alloc::string::String - Rust
Description: API documentation for the Rust `String` struct in crate `alloc`.
Keywords: rust, rustlang, rust-lang, String

# 1.0.0[−][src]Struct alloc::string::String

    pub struct String { /* fields omitted */ }

A UTF-8 encoded, growable string.

The `String` type is the most common string type that has ownership over the contents of the string. It has a close relationship with its borrowed counterpart, the primitive `str`.

# Examples

You can create a `String` from a literal string with `String::from`:

    let hello = String::from("Hello, world!");

You can append a `char` to a `String` with the `push` method, and append a `&str` with the `push_str` method:

    let mut hello = String::from("Hello, ");

    hello.push('w');
    hello.push_str("orld!");

If you have a vector of UTF-8 bytes, you can create a `String` from it with the `from_utf8` method:

    // some bytes, in a vector
    let sparkle_heart = vec![240, 159, 146, 150];

    // We know these bytes are valid, so we'll use `unwrap()`.
    let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();

    assert_eq!("💖", sparkle_heart);

# UTF-8

`String`s are always valid UTF-8. This has a few implications, the first of which is that if you need a non-UTF-8 string, consider `OsString`. It is similar, but without the UTF-8 constraint. The second implication is that you cannot index into a `String`:

ⓘThis example deliberately fails to compile

    let s = "hello";

    println!("The first letter of s is {}", s[0]); // ERROR!!!

Indexing is intended to be a constant-time operation, but UTF-8 encoding does not allow us to do this. Furthermore, it's not clear what sort of thing the index should return: a byte, a codepoint, or a grapheme cluster. The `bytes` and `chars` methods return iterators over the first two, respectively.

# Deref

`String`s implement `Deref``<Target=str>`, and so inherit all of `str`'s methods. In addition, this means that you can pass a `String` to a function which takes a `&str` by using an ampersand (`&`):

    fn takes_str(s: &str) { }

    let s = String::from("Hello");

    takes_str(&s);

This will create a `&str` from the `String` and pass it in. This conversion is very inexpensive, and so generally, functions will accept `&str`s as arguments unless they need a `String` for some specific reason.

In certain cases Rust doesn't have enough information to make this conversion, known as `Deref` coercion. In the following example a string slice `&'a str` implements the trait `TraitExample`, and the function `example_func` takes anything that implements the trait. In this case Rust would need to make two implicit conversions, which Rust doesn't have the means to do. For that reason, the following example will not compile.

ⓘThis example deliberately fails to compile

    trait TraitExample {}

    impl<'a> TraitExample for &'a str {}

    fn example_func<A: TraitExample>(example_arg: A) {}

    fn main() {
        let example_string = String::from("example_string");
        example_func(&example_string);
    }

There are two options that would work instead. The first would be to change the line `example_func(&example_string);` to `example_func(example_string.as_str());`, using the method `as_str()` to explicitly extract the string slice containing the string. The second way changes `example_func(&example_string);` to `example_func(&*example_string);`. In this case we are dereferencing a `String` to a `str`, then referencing the `str` back to `&str`. The second way is more idiomatic, however both work to do the conversion explicitly rather than relying on the implicit conversion.

# Representation

A `String` is made up of three components: a pointer to some bytes, a length, and a capacity. The pointer points to an internal buffer `String` uses to store its data. The length is the number of bytes currently stored in the buffer, and the capacity is the size of the buffer in bytes. As such, the length will always be less than or equal to the capacity.

This buffer is always stored on the heap.

You can look at these with the `as_ptr`, `len`, and `capacity` methods:

    use std::mem;

    let story = String::from("Once upon a time...");

    let ptr = story.as_ptr();
    let len = story.len();
    let capacity = story.capacity();

    // story has nineteen bytes
    assert_eq!(19, len);

    // Now that we have our parts, we throw the story away.
    mem::forget(story);

    // We can re-build a String out of ptr, len, and capacity. This is all
    // unsafe because we are responsible for making sure the components are
    // valid:
    let s = unsafe { String::from_raw_parts(ptr as *mut _, len, capacity) } ;

    assert_eq!(String::from("Once upon a time..."), s);

If a `String` has enough capacity, adding elements to it will not re-allocate. For example, consider this program:

    let mut s = String::new();

    println!("{}", s.capacity());

    for _ in 0..5 {
        s.push_str("hello");
        println!("{}", s.capacity());
    }

This will output the following:

    0
    5
    10
    20
    20
    40

At first, we have no memory allocated at all, but as we append to the string, it increases its capacity appropriately. If we instead use the `with_capacity` method to allocate the correct capacity initially:

    let mut s = String::with_capacity(25);

    println!("{}", s.capacity());

    for _ in 0..5 {
        s.push_str("hello");
        println!("{}", s.capacity());
    }

We end up with a different output:

    25
    25
    25
    25
    25
    25

Here, there's no need to allocate more memory inside the loop.

## Methods

### `impl String`[src]

#### `pub const fn new() -> String`[src]

Creates a new empty `String`.

Given that the `String` is empty, this will not allocate any initial buffer. While that means that this initial operation is very inexpensive, it may cause excessive allocation later when you add data. If you have an idea of how much data the `String` will hold, consider the `with_capacity` method to prevent excessive re-allocation.

