Struct StringU8 

pub struct StringU8<const CAP: usize> { /* private fields */ }

🧶 A UTF-8 string with fixed capacity that stores length explicitly.

---

^{📍 text/str}

---

Suited for frequently inspected or manipulated text where constant-time length access is important. Uses extra space to provide O(1) length operations. For the opposite trade-off see StringNonul.

Internally, the current length is stored as a NonMaxU8.

Methods

• Constructors:

  • new (_checked).
  • from_str, (_truncate, _unchecked).
  • from_char (7, 8, 16, utf8).
  • from_array ( _unchecked^⚠, _nleft, _nleft_unchecked^⚠, _nright, _nright_unchecked^⚠).

• Deconstructors:

  • into_array.
  • as_array.
  • as_bytes (mut^⚠).
  • as_str (mut^⚠).
  • chars.

• Queries:

  • len.
  • is_empty.
  • is_full.
  • capacity.
  • remaining_capacity.

• Modifiers:

  • clear,
  • reset,
  • sanitize,
  • pop (try_, _unchecked),
  • push (try_).
  • push_str (try_, try_ _complete).

Implementations

impl<const CAP: usize> StringU8<CAP>

Constants

pub const MAX_CAPACITY: usize

The maximum allowed capacity.

impl<const CAP: usize> StringU8<CAP>

Constructors

pub const fn new() -> Self

Creates a new empty string from with a capacity of CAP bytes.

Panics

Panics if CAP > Self::MAX_CAPACITY.

Examples

let mut s = StringU8::<10>::new();
assert![size_of_val(&s) >= 10 + size_of::<u8>()]; // + padding

pub const fn new_checked() -> Result<Self, MismatchedCapacity>

Creates a new empty string from with a capacity of CAP bytes.

Errors

Returns MismatchedCapacity if CAP > Self::MAX_CAPACITY

pub const fn from_str(string: &str) -> Result<Self, MismatchedCapacity>

Creates a new string from a complete &str.

Errors

Returns MismatchedCapacity if CAP > Self::MAX_CAPACITY or if CAP < string.len().

This is implemented via Self::try_push_str_complete().

Examples

let s = StringU8::<13>::from_str("Hello Wørld!").unwrap();
assert_eq![s.as_str(), "Hello Wørld!"];

pub const fn from_str_truncate(string: &str) -> Result<Self, MismatchedCapacity>

Creates a new string from a &str, truncating if it does not fit.

Returns MismatchedCapacity if CAP > Self::MAX_CAPACITY

This is implemented via Self::push_str().

pub const fn from_str_unchecked(string: &str) -> Self

Creates a new string from a &str, truncating if it does not fit.

Panics

Panics if CAP > Self::MAX_CAPACITY.

This is implemented via Self::push_str().

pub const fn from_char(c: char) -> Result<Self, MismatchedCapacity>

Creates a new string from a char.

Errors

Returns MismatchedCapacity if CAP > Self::MAX_CAPACITY or if CAP < c.len_utf8().

Will always succeed if CAP >= 4 && CAP <= Self::MAX_CAPACITY.

Examples

assert_eq![StringU8::<4>::from_char('🐛').unwrap().as_str(), "🐛"];
assert![StringU8::<3>::from_char('🐛').is_err()];

pub const fn from_char7(c: char7) -> Result<Self, MismatchedCapacity>

Creates a new string from a char7.

Errors

Returns MismatchedCapacity if CAP > Self::MAX_CAPACITY or if CAP < 1.

Will always succeed if CAP >= 1 && CAP <= Self::MAX_CAPACITY.

Examples

let s = StringU8::<1>::from_char7(char7::try_from_char('@').unwrap()).unwrap();
assert_eq![s.as_str(), "@"];

assert![StringU8::<0>::from_char7(char7::try_from_char('@').unwrap()).is_err()];

pub const fn from_char8(c: char8) -> Result<Self, MismatchedCapacity>

Creates a new string from a char8.

Errors

Returns MismatchedCapacity if CAP > Self::MAX_CAPACITY or if `CAP < 2.

Will always succeed if CAP >= 2 && CAP <= Self::MAX_CAPACITY.

Examples

let s = StringU8::<2>::from_char8(char8::try_from_char('ß').unwrap()).unwrap();
assert_eq![s.as_str(), "ß"];

assert![StringU8::<1>::from_char8(char8::try_from_char('ß').unwrap()).is_err()];

pub const fn from_char16(c: char16) -> Result<Self, MismatchedCapacity>

Creates a new string from a char16.

