Returns the number of elements in the slice.

§Examples

let a = [1, 2, 3];
assert_eq!(a.len(), 3);

Returns true if the slice has a length of 0.

§Examples

let a = [1, 2, 3];
assert!(!a.is_empty());

let b: &[i32] = &[];
assert!(b.is_empty());

Returns the first element of the slice, or None if it is empty.

§Examples

let v = [10, 40, 30];
assert_eq!(Some(&10), v.first());

let w: &[i32] = &[];
assert_eq!(None, w.first());

Returns a mutable reference to the first element of the slice, or None if it is empty.

§Examples

let x = &mut [0, 1, 2];

if let Some(first) = x.first_mut() {
    *first = 5;
}
assert_eq!(x, &[5, 1, 2]);

let y: &mut [i32] = &mut [];
assert_eq!(None, y.first_mut());

Returns the first and all the rest of the elements of the slice, or None if it is empty.

§Examples

let x = &[0, 1, 2];

if let Some((first, elements)) = x.split_first() {
    assert_eq!(first, &0);
    assert_eq!(elements, &[1, 2]);
}

Returns the first and all the rest of the elements of the slice, or None if it is empty.

§Examples

let x = &mut [0, 1, 2];

if let Some((first, elements)) = x.split_first_mut() {
    *first = 3;
    elements[0] = 4;
    elements[1] = 5;
}
assert_eq!(x, &[3, 4, 5]);

Returns the last and all the rest of the elements of the slice, or None if it is empty.

§Examples

let x = &[0, 1, 2];

if let Some((last, elements)) = x.split_last() {
    assert_eq!(last, &2);
    assert_eq!(elements, &[0, 1]);
}

Returns the last and all the rest of the elements of the slice, or None if it is empty.

§Examples

let x = &mut [0, 1, 2];

if let Some((last, elements)) = x.split_last_mut() {
    *last = 3;
    elements[0] = 4;
    elements[1] = 5;
}
assert_eq!(x, &[4, 5, 3]);

Returns the last element of the slice, or None if it is empty.

§Examples

let v = [10, 40, 30];
assert_eq!(Some(&30), v.last());

let w: &[i32] = &[];
assert_eq!(None, w.last());

Returns a mutable reference to the last item in the slice, or None if it is empty.

§Examples

let x = &mut [0, 1, 2];

if let Some(last) = x.last_mut() {
    *last = 10;
}
assert_eq!(x, &[0, 1, 10]);

let y: &mut [i32] = &mut [];
assert_eq!(None, y.last_mut());

Returns an array reference to the first N items in the slice.

If the slice is not at least N in length, this will return None.

§Examples

let u = [10, 40, 30];
assert_eq!(Some(&[10, 40]), u.first_chunk::<2>());

let v: &[i32] = &[10];
assert_eq!(None, v.first_chunk::<2>());

let w: &[i32] = &[];
assert_eq!(Some(&[]), w.first_chunk::<0>());

Returns a mutable array reference to the first N items in the slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &mut [0, 1, 2];

if let Some(first) = x.first_chunk_mut::<2>() {
    first[0] = 5;
    first[1] = 4;
}
assert_eq!(x, &[5, 4, 2]);

assert_eq!(None, x.first_chunk_mut::<4>());

Returns an array reference to the first N items in the slice and the remaining slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &[0, 1, 2];

if let Some((first, elements)) = x.split_first_chunk::<2>() {
    assert_eq!(first, &[0, 1]);
    assert_eq!(elements, &[2]);
}

assert_eq!(None, x.split_first_chunk::<4>());

Returns a mutable array reference to the first N items in the slice and the remaining slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &mut [0, 1, 2];

if let Some((first, elements)) = x.split_first_chunk_mut::<2>() {
    first[0] = 3;
    first[1] = 4;
    elements[0] = 5;
}
assert_eq!(x, &[3, 4, 5]);

assert_eq!(None, x.split_first_chunk_mut::<4>());

Returns an array reference to the last N items in the slice and the remaining slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &[0, 1, 2];

if let Some((elements, last)) = x.split_last_chunk::<2>() {
    assert_eq!(elements, &[0]);
    assert_eq!(last, &[1, 2]);
}

assert_eq!(None, x.split_last_chunk::<4>());

Returns a mutable array reference to the last N items in the slice and the remaining slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &mut [0, 1, 2];

if let Some((elements, last)) = x.split_last_chunk_mut::<2>() {
    last[0] = 3;
    last[1] = 4;
    elements[0] = 5;
}
assert_eq!(x, &[5, 3, 4]);

assert_eq!(None, x.split_last_chunk_mut::<4>());

Returns an array reference to the last N items in the slice.

If the slice is not at least N in length, this will return None.

§Examples

let u = [10, 40, 30];
assert_eq!(Some(&[40, 30]), u.last_chunk::<2>());

let v: &[i32] = &[10];
assert_eq!(None, v.last_chunk::<2>());

let w: &[i32] = &[];
assert_eq!(Some(&[]), w.last_chunk::<0>());

Returns a mutable array reference to the last N items in the slice.

If the slice is not at least N in length, this will return None.

§Examples

let x = &mut [0, 1, 2];

if let Some(last) = x.last_chunk_mut::<2>() {
    last[0] = 10;
    last[1] = 20;
}
assert_eq!(x, &[0, 10, 20]);

assert_eq!(None, x.last_chunk_mut::<4>());

Returns a reference to an element or subslice depending on the type of index.

• If given a position, returns a reference to the element at that position or None if out of bounds.
• If given a range, returns the subslice corresponding to that range, or None if out of bounds.

§Examples

let v = [10, 40, 30];
assert_eq!(Some(&40), v.get(1));
assert_eq!(Some(&[10, 40][..]), v.get(0..2));
assert_eq!(None, v.get(3));
assert_eq!(None, v.get(0..4));

Returns a mutable reference to an element or subslice depending on the type of index (see get) or None if the index is out of bounds.

§Examples

let x = &mut [0, 1, 2];

if let Some(elem) = x.get_mut(1) {
    *elem = 42;
}
assert_eq!(x, &[0, 42, 2]);

Returns a reference to an element or subslice, without doing bounds checking.

For a safe alternative see get.

§Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used.

You can think of this like .get(index).unwrap_unchecked(). It’s UB to call .get_unchecked(len), even if you immediately convert to a pointer. And it’s UB to call .get_unchecked(..len + 1), .get_unchecked(..=len), or similar.

§Examples

let x = &[1, 2, 4];

unsafe {
    assert_eq!(x.get_unchecked(1), &2);
}

Returns a mutable reference to an element or subslice, without doing bounds checking.

For a safe alternative see get_mut.

§Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used.

You can think of this like .get_mut(index).unwrap_unchecked(). It’s UB to call .get_unchecked_mut(len), even if you immediately convert to a pointer. And it’s UB to call .get_unchecked_mut(..len + 1), .get_unchecked_mut(..=len), or similar.

§Examples

let x = &mut [1, 2, 4];

unsafe {
    let elem = x.get_unchecked_mut(1);
    *elem = 13;
}
assert_eq!(x, &[1, 13, 4]);

Returns a raw pointer to the slice’s buffer.

The caller must ensure that the slice outlives the pointer this function returns, or else it will end up dangling.

The caller must also ensure that the memory the pointer (non-transitively) points to is never written to (except inside an UnsafeCell) using this pointer or any pointer derived from it. If you need to mutate the contents of the slice, use as_mut_ptr.

Modifying the container referenced by this slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

§Examples

let x = &[1, 2, 4];
let x_ptr = x.as_ptr();

unsafe {
    for i in 0..x.len() {
        assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
    }
}

Returns an unsafe mutable pointer to the slice’s buffer.

The caller must ensure that the slice outlives the pointer this function returns, or else it will end up dangling.

Modifying the container referenced by this slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

§Examples

let x = &mut [1, 2, 4];
let x_ptr = x.as_mut_ptr();

unsafe {
    for i in 0..x.len() {
        *x_ptr.add(i) += 2;
    }
}
assert_eq!(x, &[3, 4, 6]);

Returns the two raw pointers spanning the slice.

The returned range is half-open, which means that the end pointer points one past the last element of the slice. This way, an empty slice is represented by two equal pointers, and the difference between the two pointers represents the size of the slice.

See as_ptr for warnings on using these pointers. The end pointer requires extra caution, as it does not point to a valid element in the slice.

This function is useful for interacting with foreign interfaces which use two pointers to refer to a range of elements in memory, as is common in C++.

It can also be useful to check if a pointer to an element refers to an element of this slice:

let a = [1, 2, 3];
let x = &a[1] as *const _;
let y = &5 as *const _;

assert!(a.as_ptr_range().contains(&x));
assert!(!a.as_ptr_range().contains(&y));

Returns the two unsafe mutable pointers spanning the slice.

The returned range is half-open, which means that the end pointer points one past the last element of the slice. This way, an empty slice is represented by two equal pointers, and the difference between the two pointers represents the size of the slice.

See as_mut_ptr for warnings on using these pointers. The end pointer requires extra caution, as it does not point to a valid element in the slice.