# Examples

Basic usage:

    let s = String::new();

#### `pub fn with_capacity(capacity: usize) -> String`[src]

Creates a new empty `String` with a particular capacity.

`String`s have an internal buffer to hold their data. The capacity is the length of that buffer, and can be queried with the `capacity` method. This method creates an empty `String`, but one with an initial buffer that can hold `capacity` bytes. This is useful when you may be appending a bunch of data to the `String`, reducing the number of reallocations it needs to do.

If the given capacity is `0`, no allocation will occur, and this method is identical to the `new` method.

# Examples

Basic usage:

    let mut s = String::with_capacity(10);

    // The String contains no chars, even though it has capacity for more
    assert_eq!(s.len(), 0);

    // These are all done without reallocating...
    let cap = s.capacity();
    for _ in 0..10 {
        s.push('a');
    }

    assert_eq!(s.capacity(), cap);

    // ...but this may make the vector reallocate
    s.push('a');

#### `pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error>`[src]

Converts a vector of bytes to a `String`.

A string slice (`&str`) is made of bytes (`u8`), and a vector of bytes (`Vec<u8>`) is made of bytes, so this function converts between the two. Not all byte slices are valid `String`s, however: `String` requires that it is valid UTF-8. `from_utf8()` checks to ensure that the bytes are valid UTF-8, and then does the conversion.

If you are sure that the byte slice is valid UTF-8, and you don't want to incur the overhead of the validity check, there is an unsafe version of this function, `from_utf8_unchecked`, which has the same behavior but skips the check.

This method will take care to not copy the vector, for efficiency's sake.

If you need a `&str` instead of a `String`, consider `str::from_utf8`.

The inverse of this method is `as_bytes`.

# Errors

Returns `Err` if the slice is not UTF-8 with a description as to why the provided bytes are not UTF-8. The vector you moved in is also included.

# Examples

Basic usage:

    // some bytes, in a vector
    let sparkle_heart = vec![240, 159, 146, 150];

    // We know these bytes are valid, so we'll use `unwrap()`.
    let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();

    assert_eq!("💖", sparkle_heart);

Incorrect bytes:

    // some invalid bytes, in a vector
    let sparkle_heart = vec![0, 159, 146, 150];

    assert!(String::from_utf8(sparkle_heart).is_err());

See the docs for `FromUtf8Error` for more details on what you can do with this error.

#### `pub fn from_utf8_lossy(v: &[u8]) -> Cow<str>`[src]

Converts a slice of bytes to a string, including invalid characters.

Strings are made of bytes (`u8`), and a slice of bytes (`&[u8]`) is made of bytes, so this function converts between the two. Not all byte slices are valid strings, however: strings are required to be valid UTF-8. During this conversion, `from_utf8_lossy()` will replace any invalid UTF-8 sequences with `U+FFFD REPLACEMENT CHARACTER`, which looks like this: �

If you are sure that the byte slice is valid UTF-8, and you don't want to incur the overhead of the conversion, there is an unsafe version of this function, `from_utf8_unchecked`, which has the same behavior but skips the checks.

This function returns a `Cow<'a, str>`. If our byte slice is invalid UTF-8, then we need to insert the replacement characters, which will change the size of the string, and hence, require a `String`. But if it's already valid UTF-8, we don't need a new allocation. This return type allows us to handle both cases.

# Examples

Basic usage:

    // some bytes, in a vector
    let sparkle_heart = vec![240, 159, 146, 150];

    let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);

    assert_eq!("💖", sparkle_heart);

Incorrect bytes:

    // some invalid bytes
    let input = b"Hello \xF0\x90\x80World";
    let output = String::from_utf8_lossy(input);

    assert_eq!("Hello �World", output);

#### `pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error>`[src]

Decode a UTF-16 encoded vector `v` into a `String`, returning `Err` if `v` contains any invalid data.

# Examples

Basic usage:

    // 𝄞music
    let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
              0x0073, 0x0069, 0x0063];
    assert_eq!(String::from("𝄞music"),
               String::from_utf16(v).unwrap());

    // 𝄞mu<invalid>ic
    let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
              0xD800, 0x0069, 0x0063];
    assert!(String::from_utf16(v).is_err());

#### `pub fn from_utf16_lossy(v: &[u16]) -> String`[src]

Decode a UTF-16 encoded slice `v` into a `String`, replacing invalid data with the replacement character (`U+FFFD`).

Unlike `from_utf8_lossy` which returns a `Cow<'a, str>`, `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8 conversion requires a memory allocation.

# Examples

Basic usage:

    // 𝄞mus<invalid>ic<invalid>
    let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
              0x0073, 0xDD1E, 0x0069, 0x0063,
              0xD834];

    assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
               String::from_utf16_lossy(v));

#### `pub unsafe fn from_raw_parts(
buf: *mut u8,
length: usize,
capacity: usize
) -> String`[src]

Creates a new `String` from a length, capacity, and pointer.

# Safety

This is highly unsafe, due to the number of invariants that aren't checked:

- The memory at `ptr` needs to have been previously allocated by the same allocator the standard library uses.
- `length` needs to be less than or equal to `capacity`.
- `capacity` needs to be the correct value.

Violating these may cause problems like corrupting the allocator's internal data structures.

