[webkit-dev] JS: Getter/Setter callbacks at Property level

[Geoffrey Garen]

Hi Brian.

I see what you mean now.

In JavaScriptCore, there's no API for defining C getters and setters  
individually. There's an API for associating a set of C getters and  
setters with a class, and there's an API for defining a generic  
fallback getter and setter for a class.

I looked briefly, and it seems like it would be relatively easy to add  
an API for adding C getters and setters to a class individually. So,  
that seems like a reasonable feature request.

I'm not sure how important it is to you to be able to add C getters  
and setters to objects, as opposed to classes, individually. I think  
that would be a trickier API to get right. The main challenge is that  
getters and setters of that dynamic nature tend to slow down the  
object system. So, we would either want to engineer a way to avoid the  
performance cost in most cases, or we would want to design a way to  
steer API users away from that particular API in the general case. If  
you have a good example of how this feature would be generally useful  
to API clients, it's still a reasonable request, though.

Geoff

On Jul 20, 2009, at 10:21 AM, Brian Barnes wrote:

> In SpiderMonkey, you can create an object, and that object has a  
> callback to a getter or a setter in C.  You get the name, look it  
> up, return or set a value.  Nitro has that same functionality.
>
> On SpiderMonkey, though, when creating a property, you can also do  
> this:
>
> JS_DefineProperty(context,object,name,value,getter,setter,flags);
>
> Where "getter" and "setter" are direct calls for the property, for  
> only that property.  There's no lookup logic in my code.
>
> So, in pseudo code, at object level, we'd have a single getter:
>
> void getMyObjectValues(.... name ...)
> {
>  if (name == 'red') return(red)
>  if (name == 'green') return(green)
>  if (name == 'blue') return(blue)
> }
>
> And property level, we'd have 3 getters:
>
> void getMyObjectRed(...)
> {
> return(red);
> }
>
> void getMyObjectGreen(...)
> {
> return(green);
> }
>
> void getMyObjectBlue(...)
> {
> return(blue);
> }
>
> [>] Brian
>
> Geoffrey Garen wrote:
>> Hi Brian.
>>
>> I don't understand the distinction you're drawing between "the  
>> property level" and "the object level". Can you explain what those  
>> mean and give an example of each?
>>
>> Thanks,
>> Geoff
>>
>> On Jul 20, 2009, at 9:14 AM, Brian Barnes wrote:
>>
>>> I was getting ready to try the first move from SpiderMonkey to  
>>> Nitro, and ran into a large problem.  Right now, all my getters  
>>> and setters are at the property level.  In the documentation I  
>>> have, Nitro only seems to put them at the object level.  This  
>>> would force a huge refactoring of my code (which I'm willing to do  
>>> if I have to, I would just like to avoid it as I have hundred or  
>>> so objects.)
>>>
>>> Is my documentation old, did I miss something, or am I stuck?  If  
>>> I'm stuck, is there any call to have this put into Nitro at some  
>>> time in the future?
>>>
>>> [>] Brian
>>>
>>>
>>> _______________________________________________
>>> webkit-dev mailing list
>>> webkit-dev at lists.webkit.org
>>> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
>>
>>
>