You can already define functions that work on every type that implements Foo, no? I've never coded in go, but I thought that was the whole point of interfaces.

You can already define functions that work on every type that implements Foo, no? I've never coded in go, but I thought that was the whole point of interfaces. And I don't see how adding generics would solve the problem of being able to add a FooImpl2 to a slice of FooImpls. Java has generics and they don't allow covariant generic collections for this same reason.