Am Mittwoch, 7. Mai 2008 03:09:56 schrieb Will Duquette:
>  On May 6, 2008, at 2:37 AM, Donal K. Fellows wrote:
>  > Ah, the "public vs private" state issue. Other languages get
>  > themselves
>  > in a proper tangle over this, so I know we have to treat carefully.
>  >
>  > As a matter of principle, I don't want to have state that the object
>  > can't inspect on itself; I think that that would be un-Tclish.
> 
>  This I agree with; and Snit doesn't implement "private" state as such.
>  (Of course, you don't get inheritance, either, so in a sense all
>  instance variables are private by default; but that's happenstance.)
> 
>  > That in
>  > turn means that I'm inclined to say that if two classes use the same
>  > variable name, they get the same variable (which greatly reduces the
>  > complexity of the implementation).
> 
>  This I think would be a big mistake, as it makes it to easy for changes
>  to superclass A (possibly written by developer B and included in package
>  C) to break subclass D, written by application developer E.  Trevor
>  suggests we protect against this by using a naming convention for
>  instance variables, to which I can only say "Ugh!"  Isn't that what
>  namespaces are for?
> 
>  Itcl has a solution that allows public variables defined by a class
>  and its ancestors to be shared without name collisions; and Arnulf
>  has already written a variable resolver for TclOO that implements it.
>  I suggest we adopt it for TclOO in general.
> 
>  Will

just to make it easier to discuss about that area, I will describe my current 
way to solve the problem, also I am not yet really happy with that solution 
yet:

here is an example (not fully itcl syntax!)

class animal 
   private variable priv  priv_animal
   protected variabled prov_animal
   public variable pubv pub_animal
   protected variable prov_animal_only prov_animal_only

   public method show_animal_vars {} { 
      puts "priv!$priv!prov!$prov!pubv!$pubv!prov_animal_only!
$prov_animal_only!" 
   }

class cat
  inherit animal
  private variable priv priv_cat
  protected variable prov prov_cat
  public variable pubv pub_cat
  # prov_animal_only is also usable here !!

   public method show_cat_vars {} { 
      puts "priv!$priv!prov!$prov!pubv!$pubv!prov_animal_only!
$prov_animal_only!" 
   }

cat leo ; # creates object leo

leo show_animal_vars produces: 
priv!priv_animal!prov!prov_animal!pubv!pubv_animal!prov_animal_only!prov_animal_only!

leo show_cat_vars produces: 
priv!priv_cat!prov!prov_cat!pubv!pubv_cat!prov_animal_only!prov_animal_only!
 

And here is what I am doing in itcl-ng:

In itcl-ng I create a namespace leo for the object leo (which is also a 
command!). Within namespace leo there is a namespace for every class of the 
object

leo
  animal
  cat

the variables are in these namespaces and are "mapped" using the namespace 
resolver

leo
  animal
     priv
     prov
     pubv
     prov_animal_only
  cat
     priv
     prov
     pubv

That is working, but I am not very happy with it. What I would like to have is 
some construct like this or similar in Tcl core with fast access, as creation 
of that structure takes a lot of time at the moment, when creating the 
object. Would be also useful, if there would be support for optional (for the 
extensions which need it) checking of the protection/storage class 

Arnulf


Arnulf
> 
> 
> 
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>  http://foothills.wjduquette.com/blog | The View from the Foothills
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