You could mark the constructor as obsolete with a message pointing people to the factory. Then use a pragma to suppress the warning in your factory when you call the constructor. It might look a bit ugly, but it will clearly point developers to the correct usage. Sometimes practical and explicit is more important than pretty. :) For the discussion about using your pattern in the first place - Typically I would lean more towards an interface in Java and an abstract base class in .NET. This is what the respective developers would expect, and there are actually very good reasons for this difference as there are fundamental differences between the languages in this area.

BobJanova wrote: I think that you are only going to be sacrificing a bit of performance, not creating subtle bugs, because the .Net hashtable will look through all the items if it doesn't get a hash hit. No, it won't. Mutating an object that is used as a dictionary key will cause bugs. The correct solution is to remove the object from the dictionary, then mutate the key, then re-add it. Or better, just make the key immutable, remove the object from the dictionary, and re-add it using another key.

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