or the allocator reports a failure, then an error
992 /// #![feature(try_reserve)]
993 /// use std::collections::TryReserveError;
995 /// fn process_data(data: &str) -> Result<String, TryReserveError> {
996 /// let mut output = String::new();
998 /// // Pre-reserve the memory, exiting if we can't
999 /// output.try_reserve(data.len())?;
1001 /// // Now we know this can't OOM in the middle of our complex work
1002 /// output.push_str(data);
1006 /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?");
1008 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
1009 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
1010 self.vec.try_reserve_exact(additional)
1013 /// Shrinks the capacity of this `String` to match its length.
1020 /// let mut s = String::from("foo");
1023 /// assert!(s.capacity() >= 100);
1025 /// s.shrink_to_fit();
1026 /// assert_eq!(3, s.capacity());
1029 #[stable(feature = "rust1", since = "1.0.0")]
1030 pub fn shrink_to_fit(&mut self) {
1031 self.vec.shrink_to_fit()
1034 /// Shrinks the capacity of this `String` with a lower bound.
1036 /// The capacity will remain at least as large as both the length
1037 /// and the supplied value.
1039 /// If the current capacity is less than the lower limit, this is a no-op.
1044 /// #![feature(shrink_to)]
1045 /// let mut s = String::from("foo");
1048 /// assert!(s.capacity() >= 100);
1050 /// s.shrink_to(10);
1051 /// assert!(s.capacity() >= 10);
1053 /// assert!(s.capacity() >= 3);
1056 #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")]
1057 pub fn shrink_to(&mut self, min_capacity: usize) {
1058 self.vec.shrink_to(min_capacity)
1061 /// Appends the given [`char`] to the end of this `String`.
1068 /// let mut s = String::from("abc");
1074 /// assert_eq!("abc123", s);
1077 #[stable(feature = "rust1", since = "1.0.0")]
1078 pub fn push(&mut self, ch: char) {
1079 match ch.len_utf8() {
1080 1 => self.vec.push(ch as u8),
1081 _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
1085 /// Returns a byte slice of this `String`'s contents.
1087 /// The inverse of this method is [`from_utf8`].
1089 /// [`from_utf8`]: String::from_utf8
1096 /// let s = String::from("hello");
1098 /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
1101 #[stable(feature = "rust1", since = "1.0.0")]
1102 pub fn as_bytes(&self) -> &[u8] {
1106 /// Shortens this `String` to the specified length.
1108 /// If `new_len` is greater than the string's current length, this has no
1111 /// Note that this method has no effect on the allocated capacity
1116 /// Panics if `new_len` does not lie on a [`char`] boundary.
1123 /// let mut s = String::from("hello");
1127 /// assert_eq!("he", s);
1130 #[stable(feature = "rust1", since = "1.0.0")]
1131 pub fn truncate(&mut self, new_len: usize) {
1132 if new_len <= self.len() {
1133 assert!(self.is_char_boundary(new_len));
1134 self.vec.truncate(new_len)
1138 /// Removes the last character from the string buffer and returns it.
1140 /// Returns [`None`] if this `String` is empty.
1147 /// let mut s = String::from("foo");
1149 /// assert_eq!(s.pop(), Some('o'));
1150 /// assert_eq!(s.pop(), Some('o'));
1151 /// assert_eq!(s.pop(), Some('f'));
1153 /// assert_eq!(s.pop(), None);
1156 #[stable(feature = "rust1", since = "1.0.0")]
1157 pub fn pop(&mut self) -> Option<char> {
1158 let ch = self.chars().rev().next()?;
1159 let newlen = self.len() - ch.len_utf8();
1161 self.vec.set_len(newlen);
1166 /// Removes a [`char`] from this `String` at a byte position and returns it.
1168 /// This is an *O*(*n*) operation, as it requires copying every element in the
1173 /// Panics if `idx` is larger than or equal to the `String`'s length,
1174 /// or if it does not lie on a [`char`] boundary.
1181 /// let mut s = String::from("foo");
1183 /// assert_eq!(s.remove(0), 'f');
1184 /// assert_eq!(s.remove(1), 'o');
1185 /// assert_eq!(s.remove(0), 'o');
1188 #[stable(feature = "rust1", since = "1.0.0")]
1189 pub fn remove(&mut self, idx: usize) -> char {
1190 let ch = match self[idx..].chars().next() {
1192 None => panic!("cannot remove a char from the end of a string"),
1195 let next = idx + ch.len_utf8();
1196 let len = self.len();
1198 ptr::copy(self.vec.as_ptr().add(next), self.vec.as_mut_ptr().add(idx), len - next);
1199 self.vec.set_len(len - (next - idx));
1204 /// Retains only the characters specified by the predicate.
