Struct heapless::String

pub struct String<const N: usize> { /* private fields */ }

A fixed capacity String

Implementations

impl<const N: usize> String<N>

pub const fn new() -> Self

Constructs a new, empty String with a fixed capacity of N bytes

Examples

Basic usage:

use heapless::String;

// allocate the string on the stack
let mut s: String<4> = String::new();

// allocate the string in a static variable
static mut S: String<4> = String::new();

pub fn from_utf8(vec: Vec<u8, N>) -> Result<Self, Utf8Error>

Convert UTF-8 bytes into a String.

Examples

Basic usage:

use heapless::{String, Vec};

let mut sparkle_heart = Vec::<u8, 4>::new();
sparkle_heart.extend_from_slice(&[240, 159, 146, 150]);

let sparkle_heart: String<4> = String::from_utf8(sparkle_heart)?;
assert_eq!("💖", sparkle_heart);

Invalid UTF-8:

use core::str::Utf8Error;
use heapless::{String, Vec};

let mut vec = Vec::<u8, 4>::new();
vec.extend_from_slice(&[0, 159, 146, 150]);

let e: Utf8Error = String::from_utf8(vec).unwrap_err();
assert_eq!(e.valid_up_to(), 1);

pub unsafe fn from_utf8_unchecked(vec: Vec<u8, N>) -> Self

Convert UTF-8 bytes into a String, without checking that the string contains valid UTF-8.

Safety

The bytes passed in must be valid UTF-8.

Examples

Basic usage:

use heapless::{String, Vec};

let mut sparkle_heart = Vec::<u8, 4>::new();
sparkle_heart.extend_from_slice(&[240, 159, 146, 150]);

// Safety: `sparkle_heart` Vec is known to contain valid UTF-8
let sparkle_heart: String<4> = unsafe { String::from_utf8_unchecked(sparkle_heart) };
assert_eq!("💖", sparkle_heart);

pub fn into_bytes(self) -> Vec<u8, N>

Converts a String into a byte vector.

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

Examples

Basic usage:

use heapless::String;

let s: String<4> = String::try_from("ab")?;
let b = s.into_bytes();
assert!(b.len() == 2);

assert_eq!(&['a' as u8, 'b' as u8], &b[..]);

pub fn as_str(&self) -> &str

Extracts a string slice containing the entire string.

Examples

Basic usage:

use heapless::String;

let mut s: String<4> = String::try_from("ab")?;
assert!(s.as_str() == "ab");

let _s = s.as_str();
// s.push('c'); // <- cannot borrow `s` as mutable because it is also borrowed as immutable

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

Converts a String into a mutable string slice.

Examples

Basic usage:

use heapless::String;

let mut s: String<4> = String::try_from("ab")?;
let s = s.as_mut_str();
s.make_ascii_uppercase();

pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8, N>

Returns a mutable reference to the contents of this String.

Safety

This function is unsafe because it does not check that the bytes passed to it are valid UTF-8. If this constraint is violated, it may cause memory unsafety issues with future users of the String, as the rest of the library assumes that Strings are valid UTF-8.

Examples

Basic usage:

use heapless::String;

let mut s: String<8> = String::try_from("hello")?;

unsafe {
    let vec = s.as_mut_vec();
    assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);

    vec.reverse();
}
assert_eq!(s, "olleh");

pub fn push_str(&mut self, string: &str) -> Result<(), ()>

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

Examples

Basic usage:

use heapless::String;

let mut s: String<8> = String::try_from("foo")?;

assert!(s.push_str("bar").is_ok());

assert_eq!("foobar", s);

assert!(s.push_str("tender").is_err());

pub fn capacity(&self) -> usize

Returns the maximum number of elements the String can hold

Examples

Basic usage:

use heapless::String;

let mut s: String<4> = String::new();
assert!(s.capacity() == 4);

pub fn push(&mut self, c: char) -> Result<(), ()>

Appends the given char to the end of this String.

