Re: Slice patterns in Nightly Rust

[Nicholas Wilson via Digitalmars-d]

On Sunday, 21 June 2015 at 03:23:18 UTC, Dennis Ritchie wrote:

Recently published documentation Nightly Rust. I saw this:
https://doc.rust-lang.org/nightly/book/slice-patterns.html

What do you think about this: a terrible thing or a cool feature?

fn is_symmetric(list: &[u32]) -> bool {
    match list {
        [] | [_] => true,
        [x, inside.., y] if x == y => is_symmetric(inside),
        _ => false
    }
}

fn main() {
    let sym = &[0, 1, 4, 2, 4, 1, 0];
    assert!(is_symmetric(sym));

    let not_sym = &[0, 1, 7, 2, 4, 1, 0];
    assert!(!is_symmetric(not_sym));
}

http://is.gd/TvrXSn

I see this competition slices of D. Also seen are not very clear design.

We can do this in D:

bool is_symmetric(T)(T[] arr)
{
    if (arr.length == 0 || arr.length == 1)
        return true;

    if (arr[0] == arr[$])
        return is_symmetric(arr[1..$-1]);

    return false;
}

and generally match subranges using strides:

    arr[stride..index]
where both stride and index can be arbitrary expressions.
and in higher dimensions with Ilya's and Joakim libraries.

Also implicit declaration of variables. Urgh.