# Struct std::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(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();

## Methods from Deref<Target=str>

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

Returns the length of `self`.

This length is in bytes, not `char`s or graphemes. In other words, it may not be what a human considers the length of the string.

# Examples

Basic usage:

fn main() { let len = "foo".len(); assert_eq!(3, len); let len = "ƒoo".len(); // fancy f! assert_eq!(4, len); }

    let len = "foo".len();
    assert_eq!(3, len);

    let len = "ƒoo".len(); // fancy f!
    assert_eq!(4, len);

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

Returns true if this slice has a length of zero bytes.

# Examples

Basic usage:

fn main() { let s = ""; assert!(s.is_empty()); let s = "not empty"; assert!(!s.is_empty()); }

    let s = "";
    assert!(s.is_empty());

    let s = "not empty";
    assert!(!s.is_empty());

#### `fn is_char_boundary(&self, index: usize) -> bool`

Unstable (`str_char` #27754)

: it is unclear whether this method pulls its weight with the existence of the char_indices iterator or this method may want to be replaced with checked slicing

Checks that `index`-th byte lies at the start and/or end of a UTF-8 code point sequence.

The start and end of the string (when `index == self.len()`) are considered to be boundaries.

Returns `false` if `index` is greater than `self.len()`.

# Examples

#![feature(str_char)] fn main() { let s = "Löwe 老虎 Léopard"; assert!(s.is_char_boundary(0)); // start of `老` assert!(s.is_char_boundary(6)); assert!(s.is_char_boundary(s.len())); // second byte of `ö` assert!(!s.is_char_boundary(2)); // third byte of `老` assert!(!s.is_char_boundary(8)); }

    #![feature(str_char)]

    let s = "Löwe 老虎 Léopard";
    assert!(s.is_char_boundary(0));
    // start of `老`
    assert!(s.is_char_boundary(6));
    assert!(s.is_char_boundary(s.len()));

    // second byte of `ö`
    assert!(!s.is_char_boundary(2));

    // third byte of `老`
    assert!(!s.is_char_boundary(8));

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

Converts a string slice to a byte slice.

# Examples

Basic usage:

fn main() { let bytes = "bors".as_bytes(); assert_eq!(b"bors", bytes); }

    let bytes = "bors".as_bytes();
    assert_eq!(b"bors", bytes);

#### `fn as_ptr(&self) -> *const u8`

Converts a string slice to a raw pointer.

As string slices are a slice of bytes, the raw pointer points to a `u8`. This pointer will be pointing to the first byte of the string slice.

# Examples

Basic usage:

fn main() { let s = "Hello"; let ptr = s.as_ptr(); }

    let s = "Hello";
    let ptr = s.as_ptr();

#### `unsafe fn slice_unchecked(&self, begin: usize, end: usize) -> &str`

Creates a string slice from another string slice, bypassing safety checks.

This new slice goes from `begin` to `end`, including `begin` but excluding `end`.

To get a mutable string slice instead, see the `slice_mut_unchecked()` method.

# Safety

Callers of this function are responsible that three preconditions are satisfied:

- `begin` must come before `end`.
- `begin` and `end` must be byte positions within the string slice.
- `begin` and `end` must lie on UTF-8 sequence boundaries.

# Examples

Basic usage:

fn main() { let s = "Löwe 老虎 Léopard"; unsafe { assert_eq!("Löwe 老虎 Léopard", s.slice_unchecked(0, 21)); } let s = "Hello, world!"; unsafe { assert_eq!("world", s.slice_unchecked(7, 12)); } }

    let s = "Löwe 老虎 Léopard";

    unsafe {
        assert_eq!("Löwe 老虎 Léopard", s.slice_unchecked(0, 21));
    }

    let s = "Hello, world!";

    unsafe {
        assert_eq!("world", s.slice_unchecked(7, 12));
    }

#### 1.5.0 `unsafe fn slice_mut_unchecked(&mut self, begin: usize, end: usize) -> &mut str`

Creates a string slice from another string slice, bypassing safety checks.

This new slice goes from `begin` to `end`, including `begin` but excluding `end`.

To get an immutable string slice instead, see the `slice_unchecked()` method.

# Safety

Callers of this function are responsible that three preconditions are satisfied:

- `begin` must come before `end`.
- `begin` and `end` must be byte positions within the string slice.
- `begin` and `end` must lie on UTF-8 sequence boundaries.

#### `fn char_range_at(&self, start: usize) -> CharRange`

Unstable (`str_char` #27754)

: often replaced by char_indices, this method may be removed in favor of just char_at() or eventually removed altogether

Given a byte position, returns the next `char` and its index.

# Panics

If `i` is greater than or equal to the length of the string. If `i` is not the index of the beginning of a valid UTF-8 sequence.

# Examples

This example manually iterates through the code points of a string; this should normally be done by `.chars()` or `.char_indices()`.

#![feature(str_char)] fn main() { use std::str::CharRange; let s = "中华Việt Nam"; let mut i = 0; while i < s.len() { let CharRange {ch, next} = s.char_range_at(i); println!("{}: {}", i, ch); i = next; } }

    #![feature(str_char)]

    use std::str::CharRange;

    let s = "中华Việt Nam";
    let mut i = 0;
    while i < s.len() {
        let CharRange {ch, next} = s.char_range_at(i);
        println!("{}: {}", i, ch);
        i = next;
    }

This outputs:

    0: 中
    3: 华
    6: V
    7: i
    8: e
    9:
    11:
    13: t
    14:
    15: N
    16: a
    17: m

#### `fn char_range_at_reverse(&self, start: usize) -> CharRange`

Unstable (`str_char` #27754)

: often replaced by char_indices, this method may be removed in favor of just char_at_reverse() or eventually removed altogether

Given a byte position, returns the previous `char` and its position.

Note that Unicode has many features, such as combining marks, ligatures, and direction marks, that need to be taken into account to correctly reverse a string.

Returns 0 for next index if called on start index 0.

# Panics

If `i` is greater than the length of the string. If `i` is not an index following a valid UTF-8 sequence.

# Examples

This example manually iterates through the code points of a string; this should normally be done by `.chars().rev()` or `.char_indices()`.

#![feature(str_char)] fn main() { use std::str::CharRange; let s = "中华Việt Nam"; let mut i = s.len(); while i > 0 { let CharRange {ch, next} = s.char_range_at_reverse(i); println!("{}: {}", i, ch); i = next; } }

    #![feature(str_char)]

    use std::str::CharRange;

    let s = "中华Việt Nam";
    let mut i = s.len();
    while i > 0 {
        let CharRange {ch, next} = s.char_range_at_reverse(i);
        println!("{}: {}", i, ch);
        i = next;
    }

This outputs:

    18: m
    17: a
    16: N
    15:
    14: t
    13:
    11:
    9: e
    8: i
    7: V
    6: 华
    3: 中

#### `fn char_at(&self, i: usize) -> char`

Unstable (`str_char` #27754)

: frequently replaced by the chars() iterator, this method may be removed or possibly renamed in the future; it is normally replaced by chars/char_indices iterators or by getting the first char from a subslice

Given a byte position, returns the `char` at that position.

