String in alloc::string - Rust
Description: A UTF-8–encoded, growable string.

alloc::string

# Struct String

1.36.0 · Source

    pub struct String { /* private fields */ }

Expand description

A UTF-8–encoded, growable string.

`String` is the most common string type. It has ownership over the contents of the string, stored in a heap-allocated buffer (see Representation). It is closely related to its borrowed counterpart, the primitive `str`.

## §Examples

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

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

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

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

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

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

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

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

    assert_eq!("💖", sparkle_heart);

## §UTF-8

`String`s are always valid UTF-8. If you need a non-UTF-8 string, consider `OsString`. It is similar, but without the UTF-8 constraint. Because UTF-8 is a variable width encoding, `String`s are typically smaller than an array of the same `char`s:

    use std::mem;

    // `s` is ASCII which represents each `char` as one byte
    let s = "hello";
    assert_eq!(s.len(), 5);

    // A `char` array with the same contents would be longer because
    // every `char` is four bytes
    let s = ['h', 'e', 'l', 'l', 'o'];
    let size: usize = s.into_iter().map(|c| mem::size_of_val(&c)).sum();
    assert_eq!(size, 20);

    // However, for non-ASCII strings, the difference will be smaller
    // and sometimes they are the same
    let s = "💖💖💖💖💖";
    assert_eq!(s.len(), 20);

    let s = ['💖', '💖', '💖', '💖', '💖'];
    let size: usize = s.into_iter().map(|c| mem::size_of_val(&c)).sum();
    assert_eq!(size, 20);

This raises interesting questions as to how `s[i]` should work. What should `i` be here? Several options include byte indices and `char` indices but, because of UTF-8 encoding, only byte indices would provide constant time indexing. Getting the `i`th `char`, for example, is available using `chars`:

    let s = "hello";
    let third_character = s.chars().nth(2);
    assert_eq!(third_character, Some('l'));

    let s = "💖💖💖💖💖";
    let third_character = s.chars().nth(2);
    assert_eq!(third_character, Some('💖'));

Next, what should `s[i]` return? Because indexing returns a reference to underlying data it could be `&u8`, `&[u8]`, or something else similar. Since we’re only providing one index, `&u8` makes the most sense but that might not be what the user expects and can be explicitly achieved with `as_bytes()`:

    // The first byte is 104 - the byte value of `'h'`
    let s = "hello";
    assert_eq!(s.as_bytes()[0], 104);
    // or
    assert_eq!(s.as_bytes()[0], b'h');

    // The first byte is 240 which isn't obviously useful
    let s = "💖💖💖💖💖";
    assert_eq!(s.as_bytes()[0], 240);

Due to these ambiguities/restrictions, indexing with a `usize` is simply forbidden:

ⓘ

    let s = "hello";

    // The following will not compile!
    println!("The first letter of s is {}", s[0]);

It is more clear, however, how `&s[i..j]` should work (that is, indexing with a range). It should accept byte indices (to be constant-time) and return a `&str` which is UTF-8 encoded. This is also called “string slicing”. Note this will panic if the byte indices provided are not character boundaries - see `is_char_boundary` for more details. See the implementations for `SliceIndex<str>` for more details on string slicing. For a non-panicking version of string slicing, see `get`.

The `bytes` and `chars` methods return iterators over the bytes and codepoints of the string, respectively. To iterate over codepoints along with byte indices, use `char_indices`.

## §Deref

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

    fn takes_str(s: &str) { }

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

    takes_str(&s);

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

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

ⓘ

    trait TraitExample {}

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

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

    let example_string = String::from("example_string");
    example_func(&example_string);

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

## §Representation

A `String` is made up of three components: a pointer to some bytes, a length, and a capacity. The pointer points to the internal buffer which `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...");

    // Prevent automatically dropping the String's data
    let mut story = mem::ManuallyDrop::new(story);

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

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

    // 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, len, capacity) } ;

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

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

    let mut s = String::new();

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

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

This will output the following:

    0
    8
    16
    16
    32
    32

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

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

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

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

We end up with a different output:

    25
    25
    25
    25
    25
    25

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

## Implementations§

Source§

### impl String

1.0.0 (const: 1.39.0) · Source

#### pub const 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, it may cause excessive allocation later when you add data. If you have an idea of how much data the `String` will hold, consider the `with_capacity` method to prevent excessive re-allocation.

##### §Examples

    let s = String::new();

1.0.0 · Source

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

Creates a new empty `String` with at least the specified 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 at least `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

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

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

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

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

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

Source

#### pub fn try_with_capacity(capacity: usize) -> Result<String, TryReserveError>

🔬This is a nightly-only experimental API. (`try_with_capacity` #91913)

Creates a new empty `String` with at least the specified capacity.

##### §Errors

Returns `Err` if the capacity exceeds `isize::MAX` bytes, or if the memory allocator reports failure.

1.0.0 · Source

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

Converts a vector of bytes to a `String`.

A string (`String`) 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 `into_bytes`.

##### §Errors

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

##### §Examples

Basic usage:

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

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

    assert_eq!("💖", sparkle_heart);

Incorrect bytes:

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

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

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

1.0.0 · Source

#### pub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, 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);

Incorrect bytes:

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

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

Source

#### pub fn from_utf8_lossy_owned(v: Vec<u8>) -> String

🔬This is a nightly-only experimental API. (`string_from_utf8_lossy_owned` #129436)

Converts a `Vec<u8>` to a `String`, substituting invalid UTF-8 sequences with replacement characters.

See `from_utf8_lossy` for more details.

Note that this function does not guarantee reuse of the original `Vec` allocation.

##### §Examples

Basic usage:

    #![feature(string_from_utf8_lossy_owned)]
    // some bytes, in a vector
    let sparkle_heart = vec![240, 159, 146, 150];

    let sparkle_heart = String::from_utf8_lossy_owned(sparkle_heart);

    assert_eq!(String::from("💖"), sparkle_heart);

Incorrect bytes:

    #![feature(string_from_utf8_lossy_owned)]
    // some invalid bytes
    let input: Vec<u8> = b"Hello \xF0\x90\x80World".into();
    let output = String::from_utf8_lossy_owned(input);

    assert_eq!(String::from("Hello �World"), output);

1.0.0 · Source

#### pub 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

    // 𝄞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());

1.0.0 · Source

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

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

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

##### §Examples

    // 𝄞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));

Source

#### pub fn from_utf16le(v: &[u8]) -> Result<String, FromUtf16Error>

🔬This is a nightly-only experimental API. (`str_from_utf16_endian` #116258)

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

##### §Examples

Basic usage:

    #![feature(str_from_utf16_endian)]
    // 𝄞music
    let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
              0x73, 0x00, 0x69, 0x00, 0x63, 0x00];
    assert_eq!(String::from("𝄞music"),
               String::from_utf16le(v).unwrap());

    // 𝄞mu<invalid>ic
    let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
              0x00, 0xD8, 0x69, 0x00, 0x63, 0x00];
    assert!(String::from_utf16le(v).is_err());

Source

#### pub fn from_utf16le_lossy(v: &[u8]) -> String

🔬This is a nightly-only experimental API. (`str_from_utf16_endian` #116258)

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

Unlike `from_utf8_lossy` which returns a `Cow<'a, str>`, `from_utf16le_lossy` returns a `String` since the UTF-16 to UTF-8 conversion requires a memory allocation.

