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How about a warning "you may not be using the optimal tool for the job" until then?

I'm having a hard time getting excited about that.

:)

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Are the finite state machine libraries in Boost usable for this at all?

I don't know. At BoostCon, Christophe presented some interesting results pitting MSM against xpressive for some simple regexing. An interesting research project would be to investigate whether xpressive's hybrid static/dynamic NFA design can be applied to DFAs as well, with similar perf wins. This would be a non-trivial undertaking, like completely reimplementing xpressive.

I think MSM could be a possibility, and it seems to be quite fast for some cases. I was actually thinking of handling static Xpressive as a MSM-compatible front-end, so that the user could switch at will between Xpressive and MSM, which happen to be complementary because most performant on different types of regexes. But there is a long way (and a fair number of technical issues) between a toy example and a real library so it could take a while before I get to it (besides, I am not a domain expert). Note: there is an example provided with the BoostCon slides. I have more and I can pack them with MSM's examples. Christophe