Struct QuditPermutation 

pub struct QuditPermutation { /* private fields */ }

A permutation of qudits.

Qudit systems are often shuffled around in compiler pipelines. This object captures a specific shuffling operation which can be represented in many ways.

Implementations

impl QuditPermutation

pub fn new<R: Into<Radices>>(radices: R, perm: &[usize]) -> QuditPermutation

Returns a permutation mapping qudit i to perm[i].

Arguments

• radices - The radices of the system being permuted

• perm - A vector describing the permutation. The resulting operation will shift the i-th qudit to the perm[i]-th qudit.

Panics

• If the supplied permutation is not a proper permutation. This can happen when there is a duplicate or invalid qudit index.

• If the permutation and radices describe systems with different qudit counts, i.e. they have different lengths.

Examples

use qudit_core::{Radices, QuditPermutation};

let three_qubits = Radices::new([2; 3]);
let qudit_shift = QuditPermutation::new(three_qubits, &vec![2, 0, 1]);

See Also

• Self::from_qubit_location - A convenience constructor for qubit permutations.
• Self::from_qudit_location - A convenience constructor for qudit permutations.

pub fn from_qubit_location(perm: &[usize]) -> QuditPermutation

Returns a qubit permutation specifed by perm.

Arguments

• perm - The qubit permutation.

Panics

• If the supplied permutation is not a proper permutation. This can happen when there is a duplicate or invalid qudit index.

Examples

use qudit_core::{Radices, QuditPermutation};

let qubit_shift = QuditPermutation::from_qubit_location(&vec![2, 0, 1]);

See Also

• Self::new - A general constructor for qudit permutations.
• Self::from_qudit_location - A convenience constructor for qudit permutations.

pub fn from_qudit_location<T: Into<Radix>>( radix: T, perm: &[usize], ) -> QuditPermutation

Returns a qudit permutation specifed by perm with a uniform radix.

Arguments

• perm - The qubit permutation.

• radix - The radix of the qudits being permuted.

Panics

• If the supplied permutation is not a proper permutation. This can happen when there is a duplicate or invalid qudit index.

• If the radix is not a valid radix.

Examples

use qudit_core::{Radices, QuditPermutation};

let qutrit_swap = QuditPermutation::from_qudit_location(3, &vec![1, 0]);

See Also

• Self::new - A general constructor for qudit permutations.
• Self::from_qubit_location - A convenience constructor for qubit permutations.

pub fn is_physically_implementable(&self) -> bool

Returns true if the permutation has physical meaning.

A permutation cannot be physically implemented if it permutes qudits of different radices.

Examples

use qudit_core::{Radices, QuditPermutation};

let three_qubits = Radices::new([2; 3]);
let qudit_shift = QuditPermutation::new(three_qubits, &vec![2, 0, 1]);
assert!(qudit_shift.is_physically_implementable());

let three_qutrits = Radices::new([3; 3]);
let qudit_shift = QuditPermutation::new(three_qutrits, &vec![2, 0, 1]);
assert!(qudit_shift.is_physically_implementable());

let three_qudits = Radices::new([2, 3, 4]);
let qudit_shift = QuditPermutation::new(three_qudits, &vec![2, 0, 1]);
assert!(!qudit_shift.is_physically_implementable());

pub fn locally_invert_location( radices: Radices, loc: &[usize], ) -> QuditPermutation

Returns a permutation that sorts the circuit location

Arguments

• loc - The index list to be sorted.

• radices - The radices of the system being permuted.

Panics

• If the supplied radices are invalid.

Examples

use qudit_core::{Radices, QuditPermutation};
let radices = Radices::new([2, 3]);
let loc = vec![37, 24];
let hybrid_swap = QuditPermutation::locally_invert_location(radices.clone(), &loc);
assert_eq!(hybrid_swap, QuditPermutation::new(radices, &vec![1, 0]));

pub fn index_perm(&self) -> &[usize]

Returns the permutation in the index space.

The qudit permutation describes how the qudits of a system are permuted. This ultimately results in the permutation of the index space of the system. For example, two qubits have four basis states: |00>, |01>, |10>, and |11>. If the qubits are permuted, the basis states are permuted as well. The index permutation describes this permutation of the basis states.