The ownership of `ptr` is effectively transferred to the `String` which may then deallocate, reallocate or change the contents of memory pointed to by the pointer at will. Ensure that nothing else uses the pointer after calling this function.

# Examples

Basic usage:

    use std::mem;

    unsafe {
        let s = String::from("hello");
        let ptr = s.as_ptr();
        let len = s.len();
        let capacity = s.capacity();

        mem::forget(s);

        let s = String::from_raw_parts(ptr as *mut _, len, capacity);

        assert_eq!(String::from("hello"), s);
    }

#### `pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String`[src]

Converts a vector of bytes to a `String` without checking that the string contains valid UTF-8.

See the safe version, `from_utf8`, for more details.

# Safety

This function is unsafe because it does not check that the bytes passed to it are valid UTF-8. If this constraint is violated, it may cause memory unsafety issues with future users of the `String`, as the rest of the standard library assumes that `String`s are valid UTF-8.

# Examples

Basic usage:

    // some bytes, in a vector
    let sparkle_heart = vec![240, 159, 146, 150];

    let sparkle_heart = unsafe {
        String::from_utf8_unchecked(sparkle_heart)
    };

    assert_eq!("💖", sparkle_heart);

#### `pub fn into_bytes(self) -> Vec<u8>`[src]

Converts a `String` into a byte vector.

This consumes the `String`, so we do not need to copy its contents.

# Examples

Basic usage:

    let s = String::from("hello");
    let bytes = s.into_bytes();

    assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);

#### `pub fn as_str(&self) -> &str`1.7.0[src]

Extracts a string slice containing the entire `String`.

# Examples

Basic usage:

    let s = String::from("foo");

    assert_eq!("foo", s.as_str());

#### `pub fn as_mut_str(&mut self) -> &mut str`1.7.0[src]

Converts a `String` into a mutable string slice.

# Examples

Basic usage:

    let mut s = String::from("foobar");
    let s_mut_str = s.as_mut_str();

    s_mut_str.make_ascii_uppercase();

    assert_eq!("FOOBAR", s_mut_str);

#### `pub fn push_str(&mut self, string: &str)`[src]

Appends a given string slice onto the end of this `String`.

# Examples

Basic usage:

    let mut s = String::from("foo");

    s.push_str("bar");

    assert_eq!("foobar", s);

#### `pub fn capacity(&self) -> usize`[src]

Returns this `String`'s capacity, in bytes.

# Examples

Basic usage:

    let s = String::with_capacity(10);

    assert!(s.capacity() >= 10);

#### `pub fn reserve(&mut self, additional: usize)`[src]

Ensures that this `String`'s capacity is at least `additional` bytes larger than its length.

The capacity may be increased by more than `additional` bytes if it chooses, to prevent frequent reallocations.

If you do not want this "at least" behavior, see the `reserve_exact` method.

# Panics

Panics if the new capacity overflows `usize`.

# Examples

Basic usage:

    let mut s = String::new();

    s.reserve(10);

    assert!(s.capacity() >= 10);

This may not actually increase the capacity:

    let mut s = String::with_capacity(10);
    s.push('a');
    s.push('b');

    // s now has a length of 2 and a capacity of 10
    assert_eq!(2, s.len());
    assert_eq!(10, s.capacity());

    // Since we already have an extra 8 capacity, calling this...
    s.reserve(8);

    // ... doesn't actually increase.
    assert_eq!(10, s.capacity());

#### `pub fn reserve_exact(&mut self, additional: usize)`[src]

Ensures that this `String`'s capacity is `additional` bytes larger than its length.

Consider using the `reserve` method unless you absolutely know better than the allocator.

# Panics

Panics if the new capacity overflows `usize`.

# Examples

Basic usage:

    let mut s = String::new();

    s.reserve_exact(10);

    assert!(s.capacity() >= 10);

This may not actually increase the capacity:

    let mut s = String::with_capacity(10);
    s.push('a');
    s.push('b');

    // s now has a length of 2 and a capacity of 10
    assert_eq!(2, s.len());
    assert_eq!(10, s.capacity());

    // Since we already have an extra 8 capacity, calling this...
    s.reserve_exact(8);

    // ... doesn't actually increase.
    assert_eq!(10, s.capacity());

#### `pub fn try_reserve(
&mut self,
additional: usize
) -> Result<(), CollectionAllocErr>`[src]

🔬 This is a nightly-only experimental API. (`try_reserve` #48043)

new API

Tries to reserve capacity for at least `additional` more elements to be inserted in the given `String`. The collection may reserve more space to avoid frequent reallocations. After calling `reserve`, capacity will be greater than or equal to `self.len() + additional`. Does nothing if capacity is already sufficient.

# Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

# Examples

    #![feature(try_reserve)]
    use std::collections::CollectionAllocErr;

    fn process_data(data: &str) -> Result<String, CollectionAllocErr> {
        let mut output = String::new();

        // Pre-reserve the memory, exiting if we can't
        output.try_reserve(data.len())?;

        // Now we know this can't OOM in the middle of our complex work
        output.push_str(data);

        Ok(output)
    }

#### `pub fn try_reserve_exact(
&mut self,
additional: usize
) -> Result<(), CollectionAllocErr>`[src]

🔬 This is a nightly-only experimental API. (`try_reserve` #48043)

new API

Tries to reserves the minimum capacity for exactly `additional` more elements to be inserted in the given `String`. After calling `reserve_exact`, capacity will be greater than or equal to `self.len() + additional`. Does nothing if the capacity is already sufficient.

