Slices

A slice gives you a view into a larger collection:

fn main() {
    let a: [i32; 6] = [10, 20, 30, 40, 50, 60];
    println!("a: {a:?}");

    let s: &[i32] = &a[2..4];

    println!("s: {s:?}");
}

This slide should take about 7 minutes.

We create a slice by borrowing a and specifying the starting and ending indexes in brackets.
If the slice starts at index 0, Rust’s range syntax allows us to drop the starting index, meaning that &a[0..a.len()] and &a[..a.len()] are identical.
The same is true for the last index, so &a[2..a.len()] and &a[2..] are identical.
To easily create a slice of the full array, we can therefore use &a[..].
s is a reference to a slice of i32s. Notice that the type of s (&[i32]) no longer mentions the array length. This allows us to perform computation on slices of different sizes.
Slices always borrow from another object. In this example, a has to remain ‘alive’ (in scope) for at least as long as our slice.
You can’t “grow” a slice once it’s created:
- You can’t append elements of the slice, since it doesn’t own the backing buffer.
- You can’t grow a slice to point to a larger section of the backing buffer. The slice loses information about the underlying buffer and so you can’t know how larger the slice can be grown.
- To get a larger slice you have to back to the original buffer and create a larger slice from there.

Comprehensive Rust 🦀