1206 /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1207 /// This method operates in place, visiting each character exactly once in the
1208 /// original order, and preserves the order of the retained characters.
1213 /// let mut s = String::from("f_o_ob_ar");
1215 /// s.retain(|c| c != '_');
1217 /// assert_eq!(s, "foobar");
1220 /// The exact order may be useful for tracking external state, like an index.
1223 /// let mut s = String::from("abcde");
1224 /// let keep = [false, true, true, false, true];
1226 /// s.retain(|_| (keep[i], i += 1).0);
1227 /// assert_eq!(s, "bce");
1230 #[stable(feature = "string_retain", since = "1.26.0")]
1231 pub fn retain<F>(&mut self, mut f: F)
1233 F: FnMut(char) -> bool,
1235 let len = self.len();
1236 let mut del_bytes = 0;
1240 self.vec.set_len(0);
1244 let ch = unsafe { self.get_unchecked(idx..len).chars().next().unwrap() };
1245 let ch_len = ch.len_utf8();
1248 del_bytes += ch_len;
1249 } else if del_bytes > 0 {
1252 self.vec.as_ptr().add(idx),
1253 self.vec.as_mut_ptr().add(idx - del_bytes),
1259 // Point idx to the next char
1264 self.vec.set_len(len - del_bytes);
1268 /// Inserts a character into this `String` at a byte position.
1270 /// This is an *O*(*n*) operation as it requires copying every element in the
1275 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1276 /// lie on a [`char`] boundary.
1283 /// let mut s = String::with_capacity(3);
1285 /// s.insert(0, 'f');
1286 /// s.insert(1, 'o');
1287 /// s.insert(2, 'o');
1289 /// assert_eq!("foo", s);
1292 #[stable(feature = "rust1", since = "1.0.0")]
1293 pub fn insert(&mut self, idx: usize, ch: char) {
1294 assert!(self.is_char_boundary(idx));
1295 let mut bits = [0; 4];
1296 let bits = ch.encode_utf8(&mut bits).as_bytes();
1299 self.insert_bytes(idx, bits);
1303 unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1304 let len = self.len();
1305 let amt = bytes.len();
1306 self.vec.reserve(amt);
1309 ptr::copy(self.vec.as_ptr().add(idx), self.vec.as_mut_ptr().add(idx + amt), len - idx);
1310 ptr::copy(bytes.as_ptr(), self.vec.as_mut_ptr().add(idx), amt);
1311 self.vec.set_len(len + amt);
1315 /// Inserts a string slice into this `String` at a byte position.
1317 /// This is an *O*(*n*) operation as it requires copying every element in the
1322 /// Panics if `idx` is larger than the `String`'s length, or if it does not
1323 /// lie on a [`char`] boundary.
1330 /// let mut s = String::from("bar");
1332 /// s.insert_str(0, "foo");
1334 /// assert_eq!("foobar", s);
1337 #[stable(feature = "insert_str", since = "1.16.0")]
1338 pub fn insert_str(&mut self, idx: usize, string: &str) {
1339 assert!(self.is_char_boundary(idx));
1342 self.insert_bytes(idx, string.as_bytes());
1346 /// Returns a mutable reference to the contents of this `String`.
1350 /// This function is unsafe because it does not check that the bytes passed
1351 /// to it are valid UTF-8. If this constraint is violated, it may cause
1352 /// memory unsafety issues with future users of the `String`, as the rest of
1353 /// the standard library assumes that `String`s are valid UTF-8.
1360 /// let mut s = String::from("hello");
1363 /// let vec = s.as_mut_vec();
1364 /// assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1368 /// assert_eq!(s, "olleh");
1371 #[stable(feature = "rust1", since = "1.0.0")]
1372 pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1376 /// Returns the length of this `String`, in bytes, not [`char`]s or
1377 /// graphemes. In other words, it may not be what a human considers the
1378 /// length of the string.
1385 /// let a = String::from("foo");
1386 /// assert_eq!(a.len(), 3);
1388 /// let fancy_f = String::from("ƒoo");
1389 /// assert_eq!(fancy_f.len(), 4);
1390 /// assert_eq!(fancy_f.chars().count(), 3);
1392 #[doc(alias = "length")]
1394 #[stable(feature = "rust1", since = "1.0.0")]
1395 pub fn len(&self) -> usize {
1399 /// Returns `true` if this `String` has a length of zero, and `false` otherwise.
1406 /// let mut v = String::new();
1407 /// assert!(v.is_empty());
1410 /// assert!(!v.is_empty());
1413 #[stable(feature = "rust1", since = "1.0.0")]
1414 pub fn is_empty(&self) -> bool {
1418 /// Splits the string into two at the given byte index.
