[Laszlo-dev] Initialization difference between swf and dhtml

[Jim Grandy]

Agreed, but constraint satisfaction is too complex to enforce lexical  
ordering over. It's also too hard to understand what's going on if  
the two aren't in separate phases -- this is the mistake in the  
current system, which leads to lots of constraint satisfaction over  
uninitialized attributes. Plus in theory no predefined order is  
necessary for constraints -- you just start with one and keep going  
until it all settles down. I think this would be clean:

- initialize own class' attributes to constants, first by class and  
then by lexical order
- initialize instance's unique attribute to constants, in lexical order
- run all all attribute constraints, in undefined order

jim

On Nov 28, 2006, at 3:39 PM, Henry Minsky wrote:

> Note that implementing the lexical ordering is likely to break a
> couple of legacy apps
> that depend implicitly on the current ordering. Of course, several
> DHTML versions are
> already broken due to the different order now (I think I fudged a
> couple of constraints in the amazon app to work around one case
> already, with height initialization on a component) , so it's not
> really a reason to try to preserve existing behavior.
>
>
>
> On 11/28/06, Jim Grandy <jgrandy at openlaszlo.org> wrote:
>>
>> On Nov 28, 2006, at 2:33 PM, Adam Wolff wrote:
>>
>> > On Nov 28, Don Hopkins wrote:
>> > [snip]
>> >> I think it's pretty important to give class programmers the
>> >> ability to
>> >> control the order in which the attributes are initialized at class
>> >> declaration time.  It's also sometimes useful for object users to
>> >> control the initialization order at object instantiation time, but
>> >> usually they shouldn't have to care, or be required to  
>> understand the
>> >> inner workings.
>> > Agree that this is appealing and sensible, but I don't think it's
>> > practically possible. As a class user, I can say
>> >
>> >     <yourclass attr1="$once{ a }" attr2="$immediately{ b }"/>
>> >
>> > and then attr2 will be set before attr1 regardless of what you
>> > might want
>> > as the class implementor.
>> >
>> > A
>>
>> I think constraint satisfaction has to be a separate phase from
>> attribute initialization, and really needs to have indeterminate
>> execution order to preserve optimization/implementation flexibility.
>> Attribute initialization to a constant value really needs lexical
>> order, by class. The two shoud really be separate.
>>
>> jim
>>
>>
>
>
> -- 
> Henry Minsky
> Software Architect
> hminsky at laszlosystems.com