[−][src]Type Definition phantasm::Contravariant

type Contravariant<T: ?Sized> = Contravariant<T>;

Marker zst type that is contravariant over T.

"Contravariant" means that given F<_>, Super and Sub (where Sub is a subtype of Super), F<Super> is a subtype of F<Sub> (but F<Sub> is not a subtype of F<Super>)

Examples

// This struct is covariant over `T`
struct Test<T>(phantasm::Contravariant<T> /* ... */);

let _: Test<i32> = Test(phantasm::Contravariant);
let _ = Test(phantasm::Contravariant::<i32>);
ⓘThis example deliberately fails to compile
use phantasm::Contravariant;
// `F<Sub>` is **not** a subtype of `F<Super>`
fn fail<'l>(arg: Contravariant<&'static ()>) -> Contravariant<&'l ()> {
    arg
}
use phantasm::Contravariant;
// `F<Super>` **is** a subtype of `F<Sub>`
fn pass<'l>(arg: Contravariant<&'l ()>) -> Contravariant<&'static ()> {
    arg
}

See also