This function is useful for interacting with foreign interfaces which use two pointers to refer to a range of elements in memory, as is common in C++.

Gets a reference to the underlying array.

If N is not exactly equal to the length of self, then this method returns None.

Gets a mutable reference to the slice’s underlying array.

If N is not exactly equal to the length of self, then this method returns None.

Swaps two elements in the slice.

If a equals to b, it’s guaranteed that elements won’t change value.

§Arguments

• a - The index of the first element
• b - The index of the second element

§Panics

Panics if a or b are out of bounds.

§Examples

let mut v = ["a", "b", "c", "d", "e"];
v.swap(2, 4);
assert!(v == ["a", "b", "e", "d", "c"]);

Swaps two elements in the slice, without doing bounds checking.

For a safe alternative see swap.

§Arguments

• a - The index of the first element
• b - The index of the second element

§Safety

Calling this method with an out-of-bounds index is undefined behavior. The caller has to ensure that a < self.len() and b < self.len().

§Examples

#![feature(slice_swap_unchecked)]

let mut v = ["a", "b", "c", "d"];
// SAFETY: we know that 1 and 3 are both indices of the slice
unsafe { v.swap_unchecked(1, 3) };
assert!(v == ["a", "d", "c", "b"]);

Reverses the order of elements in the slice, in place.

§Examples

let mut v = [1, 2, 3];
v.reverse();
assert!(v == [3, 2, 1]);

Returns an iterator over the slice.

The iterator yields all items from start to end.

§Examples

let x = &[1, 2, 4];
let mut iterator = x.iter();

assert_eq!(iterator.next(), Some(&1));
assert_eq!(iterator.next(), Some(&2));
assert_eq!(iterator.next(), Some(&4));
assert_eq!(iterator.next(), None);

Returns an iterator that allows modifying each value.

The iterator yields all items from start to end.

§Examples

let x = &mut [1, 2, 4];
for elem in x.iter_mut() {
    *elem += 2;
}
assert_eq!(x, &[3, 4, 6]);

Returns an iterator over all contiguous windows of length size. The windows overlap. If the slice is shorter than size, the iterator returns no values.

§Panics

Panics if size is zero.

§Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.windows(3);
assert_eq!(iter.next().unwrap(), &['l', 'o', 'r']);
assert_eq!(iter.next().unwrap(), &['o', 'r', 'e']);
assert_eq!(iter.next().unwrap(), &['r', 'e', 'm']);
assert!(iter.next().is_none());

If the slice is shorter than size:

let slice = ['f', 'o', 'o'];
let mut iter = slice.windows(4);
assert!(iter.next().is_none());

Because the Iterator trait cannot represent the required lifetimes, there is no windows_mut analog to windows; [0,1,2].windows_mut(2).collect() would violate the rules of references (though a LendingIterator analog is possible). You can sometimes use Cell::as_slice_of_cells in conjunction with windows instead:

use std::cell::Cell;

let mut array = ['R', 'u', 's', 't', ' ', '2', '0', '1', '5'];
let slice = &mut array[..];
let slice_of_cells: &[Cell<char>] = Cell::from_mut(slice).as_slice_of_cells();
for w in slice_of_cells.windows(3) {
    Cell::swap(&w[0], &w[2]);
}
assert_eq!(array, ['s', 't', ' ', '2', '0', '1', '5', 'u', 'R']);

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are slices and do not overlap. If chunk_size does not divide the length of the slice, then the last chunk will not have length chunk_size.

See chunks_exact for a variant of this iterator that returns chunks of always exactly chunk_size elements, and rchunks for the same iterator but starting at the end of the slice.

If your chunk_size is a constant, consider using as_chunks instead, which will give references to arrays of exactly that length, rather than slices.

§Panics

Panics if chunk_size is zero.

§Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.chunks(2);
assert_eq!(iter.next().unwrap(), &['l', 'o']);
assert_eq!(iter.next().unwrap(), &['r', 'e']);
assert_eq!(iter.next().unwrap(), &['m']);
assert!(iter.next().is_none());

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are mutable slices, and do not overlap. If chunk_size does not divide the length of the slice, then the last chunk will not have length chunk_size.

See chunks_exact_mut for a variant of this iterator that returns chunks of always exactly chunk_size elements, and rchunks_mut for the same iterator but starting at the end of the slice.

If your chunk_size is a constant, consider using as_chunks_mut instead, which will give references to arrays of exactly that length, rather than slices.

§Panics

Panics if chunk_size is zero.

§Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

for chunk in v.chunks_mut(2) {
    for elem in chunk.iter_mut() {
        *elem += count;
    }
    count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 3]);

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are slices and do not overlap. If chunk_size does not divide the length of the slice, then the last up to chunk_size-1 elements will be omitted and can be retrieved from the remainder function of the iterator.

Due to each chunk having exactly chunk_size elements, the compiler can often optimize the resulting code better than in the case of chunks.

See chunks for a variant of this iterator that also returns the remainder as a smaller chunk, and rchunks_exact for the same iterator but starting at the end of the slice.

If your chunk_size is a constant, consider using as_chunks instead, which will give references to arrays of exactly that length, rather than slices.

§Panics

Panics if chunk_size is zero.

§Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.chunks_exact(2);
assert_eq!(iter.next().unwrap(), &['l', 'o']);
assert_eq!(iter.next().unwrap(), &['r', 'e']);
assert!(iter.next().is_none());
assert_eq!(iter.remainder(), &['m']);

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are mutable slices, and do not overlap. If chunk_size does not divide the length of the slice, then the last up to chunk_size-1 elements will be omitted and can be retrieved from the into_remainder function of the iterator.

Due to each chunk having exactly chunk_size elements, the compiler can often optimize the resulting code better than in the case of chunks_mut.

See chunks_mut for a variant of this iterator that also returns the remainder as a smaller chunk, and rchunks_exact_mut for the same iterator but starting at the end of the slice.

If your chunk_size is a constant, consider using as_chunks_mut instead, which will give references to arrays of exactly that length, rather than slices.

§Panics

Panics if chunk_size is zero.

§Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

for chunk in v.chunks_exact_mut(2) {
    for elem in chunk.iter_mut() {
        *elem += count;
    }
    count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 0]);

Splits the slice into a slice of N-element arrays, assuming that there’s no remainder.

This is the inverse operation to as_flattened.

As this is unsafe, consider whether you could use as_chunks or as_rchunks instead, perhaps via something like if let (chunks, []) = slice.as_chunks() or let (chunks, []) = slice.as_chunks() else { unreachable!() };.

§Safety

This may only be called when

• The slice splits exactly into N-element chunks (aka self.len() % N == 0).
• N != 0.

§Examples

let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
let chunks: &[[char; 1]] =
    // SAFETY: 1-element chunks never have remainder
    unsafe { slice.as_chunks_unchecked() };
assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
let chunks: &[[char; 3]] =
    // SAFETY: The slice length (6) is a multiple of 3
    unsafe { slice.as_chunks_unchecked() };
assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);

// These would be unsound:
// let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
// let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed

Splits the slice into a slice of N-element arrays, starting at the beginning of the slice, and a remainder slice with length strictly less than N.

The remainder is meaningful in the division sense. Given let (chunks, remainder) = slice.as_chunks(), then:

• chunks.len() equals slice.len() / N,
• remainder.len() equals slice.len() % N, and
• slice.len() equals chunks.len() * N + remainder.len().

You can flatten the chunks back into a slice-of-T with as_flattened.

§Panics

Panics if N is zero.

Note that this check is against a const generic parameter, not a runtime value, and thus a particular monomorphization will either always panic or it will never panic.

§Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let (chunks, remainder) = slice.as_chunks();
assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
assert_eq!(remainder, &['m']);

If you expect the slice to be an exact multiple, you can combine let-else with an empty slice pattern:

let slice = ['R', 'u', 's', 't'];
let (chunks, []) = slice.as_chunks::<2>() else {
    panic!("slice didn't have even length")
};
assert_eq!(chunks, &[['R', 'u'], ['s', 't']]);

Splits the slice into a slice of N-element arrays, starting at the end of the slice, and a remainder slice with length strictly less than N.

The remainder is meaningful in the division sense. Given let (remainder, chunks) = slice.as_rchunks(), then:

• remainder.len() equals slice.len() % N,
• chunks.len() equals slice.len() / N, and
• slice.len() equals chunks.len() * N + remainder.len().

You can flatten the chunks back into a slice-of-T with as_flattened.

§Panics

Panics if N is zero.

Note that this check is against a const generic parameter, not a runtime value, and thus a particular monomorphization will either always panic or it will never panic.

§Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let (remainder, chunks) = slice.as_rchunks();
assert_eq!(remainder, &['l']);
assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);

Splits the slice into a slice of N-element arrays, assuming that there’s no remainder.

This is the inverse operation to as_flattened_mut.

As this is unsafe, consider whether you could use as_chunks_mut or as_rchunks_mut instead, perhaps via something like if let (chunks, []) = slice.as_chunks_mut() or let (chunks, []) = slice.as_chunks_mut() else { unreachable!() };.

