Struct alloc::string::String

1.0.0 · source ·
pub struct String { /* private fields */ }
Expand description

A UTF-8–encoded, growable string.

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

§Examples

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

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

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

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

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

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

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

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

assert_eq!("💖", sparkle_heart);
Run

§UTF-8

Strings 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, Strings are typically smaller than an array of the same chars:

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);
Run

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 ith 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('💖'));
Run

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);
Run

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]);
Run

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);
Run

This will create a &str from the String and pass it in. This conversion is very inexpensive, and so generally, functions will accept &strs 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);
Run

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

§Representation

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

This buffer is always stored on the heap.

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

use std::mem;

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

// 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);
Run

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

let mut s = String::new();

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

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

This will output the following:

0
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());
}
Run

We end up with a different output:

25
25
25
25
25
25

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

Implementations§

source§

impl String

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();
Run
source

pub fn with_capacity(capacity: usize) -> String

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

Strings 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');
Run
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.

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 Strings, 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);
Run

Incorrect bytes:

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

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

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

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);
Run

Incorrect bytes:

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

assert_eq!("Hello �World", output);
Run
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());
Run
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));
Run
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());
Run
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));
Run
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());
Run
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));
Run
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");
Run
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);
}
Run
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 Strings 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);
Run
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[..]);
Run
1.7.0 · 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());
Run
1.7.0 · 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);
Run
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);
Run
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");
Run
source

pub fn capacity(&self) -> usize

Returns this String’s capacity, in bytes.

§Examples
let s = String::with_capacity(10);

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

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());
Run
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);
Run

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());
Run
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)
}
Run
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)
}
Run
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());
Run
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);
Run
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);
Run
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());
Run
source

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

Shortens this String to the specified length.

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

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

§Panics

Panics if new_len does not lie on a char boundary.

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

s.truncate(2);

assert_eq!("he", s);
Run
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);
Run
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');
Run
source

pub fn remove_matches<'a, P>(&'a mut self, pat: P)
where P: for<'x> Pattern<'x>,

🔬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);
Run

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);
Run
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");
Run

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");
Run
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);
Run
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);
Run
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 Strings 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");
Run
source

pub fn len(&self) -> usize

Returns the length of this String, in bytes, not chars 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);
Run
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());
Run
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!");
Run
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());
Run
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, "");
Run
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");
Run
1.4.0 · source

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

Converts this String into a Box<str>.

This will drop any excess capacity.

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

let b = s.into_boxed_str();
Run
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 don’t want that, call into_boxed_str, and then Box::leak.

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

Methods from Deref<Target = str>§

source

pub fn replace<'a, P: Pattern<'a>>(&'a 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"));
Run

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"));
Run
1.16.0 · source

pub fn replacen<'a, P: Pattern<'a>>( &'a 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));
Run

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));
Run
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());
Run

A tricky example, with sigma:

let sigma = "Σ";

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

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

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

Languages without case are not changed:

let new_year = "农历新年";

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

Scripts without case are not changed:

let new_year = "农历新年";

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

One character can become multiple:

let s = "tschüß";

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

A panic upon overflow:

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

pub fn len(&self) -> usize

Returns the length of self.

This length is in bytes, not chars 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);
Run
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());
Run
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));
Run
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], "❤️🧡");
Run
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], "❤️🧡💛");
Run
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);
Run
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);
Run

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);
Run
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();
Run
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());
Run
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);
Run
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));
}
Run
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));
}
Run
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));
}
Run
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)

Divide one string slice into two at an index.

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

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

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

§Panics

Panics if mid is not on a UTF-8 code point boundary, or if it is 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);
Run
1.4.0 · source

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

Divide one mutable string slice into two at an index.

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

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

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

§Panics

Panics if mid is not on a UTF-8 code point boundary, or if it is 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);
Run
source

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

🔬This is a nightly-only experimental API. (split_at_checked #119128)

Divide 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
#![feature(split_at_checked)]

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
Run
source

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

🔬This is a nightly-only experimental API. (split_at_checked #119128)

Divide 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
#![feature(split_at_checked)]

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
Run
source

pub fn chars(&self) -> Chars<'_>

Returns an iterator over the chars 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());
Run

Remember, chars 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());
Run
source

pub fn char_indices(&self) -> CharIndices<'_>

Returns an iterator over the chars 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 chars, as well as their byte positions.

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

§Examples

Basic usage:

let word = "goodbye";

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

let mut char_indices = word.char_indices();

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

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

Remember, chars 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());
Run
source

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

An iterator over the bytes of a string slice.

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

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

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

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

All kinds of whitespace are considered:

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

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

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);
Run
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());
Run

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());
Run

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);
Run
source

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

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());
Run

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());
Run
source

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

👎Deprecated since 1.4.0: use lines() instead now

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);
Run
source

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

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

Returns false if it does not.

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

§Examples
let bananas = "bananas";

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

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

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

Returns false if it does not.

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 chars, 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 chars.

§Examples
let bananas = "bananas";

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

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

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

Returns false if it does not.

The pattern can be a &str, char, a slice of chars, 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"));
Run
source

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

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

Returns None if the pattern doesn’t match.

