public model Rectangle
    width
    height
end

implement Rectangle
    function area(this)
        this.width * this.height
    end
end

function regular()
    local rect = Rectangle(10, 20)

    rect.width == 10 and rect.height == 20 and rect.area() == 200
end

model MyRectangle
    width
    height
end

apply Rectangle to MyRectangle

implement MyRectangle
    function new()
        MyRectangle(20, 30)
    end
end

function with_apply()
    local rect = MyRectangle.new()

    rect.width == 20 and rect.height == 30 and rect.area() == 600
end