# Panics

If `i` is greater than or equal to the length of the string. If `i` is not the index of the beginning of a valid UTF-8 sequence.

# Examples

#![feature(str_char)] fn main() { let s = "abπc"; assert_eq!(s.char_at(1), 'b'); assert_eq!(s.char_at(2), 'π'); assert_eq!(s.char_at(4), 'c'); }

    #![feature(str_char)]

    let s = "abπc";
    assert_eq!(s.char_at(1), 'b');
    assert_eq!(s.char_at(2), 'π');
    assert_eq!(s.char_at(4), 'c');

#### `fn char_at_reverse(&self, i: usize) -> char`

Unstable (`str_char` #27754)

: see char_at for more details, but reverse semantics are also somewhat unclear, especially with which cases generate panics

Given a byte position, returns the `char` at that position, counting from the end.

# Panics

If `i` is greater than the length of the string. If `i` is not an index following a valid UTF-8 sequence.

# Examples

#![feature(str_char)] fn main() { let s = "abπc"; assert_eq!(s.char_at_reverse(1), 'a'); assert_eq!(s.char_at_reverse(2), 'b'); assert_eq!(s.char_at_reverse(3), 'π'); }

    #![feature(str_char)]

    let s = "abπc";
    assert_eq!(s.char_at_reverse(1), 'a');
    assert_eq!(s.char_at_reverse(2), 'b');
    assert_eq!(s.char_at_reverse(3), 'π');

#### `fn slice_shift_char(&self) -> Option<(char, &str)>`

Unstable (`str_char` #27754)

: awaiting conventions about shifting and slices and may not be warranted with the existence of the chars and/or char_indices iterators

Retrieves the first `char` from a `&str` and returns it.

Note that a single Unicode character (grapheme cluster) can be composed of multiple `char`s.

This does not allocate a new string; instead, it returns a slice that points one code point beyond the code point that was shifted.

`None` is returned if the slice is empty.

# Examples

#![feature(str_char)] fn main() { let s = "Łódź"; // \u{141}o\u{301}dz\u{301} let (c, s1) = s.slice_shift_char().unwrap(); assert_eq!(c, 'Ł'); assert_eq!(s1, "ódź"); let (c, s2) = s1.slice_shift_char().unwrap(); assert_eq!(c, 'o'); assert_eq!(s2, "\u{301}dz\u{301}"); }

    #![feature(str_char)]

    let s = "Łódź"; // \u{141}o\u{301}dz\u{301}
    let (c, s1) = s.slice_shift_char().unwrap();

    assert_eq!(c, 'Ł');
    assert_eq!(s1, "ódź");

    let (c, s2) = s1.slice_shift_char().unwrap();

    assert_eq!(c, 'o');
    assert_eq!(s2, "\u{301}dz\u{301}");

#### 1.4.0 `fn split_at(&self, mid: usize) -> (&str, &str)`

Divide one string slice into two at an index.

The argument, `mid`, should be a byte offset from the start of the string. It must also be on the boundary of a UTF-8 code point.

The two slices returned go from the start of the string slice to `mid`, and from `mid` to the end of the string slice.

To get mutable string slices instead, see the `split_at_mut()` method.

# Panics

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

# Examples

Basic usage:

fn main() { let s = "Per Martin-Löf"; let (first, last) = s.split_at(3); assert_eq!("Per", first); assert_eq!(" Martin-Löf", last); }

    let s = "Per Martin-Löf";

    let (first, last) = s.split_at(3);

    assert_eq!("Per", first);
    assert_eq!(" Martin-Löf", last);

#### 1.4.0 `fn split_at_mut(&mut self, mid: usize) -> (&mut str, &mut str)`

Divide one mutable string slice into two at an index.

The argument, `mid`, should be a byte offset from the start of the string. It must also be on the boundary of a UTF-8 code point.

The two slices returned go from the start of the string slice to `mid`, and from `mid` to the end of the string slice.

To get immutable string slices instead, see the `split_at()` method.

# Panics

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

# Examples

Basic usage:

fn main() { let s = "Per Martin-Löf"; let (first, last) = s.split_at(3); assert_eq!("Per", first); assert_eq!(" Martin-Löf", last); }

    let s = "Per Martin-Löf";

    let (first, last) = s.split_at(3);

    assert_eq!("Per", first);
    assert_eq!(" Martin-Löf", last);

#### `fn chars(&self) -> Chars`

Returns an iterator over the `char`s of a string slice.

As a string slice consists of valid UTF-8, we can iterate through a string slice by `char`. This method returns such an iterator.

It's important to remember that `char` represents a Unicode Scalar Value, and may not match your idea of what a 'character' is. Iteration over grapheme clusters may be what you actually want.

# Examples

Basic usage:

fn main() { let word = "goodbye"; let count = word.chars().count(); assert_eq!(7, count); let mut chars = word.chars(); assert_eq!(Some('g'), chars.next()); assert_eq!(Some('o'), chars.next()); assert_eq!(Some('o'), chars.next()); assert_eq!(Some('d'), chars.next()); assert_eq!(Some('b'), chars.next()); assert_eq!(Some('y'), chars.next()); assert_eq!(Some('e'), chars.next()); assert_eq!(None, chars.next()); }

    let word = "goodbye";

    let count = word.chars().count();
    assert_eq!(7, count);

    let mut chars = word.chars();

    assert_eq!(Some('g'), chars.next());
    assert_eq!(Some('o'), chars.next());
    assert_eq!(Some('o'), chars.next());
    assert_eq!(Some('d'), chars.next());
    assert_eq!(Some('b'), chars.next());
    assert_eq!(Some('y'), chars.next());
    assert_eq!(Some('e'), chars.next());

    assert_eq!(None, chars.next());

Remember, `char`s may not match your human intuition about characters:

fn main() { let y = "y̆"; let mut chars = y.chars(); assert_eq!(Some('y'), chars.next()); // not 'y̆' assert_eq!(Some('\u{0306}'), chars.next()); assert_eq!(None, chars.next()); }

    let y = "y̆";

    let mut chars = y.chars();

    assert_eq!(Some('y'), chars.next()); // not 'y̆'
    assert_eq!(Some('\u{0306}'), chars.next());

    assert_eq!(None, chars.next());

#### `fn char_indices(&self) -> CharIndices`

Returns an iterator over the `char`s of a string slice, and their positions.

