On Jan 16, 2013, at 10:53 AM, David Bruant wrote:
> Le 16/01/2013 19:42, Brendan Eich a écrit :
>> David Bruant wrote:
>>> Hi,
>>>
>>> This is an idea naturally derived of all the current discussions about
>>> WeakMaps and Private symbols. The proposal is easily summarized by these
>>> lines of code:
>>>
>>> var wm = new WeakMap();
>>> var o = {};
>>> o[wm] = 12 // desugars to wm.set(o, 12)
>>> var a = o[wm]; // desugars to wm.get(o);
>>> wm in o // desugars to wm.has(o);
>>> delete o[wm] // desugars to wm.delete(o);
>>
>> You are not showing the desugaring in general:
>>
>> function get(o,x) {
>> return o[x];
>> }
>>
>> must transform to
>>
>> function get(o,x) {
>> return (x is WeakMap) ? x.get(o) : o[x];
>> }
> You're right, I hadn't thought of that.
>
>> This is not an acceptable hit for every []-named property access.
> I intuit (and may be wrong) that even just observing types (weakmap or
> stringified type) passed to a []-access can be a good indicator of how best
> []-named property access should be JIT-compiled. You pay the price of the (x
> is WeakMap) test only the time the JIT warms up.
> Given what's in current engines, it sounds doable.
If you want to explore this area, I suggest taking a fresh look at
http://wiki.ecmascript.org/doku.php?id=strawman:object_model_reformation
Allen
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