Trait Objects and dyn

Generics with trait bounds work great when each call uses one concrete type. But what if you want a collection of different types that all share a trait? Generics cannot hold a mix.

Trait objects solve this.

A trait object is a value referred to through a pointer plus the keyword dyn, like &dyn Trait or Box<dyn Trait>.

It lets you treat many concrete types uniformly at runtime.