Note that the allocator may give the collection more space than it requests. Therefore, capacity can not be relied upon to be precisely minimal. Prefer `reserve` if future insertions are expected.

# Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

# Examples

    #![feature(try_reserve)]
    use std::collections::CollectionAllocErr;

    fn process_data(data: &str) -> Result<String, CollectionAllocErr> {
        let mut output = String::new();

        // Pre-reserve the memory, exiting if we can't
        output.try_reserve(data.len())?;

        // Now we know this can't OOM in the middle of our complex work
        output.push_str(data);

        Ok(output)
    }

#### `pub fn shrink_to_fit(&mut self)`[src]

Shrinks the capacity of this `String` to match its length.

# Examples

Basic usage:

    let mut s = String::from("foo");

    s.reserve(100);
    assert!(s.capacity() >= 100);

    s.shrink_to_fit();
    assert_eq!(3, s.capacity());

#### `pub fn shrink_to(&mut self, min_capacity: usize)`[src]

🔬 This is a nightly-only experimental API. (`shrink_to` #56431)

new API

Shrinks the capacity of this `String` with a lower bound.

The capacity will remain at least as large as both the length and the supplied value.

Panics if the current capacity is smaller than the supplied minimum capacity.

# Examples

    #![feature(shrink_to)]
    let mut s = String::from("foo");

    s.reserve(100);
    assert!(s.capacity() >= 100);

    s.shrink_to(10);
    assert!(s.capacity() >= 10);
    s.shrink_to(0);
    assert!(s.capacity() >= 3);

#### `pub fn push(&mut self, ch: char)`[src]

Appends the given `char` to the end of this `String`.

# Examples

Basic usage:

    let mut s = String::from("abc");

    s.push('1');
    s.push('2');
    s.push('3');

    assert_eq!("abc123", s);

#### `pub fn as_bytes(&self) -> &[u8]`[src]

Returns a byte slice of this `String`'s contents.

The inverse of this method is `from_utf8`.

# Examples

Basic usage:

    let s = String::from("hello");

    assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());

#### `pub fn truncate(&mut self, new_len: usize)`[src]

Shortens this `String` to the specified length.

If `new_len` is greater than the string's current length, this has no effect.

Note that this method has no effect on the allocated capacity of the string

# Panics

Panics if `new_len` does not lie on a `char` boundary.

# Examples

Basic usage:

    let mut s = String::from("hello");

    s.truncate(2);

    assert_eq!("he", s);

#### `pub fn pop(&mut self) -> Option<char>`[src]

Removes the last character from the string buffer and returns it.

Returns `None` if this `String` is empty.

# Examples

Basic usage:

    let mut s = String::from("foo");

    assert_eq!(s.pop(), Some('o'));
    assert_eq!(s.pop(), Some('o'));
    assert_eq!(s.pop(), Some('f'));

    assert_eq!(s.pop(), None);

#### `pub fn remove(&mut self, idx: usize) -> char`[src]

Removes a `char` from this `String` at a byte position and returns it.

This is an `O(n)` operation, as it requires copying every element in the buffer.

# Panics

Panics if `idx` is larger than or equal to the `String`'s length, or if it does not lie on a `char` boundary.

# Examples

Basic usage:

    let mut s = String::from("foo");

    assert_eq!(s.remove(0), 'f');
    assert_eq!(s.remove(1), 'o');
    assert_eq!(s.remove(0), 'o');

#### `pub fn retain<F>(&mut self, f: F) where
F: FnMut(char) -> bool,` 1.26.0[src]

Retains only the characters specified by the predicate.

In other words, remove all characters `c` such that `f(c)` returns `false`. This method operates in place, visiting each character exactly once in the original order, and preserves the order of the retained characters.

# Examples

    let mut s = String::from("f_o_ob_ar");

    s.retain(|c| c != '_');

    assert_eq!(s, "foobar");

The exact order may be useful for tracking external state, like an index.

    let mut s = String::from("abcde");
    let keep = [false, true, true, false, true];
    let mut i = 0;
    s.retain(|_| (keep[i], i += 1).0);
    assert_eq!(s, "bce");

#### `pub fn insert(&mut self, idx: usize, ch: char)`[src]

Inserts a character into this `String` at a byte position.

This is an `O(n)` operation as it requires copying every element in the buffer.

# Panics

Panics if `idx` is larger than the `String`'s length, or if it does not lie on a `char` boundary.

# Examples

Basic usage:

    let mut s = String::with_capacity(3);

    s.insert(0, 'f');
    s.insert(1, 'o');
    s.insert(2, 'o');

    assert_eq!("foo", s);

#### `pub fn insert_str(&mut self, idx: usize, string: &str)`1.16.0[src]

Inserts a string slice into this `String` at a byte position.

This is an `O(n)` operation as it requires copying every element in the buffer.

# Panics

Panics if `idx` is larger than the `String`'s length, or if it does not lie on a `char` boundary.

# Examples

Basic usage:

    let mut s = String::from("bar");

    s.insert_str(0, "foo");

    assert_eq!("foobar", s);

#### `pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8>`[src]

Returns a mutable reference to the contents of this `String`.