Examples

Basic usage:

use heapless::String;

let mut s: String<8> = String::try_from("abc")?;

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

assert!("abc123" == s.as_str());

assert_eq!("abc123", s);

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

Basic usage:

use heapless::String;

let mut s: String<8> = String::try_from("hello")?;

s.truncate(2);

assert_eq!("he", s);

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

Basic usage:

use heapless::String;

let mut s: String<8> = String::try_from("foo")?;

assert_eq!(s.pop(), Some('o'));
assert_eq!(s.pop(), Some('o'));
assert_eq!(s.pop(), Some('f'));

assert_eq!(s.pop(), None);
Ok::<(), ()>(())

pub fn remove(&mut self, index: usize) -> char

Removes a char from this String at a byte position and returns it.

Note: Because this shifts over the remaining elements, it has a worst-case performance of O(n).

Panics

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

Examples

Basic usage:

use heapless::String;

let mut s: String<8> = String::try_from("foo").unwrap();

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

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

Basic usage:

use heapless::String;

let mut s: String<8> = String::try_from("foo")?;

s.clear();

assert!(s.is_empty());
assert_eq!(0, s.len());
assert_eq!(8, s.capacity());
Ok::<(), ()>(())

Methods from Deref<Target = str>

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);

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());

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));

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

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

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], "❤️🧡");

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

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

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], "❤️🧡💛");

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);

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

Converts a mutable string slice to a mutable byte slice.

Safety

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

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

Examples

Basic usage:

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

assert_eq!(b"Hello", bytes);

Mutability:

let mut s = String::from("🗻∈🌏");

unsafe {
    let bytes = s.as_bytes_mut();

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

assert_eq!("🍔∈🌏", s);

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();

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.

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());

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);

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));
}

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));
}

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));
}

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.

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.

Examples

let s = "Per Martin-Löf";

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

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

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.

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);

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());

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());

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());

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());

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());

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

Splits a string slice by whitespace.

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

‘Whitespace’ is defined according to the terms of the Unicode Derived Core Property White_Space. If you only want to split on ASCII whitespace instead, use split_ascii_whitespace.

Examples

Basic usage:

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

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

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

All kinds of whitespace are considered:

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

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

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

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

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

Splits a string slice by ASCII whitespace.

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

To split by Unicode Whitespace instead, use split_whitespace.

Examples

Basic usage:

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

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

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

All kinds of ASCII whitespace are considered:

let mut iter = " Mary   had\ta little  \n\t lamb".split_ascii_whitespace();
assert_eq!(Some("Mary"), iter.next());
assert_eq!(Some("had"), iter.next());
assert_eq!(Some("a"), iter.next());
assert_eq!(Some("little"), iter.next());
assert_eq!(Some("lamb"), iter.next());

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

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

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

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());

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());

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

👎Deprecated since 1.4.0: use lines() instead now

An iterator over the lines of a string.

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);

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"));

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

Examples

let bananas = "bananas";

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

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"));

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));

More complex patterns using point-free style and closures:

let s = "Löwe 老虎 Léopard";

assert_eq!(s.find(char::is_whitespace), Some(5));
assert_eq!(s.find(char::is_lowercase), Some(1));
assert_eq!(s.find(|c: char| c.is_whitespace() || c.is_lowercase()), Some(1));
assert_eq!(s.find(|c: char| (c < 'o') && (c > 'a')), Some(4));

Not finding the pattern:

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

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

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));

More complex patterns with closures:

let s = "Löwe 老虎 Léopard";

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

Not finding the pattern:

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

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

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"]);

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

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

A more complex pattern, using a closure:

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

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

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

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

Contiguous separators are separated by the empty string.

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

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

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

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

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

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

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

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

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

It does not give you:

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

Use split_whitespace for this behavior.

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."]);

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"]);

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"]);

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"]);

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"]);

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"]);

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, [""]);

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"]);

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"]);

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"]);

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")));

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")));

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"]);

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"]);

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`

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`

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());

pub fn trim_start(&self) -> &str

Returns a string slice with leading whitespace removed.

