public HashFunc<void*> direct_hash
Converts a gpointer to a hash value.
It can be passed to
g_hash_table_new as the
hash_func parameter, when using opaque pointers compared by pointer
value as keys in a GenericSet.
This hash function is also appropriate for keys that are integers stored in pointers, such as `GINT_TO_POINTER (n)`.
a pointer key
a hash value corresponding to the key.