Errors

Returns MismatchedCapacity if CAP > Self::MAX_CAPACITY || CAP < c.len_utf8().“]

Will always succeed if CAP >= 3 && CAP <= Self::MAX_CAPACITY.

Examples

let s = StringU8::<3>::from_char16(char16::try_from_char('€').unwrap()).unwrap();
assert_eq![s.as_str(), "€"];

assert![StringU8::<2>::from_char16(char16::try_from_char('€').unwrap()).is_err()];

pub const fn from_charu(c: charu) -> Result<Self, MismatchedCapacity>

Creates a new string from a charu.

Errors

Returns MismatchedCapacity if CAP > Self::MAX_CAPACITY || CAP < c.len_utf8().“]

Will always succeed if CAP >= 4 && CAP <= Self::MAX_CAPACITY.

Examples

let s = StringU8::<4>::from_charu(charu::from_char('🐛')).unwrap();
assert_eq![s.as_str(), "🐛"];

assert![StringU8::<3>::from_charu(charu::from_char('🐛')).is_err()];

pub const fn from_charu_unchecked(c: charu) -> Self

Creates a new string from a charu.

Panics

Panics if CAP > Self::MAX_CAPACITY || CAP < c.len_utf8().

Will always succeed if CAP >= 3 && CAP <= Self::MAX_CAPACITY.

Examples

let s = StringU8::<3>::from_charu_unchecked(charu::from_char('€'));
assert_eq![s, "€"]

StringU8::<2>::from_charu_unchecked(charu::from_char('€'));

pub const fn from_array(bytes: [u8; CAP]) -> Result<Self, InvalidText>

Returns a string from a slice of bytes.

Errors

Returns InvalidText::MismatchedCapacity if CAP > Self::MAX_CAPACITY and InvalidText::Utf8 if bytes are not valid UTF-8.

pub const unsafe fn from_array_unchecked(bytes: [u8; CAP]) -> Self

Available on crate feature unsafe_str only.

Returns a string from an array of bytes that must be valid UTF-8.

Panics

Panics if CAP > Self::MAX_CAPACITY.

Safety

The caller must ensure that the content of the slice is valid UTF-8.

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

pub const fn from_array_nleft( bytes: [u8; CAP], length: u8, ) -> Result<Self, InvalidText>

Returns a string from an array of bytes, truncated to n bytes counting from the left.

The new length is maxed out at CAP.

Errors

Returns InvalidText::MismatchedCapacity if CAP > Self::MAX_CAPACITY and InvalidText::Utf8 if bytes are not valid UTF-8.

pub const unsafe fn from_array_nleft_unchecked( bytes: [u8; CAP], length: u8, ) -> Self

Available on crate feature unsafe_str only.

Returns a string from an array of bytes, which must be valid UTF-8, truncated to n bytes counting from the left.

The new length is maxed out at CAP.

Panics

Panics if CAP > Self::MAX_CAPACITY.

Safety

The caller must ensure that the content of the truncated slice is valid UTF-8.

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

pub const fn from_array_nright( bytes: [u8; CAP], length: u8, ) -> Result<Self, InvalidText>

Returns a string from an array of bytes, truncated to n bytes counting from the right.

The new length is maxed out at CAP. Bytes are shift-copied without allocating a new array.

Errors

Returns InvalidText::MismatchedCapacity if CAP > Self::MAX_CAPACITY and InvalidText::Utf8 if bytes are not valid UTF-8.

pub const unsafe fn from_array_nright_unchecked( bytes: [u8; CAP], length: u8, ) -> Self

Available on crate feature unsafe_str only.

Returns a string from an array of bytes, which must be valid UTF-8, truncated to n bytes counting from the right.

The new length is maxed out at CAP. Bytes are shift-copied without allocating a new array.

Panics

Panics if CAP > Self::MAX_CAPACITY.

Safety

The caller must ensure that the content of the truncated slice is valid UTF-8.

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

impl<const CAP: usize> StringU8<CAP>

Deconstructors

pub const fn into_array(self) -> [u8; CAP]

Returns the inner array with the full contents.

The array contains all the bytes, including those outside the current length.

pub const fn as_array(&self) -> &[u8; CAP]

Returns a copy of the inner array with the full contents.

The array contains all the bytes, including those outside the current length.

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

Returns a byte slice of the inner string slice.

Features

Uses the unsafe_slice feature to skip validation checks.

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

Available on crate feature unsafe_str only.

