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

    pub struct String { /* fields omitted */ }

A UTF-8 encoded, growable string.

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

# Examples

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

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

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

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

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

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

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

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

    assert_eq!("💖", sparkle_heart);Run

# 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`:

    let s = "hello";

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

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

# Deref

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

    fn takes_str(s: &str) { }

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

    takes_str(&s);Run

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:

    use std::mem;

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

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

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

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

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

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

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

    let mut s = String::new();

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

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

This will output the following:

    0
    5
    10
    20
    20
    40

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

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

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

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

We end up with a different output:

    25
    25
    25
    25
    25
    25

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

## Methods

### `impl String`
[src]

#### `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:

    let s = String::new();Run

#### `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:

    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');Run

#### `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`.

The inverse of this method is `as_bytes`.

# Errors

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

# Examples

Basic usage:

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

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

    assert_eq!("💖", sparkle_heart);Run

Incorrect bytes:

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

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

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:

    // 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);Run

Incorrect bytes:

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

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

#### `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:

    // 𝄞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());Run

#### `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:

    // 𝄞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));Run

#### `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.

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

# Examples

Basic usage:

    use std::mem;

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

        mem::forget(s);

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

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

#### `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:

    // 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);Run

#### `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:

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

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

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

Extracts a string slice containing the entire string.

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

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:

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

    s.push_str("bar");

    assert_eq!("foobar", s);Run

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

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

# Examples

Basic usage:

    let s = String::with_capacity(10);

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

#### `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:

    let mut s = String::new();

    s.reserve(10);

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

This may not actually increase the capacity:

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

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

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

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

#### `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:

    let mut s = String::new();

    s.reserve_exact(10);

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

This may not actually increase the capacity:

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

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

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

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

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

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

# Examples

Basic usage:

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

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

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

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

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

# Examples

Basic usage:

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

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

    assert_eq!("abc123", s);Run

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

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

The inverse of this method is `from_utf8`.

# Examples

Basic usage:

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

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

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

Shortens this `String` to the specified length.

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

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

# Panics

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

# Examples

Basic usage:

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

    s.truncate(2);

    assert_eq!("he", s);Run

#### `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:

    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);Run

#### `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:

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

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

#### `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:

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

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

    assert_eq!("foo", s);Run

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

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

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

# Panics

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

# Examples

Basic usage:

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

    s.insert_str(0, "foo");

    assert_eq!("foobar", s);Run

#### `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:

    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");Run

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

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

# Examples

Basic usage:

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

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

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

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

Returns `false` otherwise.

# Examples

Basic usage:

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

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

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

Splits the string into two at the given index.

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

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

# Panics

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

# Examples

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

#### `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:

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

    s.clear();

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

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

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

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

# Panics

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

# Examples

Basic usage:

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

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

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

#### `fn splice<R>(&'a mut self, range: R, replace_with: &'b str) -> Splice<'a, 'b> where
R: RangeArgument<usize>,`

🔬 This is a nightly-only experimental API. (`splice` #32310)

recently added

Creates a splicing iterator that removes the specified range in the string, replaces with the given string, and yields the removed chars. The given string doesn’t need to be the same length as the range.

Note: The element range is removed when the `Splice` is dropped, 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:

    #![feature(splice)]
    let mut s = String::from("α is alpha, β is beta");
    let beta_offset = s.find('β').unwrap_or(s.len());

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

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

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

This will drop any excess capacity.

# Examples

Basic usage:

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

    let b = s.into_boxed_str();Run

## 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:

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

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

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

Returns `true` if `self` has a length of zero bytes.

# Examples

Basic usage:

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

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

#### `fn is_char_boundary(&self, index: usize) -> bool`
1.9.0

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

    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));Run

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

Converts a string slice to a byte slice.

# Examples

Basic usage:

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

#### `unsafe fn as_bytes_mut(&mut self) -> &mut [u8]`

🔬 This is a nightly-only experimental API. (`str_mut_extras` #41119)

Converts a mutable string slice to a mutable byte slice.