##### §Examples

Basic usage:

    #![feature(str_from_utf16_endian)]
    // 𝄞mus<invalid>ic<invalid>
    let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
              0x73, 0x00, 0x1E, 0xDD, 0x69, 0x00, 0x63, 0x00,
              0x34, 0xD8];

    assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
               String::from_utf16le_lossy(v));

Source

#### pub fn from_utf16be(v: &[u8]) -> Result<String, FromUtf16Error>

🔬This is a nightly-only experimental API. (`str_from_utf16_endian` #116258)

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

##### §Examples

Basic usage:

    #![feature(str_from_utf16_endian)]
    // 𝄞music
    let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
              0x00, 0x73, 0x00, 0x69, 0x00, 0x63];
    assert_eq!(String::from("𝄞music"),
               String::from_utf16be(v).unwrap());

    // 𝄞mu<invalid>ic
    let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
              0xD8, 0x00, 0x00, 0x69, 0x00, 0x63];
    assert!(String::from_utf16be(v).is_err());

Source

#### pub fn from_utf16be_lossy(v: &[u8]) -> String

🔬This is a nightly-only experimental API. (`str_from_utf16_endian` #116258)

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

Unlike `from_utf8_lossy` which returns a `Cow<'a, str>`, `from_utf16le_lossy` returns a `String` since the UTF-16 to UTF-8 conversion requires a memory allocation.

##### §Examples

Basic usage:

    #![feature(str_from_utf16_endian)]
    // 𝄞mus<invalid>ic<invalid>
    let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
              0x00, 0x73, 0xDD, 0x1E, 0x00, 0x69, 0x00, 0x63,
              0xD8, 0x34];

    assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
               String::from_utf16be_lossy(v));

Source

#### pub fn into_raw_parts(self) -> (*mut u8, usize, usize)

🔬This is a nightly-only experimental API. (`vec_into_raw_parts` #65816)

Decomposes a `String` into its raw components: `(pointer, length, capacity)`.

Returns the raw pointer to the underlying data, the length of the string (in bytes), and the allocated capacity of the data (in bytes). These are the same arguments in the same order as the arguments to `from_raw_parts`.

After calling this function, the caller is responsible for the memory previously managed by the `String`. The only way to do this is to convert the raw pointer, length, and capacity back into a `String` with the `from_raw_parts` function, allowing the destructor to perform the cleanup.

##### §Examples

    #![feature(vec_into_raw_parts)]
    let s = String::from("hello");

    let (ptr, len, cap) = s.into_raw_parts();

    let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
    assert_eq!(rebuilt, "hello");

1.0.0 · Source

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

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

##### §Safety

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

- The memory at `buf` needs to have been previously allocated by the same allocator the standard library uses, with a required alignment of exactly 1.
- `length` needs to be less than or equal to `capacity`.
- `capacity` needs to be the correct value.
- The first `length` bytes at `buf` need to be valid UTF-8.

Violating these may cause problems like corrupting the allocator’s internal data structures. For example, it is normally not safe to build a `String` from a pointer to a C `char` array containing UTF-8 unless you are certain that array was originally allocated by the Rust standard library’s allocator.

The ownership of `buf` 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

    use std::mem;

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

        // Prevent automatically dropping the String's data
        let mut s = mem::ManuallyDrop::new(s);

        let ptr = s.as_mut_ptr();
        let len = s.len();
        let capacity = s.capacity();

        let s = String::from_raw_parts(ptr, len, capacity);

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

1.0.0 · Source

#### pub 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

    // 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);

1.0.0 (const: unstable) · Source

#### pub 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

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

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

1.7.0 (const: unstable) · Source

#### pub fn as_str(&self) -> &str

Extracts a string slice containing the entire `String`.

##### §Examples

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

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

1.7.0 (const: unstable) · Source

#### pub fn as_mut_str(&mut self) -> &mut str

Converts a `String` into a mutable string slice.

##### §Examples

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

    s_mut_str.make_ascii_uppercase();

    assert_eq!("FOOBAR", s_mut_str);

1.0.0 · Source

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

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

##### §Examples

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

    s.push_str("bar");

    assert_eq!("foobar", s);

Source

#### pub fn extend_from_within<R>(&mut self, src: R)
where R: RangeBounds<usize>,

🔬This is a nightly-only experimental API. (`string_extend_from_within` #103806)

Copies elements from `src` range to the end of the string.

##### §Panics

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

##### §Examples

    #![feature(string_extend_from_within)]
    let mut string = String::from("abcde");

    string.extend_from_within(2..);
    assert_eq!(string, "abcdecde");

    string.extend_from_within(..2);
    assert_eq!(string, "abcdecdeab");

    string.extend_from_within(4..8);
    assert_eq!(string, "abcdecdeabecde");

1.0.0 (const: unstable) · Source

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

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

##### §Examples

    let s = String::with_capacity(10);

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

1.0.0 · Source

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

Reserves capacity for at least `additional` bytes more than the current length. The allocator may reserve more space to speculatively avoid frequent allocations. After calling `reserve`, capacity will be greater than or equal to `self.len() + additional`. Does nothing if capacity is already sufficient.

##### §Panics

Panics if the new capacity overflows `usize`.

##### §Examples

Basic usage:

    let mut s = String::new();

    s.reserve(10);

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

This might 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 at least 10
    let capacity = s.capacity();
    assert_eq!(2, s.len());
    assert!(capacity >= 10);

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

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

1.0.0 · Source

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

Reserves the minimum capacity for at least `additional` bytes more than the current length. Unlike `reserve`, this will not deliberately over-allocate to speculatively avoid frequent allocations. After calling `reserve_exact`, capacity will be greater than or equal to `self.len() + additional`. Does nothing if the capacity is already sufficient.

##### §Panics

Panics if the new capacity overflows `usize`.

##### §Examples

Basic usage:

    let mut s = String::new();

    s.reserve_exact(10);

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

This might 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 at least 10
    let capacity = s.capacity();
    assert_eq!(2, s.len());
    assert!(capacity >= 10);

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

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

1.57.0 · Source

#### pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError>

Tries to reserve capacity for at least `additional` bytes more than the current length. The allocator may reserve more space to speculatively avoid frequent allocations. After calling `try_reserve`, capacity will be greater than or equal to `self.len() + additional` if it returns `Ok(())`. Does nothing if capacity is already sufficient. This method preserves the contents even if an error occurs.

##### §Errors

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

##### §Examples

    use std::collections::TryReserveError;

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

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

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

        Ok(output)
    }

1.57.0 · Source

#### pub fn try_reserve_exact( &mut self, additional: usize, ) -> Result<(), TryReserveError>

Tries to reserve the minimum capacity for at least `additional` bytes more than the current length. Unlike `try_reserve`, this will not deliberately over-allocate to speculatively avoid frequent allocations. After calling `try_reserve_exact`, capacity will be greater than or equal to `self.len() + additional` if it returns `Ok(())`. Does nothing if the capacity is already sufficient.

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

##### §Errors

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

##### §Examples

    use std::collections::TryReserveError;

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

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

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

        Ok(output)
    }

1.0.0 · Source

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

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

##### §Examples

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

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

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

1.56.0 · Source

#### pub fn shrink_to(&mut self, min_capacity: usize)

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

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

If the current capacity is less than the lower limit, this is a no-op.

##### §Examples

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

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

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

1.0.0 · Source

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

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

##### §Examples

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

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

    assert_eq!("abc123", s);

1.0.0 (const: unstable) · Source

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

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

The inverse of this method is `from_utf8`.

##### §Examples

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

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

1.0.0 · Source

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

Shortens this `String` to the specified length.

If `new_len` is greater than or equal to 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

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

    s.truncate(2);

    assert_eq!("he", s);

1.0.0 · Source

#### pub 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

    let mut s = String::from("abč");

    assert_eq!(s.pop(), Some('č'));
    assert_eq!(s.pop(), Some('b'));
    assert_eq!(s.pop(), Some('a'));

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

1.0.0 · Source

#### pub 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

    let mut s = String::from("abç");

    assert_eq!(s.remove(0), 'a');
    assert_eq!(s.remove(1), 'ç');
    assert_eq!(s.remove(0), 'b');

Source

#### pub fn remove_matches<P: Pattern>(&mut self, pat: P)

🔬This is a nightly-only experimental API. (`string_remove_matches` #72826)

Remove all matches of pattern `pat` in the `String`.

