Re: Array slices and types

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

On Thu, 21 Aug 2008 08:26:26 +0300, Niklas Holsti wrote:

> But doesn't this example show that it would be useful to have 'Base 
> also for array types?

For any type, actually.

Consider this language design fault:

procedure Initialize (X : in out S) is
begin
   Initialize (T (X));
   ... -- My stuff
end Initialize;

A call to Initialize should be done automatically, but it is not. So the
parent of S must be explicitly specified and known to all descendant. This
is a really *bad* thing:

package Foo is
   type S is new T with private;
private
   type S is new Private_Decendant_Of_T with ...;
end Foo;

What would happen if Private_Decendant_Of_T overrode Initialize of T? The
result would be an inability to publicly derive from S any new types if
Initialize should be extended!

S'Base could mend it:

procedure Initialize (X : in out S) is
begin
   (S"Base (X)).Initialize; -- Call to parent whatever it be
   ... -- My stuff
end Initialize;

Presently the only way is to override Initialize, Finalize and Adjust
everywhere, even if you actually don't want to extend them:

package Foo is
   type S is new T with private;
   overriding procedure Initialize (X : in out S); -- Have to do this!
private
   type S is new Private_Decendant_Of_T with ...;
end Foo;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de