v/vlib/compiler/tests/interface_test.v

struct Dog {
	breed string
}

fn (d Dog) speak() {
	println('dog.speak()')
}

fn (d Dog) name() string {
	return 'old gray'
}

interface Speaker {
	name() string
	speak()
}

interface Speak2er {
	speak()
	name() string
}

fn perform_speak(s Speaker) bool {
	s.speak()
	return true
}

fn test_perform_speak() {
	d := Dog{}
	assert perform_speak(d)
}