##### §Examples

    #![feature(string_remove_matches)]
    let mut s = String::from("Trees are not green, the sky is not blue.");
    s.remove_matches("not ");
    assert_eq!("Trees are green, the sky is blue.", s);

Matches will be detected and removed iteratively, so in cases where patterns overlap, only the first pattern will be removed:

    #![feature(string_remove_matches)]
    let mut s = String::from("banana");
    s.remove_matches("ana");
    assert_eq!("bna", s);

1.26.0 · Source

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

Retains only the characters specified by the predicate.

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

##### §Examples

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

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

    assert_eq!(s, "foobar");

Because the elements are visited exactly once in the original order, external state may be used to decide which elements to keep.

    let mut s = String::from("abcde");
    let keep = [false, true, true, false, true];
    let mut iter = keep.iter();
    s.retain(|_| *iter.next().unwrap());
    assert_eq!(s, "bce");

1.0.0 · Source

#### pub 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

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

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

    assert_eq!("foo", s);

1.16.0 · Source

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

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

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

    s.insert_str(0, "foo");

    assert_eq!("foobar", s);

1.0.0 (const: unstable) · Source

#### pub 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 the returned `&mut Vec` allows writing bytes which are not valid UTF-8. If this constraint is violated, using the original `String` after dropping the `&mut Vec` may violate memory safety, as the rest of the standard library assumes that `String`s are valid UTF-8.

##### §Examples

    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");

1.0.0 (const: unstable) · Source

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

Returns the length of this `String`, in bytes, not `char`s or graphemes. In other words, it might not be what a human considers the length of the string.

##### §Examples

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

    let fancy_f = String::from("ƒoo");
    assert_eq!(fancy_f.len(), 4);
    assert_eq!(fancy_f.chars().count(), 3);

1.0.0 (const: unstable) · Source

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

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

##### §Examples

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

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

1.16.0 · Source

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

Splits the string into two at the given byte 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!");

1.0.0 · Source

#### pub 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

    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 · Source

#### pub fn drain<R>(&mut self, range: R) -> Drain<'_> ⓘ
where R: RangeBounds<usize>,

Removes the specified range from the string in bulk, returning all removed characters as an iterator.

The returned iterator keeps a mutable borrow on the string to optimize its implementation.

##### §Panics

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

##### §Leaking

If the returned iterator goes out of scope without being dropped (due to `core::mem::forget`, for example), the string may still contain a copy of any drained characters, or may have lost characters arbitrarily, including characters outside the range.

##### §Examples

    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, like `clear()` does
    s.drain(..);
    assert_eq!(s, "");

1.27.0 · Source

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

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

##### §Panics

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

##### §Examples

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

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

1.4.0 · Source

#### pub fn into_boxed_str(self) -> Box<str>

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

Before doing the conversion, this method discards excess capacity like `shrink_to_fit`. Note that this call may reallocate and copy the bytes of the string.

##### §Examples

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

    let b = s.into_boxed_str();

1.72.0 · Source

#### pub fn leak<'a>(self) -> &'a mut str

Consumes and leaks the `String`, returning a mutable reference to the contents, `&'a mut str`.

The caller has free choice over the returned lifetime, including `'static`. Indeed, this function is ideally used for data that lives for the remainder of the program’s life, as dropping the returned reference will cause a memory leak.

It does not reallocate or shrink the `String`, so the leaked allocation may include unused capacity that is not part of the returned slice. If you want to discard excess capacity, call `into_boxed_str`, and then `Box::leak` instead. However, keep in mind that trimming the capacity may result in a reallocation and copy.

##### §Examples

    let x = String::from("bucket");
    let static_ref: &'static mut str = x.leak();
    assert_eq!(static_ref, "bucket");

## Methods from Deref<Target = str>§

1.0.0 · Source

#### pub fn replace<P: Pattern>(&self, from: P, to: &str) -> String

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"));
    assert_eq!("than an old", s.replace("is", "an"));

When the pattern doesn’t match, it returns this string slice as `String`:

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

1.16.0 · Source

#### pub fn replacen<P: Pattern>(&self, pat: P, to: &str, count: usize) -> String

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));

When the pattern doesn’t match, it returns this string slice as `String`:

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

1.2.0 · Source

#### pub 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`.

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());

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());

Languages without case are not changed:

    let new_year = "农历新年";

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

1.2.0 · Source

#### pub 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`.

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());

Scripts without case are not changed:

    let new_year = "农历新年";

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

One character can become multiple:

    let s = "tschüß";

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

1.16.0 · Source

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

Creates a new `String` by repeating a string `n` times.

##### §Panics

This function will panic if the capacity would overflow.

##### §Examples

Basic usage:

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

A panic upon overflow:

ⓘ

    // this will panic at runtime
    let huge = "0123456789abcdef".repeat(usize::MAX);

1.23.0 · Source

#### pub fn to_ascii_uppercase(&self) -> String

Returns a copy of this string where each character is mapped to its ASCII upper case equivalent.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To uppercase the value in-place, use `make_ascii_uppercase`.

To uppercase ASCII characters in addition to non-ASCII characters, use `to_uppercase`.

##### §Examples

    let s = "Grüße, Jürgen ❤";

    assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());

1.23.0 · Source

#### pub fn to_ascii_lowercase(&self) -> String

Returns a copy of this string where each character is mapped to its ASCII lower case equivalent.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To lowercase the value in-place, use `make_ascii_lowercase`.

To lowercase ASCII characters in addition to non-ASCII characters, use `to_lowercase`.

##### §Examples

    let s = "Grüße, Jürgen ❤";

    assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());

1.0.0 · Source

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

Returns the length of `self`.

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

##### §Examples

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

    assert_eq!("ƒoo".len(), 4); // fancy f!
    assert_eq!("ƒoo".chars().count(), 3);

1.0.0 · Source

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

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

##### §Examples

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

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

1.9.0 · Source

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

Checks that `index`-th byte is the first byte in a UTF-8 code point sequence or the end of the string.

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));

Source

#### pub fn floor_char_boundary(&self, index: usize) -> usize

🔬This is a nightly-only experimental API. (`round_char_boundary` #93743)

Finds the closest `x` not exceeding `index` where `is_char_boundary(x)` is `true`.

This method can help you truncate a string so that it’s still valid UTF-8, but doesn’t exceed a given number of bytes. Note that this is done purely at the character level and can still visually split graphemes, even though the underlying characters aren’t split. For example, the emoji 🧑‍🔬 (scientist) could be split so that the string only includes 🧑 (person) instead.

##### §Examples

    #![feature(round_char_boundary)]
    let s = "❤️🧡💛💚💙💜";
    assert_eq!(s.len(), 26);
    assert!(!s.is_char_boundary(13));

    let closest = s.floor_char_boundary(13);
    assert_eq!(closest, 10);
    assert_eq!(&s[..closest], "❤️🧡");

Source

#### pub fn ceil_char_boundary(&self, index: usize) -> usize

🔬This is a nightly-only experimental API. (`round_char_boundary` #93743)

Finds the closest `x` not below `index` where `is_char_boundary(x)` is `true`.

If `index` is greater than the length of the string, this returns the length of the string.

This method is the natural complement to `floor_char_boundary`. See that method for more details.