#### `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:

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

#### `fn get<I>(&self, i: I) -> Option<&<I as SliceIndex<str>>::Output> where
I: SliceIndex<str>,`

🔬 This is a nightly-only experimental API. (`str_checked_slicing` #39932)

Returns a subslice of `str`.

This is the non-panicking alternative to indexing the `str`. Returns `None` whenever equivalent indexing operation would panic.

# Examples

    let v = "🗻∈🌏";
    assert_eq!(Some("🗻"), v.get(0..4));
    assert!(v.get(1..).is_none());
    assert!(v.get(..8).is_none());
    assert!(v.get(..42).is_none());Run

#### `fn get_mut<I>(&mut self, i: I) -> Option<&mut <I as SliceIndex<str>>::Output> where
I: SliceIndex<str>,`

🔬 This is a nightly-only experimental API. (`str_checked_slicing` #39932)

Returns a mutable subslice of `str`.

This is the non-panicking alternative to indexing the `str`. Returns `None` whenever equivalent indexing operation would panic.

# Examples

    let mut v = String::from("🗻∈🌏");
    assert_eq!(Some("🗻"), v.get_mut(0..4).map(|v| &*v));
    assert!(v.get_mut(1..).is_none());
    assert!(v.get_mut(..8).is_none());
    assert!(v.get_mut(..42).is_none());Run

#### `unsafe fn get_unchecked<I>(&self, i: I) -> &<I as SliceIndex<str>>::Output where
I: SliceIndex<str>,`

🔬 This is a nightly-only experimental API. (`str_checked_slicing` #39932)

Returns a unchecked subslice of `str`.

This is the unchecked alternative to indexing the `str`.

# Safety

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

- The starting index must come before the ending index;
- Indexes must be within bounds of the original slice;
- Indexes must lie on UTF-8 sequence boundaries.

Failing that, the returned string slice may reference invalid memory or violate the invariants communicated by the `str` type.

# Examples

    let v = "🗻∈🌏";
    unsafe {
        assert_eq!("🗻", v.get_unchecked(0..4));
        assert_eq!("∈", v.get_unchecked(4..7));
        assert_eq!("🌏", v.get_unchecked(7..11));
    }Run

#### `unsafe fn get_unchecked_mut<I>(
&mut self,
i: I
) -> &mut <I as SliceIndex<str>>::Output where
I: SliceIndex<str>,`

🔬 This is a nightly-only experimental API. (`str_checked_slicing` #39932)

Returns a mutable, unchecked subslice of `str`.

This is the unchecked alternative to indexing the `str`.

# Safety

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

- The starting index must come before the ending index;
- Indexes must be within bounds of the original slice;
- Indexes must lie on UTF-8 sequence boundaries.

Failing that, the returned string slice may reference invalid memory or violate the invariants communicated by the `str` type.

# Examples

    let mut v = String::from("🗻∈🌏");
    unsafe {
        assert_eq!("🗻", v.get_unchecked_mut(0..4));
        assert_eq!("∈", v.get_unchecked_mut(4..7));
        assert_eq!("🌏", v.get_unchecked_mut(7..11));
    }Run

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

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

This is generally not recommended, use with caution! For a safe alternative see `str` and `Index`.

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:

    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));
    }Run

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

Creates a string slice from another string slice, bypassing safety checks. This is generally not recommended, use with caution! For a safe alternative see `str` and `IndexMut`.

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

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:

    let s = "Per Martin-Löf";

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

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

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

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:

    let mut s = "Per Martin-Löf".to_string();

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

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

#### `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:

    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());Run

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

    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());Run

#### `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:

    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());Run

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

    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());Run

#### `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:

    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());Run

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

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:

    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());Run

All kinds of whitespace are considered:

    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());Run

#### `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:

    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());Run

The final line ending isn't required:

    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());Run

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

Deprecated since 1.4.0

: use lines() instead now

An iterator over the lines of a string.