As a string slice consists of valid UTF-8, we can iterate through a string slice by `char`. This method returns an iterator of both these `char`s, as well as their byte positions.

The iterator yields tuples. The position is first, the `char` is second.

# Examples

Basic usage:

fn main() { let word = "goodbye"; let count = word.char_indices().count(); assert_eq!(7, count); let mut char_indices = word.char_indices(); assert_eq!(Some((0, 'g')), char_indices.next()); assert_eq!(Some((1, 'o')), char_indices.next()); assert_eq!(Some((2, 'o')), char_indices.next()); assert_eq!(Some((3, 'd')), char_indices.next()); assert_eq!(Some((4, 'b')), char_indices.next()); assert_eq!(Some((5, 'y')), char_indices.next()); assert_eq!(Some((6, 'e')), char_indices.next()); assert_eq!(None, char_indices.next()); }

    let word = "goodbye";

    let count = word.char_indices().count();
    assert_eq!(7, count);

    let mut char_indices = word.char_indices();

    assert_eq!(Some((0, 'g')), char_indices.next());
    assert_eq!(Some((1, 'o')), char_indices.next());
    assert_eq!(Some((2, 'o')), char_indices.next());
    assert_eq!(Some((3, 'd')), char_indices.next());
    assert_eq!(Some((4, 'b')), char_indices.next());
    assert_eq!(Some((5, 'y')), char_indices.next());
    assert_eq!(Some((6, 'e')), char_indices.next());

    assert_eq!(None, char_indices.next());

Remember, `char`s may not match your human intuition about characters:

fn main() { let y = "y̆"; let mut char_indices = y.char_indices(); assert_eq!(Some((0, 'y')), char_indices.next()); // not (0, 'y̆') assert_eq!(Some((1, '\u{0306}')), char_indices.next()); assert_eq!(None, char_indices.next()); }

    let y = "y̆";

    let mut char_indices = y.char_indices();

    assert_eq!(Some((0, 'y')), char_indices.next()); // not (0, 'y̆')
    assert_eq!(Some((1, '\u{0306}')), char_indices.next());

    assert_eq!(None, char_indices.next());

#### `fn bytes(&self) -> Bytes`

An iterator over the bytes of a string slice.

As a string slice consists of a sequence of bytes, we can iterate through a string slice by byte. This method returns such an iterator.

# Examples

Basic usage:

fn main() { let mut bytes = "bors".bytes(); assert_eq!(Some(b'b'), bytes.next()); assert_eq!(Some(b'o'), bytes.next()); assert_eq!(Some(b'r'), bytes.next()); assert_eq!(Some(b's'), bytes.next()); assert_eq!(None, bytes.next()); }

    let mut bytes = "bors".bytes();

    assert_eq!(Some(b'b'), bytes.next());
    assert_eq!(Some(b'o'), bytes.next());
    assert_eq!(Some(b'r'), bytes.next());
    assert_eq!(Some(b's'), bytes.next());

    assert_eq!(None, bytes.next());

#### 1.1.0 `fn split_whitespace(&self) -> SplitWhitespace`

Split a string slice by whitespace.

The iterator returned will return string slices that are sub-slices of the original string slice, separated by any amount of whitespace.

'Whitespace' is defined according to the terms of the Unicode Derived Core Property `White_Space`.

# Examples

Basic usage:

fn main() { let mut iter = "A few words".split_whitespace(); assert_eq!(Some("A"), iter.next()); assert_eq!(Some("few"), iter.next()); assert_eq!(Some("words"), iter.next()); assert_eq!(None, iter.next()); }

    let mut iter = "A few words".split_whitespace();

    assert_eq!(Some("A"), iter.next());
    assert_eq!(Some("few"), iter.next());
    assert_eq!(Some("words"), iter.next());

    assert_eq!(None, iter.next());

All kinds of whitespace are considered:

fn main() { let mut iter = " Mary had\ta\u{2009}little \n\t lamb".split_whitespace(); assert_eq!(Some("Mary"), iter.next()); assert_eq!(Some("had"), iter.next()); assert_eq!(Some("a"), iter.next()); assert_eq!(Some("little"), iter.next()); assert_eq!(Some("lamb"), iter.next()); assert_eq!(None, iter.next()); }

    let mut iter = " Mary   had\ta\u{2009}little  \n\t lamb".split_whitespace();
    assert_eq!(Some("Mary"), iter.next());
    assert_eq!(Some("had"), iter.next());
    assert_eq!(Some("a"), iter.next());
    assert_eq!(Some("little"), iter.next());
    assert_eq!(Some("lamb"), iter.next());

    assert_eq!(None, iter.next());

#### `fn lines(&self) -> Lines`

An iterator over the lines of a string, as string slices.

Lines are ended with either a newline (`\n`) or a carriage return with a line feed (`\r\n`).

The final line ending is optional.

# Examples

Basic usage:

fn main() { let text = "foo\r\nbar\n\nbaz\n"; let mut lines = text.lines(); assert_eq!(Some("foo"), lines.next()); assert_eq!(Some("bar"), lines.next()); assert_eq!(Some(""), lines.next()); assert_eq!(Some("baz"), lines.next()); assert_eq!(None, lines.next()); }

    let text = "foo\r\nbar\n\nbaz\n";
    let mut lines = text.lines();

    assert_eq!(Some("foo"), lines.next());
    assert_eq!(Some("bar"), lines.next());
    assert_eq!(Some(""), lines.next());
    assert_eq!(Some("baz"), lines.next());

    assert_eq!(None, lines.next());

The final line ending isn't required:

fn main() { let text = "foo\nbar\n\r\nbaz"; let mut lines = text.lines(); assert_eq!(Some("foo"), lines.next()); assert_eq!(Some("bar"), lines.next()); assert_eq!(Some(""), lines.next()); assert_eq!(Some("baz"), lines.next()); assert_eq!(None, lines.next()); }

    let text = "foo\nbar\n\r\nbaz";
    let mut lines = text.lines();

    assert_eq!(Some("foo"), lines.next());
    assert_eq!(Some("bar"), lines.next());
    assert_eq!(Some(""), lines.next());
    assert_eq!(Some("baz"), lines.next());

    assert_eq!(None, lines.next());

#### `fn lines_any(&self) -> LinesAny`

Deprecated since 1.4.0

: use lines() instead now

An iterator over the lines of a string.

#### `fn utf16_units(&self) -> EncodeUtf16`

Deprecated since 1.8.0

: renamed to encode_utf16

Returns an iterator of `u16` over the string encoded as UTF-16.

#### 1.8.0 `fn encode_utf16(&self) -> EncodeUtf16`

Returns an iterator of `u16` over the string encoded as UTF-16.

