4.16 Hash Maps

For your convenience, GiNaC offers the container template exhashmap<T> that can be used as a drop-in replacement for the STL std::map<ex, T, ex_is_less>, using hash tables to provide faster, typically constant-time, element look-up than map<>.

exhashmap<> supports all map<> members and operations, with the following differences:

• no lower_bound() and upper_bound() methods
• no reverse iterators, no rbegin()/rend()
• no operator<(exhashmap, exhashmap)
• the comparison function object key_compare is hardcoded to ex_is_less
• the constructor exhashmap(size_t n) allows specifying the minimum initial hash table size (the actual table size after construction may be larger than the specified value)
• the method size_t bucket_count() returns the current size of the hash table
• insert() and erase() operations invalidate all iterators