Returns an exclusive byte slice of the inner string 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.

Features

Uses the unsafe_slice feature to skip validation checks.

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

Returns a reference to the inner string slice.

Features

Uses the unsafe_str feature to skip validation checks.

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

Available on crate feature unsafe_str only.

Returns an exclusive reference to the inner string 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.

pub const fn chars(&self) -> CharIter<'_, &str>

Returns an iterator over the chars of the string.

Features

Uses the unsafe_str feature to skip validation checks.

impl<const CAP: usize> StringU8<CAP>

Queries

pub const fn len(&self) -> usize

Returns the current string length in bytes.

pub const fn is_empty(&self) -> bool

Returns true if the current length is 0.

pub const fn is_full(&self) -> bool

Returns true if the current remaining capacity is 0.

pub const fn capacity() -> usize

Returns the total capacity in bytes.

pub const fn remaining_capacity(&self) -> usize

Returns the remaining capacity in bytes.

pub const fn eq(&self, other: &Self) -> bool

Checks the equality of two strings, with the same capacity and length.

It only checks the first self.len() bytes.

Examples

let mut a = StringU8::<16>::from_str_unchecked("hello world!");
let mut b = StringU8::<16>::from_str_unchecked("hello world!!!");
assert![!a.eq(&b)];
b.pop();
b.pop();
assert![a.eq(&b)];

impl<const CAP: usize> StringU8<CAP>

Modifiers

pub const fn clear(&mut self)

Sets the length to 0.

pub const fn reset(&mut self)

Sets the length to 0, and resets all the bytes to 0.

pub const fn sanitize(&mut self)

Zeros all unused bytes while maintaining the current length.

pub const fn pop(&mut self) -> Option<char>

Removes the last character and returns it, or None if the string is empty.

pub const fn try_pop(&mut self) -> Result<char, NotEnoughElements>

Tries to remove the last character and returns it.

Errors

Returns a NotEnoughElements error if the capacity is not enough to hold the character.

pub const fn pop_unchecked(&mut self) -> char

Removes the last character and returns it.

Panics

Panics if the string is empty.

Examples

let mut s = StringU8::<16>::new();
s.push_str("hello worlð!");
assert_eq![s.len(), 13];

assert_eq![s.pop_unchecked(), '!'];
assert_eq![s.len(), 12];

assert_eq![s.pop_unchecked(), 'ð'];
assert_eq![s.len(), 10];

pub const fn push(&mut self, character: char) -> usize

Appends to the end of the string the given character.

Returns the number of bytes written.

Returns 0 bytes if the given character doesn’t fit in the remaining capacity.

pub const fn try_push( &mut self, character: char, ) -> Result<usize, NotEnoughSpace>

Tries to append to the end of the string the given character.

Returns the number of bytes written.

Errors

Returns NotEnoughSpace if the available capacity is not enough to hold the given character.

pub const fn push_charu(&mut self, c: charu) -> usize

Appends to the end of the string the given character.

Returns the number of bytes written.

Returns 0 bytes if the given character doesn’t fit in the remaining capacity.

pub const fn push_str(&mut self, string: &str) -> usize

Appends as many complete characters from string as will fit.

Returns the number of bytes written. UTF-8 characters are never split.

Examples

let mut s = StringU8::<5>::new();
assert_eq!(s.push_str("café"), 5);
assert_eq!(s, "café");

let mut s = StringU8::<4>::new();
assert_eq!(s.push_str("café"), 3);
assert_eq!(s, "caf");

let mut s = StringU8::<2>::new();
assert_eq!(s.push_str("サ"), 0);
assert_eq!(s, "");

pub const fn try_push_str(&mut self, string: &str) -> Result<usize, usize>

Appends characters from string, returning Ok if all fit, Err if partial.

• Ok(bytes): Entire string was written successfully
• Err(partial): Only partial bytes could be written (UTF-8 safe)

In both cases, the bytes are appended to the buffer.

pub const fn try_push_str_complete( &mut self, string: &str, ) -> Result<usize, usize>

Appends the entire string or nothing at all.

Returns Ok(bytes) if the string fits completely, or Err(0) if it doesn’t. No partial writes will occur to the buffer.

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

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

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

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

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

Divides one string slice into two at an index.

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

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

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

Panics

Panics if mid is not on a UTF-8 code point boundary, or if it is past the end of the last code point of the string slice. For a non-panicking alternative see split_at_checked.

