“Singleton” factories, ok or bad?

Question

I\'ve a lot of (abstract) factories and they\'re usually implemented as singletons.

Usually for the convenience of not having to pass them through layers who really hav

Answer 1

The bad form of singleton is the one that implements the equivalent of your Factory method with:

return new CalculationFactory ();

That's much harder to stub, mock or wrap.

The version that returns an object created elsewhere is much better, although like most anything, can be misused or overused.