Comment by saywatnow

Thanks, that's clear enough :-). In hindsight I can't imagine what alternative I was thinking of .. I had some idea you might have put the additional cost in the iterator by maintaining only an epoch counter in the vector, but that's obviously not enough to do the right thing in the presence of insert and erase.

Your library looks like a good toolset. While I still find the code pretty impenetrable, the number of tests I can see give me confidence. Bookmarked for reference when I'm using C++ again.