Examples

let s = "Per Martin-Löf";

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

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

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

Divides one string slice into two at an index.

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

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

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

Examples

let s = "Per Martin-Löf";

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

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

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<'_>

Returns an iterator over the bytes of a string slice.

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

Examples

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

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

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

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.

This uses the same definition as char::is_ascii_whitespace. To split by Unicode Whitespace instead, use split_whitespace. Note that because of this difference in definition, even if s.is_ascii() is true, s.split_ascii_whitespace() behavior will differ from s.split_whitespace() if s contains U+000B VERTICAL TAB.

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());

Various kinds of ASCII whitespace are considered (see char::is_ascii_whitespace):

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<'_>

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

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

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

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

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

An empty string returns an empty iterator.

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());

An empty string returns an empty iterator:

let text = "";
let mut lines = text.lines();

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

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

👎Deprecated since 1.4.0:

use lines() instead now

Returns an iterator over the lines of a string.

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

Returns an iterator of u16 over the string encoded as native endian UTF-16 (without byte-order mark).

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<P>(&self, pat: P) -> bool

where P: Pattern,

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

Returns false if it does not.

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> bool

where P: Pattern,

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

Returns false if it does not.

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

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

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']));

pub fn ends_with<P>(&self, pat: P) -> bool

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

Returns false if it does not.

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> Option<usize>

where P: Pattern,

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

Returns None if the pattern doesn’t match.

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> Option<usize>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

Returns None if the pattern doesn’t match.

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> Split<'_, P>

where P: Pattern,

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

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

If there are no matches the full string slice is returned as the only item in the iterator.

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> = "AABBCC".split("DD").collect();
assert_eq!(v, ["AABBCC"]);

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<P>(&self, pat: P) -> SplitInclusive<'_, P>

where P: Pattern,

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

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

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> RSplit<'_, P>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> SplitTerminator<'_, P>

where P: Pattern,

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

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> RSplitTerminator<'_, P>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

The pattern can be a &str, char, a slice of 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<P>(&self, n: usize, pat: P) -> SplitN<'_, P>

where P: Pattern,

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

If n substrings are returned, the last substring (the 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<P>(&self, n: usize, pat: P) -> RSplitN<'_, P>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

If n substrings are returned, the last substring (the 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<P>(&self, delimiter: P) -> Option<(&str, &str)>

where P: Pattern,

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

Examples

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

pub fn rsplit_once<P>(&self, delimiter: P) -> Option<(&str, &str)>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

Examples

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

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

where P: Pattern,

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

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> RMatches<'_, P>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> MatchIndices<'_, P>

where P: Pattern,

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

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

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> RMatchIndices<'_, P>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

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

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> &str

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> DoubleEndedSearcher<'a>,

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

The pattern can be a char, a slice of 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<P>(&self, pat: P) -> &str

where P: Pattern,

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

The pattern can be a &str, char, a slice of 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<P>(&self, prefix: P) -> Option<&str>

where P: Pattern,

Returns a string slice with the prefix removed.

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

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

The pattern can be a &str, char, a slice of 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<P>(&self, suffix: P) -> Option<&str>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns a string slice with the suffix removed.

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

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

The pattern can be a &str, char, a slice of 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 strip_circumfix<P, S>(&self, prefix: P, suffix: S) -> Option<&str>

where P: Pattern, S: Pattern, <S as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

Returns a string slice with the prefix and suffix removed.

If the string starts with the pattern prefix and ends with the pattern suffix, returns the substring after the prefix and before the suffix, wrapped in Some. Unlike trim_start_matches and trim_end_matches, this method removes both the prefix and suffix exactly once.

If the string does not start with prefix or does not end with suffix, returns None.

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

Examples

#![feature(strip_circumfix)]

assert_eq!("bar:hello:foo".strip_circumfix("bar:", ":foo"), Some("hello"));
assert_eq!("bar:foo".strip_circumfix("foo", "foo"), None);
assert_eq!("foo:bar;".strip_circumfix("foo:", ';'), Some("bar"));

pub fn trim_prefix<P>(&self, prefix: P) -> &str

where P: Pattern,

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

Returns a string slice with the optional prefix removed.

If the string starts with the pattern prefix, returns the substring after the prefix. Unlike strip_prefix, this method always returns &str for easy method chaining, instead of returning Option<&str>.

If the string does not start with prefix, returns the original string unchanged.