1420 /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1421 /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1422 /// boundary of a UTF-8 code point.
1424 /// Note that the capacity of `self` does not change.
1428 /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1429 /// code point of the string.
1435 /// let mut hello = String::from("Hello, World!");
1436 /// let world = hello.split_off(7);
1437 /// assert_eq!(hello, "Hello, ");
1438 /// assert_eq!(world, "World!");
1442 #[stable(feature = "string_split_off", since = "1.16.0")]
1443 #[must_use = "use `.truncate()` if you don't need the other half"]
1444 pub fn split_off(&mut self, at: usize) -> String {
1445 assert!(self.is_char_boundary(at));
1446 let other = self.vec.split_off(at);
1447 unsafe { String::from_utf8_unchecked(other) }
1450 /// Truncates this `String`, removing all contents.
1452 /// While this means the `String` will have a length of zero, it does not
1453 /// touch its capacity.
1460 /// let mut s = String::from("foo");
1464 /// assert!(s.is_empty());
1465 /// assert_eq!(0, s.len());
1466 /// assert_eq!(3, s.capacity());
1469 #[stable(feature = "rust1", since = "1.0.0")]
1470 pub fn clear(&mut self) {
1474 /// Creates a draining iterator that removes the specified range in the `String`
1475 /// and yields the removed `chars`.
1477 /// Note: The element range is removed even if the iterator is not
1478 /// consumed until the end.
1482 /// Panics if the starting point or end point do not lie on a [`char`]
1483 /// boundary, or if they're out of bounds.
1490 /// let mut s = String::from("α is alpha, β is beta");
1491 /// let beta_offset = s.find('β').unwrap_or(s.len());
1493 /// // Remove the range up until the β from the string
1494 /// let t: String = s.drain(..beta_offset).collect();
1495 /// assert_eq!(t, "α is alpha, ");
1496 /// assert_eq!(s, "β is beta");
1498 /// // A full range clears the string
1500 /// assert_eq!(s, "");
1502 #[stable(feature = "drain", since = "1.6.0")]
1503 pub fn drain<R>(&mut self, range: R) -> Drain<'_>
1505 R: RangeBounds<usize>,
1509 // The String version of Drain does not have the memory safety issues
1510 // of the vector version. The data is just plain bytes.
1511 // Because the range removal happens in Drop, if the Drain iterator is leaked,
1512 // the removal will not happen.
1513 let Range { start, end } = range.assert_len(self.len());
1514 assert!(self.is_char_boundary(start));
1515 assert!(self.is_char_boundary(end));
1517 // Take out two simultaneous borrows. The &mut String won't be accessed
1518 // until iteration is over, in Drop.
1519 let self_ptr = self as *mut _;
1520 // SAFETY: `assert_len` and `is_char_boundary` do the appropriate bounds checks.
1521 let chars_iter = unsafe { self.get_unchecked(start..end) }.chars();
1523 Drain { start, end, iter: chars_iter, string: self_ptr }
1526 /// Removes the specified range in the string,
1527 /// and replaces it with the given string.
1528 /// The given string doesn't need to be the same length as the range.
1532 /// Panics if the starting point or end point do not lie on a [`char`]
1533 /// boundary, or if they're out of bounds.
1540 /// let mut s = String::from("α is alpha, β is beta");
1541 /// let beta_offset = s.find('β').unwrap_or(s.len());
1543 /// // Replace the range up until the β from the string
1544 /// s.replace_range(..beta_offset, "Α is capital alpha; ");
1545 /// assert_eq!(s, "Α is capital alpha; β is beta");
1547 #[stable(feature = "splice", since = "1.27.0")]
1548 pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
1550 R: RangeBounds<usize>,
1554 // Replace_range does not have the memory safety issues of a vector Splice.
1555 // of the vector version. The data is just plain bytes.
1557 // WARNING: Inlining this variable would be unsound (#81138)
1558 let start = range.start_bound();
1560 Included(&n) => assert!(self.is_char_boundary(n)),
1561 Excluded(&n) => assert!(self.is_char_boundary(n + 1)),
1564 // WARNING: Inlining this variable would be unsound (#81138)
1565 let end = range.end_bound();
1567 Included(&n) => assert!(self.is_char_boundary(n + 1)),
1568 Excluded(&n) => assert!(self.is_char_boundary(n)),
1572 // Using `range` again would be unsound (#81138)
1573 // We assume the bounds reported by `range` remain the same, but
1574 // an adversarial implementation could change between calls
1575 unsafe { self.as_mut_vec() }.splice((start, end), replace_with.bytes());
1578 /// Converts this `String` into a [`Box`]`<`[`str`]`>`.
