[Laszlo-dev] [Laszlo-user] How should states _really_ work?

[P T Withington]

I think we are converging on:

1) A state's primary purpose is to change the value of an attribute in  
its parent.  Typically this means the state re-declares the attribute  
with a different initial value (which may be a constant or a  
constraint).  When the state is applied, the attribute takes on the  
value specified by the state (which means removing any constraint  
specified in the parent).  When the state is removed, the attribute  
retains the final value that it had when the state was still applied.   
It is an error to specify an attribute in a state that _is_not_  
already declared in the parent.

2) A state may need to specify some 'common subroutines' to support  
its constraints.  These are written as methods in the state.  The  
methods of a state will be methods of the parent of the state, but  
they may not use `super` calls.  In this sense, they are simply common  
subroutine functions attached to the parent so that they can be  
invoked as `this.<name>`.  It is an error to specify a method in a  
state that _is_ already defined in the parent.

In summary:  A state can change the values of an attribute in its  
parent and it can specify methods to be added to the parent in support  
of computing the changed values.

In the above description, 'parent' refers to the dynamic parent of the  
state.  That is, a state is subject to placement and affects the view  
that it is placed within, not the view it is declared within.

---

There was lots of theory bandied about regarding what states might do  
in the abstract, but after surveying their current usage we believe  
the above definition is sufficient to support that usage and still  
tractable for compiling to JS2 runtimes.

On 2008-03-21, at 10:33 EDT, André Bargull wrote:
> Any news for this issue? It is still marked as 'unresolved' in my  
> local inbox..
>
>
> On 2/23/2008 9:36 PM, P T Withington wrote:
>> André points out that this example:
>>
>>  http://www.openlaszlo.org/lps4/docs/developers/constraints.html#d0e66645
>>
>> Will not work, with my fix to LPP-631, because to fix that, I made  
>> states _remove_ the parent constraint when the state sets the the  
>> same attribute, so, once you drag one of the boxes, it will no  
>> longer track the other view.
>>
>> We can't have it both ways.  Is http://jira.openlaszlo.org/jira/browse/LPP-631 
>>  not a bug after all?
>>
>>