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Message: [QUOTE="gwowen, post: 4169613"] It's only an *iterator* comparison, which isn't necessarily the same thing. Your library caches indices by design, so this iterator comparison is always cheap -- so every iterator is a potential random- access-iterator. But, you have to pay the price of invalidating all iterators even for structures where it is not absolutely necessary (deletion from a linked list or a map, say). It's a trade-off. Personally, I'd've liked defined behaviour for those containers where the check can be shown to be cheap (e.g. anything for which std::distance is O(1)), and undefined for everything else, but I can see why such asymmetry was not thought good by the standard writers. [/QUOTE]