Re: GCC 4.0 Ada.Containers Cursor danger.

[Matthew Heaney <matthewjheaney@earthlink.net>]

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

> << Does this behavior adequately satisfy your needs? >>
> 
> No, this checking is too much overhead. 

Too much overhead, compared to what?


> And my need is not in the cursors area.

Then don't use them...

 
> I would use the
> 
>    procedure Include
>      (Container : in out Map;
>       Key       : Key_Type;
>       New_Item  : Element_Type);
> 
> in this cases. (this sample was based in AI302 without Include
> routine.)

Use Include instead of ... what?

This is not equivalent to Replace_Element, for example, since Include
must look up the key.  And if the key is already in the map, then
Include replaces both the key and the element.



> But I need some more routines without cursors. For example
> 
>    procedure Iterate
>      (Container : Map;
>       Process   : not null access 
>         procedure (Key : Key_Type; 
>                    Element : Element_Type; 
>                    Stop : out Boolean));
> 
> analog of
> 
>    procedure Iterate
>      (Container : Map;
>       Process   : not null access procedure (Position : Cursor));
>
> but without cursor.


The reason that Iterate passes a cursor is to avoid a combinatorial
explosion of parameters (e.g. your example doesn't provide a way to
modify the element).

The passive iterator is designed for the common case, which is to visit
every item in the container.  Your example requires the Process
procedure to pass an additional Stop parameter, to indicate termination.
You can achieve the same effect using a cursor.

(It also incorrectly passes the Stop parameter using in-mode, instead of
in-out mode, thus forcing the actual subprogram to set the Stop
parameter each time, if even you don't want to Stop.)

I have showed in a previous post how to implement your example using the
existing primitives.


> And for every access routine with cursor there should be analog without
> cursors IMHO.

That's fine, but you should have stated your opinion 2 years ago, by
submitting your own library design proposal.