# Struct collections::string::String [−] [src]

    pub struct String {
        // some fields omitted
    }

1.0.0

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`:

fn main() { let hello = String::from("Hello, world!"); }

    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:

fn main() { let mut hello = String::from("Hello, "); hello.push('w'); hello.push_str("orld!"); }

    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:

fn main() { // 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); }

    // 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`:

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

    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. Furtheremore, it's not clear what sort of thing the index should return: a byte, a codepoint, or a grapheme cluster. The `as_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 any function which takes a `&str` by using an ampersand (`&`):

fn main() { fn takes_str(s: &str) { } let s = String::from("Hello"); takes_str(&s); }

    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.

# 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:

fn main() { 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 thirteen 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); }

    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 thirteen 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:

fn main() { let mut s = String::new(); println!("{}", s.capacity()); for _ in 0..5 { s.push_str("hello"); println!("{}", s.capacity()); } }

    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:

fn main() { let mut s = String::with_capacity(25); println!("{}", s.capacity()); for _ in 0..5 { s.push_str("hello"); println!("{}", s.capacity()); } }

    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`

#### `fn new() -> String`

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, but 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:

fn main() { let s = String::new(); }

    let s = String::new();

#### `fn with_capacity(capacity: usize) -> String`

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:

fn main() { 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 i in 0..10 { s.push('a'); } assert_eq!(s.capacity(), cap); // ...but this may make the vector reallocate s.push('a'); }

    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 i in 0..10 {
        s.push('a');
    }

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

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

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

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()`.

# 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:

fn main() { // 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); }

    // 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:

fn main() { // some invalid bytes, in a vector let sparkle_heart = vec![0, 159, 146, 150]; assert!(String::from_utf8(sparkle_heart).is_err()); }

    // 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.

#### `fn from_utf8_lossy<'a>(v: &'a [u8]) -> Cow<'a, str>`

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:

fn main() { // 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); }

    // 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:

fn main() { // some invalid bytes let input = b"Hello \xF0\x90\x80World"; let output = String::from_utf8_lossy(input); assert_eq!("Hello �World", output); }

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

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

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

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

# Examples

Basic usage:

fn main() { // 𝄞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()); }

    // 𝄞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());

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

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

# Examples

Basic usage:

fn main() { // 𝄞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)); }

    // 𝄞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));

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

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 datastructures.

# Examples

Basic usage:

fn main() { 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); } }

    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);
    }

#### `unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String`

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:

fn main() { // 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); }

    // 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);

#### `fn into_bytes(self) -> Vec<u8>`

Converts a `String` into a byte vector.

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

# Examples

Basic usage:

fn main() { let s = String::from("hello"); let bytes = s.into_bytes(); assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]); }

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

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

#### 1.7.0 `fn as_str(&self) -> &str`

Extracts a string slice containing the entire string.

#### 1.7.0 `fn as_mut_str(&mut self) -> &mut str`

Extracts a string slice containing the entire string.

#### `fn push_str(&mut self, string: &str)`

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

# Examples

Basic usage:

fn main() { let mut s = String::from("foo"); s.push_str("bar"); assert_eq!("foobar", s); }

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

    s.push_str("bar");

    assert_eq!("foobar", s);

#### `fn capacity(&self) -> usize`

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

# Examples

Basic usage:

fn main() { let s = String::with_capacity(10); assert!(s.capacity() >= 10); }

    let s = String::with_capacity(10);

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

#### `fn reserve(&mut self, additional: usize)`

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:

fn main() { let mut s = String::new(); s.reserve(10); assert!(s.capacity() >= 10); }

    let mut s = String::new();

    s.reserve(10);

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

This may not actually increase the capacity:

fn main() { 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()); }

    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());

#### `fn reserve_exact(&mut self, additional: usize)`

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:

fn main() { let mut s = String::new(); s.reserve_exact(10); assert!(s.capacity() >= 10); }

    let mut s = String::new();

    s.reserve_exact(10);

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

This may not actually increase the capacity:

fn main() { 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()); }

    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());

#### `fn shrink_to_fit(&mut self)`

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

# Examples

Basic usage:

fn main() { let mut s = String::from("foo"); s.reserve(100); assert!(s.capacity() >= 100); s.shrink_to_fit(); assert_eq!(3, s.capacity()); }

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

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

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

#### `fn push(&mut self, ch: char)`

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

# Examples

Basic usage:

fn main() { let mut s = String::from("abc"); s.push('1'); s.push('2'); s.push('3'); assert_eq!("abc123", s); }

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

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

    assert_eq!("abc123", s);

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

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

# Examples

Basic usage:

fn main() { let s = String::from("hello"); assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes()); }

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

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

#### `fn truncate(&mut self, new_len: usize)`

Shortens this `String` to the specified length.

# Panics

Panics if `new_len` > current length, or if `new_len` does not lie on a `char` boundary.