# Safety

This function is unsafe because it does not check that the bytes passed to it are valid UTF-8. If this constraint is violated, it may cause memory unsafety issues with future users of the `String`, as the rest of the standard library assumes that `String`s are valid UTF-8.

# Examples

Basic usage:

    let mut s = String::from("hello");

    unsafe {
        let vec = s.as_mut_vec();
        assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);

        vec.reverse();
    }
    assert_eq!(s, "olleh");

#### `pub fn len(&self) -> usize`[src]

Returns the length of this `String`, in bytes.

# Examples

Basic usage:

    let a = String::from("foo");

    assert_eq!(a.len(), 3);

#### `pub fn is_empty(&self) -> bool`[src]

Returns `true` if this `String` has a length of zero, and `false` otherwise.

# Examples

Basic usage:

    let mut v = String::new();
    assert!(v.is_empty());

    v.push('a');
    assert!(!v.is_empty());

#### `pub fn split_off(&mut self, at: usize) -> String`1.16.0[src]

Splits the string into two at the given index.

Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and the returned `String` contains bytes `[at, len)`. `at` must be on the boundary of a UTF-8 code point.

Note that the capacity of `self` does not change.

# Panics

Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last code point of the string.

# Examples

    let mut hello = String::from("Hello, World!");
    let world = hello.split_off(7);
    assert_eq!(hello, "Hello, ");
    assert_eq!(world, "World!");

#### `pub fn clear(&mut self)`[src]

Truncates this `String`, removing all contents.

While this means the `String` will have a length of zero, it does not touch its capacity.

# Examples

Basic usage:

    let mut s = String::from("foo");

    s.clear();

    assert!(s.is_empty());
    assert_eq!(0, s.len());
    assert_eq!(3, s.capacity());

####
ⓘImportant traits for Drain<'_>

### Important traits for Drain<'_>

`impl<'_> Iterator for Drain<'_> type Item = char;`
`pub fn drain<R>(&mut self, range: R) -> Drain where
R: RangeBounds<usize>,` 1.6.0[src]

Creates a draining iterator that removes the specified range in the `String` and yields the removed `chars`.

Note: The element range is removed even if the iterator is not consumed until the end.

# Panics

Panics if the starting point or end point do not lie on a `char` boundary, or if they're out of bounds.

# Examples

Basic usage:

    let mut s = String::from("α is alpha, β is beta");
    let beta_offset = s.find('β').unwrap_or(s.len());

    // Remove the range up until the β from the string
    let t: String = s.drain(..beta_offset).collect();
    assert_eq!(t, "α is alpha, ");
    assert_eq!(s, "β is beta");

    // A full range clears the string
    s.drain(..);
    assert_eq!(s, "");

#### `pub fn replace_range<R>(&mut self, range: R, replace_with: &str) where
R: RangeBounds<usize>,` 1.27.0[src]

Removes the specified range in the string, and replaces it with the given string. The given string doesn't need to be the same length as the range.

# Panics

Panics if the starting point or end point do not lie on a `char` boundary, or if they're out of bounds.

# Examples

Basic usage:

    let mut s = String::from("α is alpha, β is beta");
    let beta_offset = s.find('β').unwrap_or(s.len());

    // Replace the range up until the β from the string
    s.replace_range(..beta_offset, "Α is capital alpha; ");
    assert_eq!(s, "Α is capital alpha; β is beta");

####
ⓘImportant traits for Box<I>

### Important traits for Box<I>

`impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;impl<I: Iterator + Sized> Iterator for Box<I>impl<F: ?Sized + Future + Unpin> Future for Box<F> type Output = F::Output;`
`pub fn into_boxed_str(self) -> Box<str>`1.4.0[src]

Converts this `String` into a `Box``<``str``>`.

This will drop any excess capacity.

# Examples

Basic usage:

    let s = String::from("hello");

    let b = s.into_boxed_str();

## Trait Implementations

### `impl ToString for String` 1.17.0[src]

#### `fn to_string(&self) -> String`[src]

Converts the given value to a `String`. Read more

### `impl Deref for String`[src]

#### `type Target = str`

The resulting type after dereferencing.

#### `fn deref(&self) -> &str`[src]

Dereferences the value.

### `impl DerefMut for String` 1.3.0[src]

#### `fn deref_mut(&mut self) -> &mut str`[src]

Mutably dereferences the value.

### `impl PartialEq<String> for String`[src]

#### `fn eq(&self, other: &String) -> bool`[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

#### `fn ne(&self, other: &String) -> bool`[src]

This method tests for `!=`.

### `impl<'a, 'b> PartialEq<str> for String`[src]

#### `fn eq(&self, other: &str) -> bool`[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

#### `fn ne(&self, other: &str) -> bool`[src]

This method tests for `!=`.

### `impl<'a, 'b> PartialEq<String> for str`[src]

#### `fn eq(&self, other: &String) -> bool`[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

#### `fn ne(&self, other: &String) -> bool`[src]

This method tests for `!=`.

### `impl<'a, 'b> PartialEq<&'a str> for String`[src]

#### `fn eq(&self, other: &&'a str) -> bool`[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

#### `fn ne(&self, other: &&'a str) -> bool`[src]

This method tests for `!=`.