‘Whitespace’ is defined according to the terms of the Unicode Derived Core Property White_Space, which includes newlines.

Text directionality

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

Examples

Basic usage:

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

Directionality:

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

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

pub fn trim_end(&self) -> &str

Returns a string slice with trailing whitespace removed.

‘Whitespace’ is defined according to the terms of the Unicode Derived Core Property White_Space, which includes newlines.

Text directionality

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

Examples

Basic usage:

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

Directionality:

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

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

pub fn trim_left(&self) -> &str

👎Deprecated since 1.33.0: superseded by trim_start

Returns a string slice with leading whitespace removed.

‘Whitespace’ is defined according to the terms of the Unicode Derived Core Property White_Space.

Text directionality

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

Examples

Basic usage:

let s = " Hello\tworld\t";

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

Directionality:

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

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

pub fn trim_right(&self) -> &str

👎Deprecated since 1.33.0: superseded by trim_end

Returns a string slice with trailing whitespace removed.

‘Whitespace’ is defined according to the terms of the Unicode Derived Core Property White_Space.

Text directionality

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

Examples

Basic usage:

let s = " Hello\tworld\t";

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

Directionality:

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

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

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");

A more complex pattern, using a closure:

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

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");

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 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"));

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"));

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");

A more complex pattern, using a closure:

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

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");

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");

A more complex pattern, using a closure:

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

pub fn parse<F>(&self) -> Result<F, <F as FromStr>::Err>

where F: FromStr,

Parses this string slice into another type.

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

parse can parse into any type that implements the FromStr trait.

Errors

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

Examples

Basic usage

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

assert_eq!(4, four);

Using the ‘turbofish’ instead of annotating four:

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

assert_eq!(Ok(4), four);

Failing to parse:

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

assert!(nope.is_err());

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());

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

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

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

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"));

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);

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);

pub fn trim_ascii_start(&self) -> &str

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

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(), "");

pub fn trim_ascii_end(&self) -> &str

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

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(), "");

pub fn trim_ascii(&self) -> &str

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

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(), "");

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!();

Using println! directly:

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

Both are equivalent to:

println!("❤\\n!");

Using to_string:

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

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!();

Using println! directly:

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

Both are equivalent to:

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

Using to_string:

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

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!();

Using println! directly:

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

Both are equivalent to:

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

Using to_string:

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

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

where P: Pattern<'a>,

Replaces all matches of a pattern with another string.

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

Examples

Basic usage:

let s = "this is old";

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

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

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

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

where P: Pattern<'a>,

Replaces first N matches of a pattern with another string.

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

Examples

Basic usage:

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

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

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

pub fn to_lowercase(&self) -> String

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

‘Lowercase’ is defined according to the terms of the Unicode Derived Core Property Lowercase.

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

Examples

Basic usage:

let s = "HELLO";

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

A tricky example, with sigma:

let sigma = "Σ";

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

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

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

Languages without case are not changed:

let new_year = "农历新年";

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

pub fn to_uppercase(&self) -> String

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

‘Uppercase’ is defined according to the terms of the Unicode Derived Core Property Uppercase.

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

Examples

Basic usage:

let s = "hello";

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

Scripts without case are not changed:

let new_year = "农历新年";

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

One character can become multiple:

let s = "tschüß";

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

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

Creates a new String by repeating a string n times.

Panics

This function will panic if the capacity would overflow.