§Safety

This may only be called when

• The slice splits exactly into N-element chunks (aka self.len() % N == 0).
• N != 0.

§Examples

let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
let chunks: &mut [[char; 1]] =
    // SAFETY: 1-element chunks never have remainder
    unsafe { slice.as_chunks_unchecked_mut() };
chunks[0] = ['L'];
assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
let chunks: &mut [[char; 3]] =
    // SAFETY: The slice length (6) is a multiple of 3
    unsafe { slice.as_chunks_unchecked_mut() };
chunks[1] = ['a', 'x', '?'];
assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);

// These would be unsound:
// let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
// let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed

Splits the slice into a slice of N-element arrays, starting at the beginning of the slice, and a remainder slice with length strictly less than N.

The remainder is meaningful in the division sense. Given let (chunks, remainder) = slice.as_chunks_mut(), then:

• chunks.len() equals slice.len() / N,
• remainder.len() equals slice.len() % N, and
• slice.len() equals chunks.len() * N + remainder.len().

You can flatten the chunks back into a slice-of-T with as_flattened_mut.

§Panics

Panics if N is zero.

Note that this check is against a const generic parameter, not a runtime value, and thus a particular monomorphization will either always panic or it will never panic.

§Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

let (chunks, remainder) = v.as_chunks_mut();
remainder[0] = 9;
for chunk in chunks {
    *chunk = [count; 2];
    count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 9]);

Splits the slice into a slice of N-element arrays, starting at the end of the slice, and a remainder slice with length strictly less than N.

The remainder is meaningful in the division sense. Given let (remainder, chunks) = slice.as_rchunks_mut(), then:

• remainder.len() equals slice.len() % N,
• chunks.len() equals slice.len() / N, and
• slice.len() equals chunks.len() * N + remainder.len().

You can flatten the chunks back into a slice-of-T with as_flattened_mut.

§Panics

Panics if N is zero.

Note that this check is against a const generic parameter, not a runtime value, and thus a particular monomorphization will either always panic or it will never panic.

§Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

let (remainder, chunks) = v.as_rchunks_mut();
remainder[0] = 9;
for chunk in chunks {
    *chunk = [count; 2];
    count += 1;
}
assert_eq!(v, &[9, 1, 1, 2, 2]);

Returns an iterator over overlapping windows of N elements of a slice, starting at the beginning of the slice.

This is the const generic equivalent of windows.

If N is greater than the size of the slice, it will return no windows.

§Panics

Panics if N is zero. This check will most probably get changed to a compile time error before this method gets stabilized.

§Examples

#![feature(array_windows)]
let slice = [0, 1, 2, 3];
let mut iter = slice.array_windows();
assert_eq!(iter.next().unwrap(), &[0, 1]);
assert_eq!(iter.next().unwrap(), &[1, 2]);
assert_eq!(iter.next().unwrap(), &[2, 3]);
assert!(iter.next().is_none());

Returns an iterator over chunk_size elements of the slice at a time, starting at the end of the slice.

The chunks are slices and do not overlap. If chunk_size does not divide the length of the slice, then the last chunk will not have length chunk_size.

See rchunks_exact for a variant of this iterator that returns chunks of always exactly chunk_size elements, and chunks for the same iterator but starting at the beginning of the slice.

If your chunk_size is a constant, consider using as_rchunks instead, which will give references to arrays of exactly that length, rather than slices.

§Panics

Panics if chunk_size is zero.

§Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.rchunks(2);
assert_eq!(iter.next().unwrap(), &['e', 'm']);
assert_eq!(iter.next().unwrap(), &['o', 'r']);
assert_eq!(iter.next().unwrap(), &['l']);
assert!(iter.next().is_none());

Returns an iterator over chunk_size elements of the slice at a time, starting at the end of the slice.

The chunks are mutable slices, and do not overlap. If chunk_size does not divide the length of the slice, then the last chunk will not have length chunk_size.

See rchunks_exact_mut for a variant of this iterator that returns chunks of always exactly chunk_size elements, and chunks_mut for the same iterator but starting at the beginning of the slice.

If your chunk_size is a constant, consider using as_rchunks_mut instead, which will give references to arrays of exactly that length, rather than slices.

§Panics

Panics if chunk_size is zero.

§Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

for chunk in v.rchunks_mut(2) {
    for elem in chunk.iter_mut() {
        *elem += count;
    }
    count += 1;
}
assert_eq!(v, &[3, 2, 2, 1, 1]);

Returns an iterator over chunk_size elements of the slice at a time, starting at the end of the slice.

The chunks are slices and do not overlap. If chunk_size does not divide the length of the slice, then the last up to chunk_size-1 elements will be omitted and can be retrieved from the remainder function of the iterator.

Due to each chunk having exactly chunk_size elements, the compiler can often optimize the resulting code better than in the case of rchunks.

See rchunks for a variant of this iterator that also returns the remainder as a smaller chunk, and chunks_exact for the same iterator but starting at the beginning of the slice.

If your chunk_size is a constant, consider using as_rchunks instead, which will give references to arrays of exactly that length, rather than slices.

§Panics

Panics if chunk_size is zero.

§Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.rchunks_exact(2);
assert_eq!(iter.next().unwrap(), &['e', 'm']);
assert_eq!(iter.next().unwrap(), &['o', 'r']);
assert!(iter.next().is_none());
assert_eq!(iter.remainder(), &['l']);

Returns an iterator over chunk_size elements of the slice at a time, starting at the end of the slice.

The chunks are mutable slices, and do not overlap. If chunk_size does not divide the length of the slice, then the last up to chunk_size-1 elements will be omitted and can be retrieved from the into_remainder function of the iterator.

Due to each chunk having exactly chunk_size elements, the compiler can often optimize the resulting code better than in the case of chunks_mut.

See rchunks_mut for a variant of this iterator that also returns the remainder as a smaller chunk, and chunks_exact_mut for the same iterator but starting at the beginning of the slice.

If your chunk_size is a constant, consider using as_rchunks_mut instead, which will give references to arrays of exactly that length, rather than slices.

§Panics

Panics if chunk_size is zero.

§Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

for chunk in v.rchunks_exact_mut(2) {
    for elem in chunk.iter_mut() {
        *elem += count;
    }
    count += 1;
}
assert_eq!(v, &[0, 2, 2, 1, 1]);

Returns an iterator over the slice producing non-overlapping runs of elements using the predicate to separate them.

The predicate is called for every pair of consecutive elements, meaning that it is called on slice[0] and slice[1], followed by slice[1] and slice[2], and so on.

§Examples

let slice = &[1, 1, 1, 3, 3, 2, 2, 2];

let mut iter = slice.chunk_by(|a, b| a == b);

assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
assert_eq!(iter.next(), Some(&[3, 3][..]));
assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
assert_eq!(iter.next(), None);

This method can be used to extract the sorted subslices:

let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];

let mut iter = slice.chunk_by(|a, b| a <= b);

assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
assert_eq!(iter.next(), Some(&[2, 3][..]));
assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
assert_eq!(iter.next(), None);

Returns an iterator over the slice producing non-overlapping mutable runs of elements using the predicate to separate them.

The predicate is called for every pair of consecutive elements, meaning that it is called on slice[0] and slice[1], followed by slice[1] and slice[2], and so on.

§Examples

let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];

let mut iter = slice.chunk_by_mut(|a, b| a == b);

assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
assert_eq!(iter.next(), Some(&mut [3, 3][..]));
assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
assert_eq!(iter.next(), None);

This method can be used to extract the sorted subslices:

let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];

let mut iter = slice.chunk_by_mut(|a, b| a <= b);

assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
assert_eq!(iter.next(), Some(&mut [2, 3][..]));
assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
assert_eq!(iter.next(), None);

Divides one slice into two at an index.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

§Panics

Panics if mid > len. For a non-panicking alternative see split_at_checked.

§Examples

let v = ['a', 'b', 'c'];

{
   let (left, right) = v.split_at(0);
   assert_eq!(left, []);
   assert_eq!(right, ['a', 'b', 'c']);
}

{
    let (left, right) = v.split_at(2);
    assert_eq!(left, ['a', 'b']);
    assert_eq!(right, ['c']);
}

{
    let (left, right) = v.split_at(3);
    assert_eq!(left, ['a', 'b', 'c']);
    assert_eq!(right, []);
}

Divides one mutable slice into two at an index.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

§Panics

Panics if mid > len. For a non-panicking alternative see split_at_mut_checked.

§Examples

let mut v = [1, 0, 3, 0, 5, 6];
let (left, right) = v.split_at_mut(2);
assert_eq!(left, [1, 0]);
assert_eq!(right, [3, 0, 5, 6]);
left[1] = 2;
right[1] = 4;
assert_eq!(v, [1, 2, 3, 4, 5, 6]);

Divides one slice into two at an index, without doing bounds checking.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

For a safe alternative see split_at.

§Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used. The caller has to ensure that 0 <= mid <= self.len().