Examples

use qudit_core::{Radices, QuditPermutation};

let qubit_swap = QuditPermutation::from_qubit_location(&vec![1, 0]);
assert_eq!(qubit_swap.index_perm(), &vec![0, 2, 1, 3]);

pub fn permuted_radices(&self) -> Radices

Returns the radices of the system after being permuted.

Examples

use qudit_core::{Radices, QuditPermutation};
let qudit_swap = QuditPermutation::new(Radices::new([2, 3]), &vec![1, 0]);
assert_eq!(qudit_swap.permuted_radices(), Radices::new([3, 2]));

let qudit_swap = QuditPermutation::new(Radices::new([2, 3, 4]), &vec![1, 0, 2]);
assert_eq!(qudit_swap.permuted_radices(), Radices::new([3, 2, 4]));

pub fn is_identity(&self) -> bool

Returns true is this permutation does not permute any qudit.

Examples

use qudit_core::QuditPermutation;
let identity = QuditPermutation::from_qubit_location(&vec![0, 1]);
assert!(identity.is_identity());

use qudit_core::QuditPermutation;
let identity = QuditPermutation::from_qubit_location(&vec![1, 0]);
assert!(!identity.is_identity());

pub fn compose(&self, arg_perm: &QuditPermutation) -> QuditPermutation

Returns a new permutation that composes self with arg_perm.

Panics

If the permutations have incompatible radices.

Examples

use qudit_core::QuditPermutation;
let p1 = QuditPermutation::from_qubit_location(&vec![1, 0]);
let p2 = QuditPermutation::from_qubit_location(&vec![1, 0]);
assert!(p1.compose(&p2).is_identity());

let p1 = QuditPermutation::from_qubit_location(&vec![0, 2, 1, 3]);
let p2 = QuditPermutation::from_qubit_location(&vec![1, 0, 3, 2]);
assert_eq!(p1.compose(&p2), QuditPermutation::from_qubit_location(&vec![2, 0, 3, 1]));

pub fn invert(&self) -> QuditPermutation

Returns a new permutation that inverts self.

Examples

use qudit_core::QuditPermutation;
let p1 = QuditPermutation::from_qubit_location(&vec![1, 0]);
assert_eq!(p1.invert(), p1);

use qudit_core::QuditPermutation;
let p1 = QuditPermutation::from_qubit_location(&vec![2, 0, 3, 1]);
assert_eq!(p1.invert(), QuditPermutation::from_qubit_location(&vec![1, 3, 0, 2]));

pub fn cycles(&self) -> Vec<Vec<usize>>

Returns the permutation as a sequence of cycles.

Any permutation can be represented as a product of disjoint cycles. This function performs that decompositions.

Returns

A vector of cycles, where each cycle is a vector of qudit indices.

Examples

use qudit_core::{Radices, QuditPermutation};
let qubit_swap = QuditPermutation::from_qubit_location(&vec![1, 0]);
assert_eq!(qubit_swap.cycles(), vec![vec![0, 1]]);

let complex_perm = QuditPermutation::from_qudit_location(3, &vec![1, 2, 0]);
assert_eq!(complex_perm.cycles(), vec![vec![0, 1, 2]]);

let complex_perm = QuditPermutation::from_qubit_location(&vec![1, 0, 3, 2]);
assert_eq!(complex_perm.cycles(), vec![vec![0, 1], vec![2, 3]]);

Notes

The cycles are not unique. For example, the permutation (0, 1, 2) can be represented as either (0, 1, 2) or (2, 0, 1). This function returns the former. Each new cycle starts with the smallest index.

See Also

• Self::transpositions - Returns the permutation as a sequence of qudit swaps.
• Self::index_cycles - Returns the permutation as a sequence of index swaps.
• Self::index_transpositions - Returns the permutation as a sequence of index swaps.

pub fn index_cycles(&self) -> Vec<Vec<usize>>

Returns the index-space permutation as a sequence of cycles.

Returns

A vector of cycles, where each cycle is a vector of qudit indices.

