Skipping a C++ template parameter

If the has map type has some public typedef for the HashCompare template parameter, you could write a meta function that uses a vanilla hash map type to get the std comparator. Something like this:

template< typename Key, typename T, typename Allocator>
struct hash_map_type {
  typedef typename hash_map<Key,T>::key_compare key_compare;
  typedef mash_map<Key,T,key_compare,Allocator> result_t;
};

typedef hash_map_type<int,string,my_allocator>::result_type my_hash_map;

This, however, depends on something like the above hash_map<Key,T>::key_compare being accessible.