#### `fn contains<'a, P>(&'a self, pat: P) -> bool where P: Pattern<'a>`

Returns `true` if the given pattern matches a sub-slice of this string slice.

Returns `false` if it does not.

# Examples

Basic usage:

fn main() { let bananas = "bananas"; assert!(bananas.contains("nana")); assert!(!bananas.contains("apples")); }

    let bananas = "bananas";

    assert!(bananas.contains("nana"));
    assert!(!bananas.contains("apples"));

#### `fn starts_with<'a, P>(&'a self, pat: P) -> bool where P: Pattern<'a>`

Returns `true` if the given pattern matches a prefix of this string slice.

Returns `false` if it does not.

# Examples

Basic usage:

fn main() { let bananas = "bananas"; assert!(bananas.starts_with("bana")); assert!(!bananas.starts_with("nana")); }

    let bananas = "bananas";

    assert!(bananas.starts_with("bana"));
    assert!(!bananas.starts_with("nana"));

#### `fn ends_with<'a, P>(&'a self, pat: P) -> bool where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`

Returns `true` if the given pattern matches a suffix of this string slice.

Returns `false` if it does not.

# Examples

Basic usage:

fn main() { let bananas = "bananas"; assert!(bananas.ends_with("anas")); assert!(!bananas.ends_with("nana")); }

    let bananas = "bananas";

    assert!(bananas.ends_with("anas"));
    assert!(!bananas.ends_with("nana"));

#### `fn find<'a, P>(&'a self, pat: P) -> Option<usize> where P: Pattern<'a>`

Returns the byte index of the first character of this string slice that matches the pattern.

Returns `None` if the pattern doesn't match.

The pattern can be a `&str`, `char`, or a closure that determines if a character matches.

# Examples

Simple patterns:

fn main() { let s = "Löwe 老虎 Léopard"; assert_eq!(s.find('L'), Some(0)); assert_eq!(s.find('é'), Some(14)); assert_eq!(s.find("Léopard"), Some(13)); }

    let s = "Löwe 老虎 Léopard";

    assert_eq!(s.find('L'), Some(0));
    assert_eq!(s.find('é'), Some(14));
    assert_eq!(s.find("Léopard"), Some(13));

More complex patterns with closures:

fn main() { let s = "Löwe 老虎 Léopard"; assert_eq!(s.find(char::is_whitespace), Some(5)); assert_eq!(s.find(char::is_lowercase), Some(1)); }

    let s = "Löwe 老虎 Léopard";

    assert_eq!(s.find(char::is_whitespace), Some(5));
    assert_eq!(s.find(char::is_lowercase), Some(1));

Not finding the pattern:

fn main() { let s = "Löwe 老虎 Léopard"; let x: &[_] = &['1', '2']; assert_eq!(s.find(x), None); }

    let s = "Löwe 老虎 Léopard";
    let x: &[_] = &['1', '2'];

    assert_eq!(s.find(x), None);

#### `fn rfind<'a, P>(&'a self, pat: P) -> Option<usize> where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`

Returns the byte index of the last character of this string slice that matches the pattern.

Returns `None` if the pattern doesn't match.

The pattern can be a `&str`, `char`, or a closure that determines if a character matches.

# Examples

Simple patterns:

fn main() { let s = "Löwe 老虎 Léopard"; assert_eq!(s.rfind('L'), Some(13)); assert_eq!(s.rfind('é'), Some(14)); }

    let s = "Löwe 老虎 Léopard";

    assert_eq!(s.rfind('L'), Some(13));
    assert_eq!(s.rfind('é'), Some(14));

More complex patterns with closures:

fn main() { let s = "Löwe 老虎 Léopard"; assert_eq!(s.rfind(char::is_whitespace), Some(12)); assert_eq!(s.rfind(char::is_lowercase), Some(20)); }

    let s = "Löwe 老虎 Léopard";

    assert_eq!(s.rfind(char::is_whitespace), Some(12));
    assert_eq!(s.rfind(char::is_lowercase), Some(20));

Not finding the pattern:

fn main() { let s = "Löwe 老虎 Léopard"; let x: &[_] = &['1', '2']; assert_eq!(s.rfind(x), None); }

    let s = "Löwe 老虎 Léopard";
    let x: &[_] = &['1', '2'];

    assert_eq!(s.rfind(x), None);

#### `fn split<'a, P>(&'a self, pat: P) -> Split<'a, P> where P: Pattern<'a>`

An iterator over substrings of this string slice, separated by characters matched by a pattern.

The pattern can be a `&str`, `char`, or a closure that determines the split.

# Iterator behavior

The returned iterator will be a `DoubleEndedIterator` if the pattern allows a reverse search and forward/reverse search yields the same elements. This is true for, eg, `char` but not for `&str`.

If the pattern allows a reverse search but its results might differ from a forward search, the `rsplit()` method can be used.

# Examples

Simple patterns:

fn main() { let v: Vec<&str> = "Mary had a little lamb".split(' ').collect(); assert_eq!(v, ["Mary", "had", "a", "little", "lamb"]); let v: Vec<&str> = "".split('X').collect(); assert_eq!(v, [""]); let v: Vec<&str> = "lionXXtigerXleopard".split('X').collect(); assert_eq!(v, ["lion", "", "tiger", "leopard"]); let v: Vec<&str> = "lion::tiger::leopard".split("::").collect(); assert_eq!(v, ["lion", "tiger", "leopard"]); let v: Vec<&str> = "abc1def2ghi".split(char::is_numeric).collect(); assert_eq!(v, ["abc", "def", "ghi"]); let v: Vec<&str> = "lionXtigerXleopard".split(char::is_uppercase).collect(); assert_eq!(v, ["lion", "tiger", "leopard"]); }

    let v: Vec<&str> = "Mary had a little lamb".split(' ').collect();
    assert_eq!(v, ["Mary", "had", "a", "little", "lamb"]);

    let v: Vec<&str> = "".split('X').collect();
    assert_eq!(v, [""]);

    let v: Vec<&str> = "lionXXtigerXleopard".split('X').collect();
    assert_eq!(v, ["lion", "", "tiger", "leopard"]);

    let v: Vec<&str> = "lion::tiger::leopard".split("::").collect();
    assert_eq!(v, ["lion", "tiger", "leopard"]);

    let v: Vec<&str> = "abc1def2ghi".split(char::is_numeric).collect();
    assert_eq!(v, ["abc", "def", "ghi"]);

    let v: Vec<&str> = "lionXtigerXleopard".split(char::is_uppercase).collect();
    assert_eq!(v, ["lion", "tiger", "leopard"]);

