[pierrebai]

OTOH, 99% of use cases don't care about performance and just want a portable implementation.

While it could be useful to have a "fast" variation that offers no guarantee at all, what you would end up with (because people are vain) is that too may people would use those instead "because perf", even though the actual usage is not performance critical, and have code that breaks whenever the compiler or platform changes.

[usefulcat]

> OTOH, 99% of use cases don't care about performance

For many other languages, I'd agree with '99%', but in the case of c++, performance is one of the main reasons it's still used, so I doubt the number is nearly that high.

With hindsight, I'd say that std::unordered_map is fine for what it is, but there are a lot of cases where it's really not suitable due to having a dynamic allocation for each element and the resulting lack of cache locality, and because of that many people have to go looking elsewhere for a usable hash map. There are good reasons why we have both std::vector and std::list.