##### §Examples

    #![feature(round_char_boundary)]
    let s = "❤️🧡💛💚💙💜";
    assert_eq!(s.len(), 26);
    assert!(!s.is_char_boundary(13));

    let closest = s.ceil_char_boundary(13);
    assert_eq!(closest, 14);
    assert_eq!(&s[..closest], "❤️🧡💛");

1.0.0 · Source

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

Converts a string slice to a byte slice. To convert the byte slice back into a string slice, use the `from_utf8` function.

##### §Examples

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

1.20.0 · Source

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

Converts a mutable string slice to a mutable byte slice.

##### §Safety

The caller must ensure that the content of the slice is valid UTF-8 before the borrow ends and the underlying `str` is used.

Use of a `str` whose contents are not valid UTF-8 is undefined behavior.

##### §Examples

Basic usage:

    let mut s = String::from("Hello");
    let bytes = unsafe { s.as_bytes_mut() };

    assert_eq!(b"Hello", bytes);

Mutability:

    let mut s = String::from("🗻∈🌏");

    unsafe {
        let bytes = s.as_bytes_mut();

        bytes[0] = 0xF0;
        bytes[1] = 0x9F;
        bytes[2] = 0x8D;
        bytes[3] = 0x94;
    }

    assert_eq!("🍔∈🌏", s);

1.0.0 · Source

#### pub 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.

The caller must ensure that the returned pointer is never written to. If you need to mutate the contents of the string slice, use `as_mut_ptr`.

##### §Examples

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

1.36.0 · Source

#### pub fn as_mut_ptr(&mut self) -> *mut u8

Converts a mutable 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.

It is your responsibility to make sure that the string slice only gets modified in a way that it remains valid UTF-8.

1.20.0 · Source

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

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 = String::from("🗻∈🌏");

    assert_eq!(Some("🗻"), v.get(0..4));

    // indices not on UTF-8 sequence boundaries
    assert!(v.get(1..).is_none());
    assert!(v.get(..8).is_none());

    // out of bounds
    assert!(v.get(..42).is_none());

1.20.0 · Source

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

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("hello");
    // correct length
    assert!(v.get_mut(0..5).is_some());
    // out of bounds
    assert!(v.get_mut(..42).is_none());
    assert_eq!(Some("he"), v.get_mut(0..2).map(|v| &*v));

    assert_eq!("hello", v);
    {
        let s = v.get_mut(0..2);
        let s = s.map(|s| {
            s.make_ascii_uppercase();
            &*s
        });
        assert_eq!(Some("HE"), s);
    }
    assert_eq!("HEllo", v);

1.20.0 · Source

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

Returns an 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 not exceed 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));
    }

1.20.0 · Source

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

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 not exceed 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));
    }

1.0.0 · Source

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

👎Deprecated since 1.29.0: use `get_unchecked(begin..end)` instead

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 not exceed `end`.
- `begin` and `end` must be byte positions within the string slice.
- `begin` and `end` must lie on UTF-8 sequence boundaries.

##### §Examples

    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 · Source

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

👎Deprecated since 1.29.0: use `get_unchecked_mut(begin..end)` instead

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 not exceed `end`.
- `begin` and `end` must be byte positions within the string slice.
- `begin` and `end` must lie on UTF-8 sequence boundaries.

1.4.0 · Source

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

Divides 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 past the end of the last code point of the string slice. For a non-panicking alternative see `split_at_checked`.

##### §Examples

    let s = "Per Martin-Löf";

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

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

1.4.0 · Source

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

Divides 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 past the end of the last code point of the string slice. For a non-panicking alternative see `split_at_mut_checked`.

##### §Examples

    let mut s = "Per Martin-Löf".to_string();
    {
        let (first, last) = s.split_at_mut(3);
        first.make_ascii_uppercase();
        assert_eq!("PER", first);
        assert_eq!(" Martin-Löf", last);
    }
    assert_eq!("PER Martin-Löf", s);

1.80.0 · Source

#### pub fn split_at_checked(&self, mid: usize) -> Option<(&str, &str)>

Divides one string slice into two at an index.

The argument, `mid`, should be a valid byte offset from the start of the string. It must also be on the boundary of a UTF-8 code point. The method returns `None` if that’s not the case.

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_checked` method.

##### §Examples

    let s = "Per Martin-Löf";

    let (first, last) = s.split_at_checked(3).unwrap();
    assert_eq!("Per", first);
    assert_eq!(" Martin-Löf", last);

    assert_eq!(None, s.split_at_checked(13));  // Inside “ö”
    assert_eq!(None, s.split_at_checked(16));  // Beyond the string length

1.80.0 · Source

#### pub fn split_at_mut_checked( &mut self, mid: usize, ) -> Option<(&mut str, &mut str)>

Divides one mutable string slice into two at an index.

The argument, `mid`, should be a valid byte offset from the start of the string. It must also be on the boundary of a UTF-8 code point. The method returns `None` if that’s not the case.

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_checked` method.

##### §Examples

    let mut s = "Per Martin-Löf".to_string();
    if let Some((first, last)) = s.split_at_mut_checked(3) {
        first.make_ascii_uppercase();
        assert_eq!("PER", first);
        assert_eq!(" Martin-Löf", last);
    }
    assert_eq!("PER Martin-Löf", s);

    assert_eq!(None, s.split_at_mut_checked(13));  // Inside “ö”
    assert_eq!(None, s.split_at_mut_checked(16));  // Beyond the string length

1.0.0 · Source

#### pub 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 might not match your idea of what a ‘character’ is. Iteration over grapheme clusters may be what you actually want. This functionality is not provided by Rust’s standard library, check crates.io instead.

##### §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());

Remember, `char`s might not match your 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());

1.0.0 · Source

#### pub 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());

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

    let yes = "y̆es";

    let mut char_indices = yes.char_indices();

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

    // note the 3 here - the previous character took up two bytes
    assert_eq!(Some((3, 'e')), char_indices.next());
    assert_eq!(Some((4, 's')), char_indices.next());

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

1.0.0 · Source

#### pub fn bytes(&self) -> Bytes<'_> ⓘ

Returns 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

    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 · Source

#### pub fn split_whitespace(&self) -> SplitWhitespace<'_> ⓘ

Splits 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`. If you only want to split on ASCII whitespace instead, use `split_ascii_whitespace`.

##### §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());

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());

If the string is empty or all whitespace, the iterator yields no string slices:

    assert_eq!("".split_whitespace().next(), None);
    assert_eq!("   ".split_whitespace().next(), None);

1.34.0 · Source

#### pub fn split_ascii_whitespace(&self) -> SplitAsciiWhitespace<'_> ⓘ

Splits a string slice by ASCII whitespace.

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

To split by Unicode `Whitespace` instead, use `split_whitespace`.

##### §Examples

Basic usage:

    let mut iter = "A few words".split_ascii_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 ASCII whitespace are considered:

    let mut iter = " Mary   had\ta little  \n\t lamb".split_ascii_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());

If the string is empty or all ASCII whitespace, the iterator yields no string slices:

    assert_eq!("".split_ascii_whitespace().next(), None);
    assert_eq!("   ".split_ascii_whitespace().next(), None);

1.0.0 · Source

#### pub fn lines(&self) -> Lines<'_> ⓘ

Returns an iterator over the lines of a string, as string slices.

Lines are split at line endings that are either newlines (`\n`) or sequences of a carriage return followed by a line feed (`\r\n`).

Line terminators are not included in the lines returned by the iterator.

Note that any carriage return (`\r`) not immediately followed by a line feed (`\n`) does not split a line. These carriage returns are thereby included in the produced lines.

The final line ending is optional. A string that ends with a final line ending will return the same lines as an otherwise identical string without a final line ending.