A more complex pattern, using a closure:

fn main() { let v: Vec<&str> = "abc1defXghi".split(|c| c == '1' || c == 'X').collect(); assert_eq!(v, ["abc", "def", "ghi"]); }

    let v: Vec<&str> = "abc1defXghi".split(|c| c == '1' || c == 'X').collect();
    assert_eq!(v, ["abc", "def", "ghi"]);

If a string contains multiple contiguous separators, you will end up with empty strings in the output:

fn main() { let x = "||||a||b|c".to_string(); let d: Vec<_> = x.split('|').collect(); assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]); }

    let x = "||||a||b|c".to_string();
    let d: Vec<_> = x.split('|').collect();

    assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);

This can lead to possibly surprising behavior when whitespace is used as the separator. This code is correct:

fn main() { let x = " a b c".to_string(); let d: Vec<_> = x.split(' ').collect(); assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]); }

    let x = "    a  b c".to_string();
    let d: Vec<_> = x.split(' ').collect();

    assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);

It does not give you:

fn main() { assert_eq!(d, &["a", "b", "c"]); }

    assert_eq!(d, &["a", "b", "c"]);

Use `split_whitespace()` for this behavior.

#### `fn rsplit<'a, P>(&'a self, pat: P) -> RSplit<'a, P> where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`

An iterator over substrings of the given string slice, separated by characters matched by a pattern and yielded in reverse order.

The pattern can be a `&str`, `char`, or a closure that determines the split.

# Iterator behavior

The returned iterator requires that the pattern supports a reverse search, and it will be a `DoubleEndedIterator` if a forward/reverse search yields the same elements.

For iterating from the front, the `split()` method can be used.

# Examples

Simple patterns:

fn main() { let v: Vec<&str> = "Mary had a little lamb".rsplit(' ').collect(); assert_eq!(v, ["lamb", "little", "a", "had", "Mary"]); let v: Vec<&str> = "".rsplit('X').collect(); assert_eq!(v, [""]); let v: Vec<&str> = "lionXXtigerXleopard".rsplit('X').collect(); assert_eq!(v, ["leopard", "tiger", "", "lion"]); let v: Vec<&str> = "lion::tiger::leopard".rsplit("::").collect(); assert_eq!(v, ["leopard", "tiger", "lion"]); }

    let v: Vec<&str> = "Mary had a little lamb".rsplit(' ').collect();
    assert_eq!(v, ["lamb", "little", "a", "had", "Mary"]);

    let v: Vec<&str> = "".rsplit('X').collect();
    assert_eq!(v, [""]);

    let v: Vec<&str> = "lionXXtigerXleopard".rsplit('X').collect();
    assert_eq!(v, ["leopard", "tiger", "", "lion"]);

    let v: Vec<&str> = "lion::tiger::leopard".rsplit("::").collect();
    assert_eq!(v, ["leopard", "tiger", "lion"]);

A more complex pattern, using a closure:

fn main() { let v: Vec<&str> = "abc1defXghi".rsplit(|c| c == '1' || c == 'X').collect(); assert_eq!(v, ["ghi", "def", "abc"]); }

    let v: Vec<&str> = "abc1defXghi".rsplit(|c| c == '1' || c == 'X').collect();
    assert_eq!(v, ["ghi", "def", "abc"]);

#### `fn split_terminator<'a, P>(&'a self, pat: P) -> SplitTerminator<'a, P> where P: Pattern<'a>`

An iterator over substrings of the given string slice, separated by characters matched by a pattern.

The pattern can be a `&str`, `char`, or a closure that determines the split.

Equivalent to `split()`, except that the trailing substring is skipped if empty.

This method can be used for string data that is terminated, rather than separated by a pattern.

# Iterator behavior

The returned iterator will be a `DoubleEndedIterator` if the pattern allows a reverse search and forward/reverse search yields the same elements. This is true for, eg, `char` but not for `&str`.

If the pattern allows a reverse search but its results might differ from a forward search, the `rsplit_terminator()` method can be used.

# Examples

Basic usage:

fn main() { let v: Vec<&str> = "A.B.".split_terminator('.').collect(); assert_eq!(v, ["A", "B"]); let v: Vec<&str> = "A..B..".split_terminator(".").collect(); assert_eq!(v, ["A", "", "B", ""]); }

    let v: Vec<&str> = "A.B.".split_terminator('.').collect();
    assert_eq!(v, ["A", "B"]);

    let v: Vec<&str> = "A..B..".split_terminator(".").collect();
    assert_eq!(v, ["A", "", "B", ""]);

#### `fn rsplit_terminator<'a, P>(&'a self, pat: P) -> RSplitTerminator<'a, P> where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`

An iterator over substrings of `self`, separated by characters matched by a pattern and yielded in reverse order.

The pattern can be a simple `&str`, `char`, or a closure that determines the split. Additional libraries might provide more complex patterns like regular expressions.

Equivalent to `split()`, except that the trailing substring is skipped if empty.

This method can be used for string data that is terminated, rather than separated by a pattern.

# Iterator behavior

The returned iterator requires that the pattern supports a reverse search, and it will be double ended if a forward/reverse search yields the same elements.

For iterating from the front, the `split_terminator()` method can be used.

# Examples

fn main() { let v: Vec<&str> = "A.B.".rsplit_terminator('.').collect(); assert_eq!(v, ["B", "A"]); let v: Vec<&str> = "A..B..".rsplit_terminator(".").collect(); assert_eq!(v, ["", "B", "", "A"]); }

    let v: Vec<&str> = "A.B.".rsplit_terminator('.').collect();
    assert_eq!(v, ["B", "A"]);

    let v: Vec<&str> = "A..B..".rsplit_terminator(".").collect();
    assert_eq!(v, ["", "B", "", "A"]);

#### `fn splitn<'a, P>(&'a self, count: usize, pat: P) -> SplitN<'a, P> where P: Pattern<'a>`

An iterator over substrings of the given string slice, separated by a pattern, restricted to returning at most `count` items.

The last element returned, if any, will contain the remainder of the string slice.

The pattern can be a `&str`, `char`, or a closure that determines the split.

# Iterator behavior

The returned iterator will not be double ended, because it is not efficient to support.

If the pattern allows a reverse search, the `rsplitn()` method can be used.

