boost::typeindex::hash_value
// In header: <boost/type_index/type_index_facade.hpp> template<typename Derived, typename TypeInfo> std::size_t hash_value(const type_index_facade< Derived, TypeInfo > & lhs);
This free function is used by Boost's unordered containers.
<boost/container_hash/hash.hpp> has to be included if this function is used.