Struct Str

#[repr(C)]
pub struct Str<const N: usize> { /* private fields */ }

A fixed sized stack string

Str is a generic stack-based string with a maximum byte length of u8::MAX.

The generic N is a usize and represents the maximum length of the string, however all constructor functions for Str will panic at compile time if N > 255.

Size

The internal length is stored as a u8, and as such will take minimal space, allowing for longer strings to be stored.

Due to #[repr(C)], N + 1 is how many bytes your Str will take up.

Using Str in powers of 2 is recommended.

// 64 bytes in total, 63 bytes available for the string.
// This will fit in a typical CPU cache-line.
assert_eq!(std::mem::size_of::<Str::<63>>(), 64);

// Maximum string length of 255 fits into 256 bytes.
assert_eq!(std::mem::size_of::<Str::<255>>(), 256);

// Beware, due to `#[repr(C)]`, `Str` is not
// automatically re-arranged and padded by Rust.
assert_eq!(std::mem::size_of::<Str::<6>>(), 7);

Compile-time panic

Any usage of Str will panic at compile time if N > 255:

/// These will all panic at _compile time_
Str::<256>::new();
Str::<256>::try_from("");
Str::<256>::from_static_str("");
Str::<256>::from_static_bytes(b"");

Usage

// Create a `Str` with a maximum capacity of `24` bytes.
const N: usize  = 24;
let mut string = Str::<N>::new();
assert!(string.is_empty());

// Copy the bytes from an actual `str`
let other_str = "this str is 24 bytes :-)";
assert_eq!(other_str.len(), N);
string.copy_str(other_str).unwrap();

// They're the same.
assert_eq!(string, other_str);

// Clear the string.
string.clear();
assert!(string.is_empty());
assert_eq!(string.len(), 0);

// `push_str()` should be the exact same.
string.push_str(other_str).unwrap();
assert_eq!(string, other_str);

// This string is full.
assert!(string.is_full());
assert_eq!(string.len(), N);

// Pushing new strings will error.
let err = string.push_str(other_str);
assert_eq!(err, Err(24));
// Still the same.
assert_eq!(string, other_str);

// Although, we can still overwrite it.
string.copy_str("hello-------------------");
assert_eq!(string, "hello-------------------");
assert_eq!(string.len(), 24);

Implementations

impl<const N: usize> Str<N>

pub const CAPACITY: u8

The maximum length of this string as a u8.

This should == to N in valid cases.

Compile-time panic

This associated constant will cause Str constructor functions to panic at compile time is N > 255.

pub const fn new() -> Self

Returns an empty Str.

let string = Str::<4>::new();
assert!(string.is_empty());
assert_eq!(string.len(), 0);
assert!(string.as_str().is_empty());
assert_eq!(string.as_str().len(), 0);

pub const fn from_static_bytes(bytes: &'static [u8]) -> Self

Create a Self from static bytes.

The length of the input doesn’t need to be the same as N, it just needs to be equal or less.

Exact length:

const BYTES: [u8; 3] = *b"abc";
const STR: Str<3> = Str::from_static_bytes(&BYTES);

assert_eq!(STR, "abc");

Slightly less length is okay too:

const BYTES: [u8; 2] = *b"ab";
const STR: Str<3> = Str::from_static_bytes(&BYTES);

assert_eq!(STR.len(), 2);
assert_eq!(STR, "ab");

Compile-time panic

This function will panic at compile time if either:

• The byte length is longer than N
• The byte’s are not valid UTF-8 bytes

// This doesn't fit, will panic at compile time.
const STR: Str<3> = Str::from_static_bytes("abcd");

pub const fn from_static_str(s: &'static str) -> Self

Create a Self from a static str.

The length of the input doesn’t need to be the same as N, it just needs to be equal or less.

Exact length:

const S: &str = "abc";
const STR: Str<3> = Str::from_static_str(&S);

assert_eq!(STR, "abc");

Slightly less length is okay too:

const S: &str = "ab";
const STR: Str<3> = Str::from_static_str(&S);

assert_eq!(STR.len(), 2);
assert_eq!(STR, "ab");

Compile-time panic

This function will panic at compile time if the str length is longer than N.

// This doesn't fit, will panic at compile time.
const STR: Str<3> = Str::from_static_str("abcd");

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

Return all the bytes of this Str, whether valid UTF-8 or not.

let mut string = Str::<10>::new();
string.push_str("hello").unwrap();

// The string length is 5, but the slice
// returned is the full capacity, 10.
assert_eq!(string.as_bytes_all().len(), 10);

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

Return all the bytes of this Str (mutably), whether valid UTF-8 or not

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.