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

Examples

#![feature(trim_prefix_suffix)]

// Prefix present - removes it
assert_eq!("foo:bar".trim_prefix("foo:"), "bar");
assert_eq!("foofoo".trim_prefix("foo"), "foo");

// Prefix absent - returns original string
assert_eq!("foo:bar".trim_prefix("bar"), "foo:bar");

// Method chaining example
assert_eq!("<https://example.com/>".trim_prefix('<').trim_suffix('>'), "https://example.com/");

pub fn trim_suffix<P>(&self, suffix: P) -> &str

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

Returns a string slice with the optional suffix removed.

If the string ends with the pattern suffix, returns the substring before the suffix. Unlike strip_suffix, this method always returns &str for easy method chaining, instead of returning Option<&str>.

If the string does not end with suffix, returns the original string unchanged.

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

Examples

#![feature(trim_prefix_suffix)]

// Suffix present - removes it
assert_eq!("bar:foo".trim_suffix(":foo"), "bar");
assert_eq!("foofoo".trim_suffix("foo"), "foo");

// Suffix absent - returns original string
assert_eq!("bar:foo".trim_suffix("bar"), "bar:foo");

// Method chaining example
assert_eq!("<https://example.com/>".trim_prefix('<').trim_suffix('>'), "https://example.com/");

pub fn trim_end_matches<P>(&self, pat: P) -> &str

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

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

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> &str

where P: Pattern,

👎Deprecated since 1.33.0:

superseded by trim_start_matches

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

The pattern can be a &str, char, a slice of 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<P>(&self, pat: P) -> &str

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

👎Deprecated since 1.33.0:

superseded by trim_end_matches

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

The pattern can be a &str, char, a slice of 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.

An empty string returns true.

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 unsafe fn as_ascii_unchecked(&self) -> &[AsciiChar]

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

Converts this string slice into a slice of ASCII characters, without checking whether they are valid.

Safety

Every character in this string must be ASCII, or else this is UB.

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.

For Unicode-aware case-insensitive matching, consider str::eq_ignore_case_unnormalized.

Examples

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

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

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

Checks that two strings are a caseless match, according to Definition 144 in Chapter 3 of the Unicode Standard.

Same as a.to_casefold_unnormalized() == b.to_casefold_unnormalized(), but without allocating. See that method’s documentation, as well as char::to_casefold_unnormalized(), for more information about case folding.

No normalization (e.g. NFC) is performed, so visually and semantically identical strings might still compare unequal. For example, "Å" (U+00C5 LATIN CAPITAL LETTER A WITH RING ABOVE) is considered distinct from "Å" (A followed by U+030A COMBINING RING ABOVE), even though Unicode considers them canonically equivalent.

In addition, this method is independent of language/locale, so the special behavior of I/ı/İ/i in Turkish and Azeri is not handled.

Examples

#![feature(casefold)]
assert!("Ferris".eq_ignore_case_unnormalized("FERRIS"));
assert!("Ferrös".eq_ignore_case_unnormalized("FERRÖS"));
assert!("ẞ".eq_ignore_case_unnormalized("ss"));

No NFC normalization is performed:

#![feature(casefold)]
// These two strings are visually and semantically identical...
let comp = "Å";
let decomp = "Å";

// ... but not codepoint-for-codepoint equal.
assert_eq!(comp, "\u{C5}");
assert_eq!(decomp, "A\u{030A}");

// Their case-foldings are likewise unequal:
assert!(!comp.eq_ignore_case_unnormalized(decomp));

pub fn trim_ascii_start(&self) -> &str

Returns a string slice with leading ASCII whitespace removed.

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace. Importantly, this definition excludes the U+000B code point even though it has the Unicode White_Space property and is removed by str::trim_start.

Examples

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

pub fn trim_ascii_end(&self) -> &str

Returns a string slice with trailing ASCII whitespace removed.

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace. Importantly, this definition excludes the U+000B code point even though it has the Unicode White_Space property and is removed by str::trim_end.

Examples

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

pub fn trim_ascii(&self) -> &str

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

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace. Importantly, this definition excludes the U+000B code point even though it has the Unicode White_Space property and is removed by str::trim.

Examples

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

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

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

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

Examples

As an iterator:

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

Using println! directly:

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

Both are equivalent to:

println!("❤\\n!");

Using to_string:

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

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

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

Examples

As an iterator:

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

Using println! directly:

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

Both are equivalent to:

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

Using to_string:

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

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

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

Examples

As an iterator:

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

Using println! directly:

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

Both are equivalent to:

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

Using to_string:

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

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

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

Returns the range that a substring points to.