The pattern can be a &str, char, a slice of chars, 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));
Run

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));
Run

Not finding the pattern:

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

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

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

Returns the byte index 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 chars, 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));
Run

More complex patterns with closures:

let s = "Löwe 老虎 Léopard";

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

Not finding the pattern:

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

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

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

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

The pattern can be a &str, char, a slice of chars, 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"]);
Run

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"]);
Run

A more complex pattern, using a closure:

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

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

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

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

Contiguous separators are separated by the empty string.

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

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

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

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

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

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

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

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

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

It does not give you:

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

Use split_whitespace for this behavior.

1.51.0 · source

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

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 chars, 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."]);
Run

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"]);
Run
source

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

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

The pattern can be a &str, char, a slice of chars, 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"]);
Run

A more complex pattern, using a closure:

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

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

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

The pattern can be a &str, char, a slice of chars, 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"]);
Run
source

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

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

The pattern can be a &str, char, a slice of chars, 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"]);
Run
source

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

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

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

The pattern can be a &str, char, a slice of chars, 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, [""]);
Run

A more complex pattern, using a closure:

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

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

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

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

The pattern can be a &str, char, a slice of chars, 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"]);
Run

A more complex pattern, using a closure:

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

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

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")));
Run
1.52.0 · source

pub fn rsplit_once<'a, P>(&'a self, delimiter: P) -> Option<(&'a str, &'a str)>
where P: Pattern<'a>, <P as Pattern<'a>>::Searcher: 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")));
Run
1.2.0 · source

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

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

The pattern can be a &str, char, a slice of chars, 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"]);
Run
1.2.0 · source

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

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 chars, 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"]);
Run
1.5.0 · source

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

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

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

The pattern can be a &str, char, a slice of chars, 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`
Run
1.5.0 · source

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

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

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

The pattern can be a &str, char, a slice of chars, 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`
Run
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());
Run
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());
Run

Directionality:

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

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

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());
Run
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());
Run

Directionality:

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

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

Directionality:

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

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

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

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

The pattern can be a char, a slice of chars, 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");
Run

A more complex pattern, using a closure:

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

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

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

The pattern can be a &str, char, a slice of chars, 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");
Run
1.45.0 · source

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

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 chars, 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"));
Run
1.45.0 · source

pub fn strip_suffix<'a, P>(&'a self, suffix: P) -> Option<&'a str>
where P: Pattern<'a>, <P as Pattern<'a>>::Searcher: 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 chars, 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"));
Run
1.30.0 · source

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

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

The pattern can be a &str, char, a slice of chars, 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");
Run

A more complex pattern, using a closure:

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

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

👎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 chars, 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");
Run
source

pub fn trim_right_matches<'a, P>(&'a self, pat: P) -> &'a str
where P: Pattern<'a>, <P as Pattern<'a>>::Searcher: 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 chars, 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");
Run

A more complex pattern, using a closure:

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

Using the ‘turbofish’ instead of annotating four:

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

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

Failing to parse:

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

assert!(nope.is_err());
Run
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());
Run
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"));
Run
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);
Run
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);
Run
source

pub fn trim_ascii_start(&self) -> &str

🔬This is a nightly-only experimental API. (byte_slice_trim_ascii #94035)

Returns a string slice with leading ASCII whitespace removed.

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

§Examples
#![feature(byte_slice_trim_ascii)]

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(), "");
Run
source

pub fn trim_ascii_end(&self) -> &str

🔬This is a nightly-only experimental API. (byte_slice_trim_ascii #94035)

Returns a string slice with trailing ASCII whitespace removed.

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

§Examples
#![feature(byte_slice_trim_ascii)]

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(), "");
Run
source

pub fn trim_ascii(&self) -> &str

🔬This is a nightly-only experimental API. (byte_slice_trim_ascii #94035)

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

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

§Examples
#![feature(byte_slice_trim_ascii)]

assert_eq!("\r hello world\n ".trim_ascii(), "hello world");
assert_eq!("  ".trim_ascii(), "");
assert_eq!("".trim_ascii(), "");
Run
1.34.0 · source

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

Return 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!();
Run

Using println! directly:

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

Both are equivalent to:

println!("❤\\n!");
Run

Using to_string:

assert_eq!("❤\n!".escape_debug().to_string(), "❤\\n!");
Run
1.34.0 · source

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

Return 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!();
Run

Using println! directly:

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

Both are equivalent to:

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

Using to_string:

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

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

Return 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!();
Run

Using println! directly:

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

Both are equivalent to:

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

Using to_string:

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

Trait Implementations§

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 Strings takes the first by value and borrows the second:

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

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

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

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

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

type Output = String

The resulting type after applying the + operator.
source§

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.

