Subj : Re: (Spidermonkey) Converting a property name to a tinyId
To   : James Turner <zakalawe@mac.com>
From : Brendan Eich <brendan@meer.net>
Date : Sat Mar 15 2003 10:41 am

>
>
>Well ... I have no illusions about the general aplicability of this
>function to other embedders, feel free to simply post a code snippet
>that gets the job done. Anyway, the reason I need this is I'm
>'dual-purpose'ing my property setters (and maybe getters too). I.e
>they are hooked up as 'direct' JSPropertyOps in the property
>defintions for my object. But I also want to invoke the same code
>logic in response to some other events (persistence and network
>transmission, it's a long story).
>  
>

Couldn't you use JS_GetProperty and JS_SetProperty to do the getting and 
setting from native code?  True, those have to hash the property name, 
but so would any JS_GetPropertyTinyId that takes a const char *name 
parameter.  Anyway, hashing a string is cheaper by orders than executing 
a precompiled script, which is cheaper by far in turn than compiling 
(evaluating).

Here's a more general API proposal, not meant to be used if it's not 
needed, that returns the jsval id that you would get passed into your 
getters and setters:

JSBool
JS_GetPropertyUserId(JSContext *cx, JSObject *obj, const char *name, 
jsval *idp)
{
    JSAtom *atom;
    JSObject *pobj;
    JSScopeProperty *sprop;

    if (!OBJ_IS_NATIVE(obj)) {
        JS_ReportError(cx, "can't get tinyid from non-native property 
%s", name);
        return JS_FALSE;
    }
    atom = js_Atomize(cx, name, strlen(name), 0);
    if (!atom)
        return JS_FALSE;
    if (!js_LookupProperty(cx, obj, (jsid)atom, &pobj, (JSProperty 
**)&sprop))
        return JS_FALSE;
    *idp = SPROP_USERID(sprop);
    return JS_TRUE;
}

But if you call this, then call your getter (say) directly, you're doing 
about as much work as JS_GetProperty does, for no significant gain.  For 
the setter case, you have to be sure the object has already had ad-hoc 
properties set on it, or else that you are setting only properties 
defined with the JSPROP_SHARED attribute.  Otherwise, you'll fail to 
give the particular object on which a property is being set its own map 
(scope).

So I think you should be good with JS_GetProperty and JS_SetProperty.  
Let me know if I'm missing something.

/be

.