Re: Dispatching problem.

["James S. Rogers" <jimmaureenrogers@worldnet.att.net>]

"Petter Fryklund" <petter.fryklund.konsult@dynamics.saab.se> wrote in
message news:f74cb448.0302060604.e808c22@posting.google.com...
> We have the following:
>
> package A is
>   type Msg;
>   type Msg_Ptr is access all Msg'Class;
>   type Msg is abstract tagged null record;
>   ... other declarations
>
>   type M1 is new Msg with ....
>   type M1_Ptr is access all M1;
>   type M2 is new Msg with ....
>   type M2_Ptr is access all M2;
>   ... other declarations
>
>   function X (Param : Integer) return Msg_Ptr;
> end A;
>
> with A;
> package B is
>   type Msg is abstract new A.Msg with null record;
>   type Msg_Ptr is access all Msg;
>   type B1 is new A.M1 with null record;
>   type B1_Ptr is access all B1;
>   type B2 is new A.M1 with null record;
>   type B2_Ptr is access all B2;
>
>   procedure Y (MP : access B1);
>   procedure Y (MP : access B2);
> end B;
>
> with A;
> with B;
> procedure Main is
>
>    X : A.Msg_Ptr;
>    Y : A.Msg_Ptr;
> begin
>    X := A.X (1);        -- Building a A.M1
>    Y := A.X (2);        -- Building a A.M2
>    B.Y (B.Msg_Ptr (X)); -- causes Constraint_Error Tag Check Failed to be
raised.
> end Main;
>
> How can we dispatch in package B?

You seem to have your inheritence concepts inverted here.
Every B.B1 is a member of the class rooted at A.Msg. Not every
A.Msg is a member of B.B1. For instance, A.M1 is not a B.B1.

Jim Rogers