The caller must also ensure the len is correctly set with Str::set_len or Str::set_len_u8.

let mut string = Str::<5>::new();
string.push_str("hi").unwrap();
assert_eq!(string, "hi");
assert_eq!(string.len(), 2);

// Safety: We must ensure we leave
// leave the bytes as valid UTF-8 bytes
// and that we set the length correctly.
unsafe {
    // Mutate to valid UTF-8 bytes.
    let mut_ref = string.as_bytes_all_mut();
    mut_ref.copy_from_slice(&b"world"[..]);
    // Set the new length.
    string.set_len(5);
}

assert_eq!(string, "world");
assert_eq!(string.len(), 5);

pub const fn len(&self) -> usize

Return the length of the valid UTF-8 bytes of this Str

let mut s = Str::<5>::new();
s.push_str("h").unwrap();
assert_eq!(s.len(), 1_usize);

s.push_str("ello").unwrap();
assert_eq!(s.len(), 5_usize);

pub const fn len_u8(&self) -> u8

Return the length of the valid UTF-8 bytes of this Str as a u8

let mut s = Str::<5>::new();
s.push_str("h").unwrap();
assert_eq!(s.len_u8(), 1_u8);

s.push_str("ello").unwrap();
assert_eq!(s.len_u8(), 5_u8);

pub unsafe fn set_len(&mut self, len: usize)

Set the length of the valid UTF-8 bytes of this Str

This will usually be used when manually mutating Str with Str::as_bytes_all_mut().

let mut s = Str::<3>::new();
assert_eq!(s.len(), 0);

unsafe { s.set_len(3); } // <- Using the `Str`
assert_eq!(s.len(), 3);  //    beyond this point
                         //    is a bad idea.

// This wouldn't be undefined behavior,
// but the inner buffer is all zeros.
assert_eq!(s.as_str(), "\0\0\0");

// Overwrite the bytes.
unsafe {
    let mut_ref = s.as_bytes_all_mut();
    mut_ref[0] = b'a';
    mut_ref[1] = b'b';
    mut_ref[2] = b'c';
}
// Should be safe from this point.
assert_eq!(s.as_str(), "abc");
assert_eq!(s.len(),    3);

Safety

Other functions will rely on the internal length to be correct, so the caller must ensure this length is actually correct.

pub unsafe fn set_len_u8(&mut self, len: u8)

Set the length of the valid UTF-8 bytes of this Str

This will usually be used when manually mutating Str with Str::as_bytes_all_mut().

let mut s = Str::<3>::new();
assert_eq!(s.len(), 0);

unsafe { s.set_len_u8(3); } // <- Using the `Str`
assert_eq!(s.len(), 3);     //    beyond this point
                            //    is a bad idea.

// This wouldn't be undefined behavior,
// but the inner buffer is all zeros.
assert_eq!(s.as_str(), "\0\0\0");

// Overwrite the bytes.
unsafe {
    let mut_ref = s.as_bytes_all_mut();
    mut_ref[0] = b'a';
    mut_ref[1] = b'b';
    mut_ref[2] = b'c';
}
// Should be safe from this point.
assert_eq!(s.as_str(), "abc");
assert_eq!(s.len(),    3);

Safety

Other functions will rely on the internal length to be correct, so the caller must ensure this length is actually correct.

pub const fn remaining(&self) -> usize

How many available bytes are left in this Str before the Self::CAPACITY is completely filled.

let mut s = Str::<5>::new();
s.push_str("hi");
assert_eq!(s.remaining(), 3);

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

Returns only the valid UTF-8 bytes of this Str as a byte slice.

let s = Str::<10>::from_static_str("hello");
assert_eq!(s.as_bytes().len(), 5);

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

Self::as_bytes(), but returns mutable bytes

Safety

The length must be set correctly if mutated.

let mut s = Str::<10>::from_static_str("hello");
assert_eq!(s.as_bytes().len(), 5);

unsafe {

    // Length not set yet.
    s.as_bytes_mut().copy_from_slice(&[0; 5]);
    assert_eq!(s.as_bytes_mut().len(), 5);

    // Set.
    s.set_len(0);
}

assert_eq!(s.as_str(),         "");
assert_eq!(s.as_bytes().len(), 0);

pub const fn as_ptr(&self) -> *const u8

Returns a pointer to the first byte in the string array.

let s = Str::<5>::from_static_str("hello");

let ptr = s.as_ptr();
unsafe {
    // The first byte is the char `h`.
    assert_eq!(*ptr, b'h');
}

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

Returns a mutable pointer to the first byte in the string array.

let mut s = Str::<5>::from_static_str("hello");

let ptr = s.as_mut_ptr();
unsafe {
    // The first byte is the char `h`.
    assert_eq!(*ptr, b'h');
    // Let's change it.
    *ptr = b'e';
}

assert_eq!(s, "eello");

pub fn into_vec(self) -> Vec<u8>

Returns only the valid UTF-8 bytes of this Str as a Vec<u8>

let s = Str::<10>::from_static_str("hello");
let v = s.into_vec();
assert_eq!(v.len(), 5);

let s = unsafe { String::from_utf8_unchecked(v) };
assert_eq!(s, "hello");

pub const fn invalid(&self) -> bool

Check this Str for correctness.