1580 /// This will drop any excess capacity.
1582 /// [`str`]: prim@str
1589 /// let s = String::from("hello");
1591 /// let b = s.into_boxed_str();
1593 #[stable(feature = "box_str", since = "1.4.0")]
1595 pub fn into_boxed_str(self) -> Box<str> {
1596 let slice = self.vec.into_boxed_slice();
1597 unsafe { from_boxed_utf8_unchecked(slice) }
1601 impl FromUtf8Error {
1602 /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1609 /// // some invalid bytes, in a vector
1610 /// let bytes = vec![0, 159];
1612 /// let value = String::from_utf8(bytes);
1614 /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1616 #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")]
1617 pub fn as_bytes(&self) -> &[u8] {
1621 /// Returns the bytes that were attempted to convert to a `String`.
1623 /// This method is carefully constructed to avoid allocation. It will
1624 /// consume the error, moving out the bytes, so that a copy of the bytes
1625 /// does not need to be made.
1632 /// // some invalid bytes, in a vector
1633 /// let bytes = vec![0, 159];
1635 /// let value = String::from_utf8(bytes);
1637 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1639 #[stable(feature = "rust1", since = "1.0.0")]
1640 pub fn into_bytes(self) -> Vec<u8> {
1644 /// Fetch a `Utf8Error` to get more details about the conversion failure.
1646 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1647 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1648 /// an analogue to `FromUtf8Error`. See its documentation for more details
1651 /// [`std::str`]: core::str
1652 /// [`&str`]: prim@str
1659 /// // some invalid bytes, in a vector
1660 /// let bytes = vec![0, 159];
1662 /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1664 /// // the first byte is invalid here
1665 /// assert_eq!(1, error.valid_up_to());
1667 #[stable(feature = "rust1", since = "1.0.0")]
1668 pub fn utf8_error(&self) -> Utf8Error {
1673 #[stable(feature = "rust1", since = "1.0.0")]
1674 impl fmt::Display for FromUtf8Error {
1675 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1676 fmt::Display::fmt(&self.error, f)
1680 #[stable(feature = "rust1", since = "1.0.0")]
1681 impl fmt::Display for FromUtf16Error {
1682 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1683 fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
1687 #[stable(feature = "rust1", since = "1.0.0")]
1688 impl Clone for String {
1689 fn clone(&self) -> Self {
1690 String { vec: self.vec.clone() }
1693 fn clone_from(&mut self, source: &Self) {
1694 self.vec.clone_from(&source.vec);
1698 #[stable(feature = "rust1", since = "1.0.0")]
1699 impl FromIterator<char> for String {
1700 fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
1701 let mut buf = String::new();
1707 #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
1708 impl<'a> FromIterator<&'a char> for String {
1709 fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
1710 let mut buf = String::new();
1716 #[stable(feature = "rust1", since = "1.0.0")]
1717 impl<'a> FromIterator<&'a str> for String {
1718 fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
1719 let mut buf = String::new();
1725 #[stable(feature = "extend_string", since = "1.4.0")]
1726 impl FromIterator<String> for String {
1727 fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
1728 let mut iterator = iter.into_iter();
1730 // Because we're iterating over `String`s, we can avoid at least
1731 // one allocation by getting the first string from the iterator
1732 // and appending to it all the subsequent strings.
1733 match iterator.next() {
1734 None => String::new(),
1736 buf.extend(iterator);
1743 #[stable(feature = "box_str2", since = "1.45.0")]
1744 impl FromIterator<Box<str>> for String {
1745 fn from_iter<I: IntoIterator<Item = Box<str>>>(iter: I) -> String {
1746 let mut buf = String::new();
1752 #[stable(feature = "herd_cows", since = "1.19.0")]
1753 impl<'a> FromIterator<Cow<'a, str>> for String {
1754 fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
1755 let mut iterator = iter.into_iter();
1757 // Because we're iterating over CoWs, we can (potentially) avoid at least
1758 // one allocation by getting the first item and appending to it all the
1759 // subsequent items.
