[Laszlo-dev] referencing nodes by id, how to set global vars?

[P T Withington]

I think that you should be able to make it a static class, since `id`  
is defined as being "tag only, and final" which means that it cannot  
be set at run time (even though that is how it is presently  
implemented).  I would hope that by making it a static class, the JS2  
compiler can completely optimize away the dynamic lookup that the  
`with` would otherwise imply.

BUT: there is one other "gotcha" I forgot to mention as to why you  
can't "wrap every function's contents with 'with (global)'".  Consider  
the following:

global.foo = '42';

class bar {
   static var foo = 13'
   var foo = 7;

   function zot ():Function {
     var foo = -3;

     return function () { return foo; }
   }
}

((new bar).zot())() => ?

Should yield `-3`, but if you take the simple approach of wrapping  
`with (global)`, will yield `42`.  (And similarly for the instance and  
class `foo` if the closer binding were not present.)

The compiler already also can tell you about closed-over variables,  
so, I think the best solution is to simply rewrite free references (to  
global.foo) when they match declared id's (which the tag compiler can  
tell the script compiler in advance, because it is going to put them  
in a static class with a singleton instance).  The one additional  
piece of analysis that is needed is to find the instance (including  
inherited) and class variables that could match the free reference --  
those should not be rewritten, but I'm not sure the compiler takes  
those into account when doing its analysis.

On 2008-02-09, at 13:52 EST, Henry Minsky wrote:

> OK I'd like to try doing this. I wonder if I should make a static
> class named 'global', as opposed to just an Object bound to a global
> var. That way the compiler could declare all the id's that are known
> at compile time as 'fixtures', and presumably new
> properties could be added at runtime when needed.
>
> On Sat, Feb 9, 2008 at 1:07 PM, P T Withington <ptw at pobox.com> wrote:
>> I only suggest the conditional wrapping for performance reasons...
>> 'with' does not come for free. And the compiler is already doing the
>> necessary analysis.
>>
>>
>>
>> On Feb 9, 2008, at 10:15, Donald Anderson <dda at ddanderson.com> wrote:
>>
>>> Why not wrap every function's contents with 'with (global)' ?
>>>
>>> And can user code do this with top level vars?
>>>
>>>  var blah = globalvar;
>>>
>>> That would need to be fully qualified (either by smart compiler or
>>> user).
>>>
>>> On Feb 9, 2008, at 7:32 AM, P T Withington wrote:
>>>
>>>> This is probably the right time to bite the bullet and stop using
>>>> the global namespace.  It has already cause problems with name
>>>> collisions.  Per my comment, "global" should probably only mean "in
>>>> this canvas's scope".  So, yes create an object that holds these
>>>> global names.  Heck, you could even call it `global`... :)
>>>>
>>>> Our compiler already analyzes each method to determine if there are
>>>> free references in the method.  We could use this analysis to
>>>> insert a `with (global)` block around any such code, so that no
>>>> user code would have to change.
>>>>
>>>> On 2008-02-08, at 23:31 EST, Henry Minsky wrote:
>>>>
>>>>> In DHTML and AS2, we get away with doing this for setting node
>>>>> id's to
>>>>> be global vars:
>>>>>
>>>>> function setID ( id ){
>>>>> //support for current system
>>>>> if ((typeof(id) == 'string') && id.length) {
>>>>>     if ($debug) {
>>>>>         if (global[id] && global[id] !== this) {
>>>>>             Debug.warn('Redefining #%s from %w to %w',
>>>>>                        id, global[id], this);
>>>>>         }
>>>>>     }
>>>>>     this.id = id;
>>>>>     // TODO: [2006-03-22 ptw] Should id's really go in the
>>>>> user/canvas module?
>>>>>     global[ id ] = this;
>>>>> } else {
>>>>>     if ($debug) {
>>>>>         // id is permitted to be null or undefined, meaning
>>>>>         // "don't id me"
>>>>>         if (id) {
>>>>>             Debug.error('Invalid id %w for %w', id, this);
>>>>>         }
>>>>>     }
>>>>>  }
>>>>> //namespace system
>>>>> //app[ id ] = this;
>>>>> //local reference
>>>>>
>>>>> }
>>>>>
>>>>> This works because we aliased "global" to _root in AS2, and to
>>>>> "window" in DHTML.
>>>>>
>>>>> I don't see any way to do this in AS3. There doesn't seem to be  
>>>>> any
>>>>> magic object whose properties
>>>>> become global vars. I'm not even sure how to get the runtime to  
>>>>> set
>>>>> global id variables by name procedurally during
>>>>> instantiation even if we declare them.  I hacked the tag  
>>>>> compiler to
>>>>> emit a list of top level var declarations for all id's, but
>>>>> I don't see how to emit the code for the instantiator to bind to
>>>>> them
>>>>> when the nodes are created, because what can you put on the
>>>>> left side of the assignment?
>>>>>
>>>>> One solution would be to make an API change, and require all
>>>>> globally
>>>>> named nodes to be referenced via some object
>>>>> like "lz", which we already are kind of pushing for class names.
>>>>> Tons
>>>>> of user code would  have to be updated.
>>>>>
>>>>> To add one more twist of the knife, for the debugger eval  
>>>>> mechanism,
>>>>> if we want to use globals, we need to have a list of them
>>>>> someplace to compile in to the little debugger stub template app,
>>>>> because that code is compiled independent of the application code.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Henry Minsky
>>>>> Software Architect
>>>>> hminsky at laszlosystems.com
>>>>
>>>
>>>
>>> --
>>>
>>> Don Anderson
>>> Java/C/C++, Berkeley DB, systems consultant
>>>
>>> voice: 617-547-7881
>>> email: dda at ddanderson.com
>>> www: http://www.ddanderson.com
>>>
>>>
>>>
>>>
>>
>
>
>
> -- 
> Henry Minsky
> Software Architect
> hminsky at laszlosystems.com