I tried this code:
#![feature(min_const_generics)]
struct X<const S: usize>;
impl<const S: usize> X<S> {
const LEN: usize = S + 1;
}
struct Y<const S: usize> {
stuff: [u8; { S + 1 }],
}This gave an error message:
error: generic parameters may not be used in const operations
--> src/lib.rs:10:17
|
10 | stuff: [u8; { S + 1 }],
| ^ cannot perform const operation using `S`
|
= help: const parameters may only be used as standalone arguments, i.e. `S`
= help: use `#![feature(const_generics)]` and `#![feature(const_evaluatable_checked)]` to allow generic const expressions
But you can see in X::LEN that you can perform const operations using S, the restriction this hits is more subtle in that you cannot perform const operations using generic parameters when these will impact the type system (as I understand it, I may be wrong). This also comes up if a generic parameter is used in defining an associated type.
I tried this code:
This gave an error message:
But you can see in
X::LENthat you can perform const operations usingS, the restriction this hits is more subtle in that you cannot perform const operations using generic parameters when these will impact the type system (as I understand it, I may be wrong). This also comes up if a generic parameter is used in defining an associated type.