Of course it's valid.
You see, when you say Class(), you're creating a temporary object, on which you're welcome to call a method. If a function requires a Class variable as a parameter, you can create one with Class(...) on the spot. It's the same idea.
Try it. :P
[edit] I guess you could think of it this way: a constructor returns an instance of the class type being constructed , , , , I'm not sure if that's a technically valid description, but hey. [/edit]