source§

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

Performs the += operation. Read more
1.43.0 · source§

impl AsMut<str> for String

source§

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

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

impl AsRef<[u8]> for String

source§

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

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

impl AsRef<str> for String

source§

fn as_ref(&self) -> &str

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

impl Borrow<str> for String

source§

fn borrow(&self) -> &str

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

impl BorrowMut<str> for String

source§

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

Mutably borrows from an owned value. Read more
source§

impl Clone for String

source§

fn clone(&self) -> Self

Returns a copy of the value. Read more
source§

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

Performs copy-assignment from source. Read more
source§

impl Debug for String

source§

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

Formats the value using the given formatter. Read more
source§

impl Default for String

source§

fn default() -> String

Creates an empty String.

source§

impl Deref for String

§

type Target = str

The resulting type after dereferencing.
source§

fn deref(&self) -> &str

Dereferences the value.
1.3.0 · source§

impl DerefMut for String

source§

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

Mutably dereferences the value.
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
source§

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.
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
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
source§

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 Extend<Box<str>> for String

source§

fn extend<I: IntoIterator<Item = Box<str>>>(&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

source§

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
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>

source§

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"));
Run
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

source§

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

Converts a &mut str into a String.

The result is allocated on the heap.

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)
Run
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");
Run
1.21.0 · source§

impl From<String> for Arc<str>

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

Allocate a reference-counted str and copy v into it.

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

impl From<String> for Box<str>

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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)
Run
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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));
Run
1.21.0 · source§

impl From<String> for Rc<str>

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

Allocate a reference-counted string slice and copy v into it.

§Example
let original: String = "statue".to_owned();
let shared: Rc<str> = Rc::from(original);
assert_eq!("statue", &shared[..]);
Run
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}");
}
Run
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[..]);
Run
1.17.0 · source§

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

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

Creates a value from an iterator. Read more
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impl<'a> FromIterator<&'a str> for String

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

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

impl FromIterator<Box<str>> for String

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fn from_iter<I: IntoIterator<Item = Box<str>>>(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
1.12.0 · 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

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

Creates a value from an iterator. Read more
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impl FromIterator<char> for String

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

Creates a value from an iterator. Read more
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impl FromStr for String

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type Err = Infallible

The associated error which can be returned from parsing.
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fn from_str(s: &str) -> Result<String, Self::Err>

Parses a string s to return a value of this type. Read more
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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
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impl<I> Index<I> for String
where I: SliceIndex<str>,

§

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

The returned type after indexing.
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fn index(&self, index: I) -> &I::Output

Performs the indexing (container[index]) operation. Read more
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impl<I> IndexMut<I> for String
where I: SliceIndex<str>,

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

Performs the mutable indexing (container[index]) operation. Read more
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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 + PartialOrd,

Restrict a value to a certain interval. Read more
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impl<'a, 'b> PartialEq<&'a str> for String

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

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

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<'a, 'b> PartialEq<Cow<'a, str>> for String

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

This method 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

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<'a, 'b> PartialEq<String> for &'a str

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

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &String) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<'a, 'b> PartialEq<String> for Cow<'a, str>

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

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &String) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<'a, 'b> PartialEq<String> for str

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

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &String) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<'a, 'b> PartialEq<str> for String

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

This method tests for self and other values to be equal, and is used by ==.
source§

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

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl PartialEq for String

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

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl PartialOrd for String

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

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more
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impl<'a, 'b> Pattern<'a> for &'b String

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

§Examples

assert_eq!(String::from("Hello world").find("world"), Some(6));
Run
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type Searcher = <&'b str as Pattern<'a>>::Searcher

🔬This is a nightly-only experimental API. (pattern #27721)
Associated searcher for this pattern
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fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher

🔬This is a nightly-only experimental API. (pattern #27721)
Constructs the associated searcher from self and the haystack to search in.
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fn is_contained_in(self, haystack: &'a str) -> bool

🔬This is a nightly-only experimental API. (pattern #27721)
Checks whether the pattern matches anywhere in the haystack
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fn is_prefix_of(self, haystack: &'a str) -> bool

🔬This is a nightly-only experimental API. (pattern #27721)
Checks whether the pattern matches at the front of the haystack
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fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str>

🔬This is a nightly-only experimental API. (pattern #27721)
Removes the pattern from the front of haystack, if it matches.
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fn is_suffix_of(self, haystack: &'a str) -> bool

🔬This is a nightly-only experimental API. (pattern #27721)
Checks whether the pattern matches at the back of the haystack
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fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str>

🔬This is a nightly-only experimental API. (pattern #27721)
Removes the pattern from the back of haystack, if it matches.
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impl Write for String

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

Writes a string slice into this writer, returning whether the write succeeded. Read more
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fn write_char(&mut self, c: char) -> Result

Writes a char into this writer, returning whether the write succeeded. Read more
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fn write_fmt(&mut self, args: Arguments<'_>) -> Result<(), Error>

Glue for usage of the write! macro with implementors of this trait. Read more
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impl Eq for String

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impl StructuralPartialEq for String

Auto Trait Implementations§

§

impl Freeze for String

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impl RefUnwindSafe for String

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impl Send for String

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impl Sync for String

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impl Unpin for String

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impl UnwindSafe for String

Blanket Implementations§

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

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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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,

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

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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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.
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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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default 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>,

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type Error = Infallible

The type returned in the event of a conversion error.
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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>,

§

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

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.