https://doc.rust-lang.org/book/associated-constants.html

#![feature(associated_consts)]

trait Foo {
    const ID: usize;
}

impl Foo for i32 {
    const ID: usize = 1;
}
fn main() {
    let arr: [i32; i32::ID];
}

https://is.gd/L4Fg4k

array length constant evaluation error: non-constant path in constant expression

I had a quick look at the rfc but I couldn't find out if it should be legal to use associated-constants in constant expressions.