Shared via Rust Playground

playground.rs

struct A{_x:f32}
struct B{_y:u32}

// #[derive(EnumKey(FooKey))]
enum Foo {
    A(A), 
    B(B)
}

fn main() {
    let _a = Foo::A(A {_x:1.0});
    let _b = Foo::B(B {_y:1});
    assert!(_a.key() == FooKey::A);
    assert!(_b.key() == FooKey::B);
}


// The following impl could be autoderived
pub trait Key {
    type Key;
    fn key(&self) -> Self::Key;
}

#[derive(Clone,Copy,Debug,PartialEq,Eq)]
enum FooKey {A,B}

impl Key for Foo {
    type Key=FooKey;
    fn key(&self) -> Self::Key {
        match self {
            &Foo::A(..) => FooKey::A,
            &Foo::B(..) => FooKey::B,
        }
    }
}