Re: [TCLCORE] TIP #320: Improved Variable Handling in the Core Object System

[Arnulf W. <ar...@wi...>]

Am Sonntag, 15. Juni 2008 13:08:43 schrieb Donal K. Fellows:
> Will Duquette wrote:
> > Arnulf Wiedemann wrote:
> >> I think I have not yet fully understood, how that will work.
> >>
> >> For example: class cat has a variable cat_color defined and I have
> >> 2 objects which have as object class cat and these are named cat1
> >> and cat2. Will variable cat_color be shared between the objects? So
> >> if I set cat1 cat_color to black with a class method, will a class
> >> method of cat2 get back black as cat_color?
> >>
> >> Are object specific variables also accessible by class methods?
> >
> > I am curious about this point as well.  As I read it, normal variables
> > declared by class cat are instance variables; cat1 and cat2 do not
> > share values.  However, variables can also be declared by the class
> > using "self"; in this case, the variable  is a "typevariable" in Snit
> > parlance.  Is that correct?
> >
> > Will such class variables be visible without declaration or
> > qualification in instance methods? (I'd presume so.)
> >
> > And I presume that class and instance variables declared by ancestors
> > will also be accessible, but *with* qualification (mechanism clearly
> > to be fleshed out later)?
>
> This TIP is about making instance variables available in methods without
> explicitly having to bring them in for each method. Class variables as
> such don't exist (the 'self' path leads to instance variables on the
> class objects) but you can link variables using [upvar] so that should
> not be a big problem. It's orthogonal to this TIP (at the moment).
>
> All instance variables will be available through [my variable], wherever
> they are declared (or even if they aren't declared at all). I don't want
> to do name mangling or other concealment if I can avoid it.
>

That looks ok for itcl as far as I can see at the moment. Will method speak2 
work as I have written it (see below)? 

Arnulf

> Perhaps an example will be more helpful:
>
>   namespace path oo
>   class create animal {
>      variable utterance
>      constructor says {
>         set utterance $says
>      }
>      method speak {} {
>         puts $utterance
>      }
>   }
>   class create cat {
>      superclass animal
>      constructor {} {
>         next Meow
>      }
       method speak2 {} {
          puts $utterance
        }
>   }
>   class create dog {
>      superclass animal
>      constructor {} {
>         next Woof
>      }
>      variable utterance
>      method speak {} {
>         set word [lindex $utterance 0]
>         set utterance [lrepeat [expr {3-[llength $utterance]}] $word]
>         next
>      }
>   }
>   cat create Tiddles
>   dog create Fido
>
> With that, we would then get this:
>
>   % Tiddles speak
>   Meow

    % Tiddles speak2
    Meow

>   % Fido speak
>   Woof Woof
>   % Tiddles speak
>   Meow
>   % Fido speak
>   Woof
>   % Fido speak
>   Woof Woof
>
> Donal.
>
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