# Examples

Simple patterns:

fn main() { let v: Vec<&str> = "Mary had a little lambda".splitn(3, ' ').collect(); assert_eq!(v, ["Mary", "had", "a little lambda"]); let v: Vec<&str> = "lionXXtigerXleopard".splitn(3, "X").collect(); assert_eq!(v, ["lion", "", "tigerXleopard"]); let v: Vec<&str> = "abcXdef".splitn(1, 'X').collect(); assert_eq!(v, ["abcXdef"]); let v: Vec<&str> = "".splitn(1, 'X').collect(); assert_eq!(v, [""]); }

    let v: Vec<&str> = "Mary had a little lambda".splitn(3, ' ').collect();
    assert_eq!(v, ["Mary", "had", "a little lambda"]);

    let v: Vec<&str> = "lionXXtigerXleopard".splitn(3, "X").collect();
    assert_eq!(v, ["lion", "", "tigerXleopard"]);

    let v: Vec<&str> = "abcXdef".splitn(1, 'X').collect();
    assert_eq!(v, ["abcXdef"]);

    let v: Vec<&str> = "".splitn(1, 'X').collect();
    assert_eq!(v, [""]);

A more complex pattern, using a closure:

fn main() { let v: Vec<&str> = "abc1defXghi".splitn(2, |c| c == '1' || c == 'X').collect(); assert_eq!(v, ["abc", "defXghi"]); }

    let v: Vec<&str> = "abc1defXghi".splitn(2, |c| c == '1' || c == 'X').collect();
    assert_eq!(v, ["abc", "defXghi"]);

#### `fn rsplitn<'a, P>(&'a self, count: usize, pat: P) -> RSplitN<'a, P> where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`

An iterator over substrings of this string slice, separated by a pattern, starting from the end of the string, restricted to returning at most `count` items.

The last element returned, if any, will contain the remainder of the string slice.

The pattern can be a `&str`, `char`, or a closure that determines the split.

# Iterator behavior

The returned iterator will not be double ended, because it is not efficient to support.

For splitting from the front, the `splitn()` method can be used.

# Examples

Simple patterns:

fn main() { let v: Vec<&str> = "Mary had a little lamb".rsplitn(3, ' ').collect(); assert_eq!(v, ["lamb", "little", "Mary had a"]); let v: Vec<&str> = "lionXXtigerXleopard".rsplitn(3, 'X').collect(); assert_eq!(v, ["leopard", "tiger", "lionX"]); let v: Vec<&str> = "lion::tiger::leopard".rsplitn(2, "::").collect(); assert_eq!(v, ["leopard", "lion::tiger"]); }

    let v: Vec<&str> = "Mary had a little lamb".rsplitn(3, ' ').collect();
    assert_eq!(v, ["lamb", "little", "Mary had a"]);

    let v: Vec<&str> = "lionXXtigerXleopard".rsplitn(3, 'X').collect();
    assert_eq!(v, ["leopard", "tiger", "lionX"]);

    let v: Vec<&str> = "lion::tiger::leopard".rsplitn(2, "::").collect();
    assert_eq!(v, ["leopard", "lion::tiger"]);

A more complex pattern, using a closure:

fn main() { let v: Vec<&str> = "abc1defXghi".rsplitn(2, |c| c == '1' || c == 'X').collect(); assert_eq!(v, ["ghi", "abc1def"]); }

    let v: Vec<&str> = "abc1defXghi".rsplitn(2, |c| c == '1' || c == 'X').collect();
    assert_eq!(v, ["ghi", "abc1def"]);

#### 1.2.0 `fn matches<'a, P>(&'a self, pat: P) -> Matches<'a, P> where P: Pattern<'a>`

An iterator over the matches of a pattern within the given string slice.

The pattern can be a `&str`, `char`, or a closure that determines if a character matches.

# Iterator behavior

The returned iterator will be a `DoubleEndedIterator` if the pattern allows a reverse search and forward/reverse search yields the same elements. This is true for, eg, `char` but not for `&str`.

If the pattern allows a reverse search but its results might differ from a forward search, the `rmatches()` method can be used.

# Examples

Basic usage:

fn main() { let v: Vec<&str> = "abcXXXabcYYYabc".matches("abc").collect(); assert_eq!(v, ["abc", "abc", "abc"]); let v: Vec<&str> = "1abc2abc3".matches(char::is_numeric).collect(); assert_eq!(v, ["1", "2", "3"]); }

    let v: Vec<&str> = "abcXXXabcYYYabc".matches("abc").collect();
    assert_eq!(v, ["abc", "abc", "abc"]);

    let v: Vec<&str> = "1abc2abc3".matches(char::is_numeric).collect();
    assert_eq!(v, ["1", "2", "3"]);

#### 1.2.0 `fn rmatches<'a, P>(&'a self, pat: P) -> RMatches<'a, P> where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`

An iterator over the matches of a pattern within this string slice, yielded in reverse order.

The pattern can be a `&str`, `char`, or a closure that determines if a character matches.

# Iterator behavior

The returned iterator requires that the pattern supports a reverse search, and it will be a `DoubleEndedIterator` if a forward/reverse search yields the same elements.

For iterating from the front, the `matches()` method can be used.

# Examples

Basic usage:

fn main() { let v: Vec<&str> = "abcXXXabcYYYabc".rmatches("abc").collect(); assert_eq!(v, ["abc", "abc", "abc"]); let v: Vec<&str> = "1abc2abc3".rmatches(char::is_numeric).collect(); assert_eq!(v, ["3", "2", "1"]); }

    let v: Vec<&str> = "abcXXXabcYYYabc".rmatches("abc").collect();
    assert_eq!(v, ["abc", "abc", "abc"]);

    let v: Vec<&str> = "1abc2abc3".rmatches(char::is_numeric).collect();
    assert_eq!(v, ["3", "2", "1"]);

#### 1.5.0 `fn match_indices<'a, P>(&'a self, pat: P) -> MatchIndices<'a, P> where P: Pattern<'a>`

An iterator over the disjoint matches of a pattern within this string slice as well as the index that the match starts at.

For matches of `pat` within `self` that overlap, only the indices corresponding to the first match are returned.

The pattern can be a `&str`, `char`, or a closure that determines if a character matches.

# Iterator behavior

The returned iterator will be a `DoubleEndedIterator` if the pattern allows a reverse search and forward/reverse search yields the same elements. This is true for, eg, `char` but not for `&str`.

If the pattern allows a reverse search but its results might differ from a forward search, the `rmatch_indices()` method can be used.

# Examples

Basic usage:

fn main() { let v: Vec<_> = "abcXXXabcYYYabc".match_indices("abc").collect(); assert_eq!(v, [(0, "abc"), (6, "abc"), (12, "abc")]); let v: Vec<_> = "1abcabc2".match_indices("abc").collect(); assert_eq!(v, [(1, "abc"), (4, "abc")]); let v: Vec<_> = "ababa".match_indices("aba").collect(); assert_eq!(v, [(0, "aba")]); // only the first `aba` }

    let v: Vec<_> = "abcXXXabcYYYabc".match_indices("abc").collect();
    assert_eq!(v, [(0, "abc"), (6, "abc"), (12, "abc")]);

    let v: Vec<_> = "1abcabc2".match_indices("abc").collect();
    assert_eq!(v, [(1, "abc"), (4, "abc")]);

    let v: Vec<_> = "ababa".match_indices("aba").collect();
    assert_eq!(v, [(0, "aba")]); // only the first `aba`

#### 1.5.0 `fn rmatch_indices<'a, P>(&'a self, pat: P) -> RMatchIndices<'a, P> where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`

An iterator over the disjoint matches of a pattern within `self`, yielded in reverse order along with the index of the match.