§Examples

let v = ['a', 'b', 'c'];

unsafe {
   let (left, right) = v.split_at_unchecked(0);
   assert_eq!(left, []);
   assert_eq!(right, ['a', 'b', 'c']);
}

unsafe {
    let (left, right) = v.split_at_unchecked(2);
    assert_eq!(left, ['a', 'b']);
    assert_eq!(right, ['c']);
}

unsafe {
    let (left, right) = v.split_at_unchecked(3);
    assert_eq!(left, ['a', 'b', 'c']);
    assert_eq!(right, []);
}

Divides one mutable slice into two at an index, without doing bounds checking.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

For a safe alternative see split_at_mut.

§Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used. The caller has to ensure that 0 <= mid <= self.len().

§Examples

let mut v = [1, 0, 3, 0, 5, 6];
// scoped to restrict the lifetime of the borrows
unsafe {
    let (left, right) = v.split_at_mut_unchecked(2);
    assert_eq!(left, [1, 0]);
    assert_eq!(right, [3, 0, 5, 6]);
    left[1] = 2;
    right[1] = 4;
}
assert_eq!(v, [1, 2, 3, 4, 5, 6]);

Divides one slice into two at an index, returning None if the slice is too short.

If mid ≤ len returns a pair of slices where the first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

Otherwise, if mid > len, returns None.

§Examples

let v = [1, -2, 3, -4, 5, -6];

{
   let (left, right) = v.split_at_checked(0).unwrap();
   assert_eq!(left, []);
   assert_eq!(right, [1, -2, 3, -4, 5, -6]);
}

{
    let (left, right) = v.split_at_checked(2).unwrap();
    assert_eq!(left, [1, -2]);
    assert_eq!(right, [3, -4, 5, -6]);
}

{
    let (left, right) = v.split_at_checked(6).unwrap();
    assert_eq!(left, [1, -2, 3, -4, 5, -6]);
    assert_eq!(right, []);
}

assert_eq!(None, v.split_at_checked(7));

Divides one mutable slice into two at an index, returning None if the slice is too short.

If mid ≤ len returns a pair of slices where the first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

Otherwise, if mid > len, returns None.

§Examples

let mut v = [1, 0, 3, 0, 5, 6];

if let Some((left, right)) = v.split_at_mut_checked(2) {
    assert_eq!(left, [1, 0]);
    assert_eq!(right, [3, 0, 5, 6]);
    left[1] = 2;
    right[1] = 4;
}
assert_eq!(v, [1, 2, 3, 4, 5, 6]);

assert_eq!(None, v.split_at_mut_checked(7));

Returns an iterator over subslices separated by elements that match pred. The matched element is not contained in the subslices.

§Examples

let slice = [10, 40, 33, 20];
let mut iter = slice.split(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[10, 40]);
assert_eq!(iter.next().unwrap(), &[20]);
assert!(iter.next().is_none());

If the first element is matched, an empty slice will be the first item returned by the iterator. Similarly, if the last element in the slice is matched, an empty slice will be the last item returned by the iterator:

let slice = [10, 40, 33];
let mut iter = slice.split(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[10, 40]);
assert_eq!(iter.next().unwrap(), &[]);
assert!(iter.next().is_none());

If two matched elements are directly adjacent, an empty slice will be present between them:

let slice = [10, 6, 33, 20];
let mut iter = slice.split(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[10]);
assert_eq!(iter.next().unwrap(), &[]);
assert_eq!(iter.next().unwrap(), &[20]);
assert!(iter.next().is_none());

Returns an iterator over mutable subslices separated by elements that match pred. The matched element is not contained in the subslices.

§Examples

let mut v = [10, 40, 30, 20, 60, 50];

for group in v.split_mut(|num| *num % 3 == 0) {
    group[0] = 1;
}
assert_eq!(v, [1, 40, 30, 1, 60, 1]);

Returns an iterator over subslices separated by elements that match pred. The matched element is contained in the end of the previous subslice as a terminator.

§Examples

let slice = [10, 40, 33, 20];
let mut iter = slice.split_inclusive(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
assert_eq!(iter.next().unwrap(), &[20]);
assert!(iter.next().is_none());

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

let slice = [3, 10, 40, 33];
let mut iter = slice.split_inclusive(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[3]);
assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
assert!(iter.next().is_none());

Returns an iterator over mutable subslices separated by elements that match pred. The matched element is contained in the previous subslice as a terminator.

§Examples

let mut v = [10, 40, 30, 20, 60, 50];

for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
    let terminator_idx = group.len()-1;
    group[terminator_idx] = 1;
}
assert_eq!(v, [10, 40, 1, 20, 1, 1]);

Returns an iterator over subslices separated by elements that match pred, starting at the end of the slice and working backwards. The matched element is not contained in the subslices.

§Examples

let slice = [11, 22, 33, 0, 44, 55];
let mut iter = slice.rsplit(|num| *num == 0);

assert_eq!(iter.next().unwrap(), &[44, 55]);
assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
assert_eq!(iter.next(), None);

As with split(), if the first or last element is matched, an empty slice will be the first (or last) item returned by the iterator.

let v = &[0, 1, 1, 2, 3, 5, 8];
let mut it = v.rsplit(|n| *n % 2 == 0);
assert_eq!(it.next().unwrap(), &[]);
assert_eq!(it.next().unwrap(), &[3, 5]);
assert_eq!(it.next().unwrap(), &[1, 1]);
assert_eq!(it.next().unwrap(), &[]);
assert_eq!(it.next(), None);

Returns an iterator over mutable subslices separated by elements that match pred, starting at the end of the slice and working backwards. The matched element is not contained in the subslices.

§Examples

let mut v = [100, 400, 300, 200, 600, 500];

let mut count = 0;
for group in v.rsplit_mut(|num| *num % 3 == 0) {
    count += 1;
    group[0] = count;
}
assert_eq!(v, [3, 400, 300, 2, 600, 1]);

Returns an iterator over subslices separated by elements that match pred, limited to returning at most n items. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

§Examples

Print the slice split once by numbers divisible by 3 (i.e., [10, 40], [20, 60, 50]):

let v = [10, 40, 30, 20, 60, 50];

for group in v.splitn(2, |num| *num % 3 == 0) {
    println!("{group:?}");
}

Returns an iterator over mutable subslices separated by elements that match pred, limited to returning at most n items. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

§Examples

let mut v = [10, 40, 30, 20, 60, 50];

for group in v.splitn_mut(2, |num| *num % 3 == 0) {
    group[0] = 1;
}
assert_eq!(v, [1, 40, 30, 1, 60, 50]);

Returns an iterator over subslices separated by elements that match pred limited to returning at most n items. This starts at the end of the slice and works backwards. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

§Examples

Print the slice split once, starting from the end, by numbers divisible by 3 (i.e., [50], [10, 40, 30, 20]):

let v = [10, 40, 30, 20, 60, 50];

for group in v.rsplitn(2, |num| *num % 3 == 0) {
    println!("{group:?}");
}

Returns an iterator over subslices separated by elements that match pred limited to returning at most n items. This starts at the end of the slice and works backwards. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

§Examples

let mut s = [10, 40, 30, 20, 60, 50];

for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
    group[0] = 1;
}
assert_eq!(s, [1, 40, 30, 20, 60, 1]);

Splits the slice on the first element that matches the specified predicate.

If any matching elements are present in the slice, returns the prefix before the match and suffix after. The matching element itself is not included. If no elements match, returns None.

§Examples

#![feature(slice_split_once)]
let s = [1, 2, 3, 2, 4];
assert_eq!(s.split_once(|&x| x == 2), Some((
    &[1][..],
    &[3, 2, 4][..]
)));
assert_eq!(s.split_once(|&x| x == 0), None);

Splits the slice on the last element that matches the specified predicate.

If any matching elements are present in the slice, returns the prefix before the match and suffix after. The matching element itself is not included. If no elements match, returns None.

§Examples

#![feature(slice_split_once)]
let s = [1, 2, 3, 2, 4];
assert_eq!(s.rsplit_once(|&x| x == 2), Some((
    &[1, 2, 3][..],
    &[4][..]
)));
assert_eq!(s.rsplit_once(|&x| x == 0), None);

Returns true if the slice contains an element with the given value.

This operation is O(n).

Note that if you have a sorted slice, binary_search may be faster.

§Examples

let v = [10, 40, 30];
assert!(v.contains(&30));
assert!(!v.contains(&50));

If you do not have a &T, but some other value that you can compare with one (for example, String implements PartialEq<str>), you can use iter().any:

let v = [String::from("hello"), String::from("world")]; // slice of `String`
assert!(v.iter().any(|e| e == "hello")); // search with `&str`
assert!(!v.iter().any(|e| e == "hi"));

Returns true if needle is a prefix of the slice or equal to the slice.

§Examples

let v = [10, 40, 30];
assert!(v.starts_with(&[10]));
assert!(v.starts_with(&[10, 40]));
assert!(v.starts_with(&v));
assert!(!v.starts_with(&[50]));
assert!(!v.starts_with(&[10, 50]));

Always returns true if needle is an empty slice:

let v = &[10, 40, 30];
assert!(v.starts_with(&[]));
let v: &[u8] = &[];
assert!(v.starts_with(&[]));

Returns true if needle is a suffix of the slice or equal to the slice.