### `impl<'a, 'b> PartialEq<String> for &'a str`[src]

#### `fn eq(&self, other: &String) -> bool`[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

#### `fn ne(&self, other: &String) -> bool`[src]

This method tests for `!=`.

### `impl<'a, 'b> PartialEq<String> for Cow<'a, str>`[src]

#### `fn eq(&self, other: &String) -> bool`[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

#### `fn ne(&self, other: &String) -> bool`[src]

This method tests for `!=`.

### `impl<'a, 'b> PartialEq<Cow<'a, str>> for String`[src]

#### `fn eq(&self, other: &Cow<'a, str>) -> bool`[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

#### `fn ne(&self, other: &Cow<'a, str>) -> bool`[src]

This method tests for `!=`.

### `impl Eq for String`[src]

### `impl Ord for String`[src]

#### `fn cmp(&self, other: &String) -> Ordering`[src]

This method returns an `Ordering` between `self` and `other`. Read more

#### `fn max(self, other: Self) -> Self`1.21.0[src]

Compares and returns the maximum of two values. Read more

#### `fn min(self, other: Self) -> Self`1.21.0[src]

Compares and returns the minimum of two values. Read more

#### `fn clamp(self, min: Self, max: Self) -> Self`[src]

🔬 This is a nightly-only experimental API. (`clamp` #44095)

Restrict a value to a certain interval. Read more

### `impl PartialOrd<String> for String`[src]

#### `fn partial_cmp(&self, other: &String) -> Option<Ordering>`[src]

This method returns an ordering between `self` and `other` values if one exists. Read more

#### `fn lt(&self, other: &String) -> bool`[src]

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more

#### `fn le(&self, other: &String) -> bool`[src]

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more

#### `fn gt(&self, other: &String) -> bool`[src]

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more

#### `fn ge(&self, other: &String) -> bool`[src]

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more

### `impl Hash for String`[src]

#### `fn hash<H: Hasher>(&self, hasher: &mut H)`[src]

Feeds this value into the given [`Hasher`]. Read more

#### `fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,` 1.3.0[src]

Feeds a slice of this type into the given [`Hasher`]. Read more

### `impl Debug for String`[src]

#### `fn fmt(&self, f: &mut Formatter) -> Result`[src]

Formats the value using the given formatter. Read more

### `impl Display for String`[src]

#### `fn fmt(&self, f: &mut Formatter) -> Result`[src]

Formats the value using the given formatter. Read more

### `impl<'_> Add<&'_ str> for String`[src]

Implements the `+` operator for concatenating two strings.

This consumes the `String` on the left-hand side and re-uses its buffer (growing it if necessary). This is done to avoid allocating a new `String` and copying the entire contents on every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by repeated concatenation.

The string on the right-hand side is only borrowed; its contents are copied into the returned `String`.

# Examples

Concatenating two `String`s takes the first by value and borrows the second:

    let a = String::from("hello");
    let b = String::from(" world");
    let c = a + &b;
    // `a` is moved and can no longer be used here.

If you want to keep using the first `String`, you can clone it and append to the clone instead:

    let a = String::from("hello");
    let b = String::from(" world");
    let c = a.clone() + &b;
    // `a` is still valid here.

Concatenating `&str` slices can be done by converting the first to a `String`:

    let a = "hello";
    let b = " world";
    let c = a.to_string() + b;

#### `type Output = String`

The resulting type after applying the `+` operator.

#### `fn add(self, other: &str) -> String`[src]

Performs the `+` operation.

### `impl<'_> AddAssign<&'_ str> for String` 1.12.0[src]

Implements the `+=` operator for appending to a `String`.

This has the same behavior as the `push_str` method.

#### `fn add_assign(&mut self, other: &str)`[src]

Performs the `+=` operation.

### `impl Index<Range<usize>> for String`[src]

#### `type Output = str`

The returned type after indexing.

#### `fn index(&self, index: Range<usize>) -> &str`[src]

Performs the indexing (`container[index]`) operation.

### `impl Index<RangeTo<usize>> for String`[src]

#### `type Output = str`

The returned type after indexing.

#### `fn index(&self, index: RangeTo<usize>) -> &str`[src]

Performs the indexing (`container[index]`) operation.

### `impl Index<RangeFrom<usize>> for String`[src]

#### `type Output = str`

The returned type after indexing.

#### `fn index(&self, index: RangeFrom<usize>) -> &str`[src]

Performs the indexing (`container[index]`) operation.

### `impl Index<RangeFull> for String`[src]

#### `type Output = str`

The returned type after indexing.

#### `fn index(&self, _index: RangeFull) -> &str`[src]

Performs the indexing (`container[index]`) operation.

### `impl Index<RangeInclusive<usize>> for String` 1.26.0[src]

#### `type Output = str`

The returned type after indexing.

#### `fn index(&self, index: RangeInclusive<usize>) -> &str`[src]

Performs the indexing (`container[index]`) operation.

### `impl Index<RangeToInclusive<usize>> for String` 1.26.0[src]

#### `type Output = str`

The returned type after indexing.

#### `fn index(&self, index: RangeToInclusive<usize>) -> &str`[src]

Performs the indexing (`container[index]`) operation.

### `impl IndexMut<Range<usize>> for String` 1.3.0[src]

#### `fn index_mut(&mut self, index: Range<usize>) -> &mut str`[src]

Performs the mutable indexing (`container[index]`) operation.

