frozen is a header-only library that provides zero cost initialization for immutable containers, fixed-size containers, and various algorithms. It provides features such as:

• immutable (also known as frozen), constexpr-compatible versions of std::set, std::unordered_set, std::map and std::unordered_map

• fixed-capacity, constinit-compatible versions of std::map and std::unordered_map with immutable, compile-time selected keys mapped to mutable values.

• zero cost initialization version of std::search for frozen needles using Boyer-Moore or Knuth-Morris-Pratt algorithms.

The unordered_* containers are guaranteed perfect (no hash collision) and the extra storage is linear with respect to the number of keys.