On Jul 20, 2009, at 11:48 AM, Brian Barnes wrote:
I'm not sure you get exactly what I'm saying as you put class in
places where I'd expect property. For instance:
"
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. "
Replacing class with property is what I'd expect here, i.e., each
property set on an object has it's own getter and setter. Something
like:
void JSObjectSetPropertyWithCallback
(ctx
,object
,propertyName
,value,getterFunction,setterFunction,attributres,exception);
Also I'm a little worried about the word "dynamic", these are
definitely static. I have all the functions created, you just have
a pointer to them. If the pointer exist, call it for the value and
break out. If it doesn't, go down the chain. More pseudo code:
From the point of view of the runtime any property with a getter/
setter is dynamic -- they can't be optimised.
void main(...)
{
obj=JSObjectMake(ctx,NULL,NULL);
JSObjectSetPropertyWithCallback(ctx,obj,"red",JSValueMakeNull
(),myRedGetter,myRedSetter,attributes,exception);
}
JSValueRef myRedGetter(...ctx...object...exception)
{
return(JSValueMakeNumber(red_value));
}
bool myRedSetter(..ctx..object..value..exception)
{
red_value=JSValueToNumber(ctx,value,exception);
}
Here are the benefits (as I see them):
1) I don't need to define classes for objects; right now, the only
reason I would need to create classes (instead of just passing NULL)
is to setup the getters & setters. This reduces workload and
generalizes a lot of my code
However it takes more memory, the class based properties are
effectively what are used for the DOM, eg. the getters and setters are
defined on a prototype object that is shared among all instances of
the class.
2) The JS engine has already looked up the property by name; with
class based getters/setters, I also have to lookup the property by
name. With property based getters/setters, it's only looked up once
and directly called to me. This should be a big savings win and
should be more simple at the back end (if there's no getter/setter
associated with a property, just skip forward down the chain.)
I'm not sure how this could be anything but faster then class-based.
If you're using getters and setters you've already destroyed
performance as getters and setters aren't optimisable so the
additional cost is likely to be irrelevant. Additionally the per-
object instances of the getter/setter function is likely to increase
memory usage and gc pressure, both of which could actually hurt
performance.
Note: I'm not saying this isn't a reasonable feature request, i'm just
trying to emphasise that getters/setters are expensive, and
performance characteristics are hard to guess without actually
measuring.
In the mean time you could work around this API deficiency by creating
a function object and then manually calling __defineGetter__, etc to
set up your getter/setter code.
--Oliver
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