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

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:

    let bananas = "bananas";

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

#### `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:

    let bananas = "bananas";

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

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

    let bananas = "bananas";

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

#### `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:

    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));Run

More complex patterns with closures:

    let s = "Löwe 老虎 Léopard";

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

Not finding the pattern:

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

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

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

    let s = "Löwe 老虎 Léopard";

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

More complex patterns with closures:

    let s = "Löwe 老虎 Léopard";

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

Not finding the pattern:

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

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

#### `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:

    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"]);Run

A more complex pattern, using a closure:

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

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

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

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

Contiguous separators are separated by the empty string.

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

    assert_eq!(d, &["(", "", "", ")"]);Run

Separators at the start or end of a string are neighbored by empty strings.

    let d: Vec<_> = "010".split("0").collect();
    assert_eq!(d, &["", "1", ""]);Run

When the empty string is used as a separator, it separates every character in the string, along with the beginning and end of the string.

    let f: Vec<_> = "rust".split("").collect();
    assert_eq!(f, &["", "r", "u", "s", "t", ""]);Run

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

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

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

It does not give you:

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

Use `split_whitespace` for this behavior.

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

    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"]);Run

A more complex pattern, using a closure:

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

#### `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:

    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", ""]);Run

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

    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"]);Run

#### `fn splitn<'a, P>(&'a self, n: 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 `n` items.

If `n` substrings are returned, the last substring (the `n`th substring) will contain the remainder of the string.

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:

    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, [""]);Run

A more complex pattern, using a closure:

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

#### `fn rsplitn<'a, P>(&'a self, n: usize, pat: P) -> RSplitN<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::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 `n` items.

If `n` substrings are returned, the last substring (the `n`th substring) will contain the remainder of the string.

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:

    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"]);Run

A more complex pattern, using a closure:

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

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

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:

    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"]);Run

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

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:

    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"]);Run

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

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:

    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`Run

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

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:

    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`Run

#### `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:

    let s = " Hello\tworld\t";

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

#### `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:

    let s = " Hello\tworld\t";

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

Directionality:

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

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

#### `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:

    let s = " Hello\tworld\t";

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

Directionality:

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

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

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

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

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

# Examples

Simple patterns:

    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");Run

A more complex pattern, using a closure:

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

#### `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:

    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");Run

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

    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");Run

A more complex pattern, using a closure:

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

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

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

    assert_eq!(4, four);Run

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

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

    assert_eq!(Ok(4), four);Run

Failing to parse:

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

    assert!(nope.is_err());Run

#### `fn into_boxed_bytes(self: Box<str>) -> Box<[u8]>`

🔬 This is a nightly-only experimental API. (`str_box_extras` #41119)

Converts a `Box<str>` into a `Box<[u8]>` without copying or allocating.

#### `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:

    let s = "this is old";

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

When the pattern doesn't match:

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

#### `fn replacen<'a, P>(&'a self, pat: P, to: &str, count: usize) -> String where
P: Pattern<'a>,`
1.16.0

Replaces first N matches of a pattern with another string.

`replacen` 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 at most `count` times.

# Examples

Basic usage:

    let s = "foo foo 123 foo";
    assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
    assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
    assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));Run

When the pattern doesn't match:

    let s = "this is old";
    assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));Run

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

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`.

Since some characters can expand into multiple characters when changing the case, this function returns a `String` instead of modifying the parameter in-place.

# Examples

Basic usage:

    let s = "HELLO";

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

A tricky example, with sigma:

    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());Run

Languages without case are not changed:

    let new_year = "农历新年";

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

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

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`.

Since some characters can expand into multiple characters when changing the case, this function returns a `String` instead of modifying the parameter in-place.

