Your definition of polymorphism does not agree with the one at http://en.wikipedia.org/wiki/Polymorphism_(computer_science), so what makes you think that you are so right?

Polymorphism is the ability to use the same methods on different objects, not about extending the same object.

The use of a singleton has no effect on polymorphism.

The use of a singleton does not constitute a dependency.

Polymorphism is about extending a object and adding more functionality to it.

That is wrong. Polymorphism is not about extending an object, it is about extending a superclass into a subclass from which a new object can be created.

Check the names above the post it was Shrike who said it!

the Singleton object cannot be runtime polymorphic because you have referred directly to a classname rather than an object instance.

An object is not polymorphic, but an object’s methods can be. Polymorphism is about several objects sharing common method names. How those objects are instantiated, whether via a singleton or not, has absolutely nothing to do with polymorphism.

I repeat, polymorphism and singletons are unrelated, are independent of each other, so for you to say that an object which is instantiated via a singleton cannot be polymorphic is completely wrong.

This is what was said:

Polymorphism is about extending a object and adding more functionality to it.

The whole frikkin’ point of polymorphism is that you are dealing with the same *object*,

I am not dealing with the same object, I am dealing with multiple objects which just happen to inherit from the same superclass. That does *not* make them the same object.

Thats what I said!

me: No it isn’t. It’s about extending a base class to create subclasses, and hence different objects. This is “ad-hoc polymorphism”, as described in http://en.wikipedia.org/wiki/Polymorphism_(computer_science)

In OOP, ad-hoc polymorphism is generally supported through object inheritance, i.e., objects of different types may be treated uniformly as members of a common superclass.

blueyon: Using static methods seems to be the easy way out and is not OOP. You might as well just use a function.

me: It does not matter the singleton is implemented as a class or a function, it is still a singleton. Just because it is simple does not make it “not OOP”. You seem to be one of these geeks who thinks that “proper” OOP has to be as complicated as possible, whereas I follow the KISS principle.

What I do may not be to your taste, but it does not make it “not OOP”.

It makes no differnce to use a real object and pass it around to objects that need it. You have to get used to how to pass the registry object around.

Using static methods seems to be the easy way out and is not OOP. You might aswell just use a function.