Examples

use qudit_core::{Radices, QuditPermutation};
let qubit_swap = QuditPermutation::from_qubit_location(&vec![1, 0]);
assert_eq!(qubit_swap.index_cycles(), vec![vec![1, 2]]);

See Also

• Self::cycles - Returns the permutation as a sequence of cycles.
• Self::transpositions - Returns the permutation as a sequence of qudit swaps.
• Self::index_transpositions - Returns the permutation as a sequence of index swaps.

pub fn transpositions(&self) -> Vec<(usize, usize)>

Return the permutation as a sequence of qudit swaps

Any permutation can be represented as a product of transpositions (2-cycles or swaps). This function decomposes the permutation as a sequence of tranpositions.

Returns

A vector of transpositions, where each swap is a qudit index tuple.

Examples

use qudit_core::{Radices, QuditPermutation};
let qubit_swap = QuditPermutation::from_qubit_location(&vec![1, 0]);
assert_eq!(qubit_swap.transpositions(), vec![(0, 1)]);

let complex_perm = QuditPermutation::from_qudit_location(3, &vec![1, 2, 0]);
assert_eq!(complex_perm.transpositions(), vec![(0, 1), (1, 2)]);

See Also

• Self::cycles - Returns the permutation as a sequence of cycles.
• Self::index_cycles - Returns the permutation as a sequence of index swaps.
• Self::index_transpositions - Returns the index permutation as a swap sequence.

pub fn index_transpositions(&self) -> Vec<(usize, usize)>

Return the index-space permutation as a sequence of swaps

Returns

A vector of swaps, where each swap is a tuple of qudit indices.

Examples

use qudit_core::{Radices, QuditPermutation};
let qubit_swap = QuditPermutation::from_qubit_location(&vec![1, 0]);
assert_eq!(qubit_swap.index_transpositions(), vec![(1, 2)]);

See Also

• Self::cycles - Returns the permutation as a sequence of cycles.
• Self::transpositions - Returns the permutation as a sequence of qudit swaps.
• Self::index_cycles - Returns the permutation as a sequence of index swaps.

pub fn swap_rows<E: ComplexField>( &self, a: impl AsMatRef<T = E, Rows = usize, Cols = usize>, ) -> Mat<E>

Swap the rows of a matrix according to the permutation.

This function allocates and returns a new matrix. The permutation of the rows is done in index space.

Arguments

• a - The matrix to be permuted.

Returns

A new matrix with the rows permuted.

Examples

use qudit_core::{Radices, QuditPermutation};
use faer::{mat, Mat};
let qubit_swap = QuditPermutation::from_qubit_location(&vec![1, 0]);
let mat = mat![
    [1., 2., 3., 4.],
    [5., 6., 7., 8.],
    [9., 10., 11., 12.],
    [13., 14., 15., 16.]
];
let permuted_mat = qubit_swap.swap_rows(&mat);
assert_eq!(permuted_mat, mat![
    [1., 2., 3., 4.],
    [9., 10., 11., 12.],
    [5., 6., 7., 8.],
    [13., 14., 15., 16.]
]);

See Also

• Self::swap_rows_to_buf - Swaps the rows of a matrix witout allocations.
• Self::swap_cols - Swaps the columns of a matrix.

pub fn swap_rows_in_place<E: ComplexField>( &self, a: impl AsMatMut<T = E, Rows = usize, Cols = usize>, )

Swap the rows of a matrix in place according to the permutation.

Arguments

• a - The matrix to be permuted.

Panics

• If the matrix dimensions do not match the dimension of the permutation.

Examples

use qudit_core::{Radices, QuditPermutation};
use faer::{mat, Mat};
let qubit_swap = QuditPermutation::from_qubit_location(&vec![1, 0]);
let mut mat = mat![
    [1., 2., 3., 4.],
    [5., 6., 7., 8.],
    [9., 10., 11., 12.],
    [13., 14., 15., 16.]
];
qubit_swap.swap_rows_in_place(&mut mat);
assert_eq!(mat, mat![
    [1., 2., 3., 4.],
    [9., 10., 11., 12.],
    [5., 6., 7., 8.],
    [13., 14., 15., 16.]
]);

See Also

• Self::swap_rows - Swaps the rows of a matrix and returns a new matrix.
• Self::swap_rows_to_buf - Swaps the rows of a matrix without allocations.
• Self::swap_cols_in_place - Swaps the columns of a matrix in place.
• Self::swap_cols_to_buf - Swaps the columns of a matrix without allocations.
• Self::apply - Applies the permutation to a matrix and returns a new matrix.