For matches of `pat` within `self` that overlap, only the indices corresponding to the last match are returned.

The pattern can be a `&str`, `char`, or a closure that determines if a character matches.

# Iterator behavior

The returned iterator requires that the pattern supports a reverse search, and it will be a `DoubleEndedIterator` if a forward/reverse search yields the same elements.

For iterating from the front, the `match_indices()` method can be used.

# Examples

Basic usage:

fn main() { let v: Vec<_> = "abcXXXabcYYYabc".rmatch_indices("abc").collect(); assert_eq!(v, [(12, "abc"), (6, "abc"), (0, "abc")]); let v: Vec<_> = "1abcabc2".rmatch_indices("abc").collect(); assert_eq!(v, [(4, "abc"), (1, "abc")]); let v: Vec<_> = "ababa".rmatch_indices("aba").collect(); assert_eq!(v, [(2, "aba")]); // only the last `aba` }

    let v: Vec<_> = "abcXXXabcYYYabc".rmatch_indices("abc").collect();
    assert_eq!(v, [(12, "abc"), (6, "abc"), (0, "abc")]);

    let v: Vec<_> = "1abcabc2".rmatch_indices("abc").collect();
    assert_eq!(v, [(4, "abc"), (1, "abc")]);

    let v: Vec<_> = "ababa".rmatch_indices("aba").collect();
    assert_eq!(v, [(2, "aba")]); // only the last `aba`

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

Returns a string slice with leading and trailing whitespace removed.

'Whitespace' is defined according to the terms of the Unicode Derived Core Property `White_Space`.

# Examples

Basic usage:

fn main() { let s = " Hello\tworld\t"; assert_eq!("Hello\tworld", s.trim()); }

    let s = " Hello\tworld\t";

    assert_eq!("Hello\tworld", s.trim());

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

Returns a string slice with leading whitespace removed.

'Whitespace' is defined according to the terms of the Unicode Derived Core Property `White_Space`.

# Text directionality

A string is a sequence of bytes. 'Left' in this context means the first position of that byte string; for a language like Arabic or Hebrew which are 'right to left' rather than 'left to right', this will be the right side, not the left.

# Examples

Basic usage:

fn main() { let s = " Hello\tworld\t"; assert_eq!("Hello\tworld\t", s.trim_left()); }

    let s = " Hello\tworld\t";

    assert_eq!("Hello\tworld\t", s.trim_left());

Directionality:

fn main() { let s = " English"; assert!(Some('E') == s.trim_left().chars().next()); let s = " עברית"; assert!(Some('ע') == s.trim_left().chars().next()); }

    let s = "  English";
    assert!(Some('E') == s.trim_left().chars().next());

    let s = "  עברית";
    assert!(Some('ע') == s.trim_left().chars().next());

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

Returns a string slice with trailing whitespace removed.

'Whitespace' is defined according to the terms of the Unicode Derived Core Property `White_Space`.

# Text directionality

A string is a sequence of bytes. 'Right' in this context means the last position of that byte string; for a language like Arabic or Hebrew which are 'right to left' rather than 'left to right', this will be the left side, not the right.

# Examples

Basic usage:

fn main() { let s = " Hello\tworld\t"; assert_eq!(" Hello\tworld", s.trim_right()); }

    let s = " Hello\tworld\t";

    assert_eq!(" Hello\tworld", s.trim_right());

Directionality:

fn main() { let s = "English "; assert!(Some('h') == s.trim_right().chars().rev().next()); let s = "עברית "; assert!(Some('ת') == s.trim_right().chars().rev().next()); }

    let s = "English  ";
    assert!(Some('h') == s.trim_right().chars().rev().next());

    let s = "עברית  ";
    assert!(Some('ת') == s.trim_right().chars().rev().next());

#### `fn trim_matches<'a, P>(&'a self, pat: P) -> &'a str where P: Pattern<'a>, P::Searcher: DoubleEndedSearcher<'a>`

Returns a string slice with all prefixes and suffixes that match a pattern repeatedly removed.

The pattern can be a `&str`, `char`, or a closure that determines if a character matches.

# Examples

Simple patterns:

fn main() { assert_eq!("11foo1bar11".trim_matches('1'), "foo1bar"); assert_eq!("123foo1bar123".trim_matches(char::is_numeric), "foo1bar"); let x: &[_] = &['1', '2']; assert_eq!("12foo1bar12".trim_matches(x), "foo1bar"); }

    assert_eq!("11foo1bar11".trim_matches('1'), "foo1bar");
    assert_eq!("123foo1bar123".trim_matches(char::is_numeric), "foo1bar");

    let x: &[_] = &['1', '2'];
    assert_eq!("12foo1bar12".trim_matches(x), "foo1bar");

A more complex pattern, using a closure:

fn main() { assert_eq!("1foo1barXX".trim_matches(|c| c == '1' || c == 'X'), "foo1bar"); }

    assert_eq!("1foo1barXX".trim_matches(|c| c == '1' || c == 'X'), "foo1bar");

#### `fn trim_left_matches<'a, P>(&'a self, pat: P) -> &'a str where P: Pattern<'a>`

Returns a string slice with all prefixes that match a pattern repeatedly removed.

The pattern can be a `&str`, `char`, or a closure that determines if a character matches.

# Text directionality

A string is a sequence of bytes. 'Left' in this context means the first position of that byte string; for a language like Arabic or Hebrew which are 'right to left' rather than 'left to right', this will be the right side, not the left.

# Examples

Basic usage:

fn main() { assert_eq!("11foo1bar11".trim_left_matches('1'), "foo1bar11"); assert_eq!("123foo1bar123".trim_left_matches(char::is_numeric), "foo1bar123"); let x: &[_] = &['1', '2']; assert_eq!("12foo1bar12".trim_left_matches(x), "foo1bar12"); }

    assert_eq!("11foo1bar11".trim_left_matches('1'), "foo1bar11");
    assert_eq!("123foo1bar123".trim_left_matches(char::is_numeric), "foo1bar123");

    let x: &[_] = &['1', '2'];
    assert_eq!("12foo1bar12".trim_left_matches(x), "foo1bar12");

#### `fn trim_right_matches<'a, P>(&'a self, pat: P) -> &'a str where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`

Returns a string slice with all suffixes that match a pattern repeatedly removed.

The pattern can be a `&str`, `char`, or a closure that determines if a character matches.

