Compile time asserts

[ollpu]

When const_panic first stabilized, it didn't seem to be applicable for checking properties of generics, since const items inside functions can't be tied to the generics. However, an associated const on a struct seems to do the trick:

use std::mem::{align_of, size_of};

struct AssertSameLayout<A, B>(std::marker::PhantomData<(A, B)>);
impl<A, B> AssertSameLayout<A, B> {
    const OK: () = assert!(
        size_of::<A>() == size_of::<B>() && align_of::<A>() == align_of::<B>(),
        "types must have identical size and alignment"
    );
}

// used as
() = AssertSameLayout::<A, B>::OK;

Playground

Idea stolen from here.

[golddranks]

Oh, interesting!! Thanks for the pointer.

[golddranks]

Thank you! I implemented static asserts. This also means that might be possible to get forward with getting this to stdlib.