Re: Idiom for a class and an object in Ada

[Matthew Heaney <matthewjheaney@earthlink.net>]

"Matthew Heaney" <mheaney@on2.com> writes:

> I showed in an earlier post how to use access types, but hide the fact
> that access types are used:
> 
> package P is
>    type T (<>) is limited private;
>    procedure Op (O : in T);
>    function O1 return T;
>    function O2 return T;
> private
>    type Rep_Type is limited ... end record;
> 
>    type T is access all Rep_Type;
>    for T'Storage_Size use 0;
> end P;


Actually, I forgot to mention that you don't need an access type if you
use an array to hold the objects:


package P is
   type T (<>) is limited private;
   procedure Op (O : in T);
   function O1 return T;
   function O2 return T;
private
   type T is range 1 .. 2;
end P;


package body P is

   type Rep_Type is limited record ... end record;

   Objects : Rep_Type (T);

   procedure Op (O : in T) is
      OO : Rep_Type renames Objects (O);
   begin
      ...
   end;

   function O1 return T is
   begin
      return 1;
   end;

   function O2 return T is
   begin
      return 2;
   end;

end P;


In fact, you don't need the private type at all:

package P is
   type T is (O1, O2);
   procedure Op (O : in T);
end P;

package body P is

   type Rep_Type is limited record ... end record;

   Objects : Rep_Type (T);

   procedure Op (O : in T) is
      OO : Rep_Type renames Objects (O);
   begin
      ...
   end;

end P;