When constructing/receiving a Str outside of its constructors, it may not be guaranteed that the invariants are upheld.

This function will return true if:

• Internal length is greater than the internal byte array
• .as_str() would return invalid UTF-8

// Create `Str` with maximum 5 length.
let mut string = Str::<5>::new();
assert_eq!(string.invalid(), false);

// Unsafely set the length to 10.
unsafe { string.set_len(10); }
// This string is now invalid.
assert_eq!(string.invalid(), true);

pub fn clear(&mut self)

Clears all bytes of this Str.

// Create a string.
let mut s = Str::<5>::from_static_str("hello");
assert_eq!(s, "hello");

// Clear the string.
s.clear();
assert_eq!(s, "");
assert!(s.is_empty());

Note

This does not actually mutate any bytes, it simply sets the internal length to 0.

Do not rely on this to clear the actual bytes.

pub fn zero(&mut self)

Zeros all bytes of this Str and sets the length to 0

Unlike Str::clear(), this actually sets all the bytes in the internal array to 0.

// Create a string.
let mut s = Str::<5>::from_static_str("hello");
assert_eq!(s, "hello");

// Zero the string.
s.zero();
assert_eq!(s, "");
assert!(s.is_empty());

pub const fn is_empty(&self) -> bool

If this Str is empty.

let mut s = Str::<10>::new();
assert_eq!(s, "");
assert!(s.is_empty());

s.push_str("a").unwrap();
assert!(!s.is_empty());

pub const fn is_full(&self) -> bool

If this Str is full (no more capacity left).

let mut s = Str::<3>::new();
assert_eq!(s.len(), 0);
assert!(!s.is_full());

s.push_str("123").unwrap();
assert_eq!(s.len(), 3);
assert!(s.is_full());

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

This Str, as a valid UTF-8 str.

let s = Str::<5>::from_static_str("hello");
assert_eq!(s.as_str(), "hello");

Panics

This will panic in debug mode if Self::invalid returns true.

pub unsafe fn as_str_mut(&mut self) -> &mut str

This Str, as a valid, mutable, UTF-8 str.

Safety

The length must be set correctly if mutated.

The str must be valid UTF-8.

let mut s = Str::<5>::from_static_str("hello");
assert_eq!(s.as_str(), "hello");

unsafe {
    s.as_str_mut().make_ascii_uppercase();
}

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

pub fn into_string(self) -> String

Consumes self into a String

let s = Str::<5>::from_static_str("hello");

let s: String = s.into_string();
assert_eq!(s, "hello");

pub fn copy_str(&mut self, s: impl AsRef<str>) -> Result<usize, usize>

Overwrites self with the str s.

The input s must be the exact same length as N or this function will error.

Errors

If the copy was successful, Result::Ok is returned with the new length of the string.

If the copy failed because s.len() > N, Result::Err is returned with how many extra bytes couldn’t fit.

If the copy failed because s.len() != N, Result::Err is returned as Err(0).

let mut string = Str::<3>::new();

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(string.copy_str("abcd"), Err(1));

// Input string is 2 in length, not exactly 3.
// `Err(0)` will be returned to indicate this.
assert_eq!(string.copy_str("ab"), Err(0));

// This fits.
assert_eq!(string.copy_str("abc"), Ok(3));

pub fn copy_str_unchecked(&mut self, s: impl AsRef<str>) -> usize

Performs the same operation as Self::copy_str() except this function does not check if the input str s is too long.

If the copy was successful, the new length of the string is returned.

If the copy failed, this function will panic.

let mut string = Str::<3>::new();

// Input string is 3 in length, we can copy it.
assert_eq!(string.copy_str_unchecked("abc"), 3);

Panics

Instead of erroring, this function will panic if the input s.len() != N.

Input too long:

let mut string = Str::<3>::new();

// Input string is 5 in length, this will panic.
string.copy_str_unchecked("abcd");

Input not long enough:

let mut string = Str::<3>::new();

// Input string is 2 in length, this will panic.
string.copy_str_unchecked("ab");

Input is just right:

let mut string = Str::<3>::new();
string.copy_str_unchecked("abc");
assert_eq!(string, "abc")

pub fn push_str(&mut self, s: impl AsRef<str>) -> Result<usize, usize>

Appends self with the str s.

Errors

If the push was successful (or s was empty), Result::Ok is returned with the new length of the string.