Notes

This is not entirely allocation free. The list of transpositions is calculated resulting in a small allocation. To be entirely allocation free, one should use the swap_rows_to_buf method instead.

pub fn swap_rows_to_buf<E: ComplexField>( &self, a: impl AsMatRef<T = E, Rows = usize, Cols = usize>, b: impl AsMatMut<T = E, Rows = usize, Cols = usize>, )

Swap the rows of a matrix from an input into an output buffer.

This is an allocation free version of swap_rows.

Arguments

• a - The matrix to be permuted.

• b - The buffer to write the permuted matrix into.

Panics

• If the matrix dimensions do not match the dimension of the permutation.

See Also

• Self::swap_rows - Swaps the rows of a matrix and returns a new matrix.
• Self::swap_rows_in_place - Swaps the rows of a matrix in place.
• Self::swap_cols_to_buf - Swaps the columns of a matrix without allocations.
• Self::apply_to_buf - Applies the permutation to a matrix and writes the result into a buffer.

pub fn swap_cols<E: ComplexField>( &self, a: impl AsMatRef<T = E, Rows = usize, Cols = usize>, ) -> Mat<E>

Swap the columns of a matrix according to the permutation.

This function allocates and returns a new matrix. The permutation of the columns is done in index space.

Arguments

• a - The matrix to be permuted.

Returns

A new matrix with the columns permuted.

Examples

use qudit_core::{Radices, QuditPermutation};
use faer::{mat, Mat};
let qubit_swap = QuditPermutation::from_qubit_location(&vec![1, 0]);
let mat = mat![
    [1., 2., 3., 4.],
    [5., 6., 7., 8.],
    [9., 10., 11., 12.],
    [13., 14., 15., 16.]
];
let permuted_mat = qubit_swap.swap_cols(&mat);
assert_eq!(permuted_mat, mat![
    [1., 3., 2., 4.],
    [5., 7., 6., 8.],
    [9., 11., 10., 12.],
    [13., 15., 14., 16.]
]);

See Also

• Self::swap_cols_to_buf - Swaps the columns of a matrix without allocations.
• Self::swap_rows - Swaps the rows of a matrix.
• Self::apply - Applies the permutation to a matrix and returns a new matrix.

pub fn swap_cols_in_place<E: ComplexField>( &self, a: impl AsMatMut<T = E, Rows = usize, Cols = usize>, )

Swap the columns of a matrix in place according to the permutation.

Arguments

• a - The matrix to be permuted.

Panics

• If the matrix dimensions do not match the dimension of the permutation.

Examples

use qudit_core::{Radices, QuditPermutation};
use faer::{mat, Mat};
let qubit_swap = QuditPermutation::from_qubit_location(&vec![1, 0]);
let mut mat = mat![
    [1., 2., 3., 4.],
    [5., 6., 7., 8.],
    [9., 10., 11., 12.],
    [13., 14., 15., 16.]
];
qubit_swap.swap_cols_in_place(mat.as_mut());
assert_eq!(mat, mat![
   [1., 3., 2., 4.],
   [5., 7., 6., 8.],
   [9., 11., 10., 12.],
   [13., 15., 14., 16.]
]);

See Also

• Self::swap_rows - Swaps the rows of a matrix and returns a new matrix.
• Self::swap_rows_to_buf - Swaps the rows of a matrix without allocations.
• Self::swap_rows_in_place - Swaps the rows of a matrix in place.
• Self::swap_cols - Swaps the columns of a matrix with allocations.
• Self::swap_cols_to_buf - Swaps the columns of a matrix without allocations.
• Self::apply - Applies the permutation to a matrix and returns a new matrix.

Notes

This is not entirely allocation free. The list of transpositions is calculated resulting in a small allocation. To be entirely allocation free, one should use the swap_cols_to_buf method instead.

pub fn swap_cols_to_buf<E: ComplexField>( &self, a: impl AsMatRef<T = E, Rows = usize, Cols = usize>, b: impl AsMatMut<T = E, Rows = usize, Cols = usize>, )

Swap the columns of a matrix from an input into an output buffer.

This is an allocation free version of swap_cols.

Arguments

• a - The matrix to be permuted.

• b - The buffer to write the permuted matrix into.

