Re: How to hide type internals

[claude.simon@equipement.gouv.fr]

Gerd a écrit :

> Hi,
>
> I would like to write a package that exports functions using a special
> type, without showing the details in the spec (even not in the private
> part).
> In Modula-2 one can declare opaque types (which mostly are pointers but
> also can be any type of word size).

> Like this:
>
> package keys is
>   type key;
>   function GetKey return key;
>   procedure FetchElement (k : key);
> -- implementation of key not visible here
> end keys;
>
> package body keys
>  ...
>   type Data is record
>                      ...
>                     end record;
>   type key is access Data;
> ...
> end keys;


package Keys is
   type Key is private;
   function Getkey return Key;
-- ...
private
   type Imp_Key; -- deferred type to the body
   type Key is access Imp_Key;
end Keys;

package body Keys is
   type Imp_Key is new Integer; -- whatever type
   function Getkey return Key
   is
      The_Key : Key := new Imp_Key;
   begin
      return The_Key;
   end GetKey;
end Keys;