If the push failed, Result::Err is returned with how many extra bytes couldn’t fit.

let mut string = Str::<3>::new();

// Input string is 4 in length.
// We can't push it.
let err = string.push_str("abcd");
assert_eq!(err, Err(1));

// The string is still empty.
assert!(string.is_empty());

// This 2 length string will fit.
string.push_str("ab").unwrap();
assert_eq!(string, "ab");
// This 1 length string will fit.
string.push_str("c").unwrap();
assert_eq!(string, "abc");

// But not anymore.
let err = string.push_str("d");
assert_eq!(err, Err(1));
assert_eq!(string, "abc");

pub fn push_str_panic(&mut self, s: impl AsRef<str>) -> usize

Appends self with the str s.

If the push was successful (or s was empty), a usize is returned, representing the new length of the string.

let mut s = Str::<5>::new();
assert_eq!(s.push_str_panic("wow"), 3);

Panics

If the push failed, this function panics.

Input string is > than capacity:

let mut s = Str::<3>::new();
s.push_str_panic("abcd");

Str has no more remaining capacity:

let mut s = Str::<4>::from_static_str("wow");
assert_eq!(s.len(),       3);
assert_eq!(s.remaining(), 1);

// This won't fit, will panic.
s.push_str_panic("wow");

pub fn push_str_saturating(&mut self, s: impl AsRef<str>) -> usize

Appends self with the str s, saturating if there is no Self::CAPACITY left

This function returns a usize, representing how many bytes were written.

If there is no byte capacity left, this function will return 0.

UTF-8 strings are accounted for, and are split on char basis, for example:

let mut s = Str::<7>::new();

// Crab is 4 bytes.
assert_eq!(4, "🦀".len());

// Our capacity is only 7, so we can only fit 1.
assert_eq!(4, s.push_str_saturating("🦀"));
assert_eq!(s, "🦀");
assert_eq!(4, s.len());
assert_eq!(3, s.remaining());

Examples

let mut s = Str::<3>::new();

// Only 1 char, 3 bytes can fit.
assert_eq!(3, s.push_str_saturating("です"));
assert_eq!(s, "で");
s.clear();

// Only 3 ASCII characters can fit.
assert_eq!(3, s.push_str_saturating("hello"));
assert_eq!(s, "hel");
s.clear();

// Here, we push 3 characters with 1 capacity left.
s.push_str("wo").unwrap();
assert_eq!(1, s.push_str_saturating("rld"));
// And only 1 character was pushed.
assert_eq!(s, "wor");

// No matter how many times we push now, nothing will be added.
assert_eq!(0, s.push_str_saturating("!"));
assert_eq!(s, "wor");
assert_eq!(0, s.push_str_saturating("へええ"));
assert_eq!(s, "wor");
assert_eq!(0, s.push_str_saturating("枕"));
assert_eq!(s, "wor");
assert_eq!(0, s.push_str_saturating("🦀"));
assert_eq!(s, "wor");

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

Str::push_str, but with a char

This acts in the same way as Str::push_str, but the input is a single char.

let mut string = Str::<3>::new();

// Input char is 4 in length.
// We can't push it.
let err = string.push_char('🦀');
assert_eq!(err, Err(1));

// The string is still empty.
assert!(string.is_empty());

// This 3 length char will fit.
assert_eq!(string.push_char('で'), Ok(3));
assert_eq!(string, "で");

pub fn push_char_panic(&mut self, c: char) -> usize

Str::push_str_panic, but with a char

This acts in the same way as Str::push_str_panic, but the input is a single char.

let mut s = Str::<5>::new();
assert_eq!(s.push_char_panic('す'), 3);

Panics

If the push failed, this function panics.

Input char is > than capacity:

let mut s = Str::<3>::new();
s.push_char_panic('🦀');

Str has no more remaining capacity:

let mut s = Str::<4>::from_static_str("wow");
assert_eq!(s.len(),       3);
assert_eq!(s.remaining(), 1);

// This won't fit, will panic.
s.push_char_panic('🦀');

pub fn push_char_saturating(&mut self, c: char) -> usize

Str::push_str_saturating, but with a char

This acts in the same way as Str::push_str_saturating, but the input is a single char.

let mut s = Str::<7>::new();

// Crab is 4 bytes.
assert_eq!(4, "🦀".len());

// Our capacity is only 7, so we can only fit 1.
assert_eq!(4, s.push_char_saturating('🦀'));
assert_eq!(0, s.push_char_saturating('🦀'));
assert_eq!(s, "🦀");
assert_eq!(4, s.len());
assert_eq!(3, s.remaining());

