Re: Nontrivial examples of C interface with Ada

[tmoran@bix.com]

>For me, the really tricky ones are the routines that return a pointer to
>an object whose type is specified by the return value of another
>parameter. As near as I can tell, you have to either make a separate
>subprogram for each type and force the user to know what type he's
>receiving when he makes the call, or you just throw up your hands and
>return an address.
  Usually the kinds of objects the returned pointer points to, are
fairly highly related, in which case a return X'class may do the
job nicely.  In Claw, for instance, the different Device Independent
Bitmaps (different color resolution, palette use) are descendants of
a single type, so you can read an unknown .bmp file with
    function Read (Filename : in String)
        return Claw.Bitmaps.Root_DIBitmap_Type'class;
  Even more commonly, of course, an *input* parameter defines what
kind of entity the output pointer points to.  In that case, two different
Ada procedures fills the bill quite nicely.