Implementing slice for custom type

Question

I have this struct:

struct Test {
    data: Vec<u8>,
}

impl Test {
    fn new() -> Self {
        return Test { data: Vec::new() };
    }
}

let a = Test::new();
// populate something into a...

I would like to implement slice for this type, when doing e.g. &a[2..5], it returns a slice pointing to 2..5 of its internal data. Is it possible to do this in Rust?

Answer 1

You can do that by implementing the Index trait, and bounding the index to SliceIndex:

struct Test {
    data: Vec<u8>,
}

impl Test {
    fn new(data: Vec<u8>) -> Self {
        Test { data }
    }
}

impl<Idx> std::ops::Index<Idx> for Test
where
    Idx: std::slice::SliceIndex<[u8]>,
{
    type Output = Idx::Output;

    fn index(&self, index: Idx) -> &Self::Output {
        &self.data[index]
    }
}

fn main() {
    let test = Test::new(vec![1, 2, 3]);

    let slice = &test[1..];
    assert_eq!(slice, [2, 3]);

    let first = &test[0];
    assert_eq!(first, &1);
}