Most common examples of misuse of singleton class

Question

When should you NOT use a singleton class although it might be very tempting to do so? It would be very nice if we had a list of most common instances of \'singletonitis\' t

Answer 1

One of the things that tend to make it a nightmare is if it contains modifiable global state. I worked on a project where there were Singletons used all over the place for things that should have been solved in a completely different way (pass in strategies etc.) The "de-singletonification" was in some cases a major rewrite of parts of the system. I would argue that in the bigger part of the cases when people use a Singleton, it's just wrong b/c it looks nice in the first place, but turns into a problem especially in testing.