Comment by Conscat

3 hours ago

Rust cannot take a const function and evaluate that into the argument of a const generic or a proc macro. As far as I can tell, the reasons are deeply fundamental to the architecture of rustc. It's difficult to express HOW FUNDAMENTAL this is to strongly typed zero overhead abstractions, and we see where Rust is lacking here in cases like `Option` and bitset implementations.

1 comment

Conscat

aw1621107 3 hours ago

> Rust cannot take a const function and evaluate that into the argument of a const generic

Assuming I'm interpreting what you're saying here correctly, this seems wrong? For example, this compiles [0]:

    const fn foo(n: usize) -> usize {
        n + 1
    }

    fn bar<const N: usize>() -> usize {
        N + 1
    }

    pub fn baz() -> usize {
        bar::<{foo(0)}>()
    }

In any case, I'm a little confused how this is relevant to what I said?

[0]: https://rust.godbolt.org/z/rrE1Wrx36