Returns None if substr does not point within self.

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

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

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

Examples

#![feature(substr_range)]
use core::range::Range;

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

assert_eq!(iter.next(), Some(Range { start: 0, end: 1 }));
assert_eq!(iter.next(), Some(Range { start: 3, end: 4 }));
assert_eq!(iter.next(), Some(Range { start: 6, end: 7 }));
assert_eq!(iter.next(), Some(Range { start: 9, end: 10 }));

pub fn as_str(&self) -> &str

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

Returns the same string as a string slice &str.

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

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

where P: Pattern,

Available on non-no_global_oom_handling only.

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

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<P>(&self, pat: P, to: &str, count: usize) -> String

where P: Pattern,

Available on non-no_global_oom_handling only.

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

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

Available on non-no_global_oom_handling only.

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

‘Lowercase’ is defined according to the terms of Chapter 3 (Conformance) of the Unicode standard.

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

Unlike char::to_lowercase(), this method fully handles the context-dependent casing of Greek sigma. However, like that method, it does not handle locale-specific casing, like Turkish and Azeri I/ı/İ/i. See its documentation for more information.

Examples

Basic usage:

let s = "HELLO WORLD";

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

Tricky examples, 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());

let odysseus_king_of_ithaca = "Ο ΟΔΥΣΣΈΑΣ ΒΑΣΙΛΙΆΣ ΤΗΣ ΙΘΆΚΗΣ";

assert_eq!("ο οδυσσέας βασιλιάς της ιθάκης", odysseus_king_of_ithaca.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 word_to_titlecase(&self) -> String

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

Available on non-no_global_oom_handling only.

Returns the titlecase equivalent of this string slice, which is assumed to represent a single word, as a new String.

Essentially, this consists of uppercasing the first cased letter (with char::to_titlecase()), and lowercasing everything that follows.

‘Titlecase’ is defined according to the terms of Chapter 3 (Conformance) of the Unicode standard.

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

Unlike char::to_lowercase(), this method fully handles the context-dependent casing of Greek sigma. However, like that method, it does not handle locale-specific casing, like Turkish and Azeri I/ı/İ/i. See its documentation for more information.

This method does not perform any kind of word segmentation.

Examples

Basic usage:

#![feature(titlecase)]
let s = "HELLO WORLD";

assert_eq!("Hello world", s.word_to_titlecase());

The first cased letter is uppercased:

#![feature(titlecase)]
let the_night_before_christmas = "'twas";

assert_eq!("'Twas", the_night_before_christmas.word_to_titlecase());

Languages without case are not changed:

#![feature(titlecase)]
let new_year = "农历新年";

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

Georgian uppercase (“Mtavruli”) letters are not used in titlecase:

#![feature(titlecase)]
let georgian = "ერთობაშია";

assert_eq!(georgian, georgian.word_to_titlecase());

No word segmentation is performed, so only the first cased letter in the whole string gets uppercased:

#![feature(titlecase)]
let blazingly_fast = "ferris and I";

assert_eq!("Ferris and i", blazingly_fast.word_to_titlecase());

Tricky examples, with sigma:

#![feature(titlecase)]
let odysseus = "ὈΔΥΣΣΕΎΣ";

assert_eq!("Ὀδυσσεύς", odysseus.word_to_titlecase());

let odysseus_king_of_ithaca = "Ο ΟΔΥΣΣΈΑΣ ΒΑΣΙΛΙΆΣ ΤΗΣ ΙΘΆΚΗΣ";

assert_eq!("Ο οδυσσέας βασιλιάς της ιθάκης", odysseus_king_of_ithaca.word_to_titlecase());

pub fn to_uppercase(&self) -> String

Available on non-no_global_oom_handling only.

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

‘Uppercase’ is defined according to the terms of Chapter 3 (Conformance) of the Unicode standard.

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

Like char::to_uppercase() this method does not handle language-specific casing, like Turkish and Azeri I/ı/İ/i. See that method’s documentation for more information.

Examples

Basic usage:

let s = "hello world";

assert_eq!("HELLO WORLD", 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 to_casefold_unnormalized(&self) -> String

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

Available on non-no_global_oom_handling only.

Returns the case-folded equivalent of this string slice, as a new String.

Case folding is a transformation, mostly matching lowercase, that is meant to be used for case-insensitive string comparisons. Case-folded strings should not usually be exposed directly to users.

For the precise specification of case folding, see Chapter 3 (Conformance) of the Unicode standard.