### `impl IndexMut<RangeTo<usize>> for String` 1.3.0[src]

#### `fn index_mut(&mut self, index: RangeTo<usize>) -> &mut str`[src]

Performs the mutable indexing (`container[index]`) operation.

### `impl IndexMut<RangeFrom<usize>> for String` 1.3.0[src]

#### `fn index_mut(&mut self, index: RangeFrom<usize>) -> &mut str`[src]

Performs the mutable indexing (`container[index]`) operation.

### `impl IndexMut<RangeFull> for String` 1.3.0[src]

#### `fn index_mut(&mut self, _index: RangeFull) -> &mut str`[src]

Performs the mutable indexing (`container[index]`) operation.

### `impl IndexMut<RangeInclusive<usize>> for String` 1.26.0[src]

#### `fn index_mut(&mut self, index: RangeInclusive<usize>) -> &mut str`[src]

Performs the mutable indexing (`container[index]`) operation.

### `impl IndexMut<RangeToInclusive<usize>> for String` 1.26.0[src]

#### `fn index_mut(&mut self, index: RangeToInclusive<usize>) -> &mut str`[src]

Performs the mutable indexing (`container[index]`) operation.

### `impl Extend<char> for String`[src]

#### `fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I)`[src]

Extends a collection with the contents of an iterator. Read more

### `impl<'a> Extend<&'a char> for String` 1.2.0[src]

#### `fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I)`[src]

Extends a collection with the contents of an iterator. Read more

### `impl<'a> Extend<&'a str> for String`[src]

#### `fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I)`[src]

Extends a collection with the contents of an iterator. Read more

### `impl Extend<String> for String` 1.4.0[src]

#### `fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I)`[src]

Extends a collection with the contents of an iterator. Read more

### `impl<'a> Extend<Cow<'a, str>> for String` 1.19.0[src]

#### `fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I)`[src]

Extends a collection with the contents of an iterator. Read more

### `impl FromIterator<char> for String`[src]

#### `fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String`[src]

Creates a value from an iterator. Read more

### `impl<'a> FromIterator<&'a char> for String` 1.17.0[src]

#### `fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String`[src]

Creates a value from an iterator. Read more

### `impl<'a> FromIterator<&'a str> for String`[src]

#### `fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String`[src]

Creates a value from an iterator. Read more

### `impl FromIterator<String> for String` 1.4.0[src]

#### `fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String`[src]

Creates a value from an iterator. Read more

### `impl<'a> FromIterator<Cow<'a, str>> for String` 1.19.0[src]

#### `fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String`[src]

Creates a value from an iterator. Read more

### `impl<'a> FromIterator<String> for Cow<'a, str>`1.12.0[src]

#### `fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str>`[src]

Creates a value from an iterator. Read more

### `impl<'a, 'b> Pattern<'a> for &'b String`[src]

A convenience impl that delegates to the impl for `&str`

#### `type Searcher = <&'b str as Pattern<'a>>::Searcher`

🔬 This is a nightly-only experimental API. (`pattern` #27721)

API not fully fleshed out and ready to be stabilized

Associated searcher for this pattern

#### `fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher`[src]

🔬 This is a nightly-only experimental API. (`pattern` #27721)

API not fully fleshed out and ready to be stabilized

Constructs the associated searcher from `self` and the `haystack` to search in. Read more

#### `fn is_contained_in(self, haystack: &'a str) -> bool`[src]

🔬 This is a nightly-only experimental API. (`pattern` #27721)

API not fully fleshed out and ready to be stabilized

Checks whether the pattern matches anywhere in the haystack

#### `fn is_prefix_of(self, haystack: &'a str) -> bool`[src]

🔬 This is a nightly-only experimental API. (`pattern` #27721)

API not fully fleshed out and ready to be stabilized

Checks whether the pattern matches at the front of the haystack

#### `fn is_suffix_of(self, haystack: &'a str) -> bool where
Self::Searcher: ReverseSearcher<'a>,` [src]

🔬 This is a nightly-only experimental API. (`pattern` #27721)

API not fully fleshed out and ready to be stabilized

Checks whether the pattern matches at the back of the haystack

### `impl Write for String`[src]

#### `fn write_str(&mut self, s: &str) -> Result`[src]

Writes a slice of bytes into this writer, returning whether the write succeeded. Read more

#### `fn write_char(&mut self, c: char) -> Result`[src]

Writes a [`char`] into this writer, returning whether the write succeeded. Read more

#### `fn write_fmt(&mut self, args: Arguments) -> Result<(), Error>`[src]

Glue for usage of the [`write!`] macro with implementors of this trait. Read more

### `impl FromStr for String`[src]

#### `type Err = Infallible`

The associated error which can be returned from parsing.

#### `fn from_str(s: &str) -> Result<String, ParseError>`[src]

Parses a string `s` to return a value of this type. Read more

### `impl AsRef<str> for String`[src]

#### `fn as_ref(&self) -> &str`[src]

Performs the conversion.

### `impl AsRef<[u8]> for String`[src]

#### `fn as_ref(&self) -> &[u8]`[src]

Performs the conversion.

### `impl From<String> for Arc<str>`1.21.0[src]

#### `fn from(v: String) -> Arc<str>`[src]

Performs the conversion.

