Or, just don't modify the topic. I can't think of an instance where you can't do something other than modify the topic. Sounds like your initial design could do with some refactoring. Good luck!

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We are the carpenters and bricklayers of the Information Age.

The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6

Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.