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

No normalization (e.g. NFC) is performed, so visually and semantically identical strings might still casefold differently. For example, "Å" (U+00C5 LATIN CAPITAL LETTER A WITH RING ABOVE) is considered distinct from "Å" (A followed by U+030A COMBINING RING ABOVE), even though Unicode considers them canonically equivalent.

Like char::to_casefold_unnormalized() this method does not handle language-specific casing, like Turkish and Azeri I/ı/İ/i. See that method’s documentation for more information.

Examples

Basic usage:

#![feature(casefold)]
let s0 = "HELLO";
let s1 = "Hello";

assert_eq!(s0.to_casefold_unnormalized(), s1.to_casefold_unnormalized());
assert_eq!(s0.to_casefold_unnormalized(), "hello")

Scripts without case are not changed:

#![feature(casefold)]
let new_year = "农历新年";

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

One character can become multiple:

#![feature(casefold)]
let s0 = "TSCHÜẞ";
let s1 = "TSCHÜSS";
let s2 = "tschüß";

assert_eq!(s0.to_casefold_unnormalized(), s1.to_casefold_unnormalized());
assert_eq!(s0.to_casefold_unnormalized(), s2.to_casefold_unnormalized());
assert_eq!(s0.to_casefold_unnormalized(), "tschüss");

No NFC normalization is performed:

#![feature(casefold)]
// These two strings are visually and semantically identical...
let comp = "Å";
let decomp = "Å";

// ... but not codepoint-for-codepoint equal.
assert_eq!(comp, "\u{C5}");
assert_eq!(decomp, "A\u{030A}");

// Their case-foldings are likewise unequal:
assert_eq!(comp.to_casefold_unnormalized(), "\u{E5}");
assert_eq!(decomp.to_casefold_unnormalized(), "a\u{030A}");

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

Available on non-no_global_oom_handling only.

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

Available on non-no_global_oom_handling only.

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

Available on non-no_global_oom_handling only.

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 CAP: usize, const RHS: usize> AddAssign<&StringNonul<RHS>> for StringU8<CAP>

Appends non-NUL text in place, keeping the fitted UTF-8 prefix.

fn add_assign(&mut self, rhs: &StringNonul<RHS>)

Performs the += operation.

impl<const CAP: usize, const RHS: usize> AddAssign<&StringU8<RHS>> for StringNonul<CAP>

Appends text in place, skipping NULs and keeping what fits.

fn add_assign(&mut self, rhs: &StringU8<RHS>)

Performs the += operation.

impl<const CAP: usize, const RHS: usize> AddAssign<&StringU8<RHS>> for StringU8<CAP>

fn add_assign(&mut self, rhs: &StringU8<RHS>)

Concatenates by appending what fits into self’s capacity.

impl<const CAP: usize> AddAssign<&str> for StringU8<CAP>

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

Appends text in place, keeping the fitted UTF-8 prefix.

impl<const CAP: usize, const RHS: usize> AddAssign<StringNonul<RHS>> for StringU8<CAP>

Appends non-NUL text in place, keeping the fitted UTF-8 prefix.

fn add_assign(&mut self, rhs: StringNonul<RHS>)

Performs the += operation.

impl<const CAP: usize, const RHS: usize> AddAssign<StringU8<RHS>> for StringNonul<CAP>

Appends text in place, skipping NULs and keeping what fits.

fn add_assign(&mut self, rhs: StringU8<RHS>)

Performs the += operation.

impl<const CAP: usize, const RHS: usize> AddAssign<StringU8<RHS>> for StringU8<CAP>

fn add_assign(&mut self, rhs: StringU8<RHS>)

Concatenates by appending what fits into self’s capacity.

impl<const CAP: usize> AddAssign<char> for StringU8<CAP>

fn add_assign(&mut self, rhs: char)

Appends the character if it fits.

impl<const CAP: usize> AsRef<[u8]> for StringU8<CAP>

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

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

impl<const CAP: usize> AsRef<str> for StringU8<CAP>

fn as_ref(&self) -> &str

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

impl<const CAP: usize> Clone for StringU8<CAP>

fn clone(&self) -> StringU8<CAP>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<const CAP: usize> ConstInit for StringU8<CAP>

const INIT: Self

Returns an empty string.

Panics

Panics if CAP > Self::MAX_CAPACITY.

impl<const CAP: usize> Copy for StringU8<CAP>

impl<const CAP: usize> Debug for StringU8<CAP>

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

Formats the value using the given formatter.

impl<const CAP: usize> Default for StringU8<CAP>

fn default() -> Self

Returns an empty string.

