Re: generic formal derived type that inherits private op

[Tucker Taft <stt@averstar.com>]

Matthew Heaney wrote:
> 
> There's some code below that I think should work, but doesn't:
> 
> 1) A generic child package imports a generic formal type that derives
> from a (tagged) type declared in the parent package.
> 
> 2) The parent type declares a primitive operation privately; that is, in
> the private region of the parent package.
> 
> 3) The generic child package tries to call the (private) primitive
> operation of the derived type, but the compiler doesn't think the
> derived type comes with that operation.  This appears to be incorrect.
> 
> Here's the output of my compiler (GNAT v3.12p):
> 
> p-c.adb:5:19: expected type access to "T" defined at p.ads:9
> p-c.adb:5:19: found type access to "Nt" defined at p-c.ads:5
> 
> What's the scoop?  Is this correct or not?

Your code is correct.  The compiler seems to have a bug 
(and the ACVC suite seems to have a hole in this area).
> 
> (Tucker: I submitted this same code to CLA a few months ago.  Remember
> we talked about it at the ARG meeting a few weeks ago?)

Yes, and we had pretty much the same problem in our compiler, which
we have since fixed.  So now My Favorite Ada95 Front End likes your
code. ;-)

> 
> Thanks,
> Matt
> 
> --STX
> package P is
> 
>    type T is abstract tagged limited private;
> 
> private
> 
>    type T is abstract tagged limited null record;
> 
>    procedure Private_Op (O : access T);
> 
> end P;
> 
> package body P is
> 
>    procedure Private_Op (O : access T) is
>    begin
>       null;
>    end;
> 
> end P;
> 
> generic
>    type NT is new T with private;
> package P.C is
> 
>    procedure Op (O : access NT);
> 
> end P.C;
> 
> package body P.C is
> 
>    procedure Op (O : access NT) is
>    begin
>       Private_Op (O);
>    end Op;
> 
> end P.C;

-- 
-Tucker Taft   stt@averstar.com   http://www.averstar.com/~stt/
Technical Director, Distributed IT Solutions  (www.averstar.com/tools)
AverStar (formerly Intermetrics, Inc.)   Burlington, MA  USA