##### §Examples

Basic usage:

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

    assert_eq!(Some("foo"), lines.next());
    assert_eq!(Some("bar"), lines.next());
    assert_eq!(Some(""), lines.next());
    // Trailing carriage return is included in the last line
    assert_eq!(Some("baz\r"), lines.next());

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

The final line does not require any ending:

    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());

1.0.0 · Source

#### pub fn lines_any(&self) -> LinesAny<'_> ⓘ

👎Deprecated since 1.4.0: use lines() instead now

Returns an iterator over the lines of a string.

1.8.0 · Source

#### pub fn encode_utf16(&self) -> EncodeUtf16<'_> ⓘ

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

##### §Examples

    let text = "Zażółć gęślą jaźń";

    let utf8_len = text.len();
    let utf16_len = text.encode_utf16().count();

    assert!(utf16_len <= utf8_len);

1.0.0 · Source

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

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

Returns `false` if it does not.

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

##### §Examples

    let bananas = "bananas";

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

1.0.0 · Source

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

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

Returns `false` if it does not.

The pattern can be a `&str`, in which case this function will return true if the `&str` is a prefix of this string slice.

The pattern can also be a `char`, a slice of `char`s, or a function or closure that determines if a character matches. These will only be checked against the first character of this string slice. Look at the second example below regarding behavior for slices of `char`s.

##### §Examples

    let bananas = "bananas";

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

    let bananas = "bananas";

    // Note that both of these assert successfully.
    assert!(bananas.starts_with(&['b', 'a', 'n', 'a']));
    assert!(bananas.starts_with(&['a', 'b', 'c', 'd']));

1.0.0 · Source

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

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

Returns `false` if it does not.

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

##### §Examples

    let bananas = "bananas";

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

1.0.0 · Source

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

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`, a slice of `char`s, or a function or closure that determines if a character matches.

##### §Examples

Simple patterns:

    let s = "Löwe 老虎 Léopard Gepardi";

    assert_eq!(s.find('L'), Some(0));
    assert_eq!(s.find('é'), Some(14));
    assert_eq!(s.find("pard"), Some(17));

More complex patterns using point-free style and 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));
    assert_eq!(s.find(|c: char| c.is_whitespace() || c.is_lowercase()), Some(1));
    assert_eq!(s.find(|c: char| (c < 'o') && (c > 'a')), Some(4));

Not finding the pattern:

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

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

1.0.0 · Source

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

Returns the byte index for the first character of the last match of the pattern in this string slice.

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

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

##### §Examples

Simple patterns:

    let s = "Löwe 老虎 Léopard Gepardi";

    assert_eq!(s.rfind('L'), Some(13));
    assert_eq!(s.rfind('é'), Some(14));
    assert_eq!(s.rfind("pard"), Some(24));

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));

Not finding the pattern:

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

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

1.0.0 · Source

#### pub fn split<P>(&self, pat: P) -> Split<'_, P> ⓘ
where P: Pattern,

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

The pattern can be a `&str`, `char`, a slice of `char`s, or a function or 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, e.g., `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"]);

If the pattern is a slice of chars, split on each occurrence of any of the characters:

    let v: Vec<&str> = "2020-11-03 23:59".split(&['-', ' ', ':', '@'][..]).collect();
    assert_eq!(v, ["2020", "11", "03", "23", "59"]);

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"]);

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"]);

Contiguous separators are separated by the empty string.

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

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

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", ""]);

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", ""]);

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"]);

It does not give you:

ⓘ

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

Use `split_whitespace` for this behavior.

1.51.0 · Source

#### pub fn split_inclusive<P>(&self, pat: P) -> SplitInclusive<'_, P> ⓘ
where P: Pattern,

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

Differs from the iterator produced by `split` in that `split_inclusive` leaves the matched part as the terminator of the substring.

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

##### §Examples

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

If the last element of the string is matched, that element will be considered the terminator of the preceding substring. That substring will be the last item returned by the iterator.

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

1.0.0 · Source

#### pub fn rsplit<P>(&self, pat: P) -> RSplit<'_, P> ⓘ
where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns 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`, a slice of `char`s, or a function or 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 `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"]);

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"]);

1.0.0 · Source

#### pub fn split_terminator<P>(&self, pat: P) -> SplitTerminator<'_, P> ⓘ
where P: Pattern,

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

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

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, e.g., `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

    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:C.D".split_terminator(&['.', ':'][..]).collect();
    assert_eq!(v, ["A", "B", "C", "D"]);

1.0.0 · Source

#### pub fn rsplit_terminator<P>(&self, pat: P) -> RSplitTerminator<'_, P> ⓘ
where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

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

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"]);

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

1.0.0 · Source

#### pub fn splitn<P>(&self, n: usize, pat: P) -> SplitN<'_, P> ⓘ
where P: Pattern,

Returns 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`, a slice of `char`s, or a function or closure that determines if a character matches.

##### §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, [""]);

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"]);

1.0.0 · Source

#### pub fn rsplitn<P>(&self, n: usize, pat: P) -> RSplitN<'_, P> ⓘ
where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns 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`, a slice of `char`s, or a function or closure that determines if a character matches.

##### §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"]);

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"]);

1.52.0 · Source

#### pub fn split_once<P>(&self, delimiter: P) -> Option<(&str, &str)>
where P: Pattern,

Splits the string on the first occurrence of the specified delimiter and returns prefix before delimiter and suffix after delimiter.

##### §Examples

    assert_eq!("cfg".split_once('='), None);
    assert_eq!("cfg=".split_once('='), Some(("cfg", "")));
    assert_eq!("cfg=foo".split_once('='), Some(("cfg", "foo")));
    assert_eq!("cfg=foo=bar".split_once('='), Some(("cfg", "foo=bar")));

1.52.0 · Source

#### pub fn rsplit_once<P>(&self, delimiter: P) -> Option<(&str, &str)>
where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Splits the string on the last occurrence of the specified delimiter and returns prefix before delimiter and suffix after delimiter.

##### §Examples

    assert_eq!("cfg".rsplit_once('='), None);
    assert_eq!("cfg=foo".rsplit_once('='), Some(("cfg", "foo")));
    assert_eq!("cfg=foo=bar".rsplit_once('='), Some(("cfg=foo", "bar")));

1.2.0 · Source

#### pub fn matches<P>(&self, pat: P) -> Matches<'_, P> ⓘ
where P: Pattern,

Returns an iterator over the disjoint matches of a pattern within the given string slice.

The pattern can be a `&str`, `char`, a slice of `char`s, or a function or 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, e.g., `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

    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 · Source

#### pub fn rmatches<P>(&self, pat: P) -> RMatches<'_, P> ⓘ
where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

The pattern can be a `&str`, `char`, a slice of `char`s, or a function or 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

    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 · Source

#### pub fn match_indices<P>(&self, pat: P) -> MatchIndices<'_, P> ⓘ
where P: Pattern,

Returns 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`, a slice of `char`s, or a function or 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, e.g., `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

    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 · Source

#### pub fn rmatch_indices<P>(&self, pat: P) -> RMatchIndices<'_, P> ⓘ
where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns 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`, a slice of `char`s, or a function or 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

    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`

1.0.0 · Source

#### pub 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`, which includes newlines.

##### §Examples

    let s = "\n Hello\tworld\t\n";

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

1.30.0 · Source

#### pub fn trim_start(&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`, which includes newlines.

##### §Text directionality

A string is a sequence of bytes. `start` in this context means the first position of that byte string; for a left-to-right language like English or Russian, this will be left side, and for right-to-left languages like Arabic or Hebrew, this will be the right side.

##### §Examples

Basic usage:

    let s = "\n Hello\tworld\t\n";
    assert_eq!("Hello\tworld\t\n", s.trim_start());

Directionality:

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

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

1.30.0 · Source

#### pub fn trim_end(&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`, which includes newlines.

##### §Text directionality

A string is a sequence of bytes. `end` in this context means the last position of that byte string; for a left-to-right language like English or Russian, this will be right side, and for right-to-left languages like Arabic or Hebrew, this will be the left side.

