oop = require("oop/oop")

function Animal(cls)
    function cls.speak(this)
        print("animal")
    end
end

function Dog(cls)
    cls.inherit(Animal)

    function cls.speak(this)
        cls.super.speak(this)
        print("woof")
    end
end

local d = new(Dog)
d.speak() -- animal, then woof