Panics

• If the matrix dimensions do not match the dimension of the permutation.

See Also

• Self::swap_cols - Swaps the columns of a matrix and returns a new matrix.
• Self::swap_cols_in_place - Swaps the columns of a matrix in place.
• Self::swap_rows_to_buf - Swaps the rows of a matrix without allocations.
• Self::apply_to_buf - Applies the permutation to a matrix and writes the result into a buffer.
• Self::apply - Applies the permutation to a matrix and returns a new matrix.

pub fn apply<E: ComplexField>( &self, a: impl AsMatRef<T = E, Rows = usize, Cols = usize>, ) -> Mat<E>

Apply the permutation to a matrix and return a new matrix.

This is equivalent to calling swap_rows and then swap_cols.

Arguments

• a - The matrix to be permuted.

Returns

A new matrix with the rows and columns permuted.

Examples

use qudit_core::{Radices, QuditPermutation};
use faer::{mat, Mat};
let qubit_swap = QuditPermutation::from_qubit_location(&vec![1, 0]);
let mat = mat![
    [1., 2., 3., 4.],
    [5., 6., 7., 8.],
    [9., 10., 11., 12.],
    [13., 14., 15., 16.]
];
let permuted_mat = qubit_swap.apply(&mat);
assert_eq!(permuted_mat, mat![
   [1., 3., 2., 4.],
   [9., 11., 10., 12.],
   [5., 7., 6., 8.],
   [13., 15., 14., 16.]
]);

// Applying qudit permutations can help convert between little
// and big endian gates.
let big_endian_cnot = mat![
    [1., 0., 0., 0.],
    [0., 1., 0., 0.],
    [0., 0., 0., 1.],
    [0., 0., 1., 0.]
];
let little_endian_cnot = mat![
    [1., 0., 0., 0.],
    [0., 0., 0., 1.],
    [0., 0., 1., 0.],
    [0., 1., 0., 0.]
];
assert_eq!(qubit_swap.apply(&big_endian_cnot), little_endian_cnot);

See Also

• Self::swap_rows - Swaps the rows of a matrix and returns a new matrix.
• Self::swap_cols - Swaps the columns of a matrix and returns a new matrix.
• Self::apply_to_buf - Applies the permutation to a matrix and writes the result into a buffer.
• Self::apply_in_place - Swaps the rows of a matrix in place.

pub fn apply_in_place<E: ComplexField>( &self, a: impl AsMatMut<T = E, Rows = usize, Cols = usize>, )

Apply the permutation to a matrix in place.

Arguments

• a - The matrix to be permuted.

Returns

A new matrix with the rows and columns permuted.

See Also

• Self::swap_rows_in_place - Swaps the rows of a matrix in place.
• Self::swap_cols_in_place - Swaps the columns of a matrix in place.
• Self::apply_to_buf - Applies the permutation to a matrix and writes the result into a buffer.
• Self::apply - Applies the permutation to a matrix and returns a new matrix.

Notes

This is not entirely allocation free. The list of transpositions is calculated resulting in a small allocation. To be entirely allocation free, one should use the apply_to_buf method instead.

pub fn apply_to_buf<E: ComplexField>( &self, a: impl AsMatRef<T = E, Rows = usize, Cols = usize>, b: impl AsMatMut<T = E, Rows = usize, Cols = usize>, )

Apply the permutation to a matrix and write the result into a buffer.

This is an allocation free version of apply.

Arguments

• a - The matrix to be permuted.

• b - The buffer to write the permuted matrix into.

See Also

• Self::swap_rows_to_buf - Swaps the rows of a matrix without allocations.
• Self::swap_cols_to_buf - Swaps the columns of a matrix without allocations.
• Self::apply - Applies the permutation to a matrix and returns a new matrix.
• Self::apply_in_place - Swaps the rows of a matrix in place.

Methods from Deref<Target = [usize]>

pub fn len(&self) -> usize

Returns the number of elements in the slice.