§Examples

let v = [10, 40, 30];
assert!(v.ends_with(&[30]));
assert!(v.ends_with(&[40, 30]));
assert!(v.ends_with(&v));
assert!(!v.ends_with(&[50]));
assert!(!v.ends_with(&[50, 30]));

Always returns true if needle is an empty slice:

let v = &[10, 40, 30];
assert!(v.ends_with(&[]));
let v: &[u8] = &[];
assert!(v.ends_with(&[]));

Returns a subslice with the prefix removed.

If the slice starts with prefix, returns the subslice after the prefix, wrapped in Some. If prefix is empty, simply returns the original slice. If prefix is equal to the original slice, returns an empty slice.

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

§Examples

let v = &[10, 40, 30];
assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
assert_eq!(v.strip_prefix(&[10, 40, 30]), Some(&[][..]));
assert_eq!(v.strip_prefix(&[50]), None);
assert_eq!(v.strip_prefix(&[10, 50]), None);

let prefix : &str = "he";
assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
           Some(b"llo".as_ref()));

Returns a subslice with the suffix removed.

If the slice ends with suffix, returns the subslice before the suffix, wrapped in Some. If suffix is empty, simply returns the original slice. If suffix is equal to the original slice, returns an empty slice.

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

§Examples

let v = &[10, 40, 30];
assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
assert_eq!(v.strip_suffix(&[10, 40, 30]), Some(&[][..]));
assert_eq!(v.strip_suffix(&[50]), None);
assert_eq!(v.strip_suffix(&[50, 30]), None);

Returns a subslice with the prefix and suffix removed.

If the slice starts with prefix and ends with suffix, returns the subslice after the prefix and before the suffix, wrapped in Some.

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

§Examples

#![feature(strip_circumfix)]

let v = &[10, 50, 40, 30];
assert_eq!(v.strip_circumfix(&[10], &[30]), Some(&[50, 40][..]));
assert_eq!(v.strip_circumfix(&[10], &[40, 30]), Some(&[50][..]));
assert_eq!(v.strip_circumfix(&[10, 50], &[40, 30]), Some(&[][..]));
assert_eq!(v.strip_circumfix(&[50], &[30]), None);
assert_eq!(v.strip_circumfix(&[10], &[40]), None);
assert_eq!(v.strip_circumfix(&[], &[40, 30]), Some(&[10, 50][..]));
assert_eq!(v.strip_circumfix(&[10, 50], &[]), Some(&[40, 30][..]));

Returns a subslice with the optional prefix removed.

If the slice starts with prefix, returns the subslice after the prefix. If prefix is empty or the slice does not start with prefix, simply returns the original slice. If prefix is equal to the original slice, returns an empty slice.

§Examples

#![feature(trim_prefix_suffix)]

let v = &[10, 40, 30];

// Prefix present - removes it
assert_eq!(v.trim_prefix(&[10]), &[40, 30][..]);
assert_eq!(v.trim_prefix(&[10, 40]), &[30][..]);
assert_eq!(v.trim_prefix(&[10, 40, 30]), &[][..]);

// Prefix absent - returns original slice
assert_eq!(v.trim_prefix(&[50]), &[10, 40, 30][..]);
assert_eq!(v.trim_prefix(&[10, 50]), &[10, 40, 30][..]);

let prefix : &str = "he";
assert_eq!(b"hello".trim_prefix(prefix.as_bytes()), b"llo".as_ref());

Returns a subslice with the optional suffix removed.

If the slice ends with suffix, returns the subslice before the suffix. If suffix is empty or the slice does not end with suffix, simply returns the original slice. If suffix is equal to the original slice, returns an empty slice.

§Examples

#![feature(trim_prefix_suffix)]

let v = &[10, 40, 30];

// Suffix present - removes it
assert_eq!(v.trim_suffix(&[30]), &[10, 40][..]);
assert_eq!(v.trim_suffix(&[40, 30]), &[10][..]);
assert_eq!(v.trim_suffix(&[10, 40, 30]), &[][..]);

// Suffix absent - returns original slice
assert_eq!(v.trim_suffix(&[50]), &[10, 40, 30][..]);
assert_eq!(v.trim_suffix(&[50, 30]), &[10, 40, 30][..]);

Binary searches this slice for a given element. If the slice is not sorted, the returned result is unspecified and meaningless.

If the value is found then Result::Ok is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then Result::Err is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also binary_search_by, binary_search_by_key, and partition_point.

§Examples

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

assert_eq!(s.binary_search(&13),  Ok(9));
assert_eq!(s.binary_search(&4),   Err(7));
assert_eq!(s.binary_search(&100), Err(13));
let r = s.binary_search(&1);
assert!(match r { Ok(1..=4) => true, _ => false, });

If you want to find that whole range of matching items, rather than an arbitrary matching one, that can be done using partition_point:

let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

let low = s.partition_point(|x| x < &1);
assert_eq!(low, 1);
let high = s.partition_point(|x| x <= &1);
assert_eq!(high, 5);
let r = s.binary_search(&1);
assert!((low..high).contains(&r.unwrap()));

assert!(s[..low].iter().all(|&x| x < 1));
assert!(s[low..high].iter().all(|&x| x == 1));
assert!(s[high..].iter().all(|&x| x > 1));

// For something not found, the "range" of equal items is empty
assert_eq!(s.partition_point(|x| x < &11), 9);
assert_eq!(s.partition_point(|x| x <= &11), 9);
assert_eq!(s.binary_search(&11), Err(9));

If you want to insert an item to a sorted vector, while maintaining sort order, consider using partition_point:

let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
let num = 42;
let idx = s.partition_point(|&x| x <= num);
// If `num` is unique, `s.partition_point(|&x| x < num)` (with `<`) is equivalent to
// `s.binary_search(&num).unwrap_or_else(|x| x)`, but using `<=` will allow `insert`
// to shift less elements.
s.insert(idx, num);
assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);

Binary searches this slice with a comparator function.

The comparator function should return an order code that indicates whether its argument is Less, Equal or Greater the desired target. If the slice is not sorted or if the comparator function does not implement an order consistent with the sort order of the underlying slice, the returned result is unspecified and meaningless.

If the value is found then Result::Ok is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then Result::Err is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also binary_search, binary_search_by_key, and partition_point.

§Examples

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

let seek = 13;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
let seek = 4;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
let seek = 100;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
let seek = 1;
let r = s.binary_search_by(|probe| probe.cmp(&seek));
assert!(match r { Ok(1..=4) => true, _ => false, });

Binary searches this slice with a key extraction function.

Assumes that the slice is sorted by the key, for instance with sort_by_key using the same key extraction function. If the slice is not sorted by the key, the returned result is unspecified and meaningless.

If the value is found then Result::Ok is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then Result::Err is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also binary_search, binary_search_by, and partition_point.

§Examples

Looks up a series of four elements in a slice of pairs sorted by their second elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
         (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
         (1, 21), (2, 34), (4, 55)];

assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b),  Ok(9));
assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b),   Err(7));
assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
let r = s.binary_search_by_key(&1, |&(a, b)| b);
assert!(match r { Ok(1..=4) => true, _ => false, });

Sorts the slice in ascending order without preserving the initial order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(n * log(n)) worst-case.

If the implementation of Ord for T does not implement a total order, the function may panic; even if the function exits normally, the resulting order of elements in the slice is unspecified. See also the note on panicking below.

For example |a, b| (a - b).cmp(a) is a comparison function that is neither transitive nor reflexive nor total, a < b < c < a with a = 1, b = 2, c = 3. For more information and examples see the Ord documentation.

All original elements will remain in the slice and any possible modifications via interior mutability are observed in the input. Same is true if the implementation of Ord for T panics.

Sorting types that only implement PartialOrd such as f32 and f64 require additional precautions. For example, f32::NAN != f32::NAN, which doesn’t fulfill the reflexivity requirement of Ord. By using an alternative comparison function with slice::sort_unstable_by such as f32::total_cmp or f64::total_cmp that defines a total order users can sort slices containing floating-point values. Alternatively, if all values in the slice are guaranteed to be in a subset for which PartialOrd::partial_cmp forms a total order, it’s possible to sort the slice with sort_unstable_by(|a, b| a.partial_cmp(b).unwrap()).

§Current implementation

The current implementation is based on ipnsort by Lukas Bergdoll and Orson Peters, which combines the fast average case of quicksort with the fast worst case of heapsort, achieving linear time on fully sorted and reversed inputs. On inputs with k distinct elements, the expected time to sort the data is O(n * log(k)).

It is typically faster than stable sorting, except in a few special cases, e.g., when the slice is partially sorted.

§Panics

May panic if the implementation of Ord for T does not implement a total order, or if the Ord implementation panics.

§Examples

let mut v = [4, -5, 1, -3, 2];

v.sort_unstable();
assert_eq!(v, [-5, -3, 1, 2, 4]);

Sorts the slice in ascending order with a comparison function, without preserving the initial order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(n * log(n)) worst-case.

If the comparison function compare does not implement a total order, the function may panic; even if the function exits normally, the resulting order of elements in the slice is unspecified. See also the note on panicking below.