Examples

let mut s = Str::<3>::new();

assert_eq!(1, s.push_char_saturating('w'));
assert_eq!(1, s.push_char_saturating('o'));
assert_eq!(1, s.push_char_saturating('w'));
assert_eq!(s, "wow");

// No matter how many times we push now, nothing will be added.
assert_eq!(0, s.push_char_saturating('!'));
assert_eq!(s, "wow");
assert_eq!(0, s.push_char_saturating('へ'));
assert_eq!(s, "wow");
assert_eq!(0, s.push_char_saturating('枕'));
assert_eq!(s, "wow");
assert_eq!(0, s.push_char_saturating('🦀'));
assert_eq!(s, "wow");

pub const fn into_raw(self) -> ([u8; N], u8)

Decomposes a Str into its raw components

Returns the byte array buffer and the valid UTF-8 length of the Str.

let s = Str::<5>::from_static_str("hi");
let (buf, len) = s.into_raw();

assert_eq!(buf, [b'h', b'i', 0, 0, 0]);
assert_eq!(len, 2);

pub const unsafe fn from_raw(buf: [u8; N], len: u8) -> Self

Creates a new Str from a byte array buffer and a length

let buf = [b'h', b'i', 0, 0, 0];
let len = 2;

// SAFETY: The length covers valid
// UTF-8 bytes in the provided buffer.
let s = unsafe { Str::<5>::from_raw(buf, len) };
assert_eq!(s, "hi");

Safety

The caller needs to make sure the bytes covered by the len are actual valid UTF-8 bytes.

pub fn from_str_exact(string: impl AsRef<str>) -> Self

Create a Str directly from a str

let s = Str::<5>::from_str_exact("12345");
assert_eq!(s, "12345");

Panics

The input input str string’s length must be exactly equal to Self::CAPACITY or this function will panic.

// 1 too many characters, will panic.
let s = Str::<4>::from_str_exact("12345");

pub unsafe fn from_bytes_exact(bytes: impl AsRef<[u8]>) -> Self

Create a Str directly from bytes

let s = unsafe { Str::<5>::from_bytes_exact(b"12345") };
assert_eq!(s, "12345");

Safety

The bytes must be valid UTF-8.

Panics

The input bytes bytes’s length must be exactly equal to Self::CAPACITY or this function will panic.

// 1 too many characters, will panic.
let s = unsafe { Str::<4>::from_bytes_exact(b"12345") };

pub fn make_ascii_uppercase(&mut self)

Calls str::make_ascii_uppercase.

let mut s = Str::<5>::from_static_str("hello");

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

pub fn make_ascii_lowercase(&mut self)

Calls str::make_ascii_lowercase.

let mut s = Str::<5>::from_static_str("HELLO");

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

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

Shortens this Str 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

let mut s = Str::<4>::from_static_str("asdf");

s.truncate(1);
assert_eq!(s, "a");

Panics

Panics if new_len does not lie on a char boundary.

let mut s = Str::<6>::from_static_str("です");

// This does not lie on a full char, it will panic.
s.truncate(4);

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

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

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

let mut s = Str::<3>::from_static_str("foo");

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

Panics

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

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

Removes the last character from the Str and returns it.

Returns None if this Str is empty.

let mut s = Str::<3>::from_static_str("foo");

assert_eq!(s.len(), 3);
assert_eq!(s.pop(), Some('o'));
assert_eq!(s.len(), 2);
assert_eq!(s.pop(), Some('o'));
assert_eq!(s.len(), 1);
assert_eq!(s.pop(), Some('f'));
assert_eq!(s.len(), 0);
assert_eq!(s.pop(), None);

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 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.

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<'_>

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

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

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

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

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

Examples

Basic usage:

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

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

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

The final line does not require any ending:

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

assert_eq!(Some("foo"), lines.next());
assert_eq!(Some("bar"), lines.next());
assert_eq!(Some(""), lines.next());
assert_eq!(Some("baz"), lines.next());

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

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 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<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.

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<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=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 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.

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 trim_ascii_start(&self) -> &str

Returns a string slice with leading ASCII whitespace removed.

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

Examples

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

pub fn trim_ascii_end(&self) -> &str

Returns a string slice with trailing ASCII whitespace removed.

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

Examples

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

pub fn trim_ascii(&self) -> &str

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

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

Examples

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

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)]

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

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

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,

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

where P: Pattern,

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, T: AsRef<str>> Add<T> for Str<N>

fn add(self, s: T) -> Self::Output

Implements the + operator.

let mut s = Str::<6>::from_static_str("foo");

assert_eq!(s + "bar", "foobar");

Panics

This calls Str::push_str_panic and will panic in the same ways.

let mut s = Str::<3>::from_static_str("foo");

// This will panic, not enough capacity!
let _ = s + "bar";

type Output = Str<N>

The resulting type after applying the + operator.

impl<const N: usize, T: AsRef<str>> AddAssign<T> for Str<N>

fn add_assign(&mut self, s: T)

Implements the += operator.

let mut s = Str::<6>::from_static_str("foo");
s += "bar";

assert_eq!(s, "foobar");

Panics

This calls Str::push_str_panic and will panic in the same ways.

let mut s = Str::<3>::from_static_str("foo");

// This will panic, not enough capacity!
s += "bar";

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

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

Calls Str::as_bytes(), only including valid UTF-8 bytes.

