Slices

caution

This feature is experimental. You should expect it to change in future versions, cause unexpected behavior, or simply not work at all.

A slice is a dynamically-sized view into a sequence of elements. They can be resized at runtime, but because they don't own the data, they cannot be returned from a circuit. You can treat slices as arrays without a constrained size.

use dep::std::slice;

fn main() -> pub Field {
    let mut slice: [Field] = &[0; 2];

    let mut new_slice = slice.push_back(6);
    new_slice.len()
}

To write a slice literal, use a preceeding ampersand as in: &[0; 2] or &[1, 2, 3].

It is important to note that slices are not references to arrays. In Noir, &[..] is more similar to an immutable, growable vector.

View the corresponding test file here.

Methods

For convenience, the STD provides some ready-to-use, common methods for slices:

push_back

Pushes a new element to the end of the slice, returning a new slice with a length one greater than the original unmodified slice.

fn push_back<T>(_self: [T], _elem: T) -> [T]

example:

fn main() -> pub Field {
    let mut slice: [Field] = &[0; 2];

    let mut new_slice = slice.push_back(6);
    new_slice.len()
}

View the corresponding test file here.

push_front

Returns a new array with the specified element inserted at index 0. The existing elements indexes are incremented by 1.

fn push_front(_self: Self, _elem: T) -> Self

Example:

let mut new_slice: [Field] = &[];
new_slice = new_slice.push_front(20);
assert(new_slice[0] == 20); // returns true

View the corresponding test file here.

pop_front

Returns a tuple of two items, the first element of the array and the rest of the array.

fn pop_front(_self: Self) -> (T, Self)

Example:

let (first_elem, rest_of_slice) = slice.pop_front();

View the corresponding test file here.

pop_back

Returns a tuple of two items, the beginning of the array with the last element omitted and the last element.

fn pop_back(_self: Self) -> (Self, T)

Example:

let (popped_slice, last_elem) = slice.pop_back();

View the corresponding test file here.

append

Loops over a slice and adds it to the end of another.

fn append(mut self, other: Self) -> Self

Example:

let append = &[1, 2].append(&[3, 4, 5]);

insert

Inserts an element at a specified index and shifts all following elements by 1.

fn insert(_self: Self, _index: Field, _elem: T) -> Self

Example:

new_slice = rest_of_slice.insert(2, 100);
assert(new_slice[2] == 100);

View the corresponding test file here.

remove

Remove an element at a specified index, shifting all elements after it to the left, returning the altered slice and the removed element.

fn remove(_self: Self, _index: Field) -> (Self, T)

Example:

let (remove_slice, removed_elem) = slice.remove(3);

len

Returns the length of a slice

fn len(self) -> Field

Example:

fn main() {
    let slice = &[42, 42];
    assert(slice.len() == 2);
}