For example |a, b| (a - b).cmp(a) is a comparison function that is neither transitive nor reflexive nor total, a < b < c < a with a = 1, b = 2, c = 3. For more information and examples see the Ord documentation.

All original elements will remain in the slice and any possible modifications via interior mutability are observed in the input. Same is true if compare panics.

§Current implementation

The current implementation is based on ipnsort by Lukas Bergdoll and Orson Peters, which combines the fast average case of quicksort with the fast worst case of heapsort, achieving linear time on fully sorted and reversed inputs. On inputs with k distinct elements, the expected time to sort the data is O(n * log(k)).

It is typically faster than stable sorting, except in a few special cases, e.g., when the slice is partially sorted.

§Panics

May panic if the compare does not implement a total order, or if the compare itself panics.

§Examples

let mut v = [4, -5, 1, -3, 2];
v.sort_unstable_by(|a, b| a.cmp(b));
assert_eq!(v, [-5, -3, 1, 2, 4]);

// reverse sorting
v.sort_unstable_by(|a, b| b.cmp(a));
assert_eq!(v, [4, 2, 1, -3, -5]);

Sorts the slice in ascending order with a key extraction function, without preserving the initial order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(n * log(n)) worst-case.

If the implementation of Ord for K does not implement a total order, the function may panic; even if the function exits normally, the resulting order of elements in the slice is unspecified. See also the note on panicking below.

For example |a, b| (a - b).cmp(a) is a comparison function that is neither transitive nor reflexive nor total, a < b < c < a with a = 1, b = 2, c = 3. For more information and examples see the Ord documentation.

All original elements will remain in the slice and any possible modifications via interior mutability are observed in the input. Same is true if the implementation of Ord for K panics.

§Current implementation

The current implementation is based on ipnsort by Lukas Bergdoll and Orson Peters, which combines the fast average case of quicksort with the fast worst case of heapsort, achieving linear time on fully sorted and reversed inputs. On inputs with k distinct elements, the expected time to sort the data is O(n * log(k)).

It is typically faster than stable sorting, except in a few special cases, e.g., when the slice is partially sorted.

§Panics

May panic if the implementation of Ord for K does not implement a total order, or if the Ord implementation panics.

§Examples

let mut v = [4i32, -5, 1, -3, 2];

v.sort_unstable_by_key(|k| k.abs());
assert_eq!(v, [1, 2, -3, 4, -5]);

Reorders the slice such that the element at index is at a sort-order position. All elements before index will be <= to this value, and all elements after will be >= to it.

This reordering is unstable (i.e. any element that compares equal to the nth element may end up at that position), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

Returns a triple that partitions the reordered slice:

• The unsorted subslice before index, whose elements all satisfy x <= self[index].

• The element at index.

• The unsorted subslice after index, whose elements all satisfy x >= self[index].

§Current implementation

The current algorithm is an introselect implementation based on ipnsort by Lukas Bergdoll and Orson Peters, which is also the basis for sort_unstable. The fallback algorithm is Median of Medians using Tukey’s Ninther for pivot selection, which guarantees linear runtime for all inputs.

§Panics

Panics when index >= len(), and so always panics on empty slices.

May panic if the implementation of Ord for T does not implement a total order.

§Examples

let mut v = [-5i32, 4, 2, -3, 1];

// Find the items `<=` to the median, the median itself, and the items `>=` to it.
let (lesser, median, greater) = v.select_nth_unstable(2);

assert!(lesser == [-3, -5] || lesser == [-5, -3]);
assert_eq!(median, &mut 1);
assert!(greater == [4, 2] || greater == [2, 4]);

// We are only guaranteed the slice will be one of the following, based on the way we sort
// about the specified index.
assert!(v == [-3, -5, 1, 2, 4] ||
        v == [-5, -3, 1, 2, 4] ||
        v == [-3, -5, 1, 4, 2] ||
        v == [-5, -3, 1, 4, 2]);

Reorders the slice with a comparator function such that the element at index is at a sort-order position. All elements before index will be <= to this value, and all elements after will be >= to it, according to the comparator function.

This reordering is unstable (i.e. any element that compares equal to the nth element may end up at that position), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

Returns a triple partitioning the reordered slice:

• The unsorted subslice before index, whose elements all satisfy compare(x, self[index]).is_le().

• The element at index.

• The unsorted subslice after index, whose elements all satisfy compare(x, self[index]).is_ge().

§Current implementation

The current algorithm is an introselect implementation based on ipnsort by Lukas Bergdoll and Orson Peters, which is also the basis for sort_unstable. The fallback algorithm is Median of Medians using Tukey’s Ninther for pivot selection, which guarantees linear runtime for all inputs.

§Panics

Panics when index >= len(), and so always panics on empty slices.

May panic if compare does not implement a total order.

§Examples

let mut v = [-5i32, 4, 2, -3, 1];

// Find the items `>=` to the median, the median itself, and the items `<=` to it, by using
// a reversed comparator.
let (before, median, after) = v.select_nth_unstable_by(2, |a, b| b.cmp(a));

assert!(before == [4, 2] || before == [2, 4]);
assert_eq!(median, &mut 1);
assert!(after == [-3, -5] || after == [-5, -3]);

// We are only guaranteed the slice will be one of the following, based on the way we sort
// about the specified index.
assert!(v == [2, 4, 1, -5, -3] ||
        v == [2, 4, 1, -3, -5] ||
        v == [4, 2, 1, -5, -3] ||
        v == [4, 2, 1, -3, -5]);

Reorders the slice with a key extraction function such that the element at index is at a sort-order position. All elements before index will have keys <= to the key at index, and all elements after will have keys >= to it.

This reordering is unstable (i.e. any element that compares equal to the nth element may end up at that position), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

Returns a triple partitioning the reordered slice:

• The unsorted subslice before index, whose elements all satisfy f(x) <= f(self[index]).

• The element at index.

• The unsorted subslice after index, whose elements all satisfy f(x) >= f(self[index]).

§Current implementation

The current algorithm is an introselect implementation based on ipnsort by Lukas Bergdoll and Orson Peters, which is also the basis for sort_unstable. The fallback algorithm is Median of Medians using Tukey’s Ninther for pivot selection, which guarantees linear runtime for all inputs.

§Panics

Panics when index >= len(), meaning it always panics on empty slices.

May panic if K: Ord does not implement a total order.

§Examples

let mut v = [-5i32, 4, 1, -3, 2];

// Find the items `<=` to the absolute median, the absolute median itself, and the items
// `>=` to it.
let (lesser, median, greater) = v.select_nth_unstable_by_key(2, |a| a.abs());

assert!(lesser == [1, 2] || lesser == [2, 1]);
assert_eq!(median, &mut -3);
assert!(greater == [4, -5] || greater == [-5, 4]);

// We are only guaranteed the slice will be one of the following, based on the way we sort
// about the specified index.
assert!(v == [1, 2, -3, 4, -5] ||
        v == [1, 2, -3, -5, 4] ||
        v == [2, 1, -3, 4, -5] ||
        v == [2, 1, -3, -5, 4]);

Moves all consecutive repeated elements to the end of the slice according to the PartialEq trait implementation.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

If the slice is sorted, the first returned slice contains no duplicates.

§Examples

#![feature(slice_partition_dedup)]

let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];

let (dedup, duplicates) = slice.partition_dedup();

assert_eq!(dedup, [1, 2, 3, 2, 1]);
assert_eq!(duplicates, [2, 3, 1]);

Moves all but the first of consecutive elements to the end of the slice satisfying a given equality relation.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

The same_bucket function is passed references to two elements from the slice and must determine if the elements compare equal. The elements are passed in opposite order from their order in the slice, so if same_bucket(a, b) returns true, a is moved at the end of the slice.

If the slice is sorted, the first returned slice contains no duplicates.

§Examples

#![feature(slice_partition_dedup)]

let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];

let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));

assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);

Moves all but the first of consecutive elements to the end of the slice that resolve to the same key.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

If the slice is sorted, the first returned slice contains no duplicates.

§Examples

#![feature(slice_partition_dedup)]

let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];

let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);

assert_eq!(dedup, [10, 20, 30, 20, 11]);
assert_eq!(duplicates, [21, 30, 13]);

Rotates the slice in-place such that the first mid elements of the slice move to the end while the last self.len() - mid elements move to the front.

After calling rotate_left, the element previously at index mid will become the first element in the slice.

§Panics

This function will panic if mid is greater than the length of the slice. Note that mid == self.len() does not panic and is a no-op rotation.

§Complexity

Takes linear (in self.len()) time.

§Examples

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a.rotate_left(2);
assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);

Rotating a subslice:

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a[1..5].rotate_left(1);
assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);

Rotates the slice in-place such that the first self.len() - k elements of the slice move to the end while the last k elements move to the front.

After calling rotate_right, the element previously at index self.len() - k will become the first element in the slice.

§Panics

This function will panic if k is greater than the length of the slice. Note that k == self.len() does not panic and is a no-op rotation.

§Complexity

Takes linear (in self.len()) time.

