I rarely need to use maps, but everytime I had to, std::unordered_map was measurably slower than std::map. In particular in debug mode, it was really slow, and if you choose an unfortunate hashing function (I think older MSVC versions had a really bad one), it can easily become a bottleneck. In particular with small data or data that has trivial comparison functions, std::map might often be better and should be the go-to choice.
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