This repository provides constexpr incremental hash-map and set for C++20 and onwards (incremental meaning you can add/mutate values, but not remove them) :
swl::incremental_hashmap<Key, Value, Hash>
swl::incremental_hashset<Key, Hash>
Iterators and references are never invalidated.
Those containers were designed for small, "metaprogramming sized" inputs in mind, in the future I'd like to add the non-incremental equivalents, however so far I have not found any use for those in my own code.
std::hash is not used here as it is not constexpr. To provide the hash trait for your own data types, simply specialize swl::hash like you would specialize std::hash.