// 6 in capacity, but only 3 in length.
let mut s = Str::<6>::from_static_str("foo");

assert_eq!(AsRef::<[u8]>::as_ref(&s), "foo".as_bytes());

impl<const N: usize> AsRef<OsStr> for Str<N>

fn as_ref(&self) -> &OsStr

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

impl<const N: usize> AsRef<Path> for Str<N>

fn as_ref(&self) -> &Path

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

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

fn as_ref(&self) -> &str

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

impl<const N: usize> Borrow<str> for Str<N>

fn borrow(&self) -> &str

Immutably borrows from an owned value.

impl<'de, const N: usize> BorrowDecode<'de> for Str<N>

fn borrow_decode<D: BorrowDecoder<'de>>( decoder: &mut D, ) -> Result<Self, DecodeError>

Attempt to decode this type with the given BorrowDecode.

impl<const N: usize> BorshDeserialize for Str<N>

fn deserialize_reader<R: Read>(reader: &mut R) -> Result<Self>

let s: Str<5> = Str::from_str_exact("hello");

let bytes = borsh::to_vec(&s).unwrap();
assert_eq!(bytes, borsh::to_vec(&"hello").unwrap());

let s: Str<5> = borsh::from_slice(&bytes).unwrap();
assert_eq!(s, "hello");

assert!(borsh::from_slice::<Str<4>>(&bytes).is_err());

fn deserialize(buf: &mut &[u8]) -> Result<Self, Error>

Deserializes this instance from a given slice of bytes. Updates the buffer to point at the remaining bytes.

fn try_from_slice(v: &[u8]) -> Result<Self, Error>

Deserialize this instance from a slice of bytes.

fn try_from_reader<R>(reader: &mut R) -> Result<Self, Error>

where R: Read,

impl<const N: usize> BorshSerialize for Str<N>

fn serialize<W: Write>(&self, writer: &mut W) -> Result<()>

let s: Str<5> = Str::from_str_exact("hello");

let bytes = borsh::to_vec(&s).unwrap();
assert_eq!(bytes, borsh::to_vec(&"hello").unwrap());

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

fn clone(&self) -> Str<N>

Returns a copy of the value.

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

Performs copy-assignment from source.

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

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

Formats the value using the given formatter.

impl<const N: usize> Decode for Str<N>

fn decode<D: Decoder>(decoder: &mut D) -> Result<Self, DecodeError>

let s: Str<5> = Str::from_str_exact("hello");
let config = bincode::config::standard();
let bytes = bincode::encode_to_vec(&s, config).unwrap();
assert_eq!(bytes, bincode::encode_to_vec(&"hello", config).unwrap());

let s: Str<5> = bincode::decode_from_slice(&bytes, config).unwrap().0;
assert_eq!(s, "hello");

// Too long.
assert!(bincode::decode_from_slice::<Str<4>, _>(&bytes, config).is_err());

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

fn default() -> Self

Calls Self::new

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

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

Equivalent to Str::as_str().

use std::ops::Deref;
let mut s = Str::<3>::from_static_str("foo");

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

type Target = str

The resulting type after dereferencing.

impl<'de, const N: usize> Deserialize<'de> for Str<N>

fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>

where D: Deserializer<'de>,

let s: Str<5> = Str::from_str_exact("hello");
let json = serde_json::to_string(&s).unwrap();
assert_eq!(json, "\"hello\"");

let s: Str<5> = serde_json::from_str(&json).unwrap();
assert_eq!(s, "hello");

// Too long.
assert!(serde_json::from_str::<Str<4>>(&json).is_err());

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

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

Formats the value using the given formatter.

impl<const N: usize> Encode for Str<N>

fn encode<E: Encoder>(&self, encoder: &mut E) -> Result<(), EncodeError>

let s: Str<5> = Str::from_str_exact("hello");
let config = bincode::config::standard();
let bytes = bincode::encode_to_vec(&s, config).unwrap();
assert_eq!(bytes, bincode::encode_to_vec(&"hello", config).unwrap());

impl<'a, const N: usize> Extend<&'a str> for Str<N>

fn extend<T: IntoIterator<Item = &'a str>>(&mut self, iter: T)

Calls Str::push_str_panic for each str.

