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Date: Tue, 8 Dec 2015 08:45:52 -0800 (PST)
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Subject: I'm facing an issue with: call to abstract procedure must be
 dispatching
From: Serge Robyns <serge.robyns@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:28707
Date: 2015-12-08T08:45:52-08:00
List-Id: <comp.lang.ada>

Gents,

I've been trying to get my head around a way to create a solution where the=
 storage method can be changed.  For this I'm using Ada's interface languag=
e construct.  So far I've only be successful with the following construct, =
whereas store1, store2, etc are implementations to store object1, object2, =
etc.  These are created as child packages of their respective objects so th=
ey can access the private parts.

   type T_Abstract_Data_Store is limited interface
     and Store1_Interface
     and Store2_Interface
     ...

In the implementation "class"

   type T_Data_Store is limited new T_Abstract_Data_Store with record
      Store1 : T_Store1;
      Store2 : T_Store2;
      ...

This then requires to write glue code to implement a link to the different =
implementations of the stores.=20

procedure Insert (Store : in out T_Data_Store;
                  Obj   : in     T_XYZ'Class)
is
begin
    Store.Store1.Insert (Obj);
end Insert;

This could have been avoided if Ada would have allowed some form of multi-i=
nheritance of in the instance of a multi-interface "class".

Now I've been trying to resolve this through another mean but I'm now facin=
g the "call to abstract procedure must be dispatching" error message which =
I cannot explain nor resolve.

Below an a sample compile-able piece of code.

package Clients is
      -- could also be in private part ....
   type T_Client is tagged record
      ID : Natural;
   end record;
end Clients;

with Clients; use Clients;

package Abstract_Store is
   type T_Asbtract_Store is limited interface;

   procedure Insert (Store  : in out T_Asbtract_Store;
                     Client : in     T_Client'Class)
   is abstract;
   -- actually in my code Client will be a subclass of T_Client, for exampl=
e
   -- T_Client_DAO'Class
end Abstract_Store;

with Clients; use Clients;
with Abstract_Store; use Abstract_Store;

procedure test is

   type T_Store is new T_Asbtract_Store with null record;
  =20
   overriding procedure Insert (Store  : in out T_Store;
                                Client : in     T_Client'Class) is
   begin
      null;
   end Insert;
  =20
   A_Store   : access T_Asbtract_Store;
   The_Store : aliased T_Store;
   Client    : T_Client;

begin
   A_Store :=3D T_Asbtract_Store (The_Store)'Access;
   A_Store.Insert (Client);
end test;

The compiler does not like "A_Store.Insert (Client)".
Also with this construct I've to use an access variable ...

Anyone can shed a light on this or suggest a smarter Ada way?

Regards,
Serge