1760 match iterator.next() {
1761 None => String::new(),
1763 let mut buf = cow.into_owned();
1764 buf.extend(iterator);
1771 #[stable(feature = "rust1", since = "1.0.0")]
1772 impl Extend<char> for String {
1773 fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
1774 let iterator = iter.into_iter();
1775 let (lower_bound, _) = iterator.size_hint();
1776 self.reserve(lower_bound);
1777 iterator.for_each(move |c| self.push(c));
1781 fn extend_one(&mut self, c: char) {
1786 fn extend_reserve(&mut self, additional: usize) {
1787 self.reserve(additional);
1791 #[stable(feature = "extend_ref", since = "1.2.0")]
1792 impl<'a> Extend<&'a char> for String {
1793 fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
1794 self.extend(iter.into_iter().cloned());
1798 fn extend_one(&mut self, &c: &'a char) {
1803 fn extend_reserve(&mut self, additional: usize) {
1804 self.reserve(additional);
1808 #[stable(feature = "rust1", since = "1.0.0")]
1809 impl<'a> Extend<&'a str> for String {
1810 fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
1811 iter.into_iter().for_each(move |s| self.push_str(s));
1815 fn extend_one(&mut self, s: &'a str) {
1820 #[stable(feature = "box_str2", since = "1.45.0")]
1821 impl Extend<Box<str>> for String {
1822 fn extend<I: IntoIterator<Item = Box<str>>>(&mut self, iter: I) {
1823 iter.into_iter().for_each(move |s| self.push_str(&s));
1827 #[stable(feature = "extend_string", since = "1.4.0")]
1828 impl Extend<String> for String {
1829 fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
1830 iter.into_iter().for_each(move |s| self.push_str(&s));
1834 fn extend_one(&mut self, s: String) {
1839 #[stable(feature = "herd_cows", since = "1.19.0")]
1840 impl<'a> Extend<Cow<'a, str>> for String {
1841 fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
1842 iter.into_iter().for_each(move |s| self.push_str(&s));
1846 fn extend_one(&mut self, s: Cow<'a, str>) {
1851 /// A convenience impl that delegates to the impl for `&str`.
1856 /// assert_eq!(String::from("Hello world").find("world"), Some(6));
1859 feature = "pattern",
1860 reason = "API not fully fleshed out and ready to be stabilized",
1863 impl<'a, 'b> Pattern<'a> for &'b String {
1864 type Searcher = <&'b str as Pattern<'a>>::Searcher;
1866 fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
1867 self[..].into_searcher(haystack)
1871 fn is_contained_in(self, haystack: &'a str) -> bool {
1872 self[..].is_contained_in(haystack)
1876 fn is_prefix_of(self, haystack: &'a str) -> bool {
1877 self[..].is_prefix_of(haystack)
1881 fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str> {
1882 self[..].strip_prefix_of(haystack)
1886 fn is_suffix_of(self, haystack: &'a str) -> bool {
1887 self[..].is_suffix_of(haystack)
1891 fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str> {
1892 self[..].strip_suffix_of(haystack)
1896 #[stable(feature = "rust1", since = "1.0.0")]
1897 impl PartialEq for String {
1899 fn eq(&self, other: &String) -> bool {
1900 PartialEq::eq(&self[..], &other[..])
1903 fn ne(&self, other: &String) -> bool {
1904 PartialEq::ne(&self[..], &other[..])
1908 macro_rules! impl_eq {
1909 ($lhs:ty, $rhs: ty) => {
1910 #[stable(feature = "rust1", since = "1.0.0")]
1911 #[allow(unused_lifetimes)]
1912 impl<'a, 'b> PartialEq<$rhs> for $lhs {
1914 fn eq(&self, other: &$rhs) -> bool {
1915 PartialEq::eq(&self[..], &other[..])
1918 fn ne(&self, other: &$rhs) -> bool {
1919 PartialEq::ne(&self[..], &other[..])
1923 #[stable(feature = "rust1", since = "1.0.0")]
1924 #[allow(unused_lifetimes)]
1925 impl<'a, 'b> PartialEq<$lhs> for $rhs {
1927 fn eq(&self, other: &$lhs) -> bool {
1928 PartialEq::eq(&self[..], &other[..])
1931 fn ne(&self, other: &$lhs) -> bool {
1932 PartialEq::ne(&self[..], &other[..])
1938 impl_eq! { String, str }
1939 impl_eq! { String, &'a str }
1940 impl_eq! { Cow<'a, str>, str }
1941 impl_eq! { Cow<'a, str>, &'b str }
1942 impl_eq! { Cow<'a, str>, String }
1944 #[stable(feature = "rust1", since = "1.0.0")]
1945 impl Default for String {
1946 /// Creates an empty `String`.
1948 fn default() -> String {
1953 #[stable(feature = "rust1", since = "1.0.0")]
1954 impl fmt::Display for String {
1956 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1957 fmt::Display::fmt(&**self, f)
1961 #[stable(feature = "rust1", since = "1.0.0")]
1962 impl fmt::Debug for String {
1964 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1965 fmt::Debug::fmt(&**self, f)
1969 #[stable(feature = "rust1", since = "1.0.0")]
1970 impl hash::Hash for String {
1972 fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
1973 (**self).hash(hasher)
1977 /// Implements the `+` operator for concatenating two strings.
