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From: Volkert.Barr@freenet.de (Volkert)
Newsgroups: comp.lang.ada
Subject: Problems with the GNAT/C++ Interface.
Date: 1 Nov 2001 19:13:37 -0800
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Date: 2001-11-02T03:13:37+00:00
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Hello c.l.a!

Problem: I want an Ada Binding to the following recursive C++ 
class declaration:

class Chainable {

public:
       
  Chainable *next, *prev;
  
  Chainable();
  void reset();

};

The following Ada package Chainable_Type seams for me an 
obvious corresponding Ada type declaration:

package Chainable_Type is

   type Chainable;
   type Chainable_Access is access all Chainable'Class;

   type Chainable is tagged limited
      record
         next        : Chainable_Access;
         prev        : Chainable_Access;
      end record;

    ...

end Chainable_Type;

So far so good. Now i say the GNAT Compiler that the tagged type 
Chainable has to be mapped to the corresponding C++ class:

package Chainable_Type is

   type Chainable;
   type Chainable_Access is access all Chainable'Class; -- (*)

   type Chainable is tagged limited
      record
         next        : Chainable_Access;
         prev        : Chainable_Access;

         Vptr : Interfaces.CPP.Vtable_Ptr; -- new
      end record;

   pragma CPP_Class (Entity => Chainable); -- new

   ...

end Chainable_Type;

compiling this package gnat says: 
  
  error : pragma "Cpp_Class" applicable to a record, tagged record or
  record extension.

Ok, the problem seems the incomplete type declararion 
in line (*). Do is miss something?

Volkert