Re: abstract sub programs overriding

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

Hyman Rosen wrote:

> Dmitry A. Kazakov wrote:
>> C++ does everything right and anything else is not Ada.
> 
> This has nothing to do with programming language wars,
> but perhaps with English language wars. When you state
> categorically "So when T is view-convertible to T'Class,
> then two constructors have to be applied: one of T, one
> of T'Class. In the constructor of T you cannot dispatch,
> in the constructor of T'Class you can do it safely." it
> certainly sounds like you are saying that this is what
> Ada does. But this is not what Ada does, it is what you
> would like Ada to do.

No it is how Ada does it. Here is an example:

package Foo is
   type A is new Ada.Finalization.Controlled with null record;
   procedure Initialize (Object : in out A);
   type In_B is new Ada.Finalization.Controlled with null record;
   procedure Initialize (Object : in out In_B);
   type B is new A with record
      Field : In_B;
   end record;
end Foo;

with Ada.Text_IO;  use Ada.Text_IO;
package body Foo is
   procedure Initialize (Object : in out A) is
   begin
      Put_Line ("Init A");
   end Initialize ;
   procedure Initialize (Object : in out In_B) is
   begin
      Put_Line ("Init field of B");
   end Initialize;
end Foo;

Initializing of an object of B will print:

Init field of B
Init A

showing that Initialize for A is called *after* initialization of Field of
B. It means that A's Initialize may safely use any field of B.

-- 
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de