# Examples

Basic usage:

    let s = "hello";

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

Scripts without case are not changed:

    let new_year = "农历新年";

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

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

🔬 This is a nightly-only experimental API. (`str_escape` #27791)

return type may change to be an iterator

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

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

🔬 This is a nightly-only experimental API. (`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`

🔬 This is a nightly-only experimental API. (`str_escape` #27791)

return type may change to be an iterator

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

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

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

# Examples

Basic usage:

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

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

#### `fn repeat(&self, n: usize) -> String`
1.16.0

Create a `String` by repeating a string `n` times.

# Examples

Basic usage:

    assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));Run

## Trait Implementations

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

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

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

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

API not fully fleshed out and ready to be stabilized

Associated searcher for this pattern

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

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

API not fully fleshed out and ready to be stabilized

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

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

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

API not fully fleshed out and ready to be stabilized

Checks whether the pattern matches anywhere in the haystack

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

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

API not fully fleshed out and ready to be stabilized

Checks whether the pattern matches at the front of the haystack

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

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

API not fully fleshed out and ready to be stabilized

Checks whether the pattern matches at the back of the haystack

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

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

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

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

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

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

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

Immutably borrows from an owned value. Read more

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

This method tests for `!=`.

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

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

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

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

This method tests for `!=`.

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

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

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

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

This method tests for `!=`.

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

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

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

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

This method tests for `!=`.

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

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

The method called to mutably dereference a value

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

Implements the `+` operator for concatenating two strings.

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

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

# Examples

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

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

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

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

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

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

#### `type Output = String`

The resulting type after applying the `+` operator

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

The method for the `+` operator

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

#### `type Err = ParseError`

The associated error which can be returned from parsing.

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

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

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

#### `type Target = str`

The resulting type after dereferencing

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

The method called to dereference a value

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

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

Returns a copy of the value. Read more

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

Performs copy-assignment from `source`. Read more

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

#### `type Output = str`

The returned type after indexing

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

The method for the indexing (`container[index]`) operation

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

#### `type Output = str`

The returned type after indexing

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

The method for the indexing (`container[index]`) operation

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

#### `type Output = str`

The returned type after indexing

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

The method for the indexing (`container[index]`) operation

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

#### `type Output = str`

The returned type after indexing

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

The method for the indexing (`container[index]`) operation

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

#### `type Output = str`

The returned type after indexing

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

The method for the indexing (`container[index]`) operation

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

#### `type Output = str`

The returned type after indexing

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

The method for the indexing (`container[index]`) operation

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

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

Performs the conversion.

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

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

Performs the conversion.

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

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

Creates a value from an iterator. Read more

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

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

Creates a value from an iterator. Read more

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

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

Creates a value from an iterator. Read more

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

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

Creates a value from an iterator. Read more

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

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

Creates a value from an iterator. Read more

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

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

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

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

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

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

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

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

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

Formats the value using the given formatter.

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

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

The method for the mutable indexing (`container[index]`) operation

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

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

The method for the mutable indexing (`container[index]`) operation

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

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

The method for the mutable indexing (`container[index]`) operation

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

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

The method for the mutable indexing (`container[index]`) operation

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

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

The method for the mutable indexing (`container[index]`) operation

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

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

The method for the mutable indexing (`container[index]`) operation

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

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

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

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

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

Creates an empty `String`.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The method for the `+=` operator

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

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

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

Performs the conversion.

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

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

Performs the conversion.

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

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

Performs the conversion.

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

#### `fn into(self) -> Box<str>`

Performs the conversion.

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

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

Formats the value using the given formatter. Read more

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

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

Performs the conversion.

### `impl ToSocketAddrs for String`
1.16.0
[src]

#### `type Iter = IntoIter<SocketAddr>`

Returned iterator over socket addresses which this type may correspond to. Read more

#### `fn to_socket_addrs(&self) -> Result<IntoIter<SocketAddr>>`

Converts this object to an iterator of resolved `SocketAddr`s. Read more

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

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

Performs the conversion.

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