1979 /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
1980 /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
1981 /// every operation, which would lead to *O*(*n*^2) running time when building an *n*-byte string by
1982 /// repeated concatenation.
1984 /// The string on the right-hand side is only borrowed; its contents are copied into the returned
1989 /// Concatenating two `String`s takes the first by value and borrows the second:
1992 /// let a = String::from("hello");
1993 /// let b = String::from(" world");
1995 /// // `a` is moved and can no longer be used here.
1998 /// If you want to keep using the first `String`, you can clone it and append to the clone instead:
2001 /// let a = String::from("hello");
2002 /// let b = String::from(" world");
2003 /// let c = a.clone() + &b;
2004 /// // `a` is still valid here.
2007 /// Concatenating `&str` slices can be done by converting the first to a `String`:
2010 /// let a = "hello";
2011 /// let b = " world";
2012 /// let c = a.to_string() + b;
2014 #[stable(feature = "rust1", since = "1.0.0")]
2015 impl Add<&str> for String {
2016 type Output = String;
2019 fn add(mut self, other: &str) -> String {
2020 self.push_str(other);
2025 /// Implements the `+=` operator for appending to a `String`.
2027 /// This has the same behavior as the [`push_str`][String::push_str] method.
2028 #[stable(feature = "stringaddassign", since = "1.12.0")]
2029 impl AddAssign<&str> for String {
2031 fn add_assign(&mut self, other: &str) {
2032 self.push_str(other);
2036 #[stable(feature = "rust1", since = "1.0.0")]
2037 impl ops::Index<ops::Range<usize>> for String {
2041 fn index(&self, index: ops::Range<usize>) -> &str {
2045 #[stable(feature = "rust1", since = "1.0.0")]
2046 impl ops::Index<ops::RangeTo<usize>> for String {
2050 fn index(&self, index: ops::RangeTo<usize>) -> &str {
2054 #[stable(feature = "rust1", since = "1.0.0")]
2055 impl ops::Index<ops::RangeFrom<usize>> for String {
2059 fn index(&self, index: ops::RangeFrom<usize>) -> &str {
2063 #[stable(feature = "rust1", since = "1.0.0")]
2064 impl ops::Index<ops::RangeFull> for String {
2068 fn index(&self, _index: ops::RangeFull) -> &str {
2069 unsafe { str::from_utf8_unchecked(&self.vec) }
2072 #[stable(feature = "inclusive_range", since = "1.26.0")]
2073 impl ops::Index<ops::RangeInclusive<usize>> for String {
2077 fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
2078 Index::index(&**self, index)
2081 #[stable(feature = "inclusive_range", since = "1.26.0")]
2082 impl ops::Index<ops::RangeToInclusive<usize>> for String {
2086 fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
2087 Index::index(&**self, index)
2091 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2092 impl ops::IndexMut<ops::Range<usize>> for String {
2094 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
2095 &mut self[..][index]
2098 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2099 impl ops::IndexMut<ops::RangeTo<usize>> for String {
2101 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
2102 &mut self[..][index]
2105 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2106 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
2108 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
2109 &mut self[..][index]
2112 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2113 impl ops::IndexMut<ops::RangeFull> for String {
2115 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
2116 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2119 #[stable(feature = "inclusive_range", since = "1.26.0")]
2120 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
2122 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
2123 IndexMut::index_mut(&mut **self, index)
2126 #[stable(feature = "inclusive_range", since = "1.26.0")]
2127 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
2129 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
2130 IndexMut::index_mut(&mut **self, index)
2134 #[stable(feature = "rust1", since = "1.0.0")]
2135 impl ops::Deref for String {
2139 fn deref(&self) -> &str {
2140 unsafe { str::from_utf8_unchecked(&self.vec) }
2144 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
2145 impl ops::DerefMut for String {
2147 fn deref_mut(&mut self) -> &mut str {
2148 unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
2152 /// A type alias for [`Infallible`].
2154 /// This alias exists for backwards compatibility, and may be eventually deprecated.
2156 /// [`Infallible`]: core::convert::Infallible
2157 #[stable(feature = "str_parse_error", since = "1.5.0")]
2158 pub type ParseError = core::convert::Infallible;
2160 #[stable(feature = "rust1", since = "1.0.0")]
2161 impl FromStr for String {
2162 type Err = core::convert::Infallible;
2164 fn from_str(s: &str) -> Result<String, Self::Err> {
2169 /// A trait for converting a value to a `String`.