# Examples

Basic usage:

fn main() { let mut s = String::from("hello"); s.truncate(2); assert_eq!("he", s); }

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

    s.truncate(2);

    assert_eq!("he", s);

#### `fn pop(&mut self) -> Option<char>`

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

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

# Examples

Basic usage:

fn main() { 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); }

    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);

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

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:

fn main() { let mut s = String::from("foo"); assert_eq!(s.remove(0), 'f'); assert_eq!(s.remove(1), 'o'); assert_eq!(s.remove(0), 'o'); }

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

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

#### `fn insert(&mut self, idx: usize, ch: char)`

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:

fn main() { let mut s = String::with_capacity(3); s.insert(0, 'f'); s.insert(1, 'o'); s.insert(2, 'o'); assert_eq!("foo", s); }

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

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

    assert_eq!("foo", s);

#### `unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8>`

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:

fn main() { 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"); }

    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");

#### `fn len(&self) -> usize`

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

# Examples

Basic usage:

fn main() { let a = String::from("foo"); assert_eq!(a.len(), 3); }

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

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

#### `fn is_empty(&self) -> bool`

Returns `true` if this `String` has a length of zero.

Returns `false` otherwise.

# Examples

Basic usage:

fn main() { let mut v = String::new(); assert!(v.is_empty()); v.push('a'); assert!(!v.is_empty()); }

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

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

#### `fn clear(&mut self)`

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:

fn main() { let mut s = String::from("foo"); s.clear(); assert!(s.is_empty()); assert_eq!(0, s.len()); assert_eq!(3, s.capacity()); }

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

    s.clear();

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

#### 1.6.0 `fn drain<R>(&mut self, range: R) -> Drain where R: RangeArgument<usize>`

Create 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:

fn main() { 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, ""); }

    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, "");

#### 1.4.0 `fn into_boxed_str(self) -> Box<str>`

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

This will drop any excess capacity.

# Examples

Basic usage:

fn main() { let s = String::from("hello"); let b = s.into_boxed_str(); }

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

    let b = s.into_boxed_str();

## Trait Implementations

### `impl Borrow<str> for String`

#### `fn borrow(&self) -> &str`

### `impl Clone for String`

#### `fn clone(&self) -> Self`

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

### `impl FromIterator<char> for String`

#### `fn from_iter<I: IntoIterator<Item=char>>(iterable: I) -> String`

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

#### `fn from_iter<I: IntoIterator<Item=&'a str>>(iterable: I) -> String`

### `impl FromIterator<String> for String` 1.4.0

#### `fn from_iter<I: IntoIterator<Item=String>>(iterable: I) -> String`

### `impl Extend<char> for String`

#### `fn extend<I: IntoIterator<Item=char>>(&mut self, iterable: I)`

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

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

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

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

### `impl Extend<String> for String` 1.4.0

#### `fn extend<I: IntoIterator<Item=String>>(&mut self, iterable: I)`

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

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

#### `type Searcher = &'b str::Searcher`

#### `fn into_searcher(self, haystack: &'a str) -> &'b str::Searcher`

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

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

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

### `impl PartialEq for String`

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

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

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

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

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

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

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

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

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

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

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

### `impl Default for String`

#### `fn default() -> String`

### `impl Display for String`

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

### `impl Debug for String`

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

### `impl Hash for String`

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

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

### `impl<'a> Add<&'a str> for String`

#### `type Output = String`

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

### `impl Index<Range<usize>> for String`

#### `type Output = str`

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

### `impl Index<RangeTo<usize>> for String`

#### `type Output = str`

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

### `impl Index<RangeFrom<usize>> for String`

#### `type Output = str`

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

### `impl Index<RangeFull> for String`

#### `type Output = str`

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

### `impl Index<RangeInclusive<usize>> for String`

#### `type Output = str`

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

### `impl Index<RangeToInclusive<usize>> for String`

#### `type Output = str`

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

### `impl IndexMut<Range<usize>> for String` 1.2.0

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

### `impl IndexMut<RangeTo<usize>> for String` 1.2.0

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

### `impl IndexMut<RangeFrom<usize>> for String` 1.2.0

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

### `impl IndexMut<RangeFull> for String` 1.2.0

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

### `impl IndexMut<RangeInclusive<usize>> for String`

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

### `impl IndexMut<RangeToInclusive<usize>> for String`

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

### `impl Deref for String`

#### `type Target = str`

#### `fn deref(&self) -> &str`

### `impl DerefMut for String` 1.2.0

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

### `impl FromStr for String`

#### `type Err = ParseError`

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

### `impl AsRef<str> for String`

#### `fn as_ref(&self) -> &str`

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

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

### `impl<'a> From<&'a str> for String`

#### `fn from(s: &'a str) -> String`

### `impl Into<Vec<u8>> for String`

#### `fn into(self) -> Vec<u8>`

### `impl Write for String`

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

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

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

### Derived Implementations

### `impl Ord for String`

#### `fn cmp(&self, __arg_0: &String) -> Ordering`

### `impl Eq for String`

### `impl PartialOrd for String`

#### `fn partial_cmp(&self, __arg_0: &String) -> Option<Ordering>`

#### `fn lt(&self, __arg_0: &String) -> bool`

#### `fn le(&self, __arg_0: &String) -> bool`

#### `fn gt(&self, __arg_0: &String) -> bool`

#### `fn ge(&self, __arg_0: &String) -> bool`

# Help

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