Panics

Panics if CAP > Self::MAX_CAPACITY.

impl<const CAP: usize> Deref for StringU8<CAP>

type Target = str

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<const CAP: usize> Display for StringU8<CAP>

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

Formats the value using the given formatter.

impl<const CAP: usize> Eq for StringU8<CAP>

impl<const CAP: usize> Extend<char> for StringU8<CAP>

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

Creates an instance from an iterator of characters.

Processes characters until it can fit no more, discarding the rest.

Panics

Panics if CAP > Self::MAX_CAPACITY.

Examples

let chars = ['a', 'b', 'c', '€', 'さ'];
let mut s = StringU8::<6>::new();
s.extend(chars);
assert_eq![s, "abc€"];

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

Reserves capacity in a collection for the given number of additional elements.

impl<const CAP: usize> FromIterator<char> for StringU8<CAP>

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

Creates an instance from an iterator of characters.

Processes characters until it can fit no more, discarding the rest.

Panics

Panics if CAP > Self::MAX_CAPACITY.

Examples

let chars = ['a', 'b', 'c', '€', 'さ'];
assert_eq!(StringU8::<9>::from_iter(chars), "abc€さ");
assert_eq!(StringU8::<6>::from_iter(chars), "abc€");
assert_eq!(StringU8::<5>::from_iter(chars), "abc");
assert_eq!(StringU8::<2>::from_iter(chars), "ab");
assert_eq!(StringU8::<0>::from_iter(chars), "");

impl<const CAP: usize> Hash for StringU8<CAP>

fn hash<H: Hasher>(&self, state: &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 CAP: usize> Ord for StringU8<CAP>

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,

Restrict a value to a certain interval.

impl<const CAP: usize> PartialEq for StringU8<CAP>

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

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

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

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

impl<const CAP: usize> PartialEq<&[u8]> for StringU8<CAP>

fn eq(&self, bytes: &&[u8]) -> bool

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

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

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

impl<const CAP: usize> PartialEq<&str> for StringU8<CAP>

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

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

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

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

impl<const CAP: usize> PartialEq<GraphemeU8<CAP>> for StringU8<CAP>

Available on crate feature grapheme only.

fn eq(&self, other: &GraphemeU8<CAP>) -> bool

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

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

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

impl<const CAP: usize> PartialEq<StringU8<CAP>> for str

fn eq(&self, string: &StringU8<CAP>) -> bool

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

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

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

impl<const CAP: usize> PartialEq<StringU8<CAP>> for &str

fn eq(&self, string: &StringU8<CAP>) -> bool

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

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

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

impl<const CAP: usize> PartialEq<StringU8<CAP>> for &[u8]

fn eq(&self, string: &StringU8<CAP>) -> bool

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

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

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

impl<const CAP: usize> PartialEq<StringU8<CAP>> for GraphemeU8<CAP>

Available on crate feature grapheme only.

fn eq(&self, other: &StringU8<CAP>) -> bool

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

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

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

impl<const CAP: usize> PartialEq<str> for StringU8<CAP>

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

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

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

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

impl<const CAP: usize> PartialOrd for StringU8<CAP>

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

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

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

Tests less than (for self and other) and is used by the < operator.

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

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

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

Tests greater than (for self and other) and is used by the > operator.

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

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

impl<const CAP: usize> TryFrom<&[u8]> for StringU8<CAP>

fn try_from(bytes: &[u8]) -> Result<Self, InvalidText>

Tries to create a new string from the given slice of bytes.

Errors

Returns InvalidText::MismatchedCapacity if CAP > Self::MAX_CAPACITY or if CAP < bytes.len(), and InvalidText::Utf8 if bytes are not valid UTF-8.

type Error = InvalidText

The type returned in the event of a conversion error.

impl<const CAP: usize> TryFrom<&str> for StringU8<CAP>

fn try_from(string: &str) -> Result<Self, MismatchedCapacity>

Tries to create a new string from the given string slice.

This is implemented via Self::from_str().

Errors

Returns MismatchedCapacity if CAP > Self::MAX_CAPACITY or if CAP < string.len().

type Error = MismatchedCapacity

The type returned in the event of a conversion error.

impl<const CAP: usize> Write for StringU8<CAP>

Writes as much UTF-8-complete text as fits.

If the input does not fit completely, a prefix may have been written before returning FmtError.

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

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

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

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.