let mut s = Str::<12>::new();

s.extend(["hello", " ", "world", "!"]);
assert_eq!(s, "hello world!");

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 N: usize> Extend<char> for Str<N>

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

Calls Str::push_char_panic for each char.

let mut s = Str::<3>::new();

s.extend(['a', 'b', 'c']);
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 N: usize> Hash for Str<N>

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 N: usize> Index<Range<usize>> for Str<N>

type Output = str

The returned type after indexing.

fn index(&self, index: Range<usize>) -> &Self::Output

Performs the indexing (container[index]) operation.

impl<const N: usize> Index<RangeFrom<usize>> for Str<N>

type Output = str

The returned type after indexing.

fn index(&self, index: RangeFrom<usize>) -> &Self::Output

Performs the indexing (container[index]) operation.

impl<const N: usize> Index<RangeFull> for Str<N>

type Output = str

The returned type after indexing.

fn index(&self, index: RangeFull) -> &Self::Output

Performs the indexing (container[index]) operation.

impl<const N: usize> Index<RangeInclusive<usize>> for Str<N>

type Output = str

The returned type after indexing.

fn index(&self, index: RangeInclusive<usize>) -> &Self::Output

Performs the indexing (container[index]) operation.

impl<const N: usize> Index<RangeTo<usize>> for Str<N>

type Output = str

The returned type after indexing.

fn index(&self, index: RangeTo<usize>) -> &Self::Output

Performs the indexing (container[index]) operation.

impl<const N: usize> Index<RangeToInclusive<usize>> for Str<N>

type Output = str

The returned type after indexing.

fn index(&self, index: RangeToInclusive<usize>) -> &Self::Output

Performs the indexing (container[index]) operation.

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

fn cmp(&self, other: &Str<N>) -> 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 N: usize> PartialEq<&str> for Str<N>

fn eq(&self, other: &&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 N: usize> PartialEq<str> for Str<N>

fn eq(&self, other: &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 N: usize> PartialEq for Str<N>

fn eq(&self, other: &Str<N>) -> 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 N: usize> PartialOrd for Str<N>

fn partial_cmp(&self, other: &Str<N>) -> 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 N: usize> Serialize for Str<N>

fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>

where S: Serializer,

let s: Str<5> = Str::from_str_exact("hello");
let json = serde_json::to_string(&s).unwrap();
assert_eq!(json, "\"hello\"");

impl<const N: usize> TryFrom<&[u8]> for Str<N>

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

This takes in a [[u8]] of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

If the Err is 0, that means the string was not valid UTF-8.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from(b"abcd"), Err(1));

assert_eq!(Str::<3>::try_from(b"abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from(b"");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize, const ARRAY: usize> TryFrom<&[u8; ARRAY]> for Str<N>

type Error = usize

The type returned in the event of a conversion error.

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

Performs the conversion.

impl<const N: usize> TryFrom<&Arc<[u8]>> for Str<N>

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

This takes in a [[u8]] of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

If the Err is 0, that means the string was not valid UTF-8.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from(b"abcd"), Err(1));

assert_eq!(Str::<3>::try_from(b"abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from(b"");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<&Arc<str>> for Str<N>

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

This takes in a &str of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from("abcd"), Err(1));

assert_eq!(Str::<3>::try_from("abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from("");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<&Box<[u8]>> for Str<N>

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

This takes in a [[u8]] of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

If the Err is 0, that means the string was not valid UTF-8.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from(b"abcd"), Err(1));

assert_eq!(Str::<3>::try_from(b"abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from(b"");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<&Box<str>> for Str<N>

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

This takes in a &str of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from("abcd"), Err(1));

assert_eq!(Str::<3>::try_from("abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from("");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<&Cow<'_, [u8]>> for Str<N>

fn try_from(bytes: &Cow<'_, [u8]>) -> Result<Self, Self::Error>

This takes in a [[u8]] of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

If the Err is 0, that means the string was not valid UTF-8.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from(b"abcd"), Err(1));

assert_eq!(Str::<3>::try_from(b"abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from(b"");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<&Cow<'_, str>> for Str<N>

fn try_from(string: &Cow<'_, str>) -> Result<Self, Self::Error>

This takes in a &str of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from("abcd"), Err(1));

assert_eq!(Str::<3>::try_from("abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from("");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<&Rc<[u8]>> for Str<N>

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

This takes in a [[u8]] of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

If the Err is 0, that means the string was not valid UTF-8.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from(b"abcd"), Err(1));

assert_eq!(Str::<3>::try_from(b"abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from(b"");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<&Rc<str>> for Str<N>

