example.ads

with Ada.Containers.Hashed_Maps;
with Interfaces.C;

package Example is
   type UInt is new Interfaces.C.unsigned;
   type Whatever is new Integer;

   function Hash (Key : UInt) return Ada.Containers.Hash_Type;

   package My_Maps is new Ada.Containers.Hashed_Maps (
     Key_Type     => UInt,
     Element_Type => Whatever,
     Hash         => Hash,
     -- doesn't work
     Equivalent_Keys => "=");
end Example;