Example of new interfaces in Go 1.18

prog.go

//Forbid me for the ugly formatting, this is a neccessary loss for saving some visual space in the article.
type Pet interface {
	Dog | Cat
	Say() string
}

type Dog struct{}
func (d Dog) Say() string { return "I'm an incredibly intelligent dog" }

type Cat struct{}
func (c Cat) Say() string { return "Meow :/" }

type Fox struct{}
func (f Fox) Say() string { return "2013 was dope" }

func playWith[P Pet](pet P) { fmt.Printf("My pet is happy and says: %s\n", pet.Say()) }

func main() {
	playWith(Dog{})
	playWith(Cat{})
	playWith(Fox{}) //./prog.go:21:10: Fox does not implement Pet 
}