A fast & densely stored hashmap and hashset based on robin-hood backward shift deletion for C++17 and later.

The classes ankerl::unordered_dense::map and ankerl::unordered_dense::set are (almost) drop-in replacements of std::unordered_map and std::unordered_set. While they don't have as strong iterator / reference stability guarantees, they are typically much faster. Additionally, there are ankerl::unordered_dense::segmented_map and ankerl::unordered_dense::segmented_set with lower peak memory usage, and stable references (iterators are NOT stable) on insert.