##### §Examples

Basic usage:

    let s = "\n Hello\tworld\t\n";
    assert_eq!("\n Hello\tworld", s.trim_end());

Directionality:

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

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

1.0.0 · Source

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

👎Deprecated since 1.33.0: superseded by `trim_start`

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());

Directionality:

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

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

1.0.0 · Source

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

👎Deprecated since 1.33.0: superseded by `trim_end`

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());

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());

1.0.0 · Source

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

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

The pattern can be a `char`, a slice of `char`s, or a function or 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");

A more complex pattern, using a closure:

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

1.30.0 · Source

#### pub fn trim_start_matches<P>(&self, pat: P) -> &str
where P: Pattern,

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

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

##### §Text directionality

A string is a sequence of bytes. `start` in this context means the first position of that byte string; for a left-to-right language like English or Russian, this will be left side, and for right-to-left languages like Arabic or Hebrew, this will be the right side.

##### §Examples

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

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

1.45.0 · Source

#### pub fn strip_prefix<P>(&self, prefix: P) -> Option<&str>
where P: Pattern,

Returns a string slice with the prefix removed.

If the string starts with the pattern `prefix`, returns the substring after the prefix, wrapped in `Some`. Unlike `trim_start_matches`, this method removes the prefix exactly once.

If the string does not start with `prefix`, returns `None`.

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

##### §Examples

    assert_eq!("foo:bar".strip_prefix("foo:"), Some("bar"));
    assert_eq!("foo:bar".strip_prefix("bar"), None);
    assert_eq!("foofoo".strip_prefix("foo"), Some("foo"));

1.45.0 · Source

#### pub fn strip_suffix<P>(&self, suffix: P) -> Option<&str>
where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns a string slice with the suffix removed.

If the string ends with the pattern `suffix`, returns the substring before the suffix, wrapped in `Some`. Unlike `trim_end_matches`, this method removes the suffix exactly once.

If the string does not end with `suffix`, returns `None`.

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

##### §Examples

    assert_eq!("bar:foo".strip_suffix(":foo"), Some("bar"));
    assert_eq!("bar:foo".strip_suffix("bar"), None);
    assert_eq!("foofoo".strip_suffix("foo"), Some("foo"));

1.30.0 · Source

#### pub fn trim_end_matches<P>(&self, pat: P) -> &str
where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

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

##### §Text directionality

A string is a sequence of bytes. `end` in this context means the last position of that byte string; for a left-to-right language like English or Russian, this will be right side, and for right-to-left languages like Arabic or Hebrew, this will be the left side.

##### §Examples

Simple patterns:

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

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

A more complex pattern, using a closure:

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

1.0.0 · Source

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

👎Deprecated since 1.33.0: superseded by `trim_start_matches`

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

The pattern can be a `&str`, `char`, a slice of `char`s, or a function or 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

    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");

1.0.0 · Source

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

👎Deprecated since 1.33.0: superseded by `trim_end_matches`

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

The pattern can be a `&str`, `char`, a slice of `char`s, or a function or 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");

A more complex pattern, using a closure:

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

1.0.0 · Source

#### pub 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 into 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.

##### §Examples

Basic usage:

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

    assert_eq!(4, four);

Using the ‘turbofish’ instead of annotating `four`:

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

    assert_eq!(Ok(4), four);

Failing to parse:

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

    assert!(nope.is_err());

1.23.0 · Source

#### pub fn is_ascii(&self) -> bool

Checks if all characters in this string are within the ASCII range.

##### §Examples

    let ascii = "hello!\n";
    let non_ascii = "Grüße, Jürgen ❤";

    assert!(ascii.is_ascii());
    assert!(!non_ascii.is_ascii());

Source

#### pub fn as_ascii(&self) -> Option<&[AsciiChar]>

🔬This is a nightly-only experimental API. (`ascii_char` #110998)

If this string slice `is_ascii`, returns it as a slice of ASCII characters, otherwise returns `None`.

1.23.0 · Source

#### pub fn eq_ignore_ascii_case(&self, other: &str) -> bool

Checks that two strings are an ASCII case-insensitive match.

Same as `to_ascii_lowercase(a) == to_ascii_lowercase(b)`, but without allocating and copying temporaries.

##### §Examples

    assert!("Ferris".eq_ignore_ascii_case("FERRIS"));
    assert!("Ferrös".eq_ignore_ascii_case("FERRöS"));
    assert!(!"Ferrös".eq_ignore_ascii_case("FERRÖS"));

1.23.0 · Source

#### pub fn make_ascii_uppercase(&mut self)

Converts this string to its ASCII upper case equivalent in-place.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To return a new uppercased value without modifying the existing one, use `to_ascii_uppercase()`.

##### §Examples

    let mut s = String::from("Grüße, Jürgen ❤");

    s.make_ascii_uppercase();

    assert_eq!("GRüßE, JüRGEN ❤", s);

1.23.0 · Source

#### pub fn make_ascii_lowercase(&mut self)

Converts this string to its ASCII lower case equivalent in-place.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To return a new lowercased value without modifying the existing one, use `to_ascii_lowercase()`.

##### §Examples

    let mut s = String::from("GRÜßE, JÜRGEN ❤");

    s.make_ascii_lowercase();

    assert_eq!("grÜße, jÜrgen ❤", s);

1.80.0 · Source

#### pub fn trim_ascii_start(&self) -> &str

Returns a string slice with leading ASCII whitespace removed.

‘Whitespace’ refers to the definition used by `u8::is_ascii_whitespace`.

##### §Examples

    assert_eq!(" \t \u{3000}hello world\n".trim_ascii_start(), "\u{3000}hello world\n");
    assert_eq!("  ".trim_ascii_start(), "");
    assert_eq!("".trim_ascii_start(), "");

1.80.0 · Source

#### pub fn trim_ascii_end(&self) -> &str

Returns a string slice with trailing ASCII whitespace removed.

‘Whitespace’ refers to the definition used by `u8::is_ascii_whitespace`.

##### §Examples

    assert_eq!("\r hello world\u{3000}\n ".trim_ascii_end(), "\r hello world\u{3000}");
    assert_eq!("  ".trim_ascii_end(), "");
    assert_eq!("".trim_ascii_end(), "");

1.80.0 · Source

#### pub fn trim_ascii(&self) -> &str

Returns a string slice with leading and trailing ASCII whitespace removed.

‘Whitespace’ refers to the definition used by `u8::is_ascii_whitespace`.

##### §Examples

    assert_eq!("\r hello world\n ".trim_ascii(), "hello world");
    assert_eq!("  ".trim_ascii(), "");
    assert_eq!("".trim_ascii(), "");

1.34.0 · Source

#### pub fn escape_debug(&self) -> EscapeDebug<'_> ⓘ

Returns an iterator that escapes each char in `self` with `char::escape_debug`.

Note: only extended grapheme codepoints that begin the string will be escaped.

##### §Examples

As an iterator:

    for c in "❤\n!".escape_debug() {
        print!("{c}");
    }
    println!();

Using `println!` directly:

    println!("{}", "❤\n!".escape_debug());

Both are equivalent to:

    println!("❤\\n!");

Using `to_string`:

    assert_eq!("❤\n!".escape_debug().to_string(), "❤\\n!");

1.34.0 · Source

#### pub fn escape_default(&self) -> EscapeDefault<'_> ⓘ

Returns an iterator that escapes each char in `self` with `char::escape_default`.

