package main

type Interface interface {
}

type A struct {
}

type B struct {
}

func id(i Interface) Interface {
        return i
}

func withA(a A) {
}
func withB(b B) {
}

func main() {
        a, ok := id(A{}).(A)
        if ok {
                withA(a)
        }
        b, ok := id(B{}).(B)
        if ok {
                withB(b)
        }
        c, ok := id(B{}).(A)
        if ok {
                withA(c)
        }
}