Re: how to import a package

[Georg Bauhaus <bauhaus@arcor.de>]

On Mon, 2006-12-11 at 19:19 -0800, markww wrote:


> I'm wondering still if it's possible to have a data member in the
> package definition that serve as my start and end nodes.

As Jeffrey and Stuart have explained, you are still led astray
by a misconception: A C++ struct/class here corresponds to an Ada
type, not to an Ada package. Although you need a package to
associate the "methods" with the tagged type, all data members
must become the record components in the type definition.

C++: From a struct or class, you create objects.
Ada: From a type, you create objects.

C++: Operations of a type are declared within the struct/class
Ada: Operations of a type are declared after the type within
     a surrounding package.

Compare the following definitions:

namespace Geo
{
  struct Any
  {
    int x, y;
    virtual void move(int a, int b) = 0;
  };

  struct Point : public Any
  {
    virtual void move(int a, int b);
  };

  struct Circle : public Any
  {
    int r;
    virtual void move(int a, int b);
  };
}


package Geo is

   type Any is abstract tagged record
      x, y: Integer;
      -- data members of any geometric object
   end record;

   procedure move(thing: in out Any; a, b: Integer) is abstract;
   -- abstract method of Any



   type Point is new Any with record
      null;
         -- no additional data members
   end record;

   --overriding
   procedure move(thing: in out Point; a, b: Integer);



   type Circle is new Any with record
      r: Integer;
      -- Circle objects with radius
   end record;

   --overriding
   procedure move(thing: in out Circle; a, b: Integer);

end Geo;

HTH,
-- Georg