# Text directionality

A string is a sequence of bytes. 'Right' in this context means the last position of that byte string; for a language like Arabic or Hebrew which are 'right to left' rather than 'left to right', this will be the left side, not the right.

# Examples

Simple patterns:

fn main() { assert_eq!("11foo1bar11".trim_right_matches('1'), "11foo1bar"); assert_eq!("123foo1bar123".trim_right_matches(char::is_numeric), "123foo1bar"); let x: &[_] = &['1', '2']; assert_eq!("12foo1bar12".trim_right_matches(x), "12foo1bar"); }

    assert_eq!("11foo1bar11".trim_right_matches('1'), "11foo1bar");
    assert_eq!("123foo1bar123".trim_right_matches(char::is_numeric), "123foo1bar");

    let x: &[_] = &['1', '2'];
    assert_eq!("12foo1bar12".trim_right_matches(x), "12foo1bar");

A more complex pattern, using a closure:

fn main() { assert_eq!("1fooX".trim_left_matches(|c| c == '1' || c == 'X'), "fooX"); }

    assert_eq!("1fooX".trim_left_matches(|c| c == '1' || c == 'X'), "fooX");

#### `fn parse<F>(&self) -> Result<F, F::Err> where F: FromStr`

Parses this string slice into another type.

Because `parse()` is so general, it can cause problems with type inference. As such, `parse()` is one of the few times you'll see the syntax affectionately known as the 'turbofish': `::<>`. This helps the inference algorithm understand specifically which type you're trying to parse into.

`parse()` can parse any type that implements the `FromStr` trait.

# Errors

Will return `Err` if it's not possible to parse this string slice into the desired type.

# Example

Basic usage

fn main() { let four: u32 = "4".parse().unwrap(); assert_eq!(4, four); }

    let four: u32 = "4".parse().unwrap();

    assert_eq!(4, four);

Using the 'turbofish' instead of annotating `four`:

fn main() { let four = "4".parse::<u32>(); assert_eq!(Ok(4), four); }

    let four = "4".parse::<u32>();

    assert_eq!(Ok(4), four);

Failing to parse:

fn main() { let nope = "j".parse::<u32>(); assert!(nope.is_err()); }

    let nope = "j".parse::<u32>();

    assert!(nope.is_err());

#### `fn replace<'a, P>(&'a self, from: P, to: &str) -> String where P: Pattern<'a>`

Replaces all matches of a pattern with another string.

`replace` creates a new `String`, and copies the data from this string slice into it. While doing so, it attempts to find matches of a pattern. If it finds any, it replaces them with the replacement string slice.

# Examples

Basic usage:

fn main() { let s = "this is old"; assert_eq!("this is new", s.replace("old", "new")); }

    let s = "this is old";

    assert_eq!("this is new", s.replace("old", "new"));

When the pattern doesn't match:

fn main() { let s = "this is old"; assert_eq!(s, s.replace("cookie monster", "little lamb")); }

    let s = "this is old";
    assert_eq!(s, s.replace("cookie monster", "little lamb"));

#### 1.2.0 `fn to_lowercase(&self) -> String`

Returns the lowercase equivalent of this string slice, as a new `String`.

'Lowercase' is defined according to the terms of the Unicode Derived Core Property `Lowercase`.

# Examples

Basic usage:

fn main() { let s = "HELLO"; assert_eq!("hello", s.to_lowercase()); }

    let s = "HELLO";

    assert_eq!("hello", s.to_lowercase());

A tricky example, with sigma:

fn main() { let sigma = "Σ"; assert_eq!("σ", sigma.to_lowercase()); // but at the end of a word, it's ς, not σ: let odysseus = "ὈΔΥΣΣΕΎΣ"; assert_eq!("ὀδυσσεύς", odysseus.to_lowercase()); }

    let sigma = "Σ";

    assert_eq!("σ", sigma.to_lowercase());

    // but at the end of a word, it's ς, not σ:
    let odysseus = "ὈΔΥΣΣΕΎΣ";

    assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());

Languages without case are not changed:

fn main() { let new_year = "农历新年"; assert_eq!(new_year, new_year.to_lowercase()); }

    let new_year = "农历新年";

    assert_eq!(new_year, new_year.to_lowercase());

#### 1.2.0 `fn to_uppercase(&self) -> String`

Returns the uppercase equivalent of this string slice, as a new `String`.

'Uppercase' is defined according to the terms of the Unicode Derived Core Property `Uppercase`.

# Examples

Basic usage:

fn main() { let s = "hello"; assert_eq!("HELLO", s.to_uppercase()); }

    let s = "hello";

    assert_eq!("HELLO", s.to_uppercase());

Scripts without case are not changed:

fn main() { let new_year = "农历新年"; assert_eq!(new_year, new_year.to_uppercase()); }

    let new_year = "农历新年";

    assert_eq!(new_year, new_year.to_uppercase());

#### `fn escape_default(&self) -> String`

Unstable (`str_escape` #27791)

: return type may change to be an iterator

Escapes each char in `s` with `char::escape_default`.

#### `fn escape_unicode(&self) -> String`

Unstable (`str_escape` #27791)

: return type may change to be an iterator

Escapes each char in `s` with `char::escape_unicode`.

#### 1.4.0 `fn into_string(self: Box<str>) -> String`

Converts a `Box<str>` into a `String` without copying or allocating.

# Examples

Basic usage:

fn main() { let string = String::from("birthday gift"); let boxed_str = string.clone().into_boxed_str(); assert_eq!(boxed_str.into_string(), string); }

    let string = String::from("birthday gift");
    let boxed_str = string.clone().into_boxed_str();

    assert_eq!(boxed_str.into_string(), string);

## Trait Implementations

### `impl Write for String`

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

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

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

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

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

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

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

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

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

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

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

### `impl FromStr for String`

#### `type Err = ParseError`

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

### `impl DerefMut for String` 1.2.0

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

### `impl Deref for String`

#### `type Target = str`

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

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

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

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

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

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

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

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

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

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

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

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

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

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

#### `type Output = str`

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

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

#### `type Output = str`

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

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

#### `type Output = str`

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

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

#### `type Output = str`

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

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

#### `type Output = str`

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

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

#### `type Output = str`

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

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

#### `type Output = String`

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

### `impl Hash for String`

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

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

### `impl Debug for String`

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

### `impl Display for String`

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

### `impl Default for String`

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

### `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<'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<str> for String`

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

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

### `impl PartialEq<String> for String`

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

### `impl Clone for String`

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

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

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

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

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

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

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

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

### Derived Implementations

### `impl PartialOrd<String> 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`

### `impl Eq for String`

### `impl Ord for String`

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

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
⇤
  Move up in search results
⇥
  Move down in search results
⏎
  Go to active search result

## 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`)