##### §Examples

As an iterator:

    for c in "❤\n!".escape_default() {
        print!("{c}");
    }
    println!();

Using `println!` directly:

    println!("{}", "❤\n!".escape_default());

Both are equivalent to:

    println!("\\u{{2764}}\\n!");

Using `to_string`:

    assert_eq!("❤\n!".escape_default().to_string(), "\\u{2764}\\n!");

1.34.0 · Source

#### pub fn escape_unicode(&self) -> EscapeUnicode<'_> ⓘ

Returns an iterator that escapes each char in `self` with `char::escape_unicode`.

##### §Examples

As an iterator:

    for c in "❤\n!".escape_unicode() {
        print!("{c}");
    }
    println!();

Using `println!` directly:

    println!("{}", "❤\n!".escape_unicode());

Both are equivalent to:

    println!("\\u{{2764}}\\u{{a}}\\u{{21}}");

Using `to_string`:

    assert_eq!("❤\n!".escape_unicode().to_string(), "\\u{2764}\\u{a}\\u{21}");

Source

#### pub fn substr_range(&self, substr: &str) -> Option<Range<usize>>

🔬This is a nightly-only experimental API. (`substr_range` #126769)

Returns the range that a substring points to.

Returns `None` if `substr` does not point within `self`.

Unlike `str::find`, this does not search through the string. Instead, it uses pointer arithmetic to find where in the string `substr` is derived from.

This is useful for extending `str::split` and similar methods.

Note that this method may return false positives (typically either `Some(0..0)` or `Some(self.len()..self.len())`) if `substr` is a zero-length `str` that points at the beginning or end of another, independent, `str`.

##### §Examples

    #![feature(substr_range)]

    let data = "a, b, b, a";
    let mut iter = data.split(", ").map(|s| data.substr_range(s).unwrap());

    assert_eq!(iter.next(), Some(0..1));
    assert_eq!(iter.next(), Some(3..4));
    assert_eq!(iter.next(), Some(6..7));
    assert_eq!(iter.next(), Some(9..10));

Source

#### pub fn as_str(&self) -> &str

🔬This is a nightly-only experimental API. (`str_as_str` #130366)

Returns the same string as a string slice `&str`.

This method is redundant when used directly on `&str`, but it helps dereferencing other string-like types to string slices, for example references to `Box<str>` or `Arc<str>`.

## Trait Implementations§

1.0.0 · Source§

### impl Add<&str> for String

Implements the `+` operator for concatenating two strings.

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

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

#### §Examples

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

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

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

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

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

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

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#### type Output = String

The resulting type after applying the `+` operator.
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#### fn add(self, other: &str) -> String

Performs the `+` operation. Read more
1.12.0 · Source§

### impl AddAssign<&str> for String

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

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

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

Performs the `+=` operation. Read more
1.43.0 · Source§

### impl AsMut<str> for String

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#### fn as_mut(&mut self) -> &mut str

Converts this type into a mutable reference of the (usually inferred) input type.
1.0.0 · Source§

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

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

Converts this type into a shared reference of the (usually inferred) input type.
1.0.0 · Source§

### impl AsRef<str> for String

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

Converts this type into a shared reference of the (usually inferred) input type.
1.0.0 · Source§

### impl Borrow<str> for String

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

Immutably borrows from an owned value. Read more
1.36.0 · Source§

### impl BorrowMut<str> for String

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#### fn borrow_mut(&mut self) -> &mut str

Mutably borrows from an owned value. Read more
1.0.0 · Source§

### impl Clone for String

Source§

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

Clones the contents of `source` into `self`.

This method is preferred over simply assigning `source.clone()` to `self`, as it avoids reallocation if possible.

Source§

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

Returns a copy of the value. Read more
1.0.0 · Source§

### impl Debug for String

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

Formats the value using the given formatter. Read more
1.0.0 · Source§

### impl Default for String

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#### fn default() -> String

Creates an empty `String`.

1.0.0 · Source§

### impl Deref for String

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#### type Target = str

The resulting type after dereferencing.
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#### fn deref(&self) -> &str

Dereferences the value.
1.3.0 · Source§

### impl DerefMut for String

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

Mutably dereferences the value.
1.0.0 · Source§

### impl Display for String

Source§

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

Formats the value using the given formatter. Read more
1.2.0 · Source§

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

Source§

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

Extends a collection with the contents of an iterator. Read more
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#### fn extend_one(&mut self, c: &'a char)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
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#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.0.0 · Source§

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

Source§

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

Extends a collection with the contents of an iterator. Read more
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#### fn extend_one(&mut self, s: &'a str)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
Source§

#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.45.0 · Source§

### impl<A: Allocator> Extend<Box<str, A>> for String

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#### fn extend<I: IntoIterator<Item = Box<str, A>>>(&mut self, iter: I)

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

#### fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
Source§

#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.19.0 · Source§

### impl<'a> Extend<Cow<'a, str>> for String

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

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

#### fn extend_one(&mut self, s: Cow<'a, str>)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
Source§

#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.4.0 · Source§

### impl Extend<String> for String

Source§

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

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

#### fn extend_one(&mut self, s: String)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
Source§

#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.0.0 · Source§

### impl Extend<char> for String

Source§

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

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

#### fn extend_one(&mut self, c: char)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
Source§

#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.28.0 · Source§

### impl<'a> From<&'a String> for Cow<'a, str>

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

Converts a `String` reference into a `Borrowed` variant. No heap allocation is performed, and the string is not copied.

##### §Example

    let s = "eggplant".to_string();
    assert_eq!(Cow::from(&s), Cow::Borrowed("eggplant"));

1.35.0 · Source§

### impl From<&String> for String

Source§

#### fn from(s: &String) -> String

Converts a `&String` into a `String`.

This clones `s` and returns the clone.

1.44.0 · Source§

### impl From<&mut str> for String

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#### fn from(s: &mut str) -> String

Converts a `&mut str` into a `String`.

The result is allocated on the heap.

1.0.0 · Source§

### impl From<&str> for String

Source§

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

Converts a `&str` into a `String`.

The result is allocated on the heap.

1.18.0 · Source§

### impl From<Box<str>> for String

Source§

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

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

##### §Examples

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

    assert_eq!("hello world", s3)

1.14.0 · Source§

### impl<'a> From<Cow<'a, str>> for String

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

Converts a clone-on-write string to an owned instance of `String`.

This extracts the owned string, clones the string if it is not already owned.

##### §Example

    // If the string is not owned...
    let cow: Cow<'_, str> = Cow::Borrowed("eggplant");
    // It will allocate on the heap and copy the string.
    let owned: String = String::from(cow);
    assert_eq!(&owned[..], "eggplant");

1.21.0 · Source§

### impl From<String> for Arc<str>

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#### fn from(v: String) -> Arc<str>

Allocates a reference-counted `str` and copies `v` into it.

##### §Example

    let unique: String = "eggplant".to_owned();
    let shared: Arc<str> = Arc::from(unique);
    assert_eq!("eggplant", &shared[..]);

1.6.0 · Source§

### impl<'a> From<String> for Box<dyn Error + 'a>

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#### fn from(str_err: String) -> Box<dyn Error + 'a>

Converts a `String` into a box of dyn `Error`.

##### §Examples

    use std::error::Error;
    use std::mem;

    let a_string_error = "a string error".to_string();
    let a_boxed_error = Box::<dyn Error>::from(a_string_error);
    assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

1.0.0 · Source§

### impl<'a> From<String> for Box<dyn Error + Send + Sync + 'a>

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#### fn from(err: String) -> Box<dyn Error + Send + Sync + 'a>

Converts a `String` into a box of dyn `Error` + `Send` + `Sync`.