2171 /// This trait is automatically implemented for any type which implements the
2172 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
2173 /// [`Display`] should be implemented instead, and you get the `ToString`
2174 /// implementation for free.
2176 /// [`Display`]: fmt::Display
2177 #[cfg_attr(not(test), rustc_diagnostic_item = "ToString")]
2178 #[stable(feature = "rust1", since = "1.0.0")]
2179 pub trait ToString {
2180 /// Converts the given value to a `String`.
2188 /// let five = String::from("5");
2190 /// assert_eq!(five, i.to_string());
2192 #[rustc_conversion_suggestion]
2193 #[stable(feature = "rust1", since = "1.0.0")]
2194 fn to_string(&self) -> String;
2199 /// In this implementation, the `to_string` method panics
2200 /// if the `Display` implementation returns an error.
2201 /// This indicates an incorrect `Display` implementation
2202 /// since `fmt::Write for String` never returns an error itself.
2203 #[stable(feature = "rust1", since = "1.0.0")]
2204 impl<T: fmt::Display + ?Sized> ToString for T {
2205 // A common guideline is to not inline generic functions. However,
2206 // removing `#[inline]` from this method causes non-negligible regressions.
2207 // See <https://github.com/rust-lang/rust/pull/74852>, the last attempt
2208 // to try to remove it.
2210 default fn to_string(&self) -> String {
2212 let mut buf = String::new();
2213 buf.write_fmt(format_args!("{}", self))
2214 .expect("a Display implementation returned an error unexpectedly");
2219 #[stable(feature = "char_to_string_specialization", since = "1.46.0")]
2220 impl ToString for char {
2222 fn to_string(&self) -> String {
2223 String::from(self.encode_utf8(&mut [0; 4]))
2227 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
2228 impl ToString for str {
2230 fn to_string(&self) -> String {
2235 #[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
2236 impl ToString for Cow<'_, str> {
2238 fn to_string(&self) -> String {
2243 #[stable(feature = "string_to_string_specialization", since = "1.17.0")]
2244 impl ToString for String {
2246 fn to_string(&self) -> String {
2251 #[stable(feature = "rust1", since = "1.0.0")]
2252 impl AsRef<str> for String {
2254 fn as_ref(&self) -> &str {
2259 #[stable(feature = "string_as_mut", since = "1.43.0")]
2260 impl AsMut<str> for String {
2262 fn as_mut(&mut self) -> &mut str {
2267 #[stable(feature = "rust1", since = "1.0.0")]
2268 impl AsRef<[u8]> for String {
2270 fn as_ref(&self) -> &[u8] {
2275 #[stable(feature = "rust1", since = "1.0.0")]
2276 impl From<&str> for String {
2278 fn from(s: &str) -> String {
2283 #[stable(feature = "from_mut_str_for_string", since = "1.44.0")]
2284 impl From<&mut str> for String {
2285 /// Converts a `&mut str` into a `String`.
2287 /// The result is allocated on the heap.
2289 fn from(s: &mut str) -> String {
2294 #[stable(feature = "from_ref_string", since = "1.35.0")]
2295 impl From<&String> for String {
2297 fn from(s: &String) -> String {
2302 // note: test pulls in libstd, which causes errors here
2304 #[stable(feature = "string_from_box", since = "1.18.0")]
2305 impl From<Box<str>> for String {
2306 /// Converts the given boxed `str` slice to a `String`.
2307 /// It is notable that the `str` slice is owned.
2314 /// let s1: String = String::from("hello world");
2315 /// let s2: Box<str> = s1.into_boxed_str();
2316 /// let s3: String = String::from(s2);
2318 /// assert_eq!("hello world", s3)
2320 fn from(s: Box<str>) -> String {
2325 #[stable(feature = "box_from_str", since = "1.20.0")]
2326 impl From<String> for Box<str> {
2327 /// Converts the given `String` to a boxed `str` slice that is owned.
