Re: GCC 4.0 Ada.Containers Cursor danger.

[Matthew Heaney <matthewjheaney@earthlink.net>]

"Dmitriy Anisimkov" <anisimkov@yahoo.com> writes:

> I understand that using of cursors allows to reduce the number of
> routines in the Ada.Cursors. But i'm sure that using a much more
> routines without cursors would reduce a potential errors at design
> time.

You must adduce evidence for this claim.  Otherwise we're just debating
religion.


> Using the *checking* cursors would move error detection into the run
> time.

Yes, but in your original example, you were complaining about a run-time
error.  That error is detectable.


> So, I know that i could build whatever i need on top of routines with a
> cursors.

Yes, but that's the point.  A general-purpose library must be flexible
enough to meet the needs of disparate applications.  If you want the
library to be strictly key-based (sans cursors), then it's far less
flexible, and no longer a general-purpose library.


> But I think that Ada standard should try to move design process into
> the way where the errors would be avoided at the design time.

You want to legislate behavior for everyone.  This is wrong.  You should
only be concerned with your own behavior.

If you want only key-based operations, then you can just write a layered
abstraction once, and you can use it everywhere.

One way is:

generic
   type Key_Type (<>) is limited private;
   type Element_Type (<>) is limited private;
   type Container_Type (<>) is limited private;
   type Cursor_Type is private;
   with function First (C : CT) return Cursor_Type is <>;
   with procedure Next (C : in out Cursor_Type) is <>;
   ...
package Generic_Map_Operations is 

   generic
      with procedure Process 
        (K : KT; E : ET; Stop : in out Boolean) is <>;
   procedure Generic_Iteration
     (Container : Container_Type);

...
end Generic_Map_Operations;