### `impl From<String> for Rc<str>`1.21.0[src]

#### `fn from(v: String) -> Rc<str>`[src]

Performs the conversion.

### `impl<'_> From<&'_ str> for String`[src]

#### `fn from(s: &str) -> String`[src]

Performs the conversion.

### `impl<'_> From<&'_ String> for String` 1.35.0[src]

#### `fn from(s: &String) -> String`[src]

Performs the conversion.

### `impl From<Box<str>> for String` 1.18.0[src]

#### `fn from(s: Box<str>) -> String`[src]

Converts the given boxed `str` slice to a `String`. It is notable that the `str` slice is owned.

# Examples

Basic usage:

    let s1: String = String::from("hello world");
    let s2: Box<str> = s1.into_boxed_str();
    let s3: String = String::from(s2);

    assert_eq!("hello world", s3)

### `impl From<String> for Box<str>`1.20.0[src]

####
ⓘImportant traits for Box<I>

### Important traits for Box<I>

`impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;impl<I: Iterator + Sized> Iterator for Box<I>impl<F: ?Sized + Future + Unpin> Future for Box<F> type Output = F::Output;`
`fn from(s: String) -> Box<str>`[src]

Converts the given `String` to a boxed `str` slice that is owned.

# Examples

Basic usage:

    let s1: String = String::from("hello world");
    let s2: Box<str> = Box::from(s1);
    let s3: String = String::from(s2);

    assert_eq!("hello world", s3)

### `impl<'a> From<Cow<'a, str>> for String` 1.14.0[src]

#### `fn from(s: Cow<'a, str>) -> String`[src]

Performs the conversion.

### `impl<'a> From<String> for Cow<'a, str>`[src]

#### `fn from(s: String) -> Cow<'a, str>`[src]

Performs the conversion.

### `impl<'a> From<&'a String> for Cow<'a, str>`1.28.0[src]

#### `fn from(s: &'a String) -> Cow<'a, str>`[src]

Performs the conversion.

### `impl From<String> for Vec<u8>`1.14.0[src]

#### `fn from(string: String) -> Vec<u8>`[src]

Converts the given `String` to a vector `Vec` that holds values of type `u8`.

# Examples

Basic usage:

    let s1 = String::from("hello world");
    let v1 = Vec::from(s1);

    for b in v1 {
        println!("{}", b);
    }

### `impl Clone for String`[src]

#### `fn clone(&self) -> Self`[src]

Returns a copy of the value. Read more

#### `fn clone_from(&mut self, source: &Self)`[src]

Performs copy-assignment from `source`. Read more

### `impl Default for String`[src]

#### `fn default() -> String`[src]

Creates an empty `String`.

### `impl Borrow<str> for String`[src]

#### `fn borrow(&self) -> &str`[src]

Immutably borrows from an owned value. Read more

### `impl BorrowMut<str> for String` 1.36.0[src]

#### `fn borrow_mut(&mut self) -> &mut str`[src]

Mutably borrows from an owned value. Read more

## Auto Trait Implementations

### `impl Unpin for String`

### `impl Sync for String`

### `impl Send for String`

## Blanket Implementations

### `impl<T> ToOwned for T where
T: Clone,` [src]

#### `type Owned = T`

The resulting type after obtaining ownership.

#### `fn to_owned(&Self) -> T`[src]

Creates owned data from borrowed data, usually by cloning. Read more

#### `fn clone_into(&Self, &mut T)`[src]

🔬 This is a nightly-only experimental API. (`toowned_clone_into` #41263)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

### `impl<T> ToString for T where
T: Display + ?Sized,` [src]

#### `default fn to_string(&Self) -> String`[src]

Converts the given value to a `String`. Read more

### `impl<T, U> TryFrom<U> for T where
U: Into<T>,` [src]

#### `type Error = Infallible`

The type returned in the event of a conversion error.

#### `fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>`[src]

Performs the conversion.

### `impl<T, U> Into<U> for T where
U: From<T>,` [src]

#### `fn into(self) -> U`[src]

Performs the conversion.

### `impl<T> From<T> for T`[src]

#### `fn from(t: T) -> T`[src]

Performs the conversion.

### `impl<T, U> TryInto<U> for T where
U: TryFrom<T>,` [src]

#### `type Error = <U as TryFrom<T>>::Error`

The type returned in the event of a conversion error.

#### `fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>`[src]

Performs the conversion.

### `impl<T> Borrow<T> for T where
T: ?Sized,` [src]

#### `fn borrow(&self) -> &T`[src]

Immutably borrows from an owned value. Read more

### `impl<T> BorrowMut<T> for T where
T: ?Sized,` [src]

#### `fn borrow_mut(&mut self) -> &mut T`[src]

Mutably borrows from an owned value. Read more

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `fn type_id(&self) -> TypeId`[src]

Gets the `TypeId` of `self`. Read more

# Help

## Keyboard Shortcuts

`?`
  Show this help dialog
`S`
  Focus the search field
`↑`
  Move up in search results
`↓`
  Move down in search results
`↹`
  Switch tab
`⏎`
  Go to active search result
`+`
  Expand all sections
`-`
  Collapse all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g., `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g., `vec -> usize` or `* -> vec`)

Search multiple things at once by splitting your query with comma (e.g., `str,u8` or `String,struct:Vec,test`)