package main

type Duck interface{}

type WildDuck struct{}

func NewWildDuck(duckType string) *WildDuck {
	if duckType != "wild" {
		return nil
	}
	return &WildDuck{}
}

func NewDuck(duckType string) Duck {
	var duck Duck
	duck = NewWildDuck(duckType)
	if duck == nil {
		panic("Bad duck type!")
	}
	return duck
}

func main() {
	NewDuck("wild")
	NewDuck("domestic")
}