§Examples

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a.rotate_right(2);
assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);

Rotating a subslice:

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a[1..5].rotate_right(1);
assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);

Fills self with elements by cloning value.

§Examples

let mut buf = vec![0; 10];
buf.fill(1);
assert_eq!(buf, vec![1; 10]);

Fills self with elements returned by calling a closure repeatedly.

This method uses a closure to create new values. If you’d rather Clone a given value, use fill. If you want to use the Default trait to generate values, you can pass Default::default as the argument.

§Examples

let mut buf = vec![1; 10];
buf.fill_with(Default::default);
assert_eq!(buf, vec![0; 10]);

Copies the elements from src into self.

The length of src must be the same as self.

§Panics

This function will panic if the two slices have different lengths.

§Examples

Cloning two elements from a slice into another:

let src = [1, 2, 3, 4];
let mut dst = [0, 0];

// Because the slices have to be the same length,
// we slice the source slice from four elements
// to two. It will panic if we don't do this.
dst.clone_from_slice(&src[2..]);

assert_eq!(src, [1, 2, 3, 4]);
assert_eq!(dst, [3, 4]);

Rust enforces that there can only be one mutable reference with no immutable references to a particular piece of data in a particular scope. Because of this, attempting to use clone_from_slice on a single slice will result in a compile failure:

let mut slice = [1, 2, 3, 4, 5];

slice[..2].clone_from_slice(&slice[3..]); // compile fail!

To work around this, we can use split_at_mut to create two distinct sub-slices from a slice:

let mut slice = [1, 2, 3, 4, 5];

{
    let (left, right) = slice.split_at_mut(2);
    left.clone_from_slice(&right[1..]);
}

assert_eq!(slice, [4, 5, 3, 4, 5]);

Copies all elements from src into self, using a memcpy.

The length of src must be the same as self.

If T does not implement Copy, use clone_from_slice.

§Panics

This function will panic if the two slices have different lengths.

§Examples

Copying two elements from a slice into another:

let src = [1, 2, 3, 4];
let mut dst = [0, 0];

// Because the slices have to be the same length,
// we slice the source slice from four elements
// to two. It will panic if we don't do this.
dst.copy_from_slice(&src[2..]);

assert_eq!(src, [1, 2, 3, 4]);
assert_eq!(dst, [3, 4]);

Rust enforces that there can only be one mutable reference with no immutable references to a particular piece of data in a particular scope. Because of this, attempting to use copy_from_slice on a single slice will result in a compile failure:

let mut slice = [1, 2, 3, 4, 5];

slice[..2].copy_from_slice(&slice[3..]); // compile fail!

To work around this, we can use split_at_mut to create two distinct sub-slices from a slice:

let mut slice = [1, 2, 3, 4, 5];

{
    let (left, right) = slice.split_at_mut(2);
    left.copy_from_slice(&right[1..]);
}

assert_eq!(slice, [4, 5, 3, 4, 5]);

Copies elements from one part of the slice to another part of itself, using a memmove.

src is the range within self to copy from. dest is the starting index of the range within self to copy to, which will have the same length as src. The two ranges may overlap. The ends of the two ranges must be less than or equal to self.len().

§Panics

This function will panic if either range exceeds the end of the slice, or if the end of src is before the start.

§Examples

Copying four bytes within a slice:

let mut bytes = *b"Hello, World!";

bytes.copy_within(1..5, 8);

assert_eq!(&bytes, b"Hello, Wello!");

Swaps all elements in self with those in other.

The length of other must be the same as self.

§Panics

This function will panic if the two slices have different lengths.

§Example

Swapping two elements across slices:

let mut slice1 = [0, 0];
let mut slice2 = [1, 2, 3, 4];

slice1.swap_with_slice(&mut slice2[2..]);

assert_eq!(slice1, [3, 4]);
assert_eq!(slice2, [1, 2, 0, 0]);

Rust enforces that there can only be one mutable reference to a particular piece of data in a particular scope. Because of this, attempting to use swap_with_slice on a single slice will result in a compile failure:

let mut slice = [1, 2, 3, 4, 5];
slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!

To work around this, we can use split_at_mut to create two distinct mutable sub-slices from a slice:

let mut slice = [1, 2, 3, 4, 5];

{
    let (left, right) = slice.split_at_mut(2);
    left.swap_with_slice(&mut right[1..]);
}

assert_eq!(slice, [4, 5, 3, 1, 2]);

Transmutes the slice to a slice of another type, ensuring alignment of the types is maintained.

This method splits the slice into three distinct slices: prefix, correctly aligned middle slice of a new type, and the suffix slice. The middle part will be as big as possible under the given alignment constraint and element size.

This method has no purpose when either input element T or output element U are zero-sized and will return the original slice without splitting anything.

§Safety

This method is essentially a transmute with respect to the elements in the returned middle slice, so all the usual caveats pertaining to transmute::<T, U> also apply here.

§Examples

Basic usage:

unsafe {
    let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
    let (prefix, shorts, suffix) = bytes.align_to::<u16>();
    // less_efficient_algorithm_for_bytes(prefix);
    // more_efficient_algorithm_for_aligned_shorts(shorts);
    // less_efficient_algorithm_for_bytes(suffix);
}

Transmutes the mutable slice to a mutable slice of another type, ensuring alignment of the types is maintained.

This method splits the slice into three distinct slices: prefix, correctly aligned middle slice of a new type, and the suffix slice. The middle part will be as big as possible under the given alignment constraint and element size.

This method has no purpose when either input element T or output element U are zero-sized and will return the original slice without splitting anything.

§Safety

This method is essentially a transmute with respect to the elements in the returned middle slice, so all the usual caveats pertaining to transmute::<T, U> also apply here.

§Examples

Basic usage:

unsafe {
    let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
    let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
    // less_efficient_algorithm_for_bytes(prefix);
    // more_efficient_algorithm_for_aligned_shorts(shorts);
    // less_efficient_algorithm_for_bytes(suffix);
}

Splits a slice into a prefix, a middle of aligned SIMD types, and a suffix.

This is a safe wrapper around slice::align_to, so inherits the same guarantees as that method.

§Panics

This will panic if the size of the SIMD type is different from LANES times that of the scalar.

At the time of writing, the trait restrictions on Simd<T, LANES> keeps that from ever happening, as only power-of-two numbers of lanes are supported. It’s possible that, in the future, those restrictions might be lifted in a way that would make it possible to see panics from this method for something like LANES == 3.

§Examples

#![feature(portable_simd)]
use core::simd::prelude::*;

let short = &[1, 2, 3];
let (prefix, middle, suffix) = short.as_simd::<4>();
assert_eq!(middle, []); // Not enough elements for anything in the middle

// They might be split in any possible way between prefix and suffix
let it = prefix.iter().chain(suffix).copied();
assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);

fn basic_simd_sum(x: &[f32]) -> f32 {
    use std::ops::Add;
    let (prefix, middle, suffix) = x.as_simd();
    let sums = f32x4::from_array([
        prefix.iter().copied().sum(),
        0.0,
        0.0,
        suffix.iter().copied().sum(),
    ]);
    let sums = middle.iter().copied().fold(sums, f32x4::add);
    sums.reduce_sum()
}

let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);

Splits a mutable slice into a mutable prefix, a middle of aligned SIMD types, and a mutable suffix.

This is a safe wrapper around slice::align_to_mut, so inherits the same guarantees as that method.

This is the mutable version of slice::as_simd; see that for examples.

§Panics

This will panic if the size of the SIMD type is different from LANES times that of the scalar.

At the time of writing, the trait restrictions on Simd<T, LANES> keeps that from ever happening, as only power-of-two numbers of lanes are supported. It’s possible that, in the future, those restrictions might be lifted in a way that would make it possible to see panics from this method for something like LANES == 3.

Checks if the elements of this slice are sorted.

That is, for each element a and its following element b, a <= b must hold. If the slice yields exactly zero or one element, true is returned.

Note that if Self::Item is only PartialOrd, but not Ord, the above definition implies that this function returns false if any two consecutive items are not comparable.

§Examples

let empty: [i32; 0] = [];

assert!([1, 2, 2, 9].is_sorted());
assert!(![1, 3, 2, 4].is_sorted());
assert!([0].is_sorted());
assert!(empty.is_sorted());
assert!(![0.0, 1.0, f32::NAN].is_sorted());

Checks if the elements of this slice are sorted using the given comparator function.

Instead of using PartialOrd::partial_cmp, this function uses the given compare function to determine whether two elements are to be considered in sorted order.

§Examples

assert!([1, 2, 2, 9].is_sorted_by(|a, b| a <= b));
assert!(![1, 2, 2, 9].is_sorted_by(|a, b| a < b));

assert!([0].is_sorted_by(|a, b| true));
assert!([0].is_sorted_by(|a, b| false));

let empty: [i32; 0] = [];
assert!(empty.is_sorted_by(|a, b| false));
assert!(empty.is_sorted_by(|a, b| true));

Checks if the elements of this slice are sorted using the given key extraction function.

Instead of comparing the slice’s elements directly, this function compares the keys of the elements, as determined by f. Apart from that, it’s equivalent to is_sorted; see its documentation for more information.