Examples

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

pub fn is_empty(&self) -> bool

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());

pub fn first(&self) -> Option<&T>

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());

pub fn split_first(&self) -> Option<(&T, &[T])>

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]);
}

pub fn split_last(&self) -> Option<(&T, &[T])>

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]);
}

pub fn last(&self) -> Option<&T>

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());

pub fn first_chunk<const N: usize>(&self) -> Option<&[T; N]>

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>());

pub fn split_first_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])>

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>());

pub fn split_last_chunk<const N: usize>(&self) -> Option<(&[T], &[T; N])>

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>());

pub fn last_chunk<const N: usize>(&self) -> Option<&[T; N]>

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>());

pub fn get<I>(&self, index: I) -> Option<&<I as SliceIndex<[T]>>::Output>

where I: SliceIndex<[T]>,

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));

pub unsafe fn get_unchecked<I>( &self, index: I, ) -> &<I as SliceIndex<[T]>>::Output

where I: SliceIndex<[T]>,

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);
}

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

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));
    }
}

pub fn as_ptr_range(&self) -> Range<*const T>

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));

pub fn as_array<const N: usize>(&self) -> Option<&[T; N]>

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

Gets a reference to the underlying array.

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

pub fn iter(&self) -> Iter<'_, T>

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);

pub fn windows(&self, size: usize) -> Windows<'_, T>

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']);

pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T>

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());

pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T>

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']);

pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]]

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

pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T])

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']]);

pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]])

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']]);

pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N>

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

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());

pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T>

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());

pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T>

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']);

pub fn chunk_by<F>(&self, pred: F) -> ChunkBy<'_, T, F>

where F: FnMut(&T, &T) -> bool,

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);

pub fn split_at(&self, mid: usize) -> (&[T], &[T])

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, []);
}

pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T])

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, []);
}

pub fn split_at_checked(&self, mid: usize) -> Option<(&[T], &[T])>

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));

pub fn split<F>(&self, pred: F) -> Split<'_, T, F>

where F: FnMut(&T) -> bool,

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());

pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>

where F: FnMut(&T) -> bool,

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());

pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>

where F: FnMut(&T) -> bool,

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);

pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>

where F: FnMut(&T) -> bool,

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:?}");
}

pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>

where F: FnMut(&T) -> bool,

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:?}");
}

pub fn split_once<F>(&self, pred: F) -> Option<(&[T], &[T])>

where F: FnMut(&T) -> bool,

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

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);

pub fn rsplit_once<F>(&self, pred: F) -> Option<(&[T], &[T])>

where F: FnMut(&T) -> bool,

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

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);

pub fn contains(&self, x: &T) -> bool

where T: PartialEq,

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"));

pub fn starts_with(&self, needle: &[T]) -> bool

where T: PartialEq,

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(&[]));

pub fn ends_with(&self, needle: &[T]) -> bool

where T: PartialEq,

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(&[]));

pub fn strip_prefix<P>(&self, prefix: &P) -> Option<&[T]>

where P: SlicePattern<Item = T> + ?Sized, T: PartialEq,

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()));

pub fn strip_suffix<P>(&self, suffix: &P) -> Option<&[T]>

where P: SlicePattern<Item = T> + ?Sized, T: PartialEq,

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);

pub fn strip_circumfix<S, P>(&self, prefix: &P, suffix: &S) -> Option<&[T]>

where T: PartialEq, S: SlicePattern<Item = T> + ?Sized, P: SlicePattern<Item = T> + ?Sized,

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

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][..]));

pub fn trim_prefix<P>(&self, prefix: &P) -> &[T]

where P: SlicePattern<Item = T> + ?Sized, T: PartialEq,

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

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());

pub fn trim_suffix<P>(&self, suffix: &P) -> &[T]

where P: SlicePattern<Item = T> + ?Sized, T: PartialEq,

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

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][..]);

pub fn binary_search(&self, x: &T) -> Result<usize, usize>

where T: Ord,

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]);

pub fn binary_search_by<'a, F>(&'a self, f: F) -> Result<usize, usize>

where F: FnMut(&'a T) -> Ordering,

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, });

pub fn binary_search_by_key<'a, B, F>( &'a self, b: &B, f: F, ) -> Result<usize, usize>

where F: FnMut(&'a T) -> B, B: Ord,

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, });

pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T])

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);
}

pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])

where Simd<T, LANES>: AsRef<[T; LANES]>, T: SimdElement, LaneCount<LANES>: SupportedLaneCount,

