Re: Subprogram Pointer in a Generic

[mheaney@on2.com (Matthew Heaney)]

claveman@grzorgenplatz.net (Charles H. Sampson) wrote in message news:<1ftiuys.1twhum2q9qa00N%claveman@grzorgenplatz.net>...
> I'm using a procedure that takes a procedure pointer as an
> argument.  It's pretty standard stuff:
> 
>           type Parameterless_Proc_Ptr is access procedure;
>           procedure Register (The_Proc : in Parameterless_Proc_Ptr);
> 
> 
>      There are two questions.  (1) What are they trying to prevent by
> this restriction?  (2) Is there a more robust way of working around it?

The purpose of subprogram pointers in Ada95 is to implement callbacks,
e.g. for implementing a GUI.  You don't have full downward closures in
Ada95.

If you want to call a subprogram supplied by a caller, then use a
generic formal subprogram instead:

generic
   ...
package GP is 
   generic
      with procedure Op is <>;
   procedure Generic_Call_Op (...);
   ...
end GP;


Another possibility is to import the subprogram as a generic formal
subprogram of the generic package:

   generic
     with procedure Op is <>;
     ...
   package GP is ...;


Perhaps if you provided more information about what you're doing then
maybe we can give some more specific solutions.