generic_const_items

Allows generic parameters and where-clauses on free & associated const items.

The tracking issue for this feature is: #113521

Warning: This feature is an experiment and lacks an RFC. There are no guarantees that it will ever be stabilized.

See also: generic_const_exprs, min_generic_const_args.

Examples

Generic constant values

#![allow(unused)]
#![allow(incomplete_features)]
#![feature(generic_const_items)]

fn main() {
const GENERIC_VAL<const ARG: usize>: usize = ARG + 1;

#[test]
fn generic_const_arg() {
    assert_eq!(GENERIC_VAL::<1>, 2);
    assert_eq!(GENERIC_VAL::<2>, 3);
}
}

Conditional constants

#![allow(unused)]
#![allow(incomplete_features)]
#![feature(generic_const_items)]

fn main() {
// `GENERIC_VAL::<0>` will fail to compile
const GENERIC_VAL<const ARG: usize>: usize = if ARG > 0 { ARG + 1 } else { panic!("0 value") };

// Will fail to compile if the `Copy` derive is removed.
const COPY_MARKER<C: Copy>: () = ();

#[derive(Clone, Copy)]
struct Foo;

const FOO_IS_COPY: () = COPY_MARKER::<Foo>;
}