Re: Calling inherited primitive operations in Ada

[Emmanuel Briot <briot.emmanuel@gmail.com>]

I think I have a more interesting example. This one is extracted from my attempted traits containers, for which I had published a blog post at AdaCore. My enhanced fork of the library is at 
 https://github.com/briot/ada-traits-containers
if someone wants to experiment with non-trivial generics code (and containers are of course a case where generics fully make sense).

Here is the example:

generic
   type Element_Type is private;
   type Stored_Type is private;
package Elements is
end Elements;

with Elements;
generic
   type Element_Type is private;
package Definite_Elements is
   package Traits is new Elements (Element_Type, Stored_Type => Element_Type);
end Definite_Elements;

with Definite_Elements;
generic
   type Key_Type is private;
package Maps is
   package Keys is new Definite_Elements (Key_Type);
   function "=" (L, R : Keys.Traits.Stored_Type) return Boolean   --   "Stored_Type" is not a visible entity of "Traits"
      is (False);
end Maps;


This is not case where the actual is visible unless I happen to know how Definite_Element is implemented and that it will use Element_Type for Stored_Type (and this is not a knowledge I wish client packages to have, the whole point of Element and Definite_Element is to basically hide how elements can be stored in a container, and whether we need memory allocation for instance).