[bluGill]

I have yet to see a good way to do backward compatibility in anything. The only thing I've found that really works is sometimes you can add an argument with a default value. Removing an argument only works if everyone is using the same value of it anyway - otherwise they are expecting the behavior that other value causes and so you can't remove it.

Thus all arguments should be required in my opinion. If you make a change add a whole new function with the new arguments. If allowed the new function can have the same time (if overloading should be done this way is somewhat controversial - I'm coming out in favor but the arguments against do make good points which may be compelling to you). That way the complexity is managed since there is only a limited subset of the combinatorial explosion possible.