Re: System.Address to Access to function/procedure conversion

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Sun, 28 Jul 2013 15:27:48 +0000 (UTC), Tarek Ghaleb wrote:

> As for why not just pass an Access to the function directly, the
> Address is actually passed to a C function which later passes it back
> to Ada.

If you pass anything to C you should better keep it under C convention,
even if you are certain that C does not touch it. You should pass an
access-to-procedure/function to C and get it back. The access type will
have pragma Convention (C, ... set. You don't need address here. E.g.

   type Func is access procedure (...);
   pragma Convention (C, Func);

   procedure C_Stuff (...; Call_Back_Ptr : Func; ...);
   pragma Import (C, C_Stuff, "fancy_c_library_entry");

The rationale is that, maybe unlikely still the access type might have a
different size than address and/or C pointer. When you use pragma
Convention (or the corresponding aspect if in Ada 2012) it is guaranteed to
work.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de