Slices

Slices can be thought of as a pair of [*]T (the pointer to the data) and a usize (the element count). Their syntax is []T, with T being the child type. Slices are used heavily throughout Zig for when you need to operate on arbitrary amounts of data. Slices have the same attributes as pointers, meaning that there also exists const slices. For loops also operate over slices. String literals in Zig coerce to []const u8.

Here, the syntax x[n..m] is used to create a slice from an array. This is called slicing, and creates a slice of the elements starting at x[n] and ending at x[m - 1]. This example uses a const slice, as the values to which the slice points need not be modified.

const expect = @import("std").testing.expect;

fn total(values: []const u8) usize {
    var sum: usize = 0;
    for (values) |v| sum += v;
    return sum;
}

test "slices" {
    const array = [_]u8{ 1, 2, 3, 4, 5 };
    const slice = array[0..3];
    try expect(total(slice) == 6);
}

When these n and m values are both known at compile time, slicing will actually produce a pointer to an array. This is not an issue as a pointer to an array i.e. *[N]T will coerce to a []T.

const expect = @import("std").testing.expect;

test "slices 2" {
    const array = [_]u8{ 1, 2, 3, 4, 5 };
    const slice = array[0..3];
    try expect(@TypeOf(slice) == *const [3]u8);
}

The syntax x[n..] can also be used when you want to slice to the end.

test "slices 3" {
    var array = [_]u8{ 1, 2, 3, 4, 5 };
    var slice = array[0..];
    _ = slice;
}

Types that may be sliced are arrays, many pointers and slices.

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