Trait Variance
type_variance
pub trait Variance: Default + Sealed { }
A sealed trait implemented by Covariant<T>, Contravariant<T>, and Invariant<T>.
Covariant<T>
Contravariant<T>
Invariant<T>
impl<T: ?Sized> Variance for Contravariant<T>
impl<T: ?Sized> Variance for Covariant<T>
impl<T: ?Sized> Variance for Invariant<T>