[Laszlo-dev] Is this the idiom people use to set the initial value of an attribute in a class declaration?

[Henry Minsky]

For swf9, it will happen that way, when we convert the initializers for
instances into a single monolithic function block. We hope.



On 10/9/07, John Sundman <jsundman at laszlosystems.com> wrote:
> Here's a thread from this summer about class variables.
>
> Below, PTW says, "It's a weak spot in the implementation right now
> that Henry and I hope to repair as we modernize the tag compiler."
>
> Will this be addressed as part of the refactoring of the tag compiler
> now ongoing, or should I plan to document around this?
>
> Thanks,
>
> jrs
>
>
>
> On Jul 9, 2007, at 12:09 PM, P T Withington wrote:
>
> > Er, not.
> >
> > All our attributes are instance attributes.  If you leave out
> > $once, you get a micro-optimization if the initial value is a
> > constant, and you get something you probably did not want otherwise.
> >
> > It's a weak spot in the implementation right now that Henry and I
> > hope to repair as we modernize the tag compiler.
> >
> > On 2007-07-09, at 09:12 EDT, Elliot Winard wrote:
> >
> >> I always assumed that, unless $once{} was used, I was declaring a
> >> static attribute.  I thought that was noted in the docs.
> >>
> >> Maybe not?
> >> -e
> >>
> >>
> >> On Mon, Jul 9, 2007 at  7:55 AM, P T Withington wrote:
> >>
> >>> The bug we have is that we don't treat every instance initializer
> >>> as an expression, so you can't say `value="new Array"` to get
> >>> around the sharing, you have to say `value="${new Array}"`.  I
> >>> think this is an FAQ that Antun covers.
> >>>
> >>> And yes, you are right.  This would be solved by moving attribute
> >>> initializers into the class initializer.
> >>>
> >>> But if we fix this bug, we'll need to provide a way to share in
> >>> the cases where you _do_ want to share, perhaps by providing an
> >>> LZX way to declare a static attribute?
> >>>
> >>> On 2007-07-08, at 22:25 EDT, Henry Minsky wrote:
> >>>
> >>>> I've been hacking on an app this week, and realizing it's been
> >>>> awhile since
> >>>> I tried
> >>>> to actually program anything in Laszlo.
> >>>>
> >>>> There's this huge "gotcha" when setting the initial value of
> >>>> attributes to
> >>>> an object in a class
> >>>> declaration, like this
> >>>>
> >>>>
> >>>> <class name="foo">
> >>>>  <attribute name="pets" value="[]"/>
> >>>>
> >>>> Which screws you since that object will now be shared among all
> >>>> instances.
> >>>>
> >>>> The idiom I think I remember people using is
> >>>>
> >>>> <class name="foo">
> >>>>  <attribute name="pets" value="$once{[]}"/>
> >>>>
> >>>> Or more readably
> >>>>
> >>>> <class name="foo">
> >>>>  <attribute name="pets" value="$once{new Array()}"/>
> >>>>
> >>>> Is that what we recommend to do now? I guess we going to
> >>>> quietly  fix this
> >>>> issue if and when we get
> >>>> our node initialization rewritten as a compile-time-generated
> >>>> initializer
> >>>> function?
> >>>>
> >>>>
> >>>> --
> >>>> Henry Minsky
> >>>> Software Architect
> >>>> hminsky at laszlosystems.com
> >>
> >>
> >> ---=---===-------
> >> Elliot Winard
> >> Sr. Software Engineer
> >> Webtop Team
> >> ---=---===-------
> >
>
>


-- 
Henry Minsky
Software Architect
hminsky at laszlosystems.com