2334 /// let s1: String = String::from("hello world");
2335 /// let s2: Box<str> = Box::from(s1);
2336 /// let s3: String = String::from(s2);
2338 /// assert_eq!("hello world", s3)
2340 fn from(s: String) -> Box<str> {
2345 #[stable(feature = "string_from_cow_str", since = "1.14.0")]
2346 impl<'a> From<Cow<'a, str>> for String {
2347 fn from(s: Cow<'a, str>) -> String {
2352 #[stable(feature = "rust1", since = "1.0.0")]
2353 impl<'a> From<&'a str> for Cow<'a, str> {
2355 fn from(s: &'a str) -> Cow<'a, str> {
2360 #[stable(feature = "rust1", since = "1.0.0")]
2361 impl<'a> From<String> for Cow<'a, str> {
2363 fn from(s: String) -> Cow<'a, str> {
2368 #[stable(feature = "cow_from_string_ref", since = "1.28.0")]
2369 impl<'a> From<&'a String> for Cow<'a, str> {
2371 fn from(s: &'a String) -> Cow<'a, str> {
2372 Cow::Borrowed(s.as_str())
2376 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2377 impl<'a> FromIterator<char> for Cow<'a, str> {
2378 fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
2379 Cow::Owned(FromIterator::from_iter(it))
2383 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2384 impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
2385 fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
2386 Cow::Owned(FromIterator::from_iter(it))
2390 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2391 impl<'a> FromIterator<String> for Cow<'a, str> {
2392 fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
2393 Cow::Owned(FromIterator::from_iter(it))
2397 #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
2398 impl From<String> for Vec<u8> {
2399 /// Converts the given `String` to a vector `Vec` that holds values of type `u8`.
2406 /// let s1 = String::from("hello world");
2407 /// let v1 = Vec::from(s1);
2410 /// println!("{}", b);
2413 fn from(string: String) -> Vec<u8> {
2418 #[stable(feature = "rust1", since = "1.0.0")]
2419 impl fmt::Write for String {
2421 fn write_str(&mut self, s: &str) -> fmt::Result {
2427 fn write_char(&mut self, c: char) -> fmt::Result {
2433 /// A draining iterator for `String`.
2435 /// This struct is created by the [`drain`] method on [`String`]. See its
2436 /// documentation for more.
2438 /// [`drain`]: String::drain
2439 #[stable(feature = "drain", since = "1.6.0")]
2440 pub struct Drain<'a> {
2441 /// Will be used as &'a mut String in the destructor
2442 string: *mut String,
2443 /// Start of part to remove
2445 /// End of part to remove
2447 /// Current remaining range to remove
2451 #[stable(feature = "collection_debug", since = "1.17.0")]
2452 impl fmt::Debug for Drain<'_> {
2453 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2454 f.debug_tuple("Drain").field(&self.as_str()).finish()
2458 #[stable(feature = "drain", since = "1.6.0")]
2459 unsafe impl Sync for Drain<'_> {}
2460 #[stable(feature = "drain", since = "1.6.0")]
2461 unsafe impl Send for Drain<'_> {}
2463 #[stable(feature = "drain", since = "1.6.0")]
2464 impl Drop for Drain<'_> {
2465 fn drop(&mut self) {
2467 // Use Vec::drain. "Reaffirm" the bounds checks to avoid
2468 // panic code being inserted again.
2469 let self_vec = (*self.string).as_mut_vec();
2470 if self.start <= self.end && self.end <= self_vec.len() {
2471 self_vec.drain(self.start..self.end);
2477 impl<'a> Drain<'a> {
2478 /// Returns the remaining (sub)string of this iterator as a slice.
2483 /// #![feature(string_drain_as_str)]
2484 /// let mut s = String::from("abc");
2485 /// let mut drain = s.drain(..);
2486 /// assert_eq!(drain.as_str(), "abc");
2487 /// let _ = drain.next().unwrap();
2488 /// assert_eq!(drain.as_str(), "bc");
2490 #[unstable(feature = "string_drain_as_str", issue = "76905")] // Note: uncomment AsRef impls below when stabilizing.
2491 pub fn as_str(&self) -> &str {
2496 // Uncomment when stabilizing `string_drain_as_str`.
2497 // #[unstable(feature = "string_drain_as_str", issue = "76905")]
2498 // impl<'a> AsRef<str> for Drain<'a> {
2499 // fn as_ref(&self) -> &str {
2504 // #[unstable(feature = "string_drain_as_str", issue = "76905")]
2505 // impl<'a> AsRef<[u8]> for Drain<'a> {
2506 // fn as_ref(&self) -> &[u8] {
2507 // self.as_str().as_bytes()
2511 #[stable(feature = "drain", since = "1.6.0")]
2512 impl Iterator for Drain<'_> {
2516 fn next(&mut self) -> Option<char> {
2520 fn size_hint(&self) -> (usize, Option<usize>) {
2521 self.iter.size_hint()
2525 fn last(mut self) -> Option<char> {
2530 #[stable(feature = "drain", since = "1.6.0")]
2531 impl DoubleEndedIterator for Drain<'_> {
2533 fn next_back(&mut self) -> Option<char> {
2534 self.iter.next_back()
2538 #[stable(feature = "fused", since = "1.26.0")]
2539 impl FusedIterator for Drain<'_> {}
2541 #[stable(feature = "from_char_for_string", since = "1.46.0")]
2542 impl From<char> for String {
2544 fn from(c: char) -> Self {