Re: [boost] [container] Draft development plan for Boost.Container

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Performance:

You already have #248 about a performance regression in flat_map. It can currently be twice as fast to use a struct { int key; mutable int value; } in a flat_set than a flat_map. I would prioritize fixing known performance issues before looking for others, but I guess it is a worthy goal.

Yes, I previously was using type-punning to be able to use memcpy in flat_map when key and mapped_type were trivial, but compiler warnings and some suspicious aliasing issues were reported, so I had to roll-back. I'll need to revisit this, I'm not sure if other flatmap implementations (chromium, folly...) perform some type of type punning to achieve the speedup.

I have seen Abseil using a union of `pair` and `pair` for flat_map nodes. However that had led to misoptimzation due to alias violations on some systems and GCC See my Issue there for a technical analysis from some time ago: https://github.com/abseil/abseil-cpp/issues/975http://lists.boost.org/mailman/listinfo.cgi/boost As usual: While type-punning with UB might work in most cases, there will be failures in some. And there the UB was non-obvious at all. Alex