§Examples

assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));

Returns the index of the partition point according to the given predicate (the index of the first element of the second partition).

The slice is assumed to be partitioned according to the given predicate. This means that all elements for which the predicate returns true are at the start of the slice and all elements for which the predicate returns false are at the end. For example, [7, 15, 3, 5, 4, 12, 6] is partitioned under the predicate x % 2 != 0 (all odd numbers are at the start, all even at the end).

If this slice is not partitioned, the returned result is unspecified and meaningless, as this method performs a kind of binary search.

See also binary_search, binary_search_by, and binary_search_by_key.

§Examples

let v = [1, 2, 3, 3, 5, 6, 7];
let i = v.partition_point(|&x| x < 5);

assert_eq!(i, 4);
assert!(v[..i].iter().all(|&x| x < 5));
assert!(v[i..].iter().all(|&x| !(x < 5)));

If all elements of the slice match the predicate, including if the slice is empty, then the length of the slice will be returned:

let a = [2, 4, 8];
assert_eq!(a.partition_point(|x| x < &100), a.len());
let a: [i32; 0] = [];
assert_eq!(a.partition_point(|x| x < &100), 0);

If you want to insert an item to a sorted vector, while maintaining sort order:

let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
let num = 42;
let idx = s.partition_point(|&x| x <= num);
s.insert(idx, num);
assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);

Removes the subslice corresponding to the given range and returns a reference to it.

Returns None and does not modify the slice if the given range is out of bounds.

Note that this method only accepts one-sided ranges such as 2.. or ..6, but not 2..6.

§Examples

Splitting off the first three elements of a slice:

let mut slice: &[_] = &['a', 'b', 'c', 'd'];
let mut first_three = slice.split_off(..3).unwrap();

assert_eq!(slice, &['d']);
assert_eq!(first_three, &['a', 'b', 'c']);

Splitting off a slice starting with the third element:

let mut slice: &[_] = &['a', 'b', 'c', 'd'];
let mut tail = slice.split_off(2..).unwrap();

assert_eq!(slice, &['a', 'b']);
assert_eq!(tail, &['c', 'd']);

Getting None when range is out of bounds:

let mut slice: &[_] = &['a', 'b', 'c', 'd'];

assert_eq!(None, slice.split_off(5..));
assert_eq!(None, slice.split_off(..5));
assert_eq!(None, slice.split_off(..=4));
let expected: &[char] = &['a', 'b', 'c', 'd'];
assert_eq!(Some(expected), slice.split_off(..4));

Removes the subslice corresponding to the given range and returns a mutable reference to it.

Returns None and does not modify the slice if the given range is out of bounds.

Note that this method only accepts one-sided ranges such as 2.. or ..6, but not 2..6.

§Examples

Splitting off the first three elements of a slice:

let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
let mut first_three = slice.split_off_mut(..3).unwrap();

assert_eq!(slice, &mut ['d']);
assert_eq!(first_three, &mut ['a', 'b', 'c']);

Splitting off a slice starting with the third element:

let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
let mut tail = slice.split_off_mut(2..).unwrap();

assert_eq!(slice, &mut ['a', 'b']);
assert_eq!(tail, &mut ['c', 'd']);

Getting None when range is out of bounds:

let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];

assert_eq!(None, slice.split_off_mut(5..));
assert_eq!(None, slice.split_off_mut(..5));
assert_eq!(None, slice.split_off_mut(..=4));
let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
assert_eq!(Some(expected), slice.split_off_mut(..4));

Removes the first element of the slice and returns a reference to it.

Returns None if the slice is empty.

§Examples

let mut slice: &[_] = &['a', 'b', 'c'];
let first = slice.split_off_first().unwrap();

assert_eq!(slice, &['b', 'c']);
assert_eq!(first, &'a');

Removes the first element of the slice and returns a mutable reference to it.

Returns None if the slice is empty.

§Examples

let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
let first = slice.split_off_first_mut().unwrap();
*first = 'd';

assert_eq!(slice, &['b', 'c']);
assert_eq!(first, &'d');

Removes the last element of the slice and returns a reference to it.

Returns None if the slice is empty.

§Examples

let mut slice: &[_] = &['a', 'b', 'c'];
let last = slice.split_off_last().unwrap();

assert_eq!(slice, &['a', 'b']);
assert_eq!(last, &'c');

Removes the last element of the slice and returns a mutable reference to it.

Returns None if the slice is empty.

§Examples

let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
let last = slice.split_off_last_mut().unwrap();
*last = 'd';

assert_eq!(slice, &['a', 'b']);
assert_eq!(last, &'d');

Returns mutable references to many indices at once, without doing any checks.

An index can be either a usize, a Range or a RangeInclusive. Note that this method takes an array, so all indices must be of the same type. If passed an array of usizes this method gives back an array of mutable references to single elements, while if passed an array of ranges it gives back an array of mutable references to slices.

For a safe alternative see get_disjoint_mut.

§Safety

Calling this method with overlapping or out-of-bounds indices is undefined behavior even if the resulting references are not used.

§Examples

let x = &mut [1, 2, 4];

unsafe {
    let [a, b] = x.get_disjoint_unchecked_mut([0, 2]);
    *a *= 10;
    *b *= 100;
}
assert_eq!(x, &[10, 2, 400]);

unsafe {
    let [a, b] = x.get_disjoint_unchecked_mut([0..1, 1..3]);
    a[0] = 8;
    b[0] = 88;
    b[1] = 888;
}
assert_eq!(x, &[8, 88, 888]);

unsafe {
    let [a, b] = x.get_disjoint_unchecked_mut([1..=2, 0..=0]);
    a[0] = 11;
    a[1] = 111;
    b[0] = 1;
}
assert_eq!(x, &[1, 11, 111]);

Returns mutable references to many indices at once.

An index can be either a usize, a Range or a RangeInclusive. Note that this method takes an array, so all indices must be of the same type. If passed an array of usizes this method gives back an array of mutable references to single elements, while if passed an array of ranges it gives back an array of mutable references to slices.

Returns an error if any index is out-of-bounds, or if there are overlapping indices. An empty range is not considered to overlap if it is located at the beginning or at the end of another range, but is considered to overlap if it is located in the middle.

This method does a O(n^2) check to check that there are no overlapping indices, so be careful when passing many indices.

§Examples

let v = &mut [1, 2, 3];
if let Ok([a, b]) = v.get_disjoint_mut([0, 2]) {
    *a = 413;
    *b = 612;
}
assert_eq!(v, &[413, 2, 612]);

if let Ok([a, b]) = v.get_disjoint_mut([0..1, 1..3]) {
    a[0] = 8;
    b[0] = 88;
    b[1] = 888;
}
assert_eq!(v, &[8, 88, 888]);

if let Ok([a, b]) = v.get_disjoint_mut([1..=2, 0..=0]) {
    a[0] = 11;
    a[1] = 111;
    b[0] = 1;
}
assert_eq!(v, &[1, 11, 111]);

Returns the index that an element reference points to.

Returns None if element does not point to the start of an element within the slice.

This method is useful for extending slice iterators like slice::split.

Note that this uses pointer arithmetic and does not compare elements. To find the index of an element via comparison, use .iter().position() instead.

§Panics

Panics if T is zero-sized.

§Examples

Basic usage:

#![feature(substr_range)]

let nums: &[u32] = &[1, 7, 1, 1];
let num = &nums[2];

assert_eq!(num, &1);
assert_eq!(nums.element_offset(num), Some(2));

Returning None with an unaligned element:

#![feature(substr_range)]

let arr: &[[u32; 2]] = &[[0, 1], [2, 3]];
let flat_arr: &[u32] = arr.as_flattened();

let ok_elm: &[u32; 2] = flat_arr[0..2].try_into().unwrap();
let weird_elm: &[u32; 2] = flat_arr[1..3].try_into().unwrap();

assert_eq!(ok_elm, &[0, 1]);
assert_eq!(weird_elm, &[1, 2]);

assert_eq!(arr.element_offset(ok_elm), Some(0)); // Points to element 0
assert_eq!(arr.element_offset(weird_elm), None); // Points between element 0 and 1

Returns the range of indices that a subslice points to.

Returns None if subslice does not point within the slice or if it is not aligned with the elements in the slice.

This method does not compare elements. Instead, this method finds the location in the slice that subslice was obtained from. To find the index of a subslice via comparison, instead use .windows().position().

This method is useful for extending slice iterators like slice::split.

Note that this may return a false positive (either Some(0..0) or Some(self.len()..self.len())) if subslice has a length of zero and points to the beginning or end of another, separate, slice.

§Panics

Panics if T is zero-sized.

§Examples

Basic usage:

#![feature(substr_range)]

let nums = &[0, 5, 10, 0, 0, 5];

let mut iter = nums
    .split(|t| *t == 0)
    .map(|n| nums.subslice_range(n).unwrap());

assert_eq!(iter.next(), Some(0..0));
assert_eq!(iter.next(), Some(1..3));
assert_eq!(iter.next(), Some(4..4));
assert_eq!(iter.next(), Some(5..6));