You need this in Java because interfaces are explicitly implemented. You don't need this in Go because interfaces are structurally implemented. The way you spell "anything that has a method named Size which returns int" is interface{Size() int}.

Go Generics work differently than those in Java. They are specialized, meaning that they are not generic at runtime anymore. Instead, the compiler creates a different implementation for each type.

At runtime, there are only List[int], List[string], etc. List[T] is not a thing anymore.