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

This takes in a &str of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from("abcd"), Err(1));

assert_eq!(Str::<3>::try_from("abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from("");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<&String> for Str<N>

fn try_from(string: &String) -> Result<Self, Self::Error>

This takes in a &str of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from("abcd"), Err(1));

assert_eq!(Str::<3>::try_from("abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from("");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<&Vec<u8>> for Str<N>

fn try_from(bytes: &Vec<u8>) -> Result<Self, Self::Error>

This takes in a [[u8]] of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

If the Err is 0, that means the string was not valid UTF-8.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from(b"abcd"), Err(1));

assert_eq!(Str::<3>::try_from(b"abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from(b"");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<&str> for Str<N>

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

This takes in a &str of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from("abcd"), Err(1));

assert_eq!(Str::<3>::try_from("abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from("");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize, const ARRAY: usize> TryFrom<[u8; ARRAY]> for Str<N>

type Error = usize

The type returned in the event of a conversion error.

fn try_from(bytes: [u8; ARRAY]) -> Result<Self, Self::Error>

Performs the conversion.

impl<const N: usize> TryFrom<Arc<[u8]>> for Str<N>

fn try_from(bytes: Arc<[u8]>) -> Result<Self, Self::Error>

This takes in a [[u8]] of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

If the Err is 0, that means the string was not valid UTF-8.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from(b"abcd"), Err(1));

assert_eq!(Str::<3>::try_from(b"abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from(b"");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<Arc<str>> for Str<N>

fn try_from(string: Arc<str>) -> Result<Self, Self::Error>

This takes in a &str of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from("abcd"), Err(1));

assert_eq!(Str::<3>::try_from("abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from("");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<Box<[u8]>> for Str<N>

fn try_from(bytes: Box<[u8]>) -> Result<Self, Self::Error>

This takes in a [[u8]] of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

If the Err is 0, that means the string was not valid UTF-8.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from(b"abcd"), Err(1));

assert_eq!(Str::<3>::try_from(b"abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from(b"");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<Box<str>> for Str<N>

fn try_from(string: Box<str>) -> Result<Self, Self::Error>

This takes in a &str of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from("abcd"), Err(1));

assert_eq!(Str::<3>::try_from("abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from("");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<Cow<'_, [u8]>> for Str<N>

fn try_from(bytes: Cow<'_, [u8]>) -> Result<Self, Self::Error>

This takes in a [[u8]] of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

If the Err is 0, that means the string was not valid UTF-8.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from(b"abcd"), Err(1));

assert_eq!(Str::<3>::try_from(b"abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from(b"");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<Cow<'_, str>> for Str<N>

fn try_from(string: Cow<'_, str>) -> Result<Self, Self::Error>

This takes in a &str of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from("abcd"), Err(1));

assert_eq!(Str::<3>::try_from("abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from("");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<Rc<[u8]>> for Str<N>

fn try_from(bytes: Rc<[u8]>) -> Result<Self, Self::Error>

This takes in a [[u8]] of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

If the Err is 0, that means the string was not valid UTF-8.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from(b"abcd"), Err(1));

assert_eq!(Str::<3>::try_from(b"abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from(b"");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<Rc<str>> for Str<N>

fn try_from(string: Rc<str>) -> Result<Self, Self::Error>

This takes in a &str of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from("abcd"), Err(1));

assert_eq!(Str::<3>::try_from("abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from("");

type Error = usize

The type returned in the event of a conversion error.

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

fn try_from(string: String) -> Result<Self, Self::Error>

This takes in a &str of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from("abcd"), Err(1));

assert_eq!(Str::<3>::try_from("abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from("");

type Error = usize

The type returned in the event of a conversion error.

impl<const N: usize> TryFrom<Vec<u8>> for Str<N>

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

This takes in a [[u8]] of any length (equal to or less than N) and will return a Str with that same string.

If this function fails, Result::Err is returned with how many extra bytes couldn’t fit.

If the Err is 0, that means the string was not valid UTF-8.

// Input string is 4 in length, we can't copy it.
// There is 1 extra byte that can't fit.
assert_eq!(Str::<3>::try_from(b"abcd"), Err(1));

assert_eq!(Str::<3>::try_from(b"abc").unwrap(), "abc");

Compile-time panic

This function will panic at compile time if N > 255.

// Compile error!
Str::<256>::try_from(b"");

type Error = usize

The type returned in the event of a conversion error.

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

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

Calls Str::push_str()

let mut s = Str::<12>::new();

std::fmt::Write::write_str(&mut s, "hello world!").unwrap();
assert_eq!(s, "hello world!");

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

Calls Str::push_char()

let mut s = Str::<3>::new();

std::fmt::Write::write_char(&mut s, 'で').unwrap();
assert_eq!(s, "で");

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> Copy for Str<N>

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

impl<const N: usize> StructuralPartialEq for Str<N>