Examples

Basic usage:

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

A panic upon overflow:

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

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());

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());

Trait Implementations

impl<const N: usize> AsRef<[u8]> for String<N>

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

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

impl<const N: usize> AsRef<str> for String<N>

fn as_ref(&self) -> &str

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

impl<const N: usize> Clone for String<N>

fn clone(&self) -> Self

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<const N: usize> Debug for String<N>

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

Formats the value using the given formatter.

impl<const N: usize> Default for String<N>

fn default() -> Self

Returns the “default value” for a type.

impl<const N: usize> Deref for String<N>

type Target = str

The resulting type after dereferencing.

fn deref(&self) -> &str

Dereferences the value.

impl<const N: usize> DerefMut for String<N>

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

Mutably dereferences the value.

impl<const N: usize> Display for String<N>

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

Formats the value using the given formatter.

impl<'a, const N: usize> FromIterator<&'a char> for String<N>

fn from_iter<T: IntoIterator<Item = &'a char>>(iter: T) -> Self

Creates a value from an iterator.

impl<'a, const N: usize> FromIterator<&'a str> for String<N>

fn from_iter<T: IntoIterator<Item = &'a str>>(iter: T) -> Self

Creates a value from an iterator.

impl<const N: usize> FromIterator<char> for String<N>

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

Creates a value from an iterator.

impl<const N: usize> FromStr for String<N>

type Err = ()

The associated error which can be returned from parsing.

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

Parses a string s to return a value of this type.

impl<const N: usize> Hash for String<N>

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

Feeds this value into the given Hasher.

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

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<const N: usize> Ord for String<N>

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

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

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

where Self: Sized + PartialOrd,

Restrict a value to a certain interval.

impl<const N: usize> PartialEq<&str> for String<N>

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

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

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.

impl<const N: usize> PartialEq<String<N>> for &str

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

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

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

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

impl<const N: usize> PartialEq<String<N>> for str

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

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

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

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

impl<const N1: usize, const N2: usize> PartialEq<String<N2>> for String<N1>

fn eq(&self, rhs: &String<N2>) -> bool

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

fn ne(&self, rhs: &String<N2>) -> bool

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

impl<const N: usize> PartialEq<str> for String<N>

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

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

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.

impl<const N1: usize, const N2: usize> PartialOrd<String<N2>> for String<N1>

fn partial_cmp(&self, other: &String<N2>) -> Option<Ordering>

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

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

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

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

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

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

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

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

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

impl<'a, const N: usize> TryFrom<&'a str> for String<N>

type Error = ()

The type returned in the event of a conversion error.

fn try_from(s: &'a str) -> Result<Self, Self::Error>

Performs the conversion.

impl<const N: usize> TryFrom<i16> for String<N>

type Error = ()

The type returned in the event of a conversion error.

fn try_from(s: i16) -> Result<Self, Self::Error>

Performs the conversion.

impl<const N: usize> TryFrom<i32> for String<N>

type Error = ()

The type returned in the event of a conversion error.

fn try_from(s: i32) -> Result<Self, Self::Error>

Performs the conversion.

impl<const N: usize> TryFrom<i64> for String<N>

type Error = ()

The type returned in the event of a conversion error.

fn try_from(s: i64) -> Result<Self, Self::Error>

Performs the conversion.

impl<const N: usize> TryFrom<i8> for String<N>

type Error = ()

The type returned in the event of a conversion error.

fn try_from(s: i8) -> Result<Self, Self::Error>

Performs the conversion.

impl<const N: usize> TryFrom<u16> for String<N>

type Error = ()

The type returned in the event of a conversion error.

fn try_from(s: u16) -> Result<Self, Self::Error>

Performs the conversion.

impl<const N: usize> TryFrom<u32> for String<N>

type Error = ()

The type returned in the event of a conversion error.

fn try_from(s: u32) -> Result<Self, Self::Error>

Performs the conversion.

impl<const N: usize> TryFrom<u64> for String<N>

type Error = ()

The type returned in the event of a conversion error.

fn try_from(s: u64) -> Result<Self, Self::Error>

Performs the conversion.

impl<const N: usize> TryFrom<u8> for String<N>

type Error = ()

The type returned in the event of a conversion error.

fn try_from(s: u8) -> Result<Self, Self::Error>

Performs the conversion.

impl<const N: usize> Write for String<N>

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

Writes a string slice into this writer, returning whether the write succeeded.

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

Writes a char into this writer, returning whether the write succeeded.

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

Glue for usage of the write! macro with implementors of this trait.

impl<const N: usize> Eq for String<N>