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

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

Am Sonntag, 15. Juni 2008 16:46:39 schrieb Donal K. Fellows:
> Will Duquette wrote:
> > In Donal's example, we have an instance variable, utterance, declared
> > for the "animal" class; the variable is visible without declaration in
> > subclass "cat"'s methods, e.g., "speak2".
>
> Oops. I misread.
>
> The speak2 method wouldn't have worked as written without either:
>    a) the cat class defining [variable utterance], or
>    b) an explicit [my variable utterance].
>
> > This strikes me as dangerous; a new instance variable added to an
> > ancestor class that has the same name as a local variable used in a
> > subclass method can break the subclass method.
> >
> > Donal, in your example, "dog" declares utterance explicitly; does that
> > make any difference?  Given that method "cat"'s "speak2" can see
> > utterance, it would appear not.
>
> I made a mistake in reading Arnulf's extension of my example. :-)
>
> The only variables automatically brought into a method are those that
> are declared at the same level (i.e. in the same class/object) as the
> method. This should mean that if a superclass increases the set of
> variables it declares, there will only be a problem if the parent
> declares a variable that a subclass was previously declaring (and
> they're used inconsistently). But that case is one I'm explicitly not
> providing help for working around; sealing each variable to its class
> completely makes for much more difficult introspection, and I'll need
> some arm twisting to change my mind on that.
>
> Donal.
Thanks for clarifying
Arnulf
>
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