Subj : Re: [SpiderMonkey] Confused about class property
To   : Peter Paulus
From : Brendan Eich
Date : Fri Oct 07 2005 10:37 am

Peter Paulus wrote:
> Brendan Eich wrote:
> 
>> Peter Paulus wrote:
>>
>>>
>>>
>>> Not just to start a monologue, I've disassembled the javascript:
>>>
>>> var x = ColorSpace.lab;
>>>
>>> into:
>>>
>>> 00000:   0  defvar "x"
>>> main:
>>> 00003:   0  bindname "x"
>>> 00006:   0  name "ColorSpace"
>>> 00009:   0  getprop "lab"
>>> 00012:   0  setname "x"
>>> 00015:   0  pop
>>>
>>> So I guess it must be the interpreter that turns ColorSpace into a 
>>> Function object, rather than an 'ColorSpace' object.
>>>
>>> Are there flags on my JSClass struct or otherwise to manipulate this 
>>> behavior?
>>
>>
>>
>> If you don't want your call to JS_InitClass to bind a constructor to 
>> the class name in the global object, pass null for the |constructor| 
>> formal parameter.  Then the class name will denote a prototype object 
>> of your class, containing the properties and methods (not the static 
>> properties and methods) you specify.
>>
>> /be
> 
> I'm not sure I want to bind a constructor. I've looked at the 
> constructor as a convenient place to bind private data to an object 
> (JS_SetPrivate()).


Sure.


> Up till now I've been passing the constructor function to JS_InitClass() 
> and was still able to handle JSBool getClassProperty(JSContext*, 
> JSObject*, jsid, jsval*) for any class. This has worked fine, since 
> every JSClass pointed to it's own static JSBool 
> getClassProperty(JSContext*, JSObject*, jsid, jsval*) function. 


That signature looks like JSObjectOps.getProperty, not 
JSClass.getProperty (note the jsid third argument).  Are you talking 
about JSClass here, or JSObjectOps?


> Implicitely, when this function is called, you know for which class this 
> is. There was never a need to examine the JSObject* in this case. Based 
> on the id I could return an appropriate result.


This is true of instance properties, not of "class static" properties of 
the constructor.


> In my current project I'm trying to build classes dynamically in 
> SpiderMonkey from Adobe InDesign's ExtendScript, in order to use their 
> native objects from Spidermonkey. In this setup I have exactly one 
> static method: JSBool getClassProperty(JSContext*, JSObject*, jsid, 
> jsval*) to serve all classes. Now I was suprised to find that JSObject* 
> pointed to a "Function" object.


That's what a constructor object is, though.


> If I omit the constructor function with JS_InitClass() indeed the 
> getClassProperty() contains the right kind of object. But then I have 
> lost my place to augment a JSObject with my private data.
> 
> Can you advise me of a suitable place to add private data to a JSObject?


Use constructors for that.

You need to show actual code.  It's not clear how you were using 
getClassProperty for all classes, or whether it was a JSObjectOps hook 
or a JSClass hook, or why you couldn't use the static property specifier 
argument to JS_InitClass.

/be

.