##### §Examples

    use std::error::Error;
    use std::mem;

    let a_string_error = "a string error".to_string();
    let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error);
    assert!(
        mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

1.20.0 · Source§

### impl From<String> for Box<str>

Source§

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

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

##### §Examples

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

    assert_eq!("hello world", s3)

1.0.0 · Source§

### impl<'a> From<String> for Cow<'a, str>

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

Converts a `String` into an `Owned` variant. No heap allocation is performed, and the string is not copied.

##### §Example

    let s = "eggplant".to_string();
    let s2 = "eggplant".to_string();
    assert_eq!(Cow::from(s), Cow::<'static, str>::Owned(s2));

1.21.0 · Source§

### impl From<String> for Rc<str>

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#### fn from(v: String) -> Rc<str>

Allocates a reference-counted string slice and copies `v` into it.

##### §Example

    let original: String = "statue".to_owned();
    let shared: Rc<str> = Rc::from(original);
    assert_eq!("statue", &shared[..]);

1.14.0 · Source§

### impl From<String> for Vec<u8>

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#### fn from(string: String) -> Vec<u8>

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

##### §Examples

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

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

1.46.0 · Source§

### impl From<char> for String

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#### fn from(c: char) -> Self

Allocates an owned `String` from a single character.

##### §Example

    let c: char = 'a';
    let s: String = String::from(c);
    assert_eq!("a", &s[..]);

1.17.0 · Source§

### impl<'a> FromIterator<&'a char> for String

Source§

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

Creates a value from an iterator. Read more
1.0.0 · Source§

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

Source§

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

Creates a value from an iterator. Read more
1.45.0 · Source§

### impl<A: Allocator> FromIterator<Box<str, A>> for String

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#### fn from_iter<I: IntoIterator<Item = Box<str, A>>>(iter: I) -> String

Creates a value from an iterator. Read more
1.19.0 · Source§

### impl<'a> FromIterator<Cow<'a, str>> for String

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

Creates a value from an iterator. Read more
1.80.0 · Source§

### impl FromIterator<String> for Box<str>

Source§

#### fn from_iter<T: IntoIterator<Item = String>>(iter: T) -> Self

Creates a value from an iterator. Read more
1.12.0 · Source§

### impl<'a> FromIterator<String> for Cow<'a, str>

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

Creates a value from an iterator. Read more
1.4.0 · Source§

### impl FromIterator<String> for String

Source§

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

Creates a value from an iterator. Read more
1.0.0 · Source§

### impl FromIterator<char> for String

Source§

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

Creates a value from an iterator. Read more
1.0.0 · Source§

### impl FromStr for String

Source§

#### type Err = Infallible

The associated error which can be returned from parsing.
Source§

#### fn from_str(s: &str) -> Result<String, Self::Err>

Parses a string `s` to return a value of this type. Read more
1.0.0 · Source§

### impl Hash for String

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

Feeds this value into the given `Hasher`. Read more
1.3.0 · Source§

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

Feeds a slice of this type into the given `Hasher`. Read more
1.0.0 · Source§

### impl<I> Index<I> for String
where I: SliceIndex<str>,

Source§

#### type Output = <I as SliceIndex<str>>::Output

The returned type after indexing.
Source§

#### fn index(&self, index: I) -> &I::Output

Performs the indexing (`container[index]`) operation. Read more
1.0.0 · Source§

### impl<I> IndexMut<I> for String
where I: SliceIndex<str>,

Source§

#### fn index_mut(&mut self, index: I) -> &mut I::Output

Performs the mutable indexing (`container[index]`) operation. Read more
1.0.0 · Source§

### impl Ord for String

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

This method returns an `Ordering` between `self` and `other`. Read more
1.21.0 · Source§

#### fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
1.21.0 · Source§

#### fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
1.50.0 · Source§

#### fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized,

Restrict a value to a certain interval. Read more
1.0.0 · Source§

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

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

Tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &&'a str) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

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

Source§

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

Tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &Cow<'a, str>) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

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

Source§

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

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

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

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

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

Source§

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

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

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

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

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

Source§

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

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

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

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

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

Source§

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

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

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

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl PartialEq for String

Source§

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

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 · Source§

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

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl PartialOrd for String

Source§

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

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

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl<'b> Pattern for &'b String

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

#### §Examples

    assert_eq!(String::from("Hello world").find("world"), Some(6));

Source§

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

🔬This is a nightly-only experimental API. (`pattern` #27721)
Associated searcher for this pattern
Source§

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

🔬This is a nightly-only experimental API. (`pattern` #27721)
Constructs the associated searcher from `self` and the `haystack` to search in.
Source§

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

🔬This is a nightly-only experimental API. (`pattern` #27721)
Checks whether the pattern matches anywhere in the haystack
Source§

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

🔬This is a nightly-only experimental API. (`pattern` #27721)
Checks whether the pattern matches at the front of the haystack
Source§

#### fn strip_prefix_of(self, haystack: &str) -> Option<&str>

🔬This is a nightly-only experimental API. (`pattern` #27721)
Removes the pattern from the front of haystack, if it matches.
Source§

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

🔬This is a nightly-only experimental API. (`pattern` #27721)
Checks whether the pattern matches at the back of the haystack
Source§

#### fn strip_suffix_of<'a>(self, haystack: &'a str) -> Option<&'a str>
where Self::Searcher<'a>: ReverseSearcher<'a>,

🔬This is a nightly-only experimental API. (`pattern` #27721)
Removes the pattern from the back of haystack, if it matches.
Source§

#### fn as_utf8_pattern(&self) -> Option<Utf8Pattern<'_>>

🔬This is a nightly-only experimental API. (`pattern` #27721)
Returns the pattern as utf-8 bytes if possible.
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### impl TryFrom<CString> for String

Source§

#### fn try_from(value: CString) -> Result<Self, Self::Error>

Converts a `CString` into a `String` if it contains valid UTF-8 data.

This method is equivalent to `CString::into_string`.

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#### type Error = IntoStringError

The type returned in the event of a conversion error.
1.0.0 · Source§

### impl Write for String

Source§

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

Writes a string slice into this writer, returning whether the write succeeded. Read more
Source§

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

Writes a `char` into this writer, returning whether the write succeeded. Read more
1.0.0 · Source§

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

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

### impl DerefPure for String

1.0.0 · Source§

### impl Eq for String

1.0.0 · Source§

### impl StructuralPartialEq for String

## Auto Trait Implementations§

§

### impl Freeze for String

§

### impl RefUnwindSafe for String

§

### impl Send for String

§

### impl Sync for String

§

### impl Unpin for String

§

### impl UnwindSafe for String

## Blanket Implementations§

Source§

### impl<T> Any for T
where T: 'static + ?Sized,

Source§

#### fn type_id(&self) -> TypeId

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

### impl<T> Borrow<T> for T
where T: ?Sized,

Source§

#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

Source§

#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
Source§

### impl<T> CloneToUninit for T
where T: Clone,

Source§

#### unsafe fn clone_to_uninit(&self, dst: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit` #126799)
Performs copy-assignment from `self` to `dst`. Read more
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### impl<T> From<T> for T

Source§

#### fn from(t: T) -> T

Returns the argument unchanged.

Source§

### impl<T, U> Into<U> for T
where U: From<T>,

Source§

#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

Source§

### impl<P, T> Receiver for P
where P: Deref<Target = T> + ?Sized, T: ?Sized,

Source§

#### type Target = T

🔬This is a nightly-only experimental API. (`arbitrary_self_types` #44874)
The target type on which the method may be called.
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### impl<T> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
Source§

#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T> ToString for T
where T: Display + ?Sized,

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

Converts the given value to a `String`. Read more
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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

Source§

#### type Error = Infallible

The type returned in the event of a conversion error.
Source§

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

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

Source§

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

The type returned in the event of a conversion error.
Source§

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

Performs the conversion.