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

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);

pub fn is_sorted(&self) -> bool

where T: PartialOrd,

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());

pub fn is_sorted_by<'a, F>(&'a self, compare: F) -> bool

where F: FnMut(&'a T, &'a T) -> bool,

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));

pub fn is_sorted_by_key<'a, F, K>(&'a self, f: F) -> bool

where F: FnMut(&'a T) -> K, K: PartialOrd,

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()));

pub fn partition_point<P>(&self, pred: P) -> usize

where P: FnMut(&T) -> bool,

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]);

pub fn element_offset(&self, element: &T) -> Option<usize>

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

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

pub fn subslice_range(&self, subslice: &[T]) -> Option<Range<usize>>

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

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));

pub fn to_vec(&self) -> Vec<T>

where T: Clone,

Copies self into a new Vec.

Examples

let s = [10, 40, 30];
let x = s.to_vec();
// Here, `s` and `x` can be modified independently.

pub fn to_vec_in<A>(&self, alloc: A) -> Vec<T, A>

where A: Allocator, T: Clone,

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

Copies self into a new Vec with an allocator.

Examples

#![feature(allocator_api)]

use std::alloc::System;

let s = [10, 40, 30];
let x = s.to_vec_in(System);
// Here, `s` and `x` can be modified independently.

pub fn repeat(&self, n: usize) -> Vec<T>

where T: Copy,

Creates a vector by copying a slice n times.

Panics

This function will panic if the capacity would overflow.

Examples

assert_eq!([1, 2].repeat(3), vec![1, 2, 1, 2, 1, 2]);

A panic upon overflow:

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

pub fn concat<Item>(&self) -> <[T] as Concat<Item>>::Output

where [T]: Concat<Item>, Item: ?Sized,

Flattens a slice of T into a single value Self::Output.

Examples

assert_eq!(["hello", "world"].concat(), "helloworld");
assert_eq!([[1, 2], [3, 4]].concat(), [1, 2, 3, 4]);

pub fn join<Separator>( &self, sep: Separator, ) -> <[T] as Join<Separator>>::Output

where [T]: Join<Separator>,

Flattens a slice of T into a single value Self::Output, placing a given separator between each.

Examples

assert_eq!(["hello", "world"].join(" "), "hello world");
assert_eq!([[1, 2], [3, 4]].join(&0), [1, 2, 0, 3, 4]);
assert_eq!([[1, 2], [3, 4]].join(&[0, 0][..]), [1, 2, 0, 0, 3, 4]);

pub fn connect<Separator>( &self, sep: Separator, ) -> <[T] as Join<Separator>>::Output

where [T]: Join<Separator>,

👎Deprecated since 1.3.0: renamed to join

Flattens a slice of T into a single value Self::Output, placing a given separator between each.

Examples

assert_eq!(["hello", "world"].connect(" "), "hello world");
assert_eq!([[1, 2], [3, 4]].connect(&0), [1, 2, 0, 3, 4]);

Trait Implementations

impl Clone for QuditPermutation

fn clone(&self) -> QuditPermutation

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for QuditPermutation

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

Formats the value using the given formatter.

impl Deref for QuditPermutation

QuditPermutation can be dereferenced as a usize slice.

type Target = [usize]

The resulting type after dereferencing.

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

Dereferences the value.

impl Display for QuditPermutation

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

Formats the value using the given formatter.

impl Hash for QuditPermutation

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 PartialEq for QuditPermutation

fn eq(&self, other: &QuditPermutation) -> 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 QuditSystem for QuditPermutation

QuditPermutations permute a qudit system.

fn radices(&self) -> Radices

Returns the radices of the system before being permuted.

fn num_qudits(&self) -> usize

Returns the number of qudits being permuted.

fn dimension(&self) -> usize

Returns the dimension of the system being permuted.

fn is_qubit_only(&self) -> bool

Checks if the system consists only of qubits (2-level systems).

fn is_qutrit_only(&self) -> bool

Checks if the system consists only of qutrits (3-level systems).

fn is_qudit_only<T: Into<Radix>>(&self, radix: T) -> bool

Checks if the system consists only of qudits with a specified radix.

fn is_homogenous(&self) -> bool

Checks if the system is homogenous, i.e., all qudits have the same radix.

impl Eq for QuditPermutation

impl StructuralPartialEq for QuditPermutation