link:https://en.wikipedia.org/wiki/Hash_table[Hash tables^] are extremely popular computer data structures and can be found under one form or another in virtually any programming language. Whereas other associative structures such as rb-trees (used in {cpp} by `std::set` and `std::map`) have logarithmic-time complexity for insertion and lookup, hash tables, if configured properly, perform these operations in constant time on average, and are generally much faster.