Rust const : () =

名前空間を限定することによる衝突回避、型チェック

const _: () =

feat: put parts of the generated code in a private namespace (const _… · audunhalland/unimock@6d95bd4 https://github.com/audunhalland/unimock/commit/6d95bd467a0aeb0b1356d47d1988d1daa9f23752

The ability to ensure that code type checks while discarding the result is useful, especially in custom derives. For example, the following code will not compile if the type MyType doesn’t implement the trait MyTrait:

2526-const-wildcard - The Rust RFC Book https://rust-lang.github.io/rfcs/2526-const-wildcard.html