Hello Tom,
you're right I'm working with prof. Peter Thiemann.
The intention was to compare the targets not the proxy, if the
isTransparent trap is set, but your right I haven't observed your case.
But I think also the developer have to decide, if he want to
implementation the trap.
The problem of prof. Peter Thiemann is, that the Proxies aren't really
transparent and in an environment with multiple proxies for one target
he cannot compare them. I think also it would be nice to give an
alternative with an really transparent proxy. In my opinion this could
also be a new variation of proxies, but this is my opinion.
Is it eventually possible to include a check for the isTransparent trap
into the get trap to get either the target, if wanted, or the error?
At the moment I've changed the LooselyEqual and StrictlyEqual methods of
the Interpreter.cpp to get the target instead of the proxy. But after a
chat in the jsapi IRC today, I know I need to change a lot more in the
JIT to get all Fast Path cases for == and ===.
If there is a way to change only a part of the Proxy API instead, e.g.
the get trap, to get the target, if wanted. It would be really nice.
Thank you for your feedback, I hope I don't work against your opinion.
Best regards,
Andreas
Am 02.12.2013 18:10, schrieb Tom Van Cutsem:
> Hello Andreas,
>
> I'm not going to give implementation-level advice but as one of the
> designers of the Proxy API rather some high-level feedback on your
> proposal:
>
> I assume you're working with prof. Peter Thiemann who has been using
> proxies to implement contracts in JavaScript, so I think I know where
> you're coming from.
>
> Nevertheless, I'm not sure whether your goal of allowing proxies to
> intercept the '==' and '===' operators _in general_ makes much sense.
>
> Consider:
>
> var target = { x: 42 };
> var p1 = new Proxy(target, { isTransparent: function() { return true;
> } }); // a transparent forwarding proxy
> var p2 = new Proxy(target, {get: function() { throw new TypeError(); } });
>
> In this case,
>
> p1.x === 42
> p2.x // throws TypeError
>
> Yet, you want to make it possible for p1 and p2 to be identity-equal
> (if they implement your isTransparent() trap).
>
> I believe this will go against the expectations of most code, which
> assumes that if p1 and p2 are identity-equal, one should be able to
> substitute p1 for p2 without any observable difference.
>
> Is it really necessary to make a general extension to proxies to make
> your use case work?
>
> Best regards,
> Tom
>
> 2013/12/1 Brendan Eich <bren...@mozilla.com <mailto:bren...@mozilla.com>>
>
> This just came in on the SpiderMonkey internals dev list -- can
> you provide guidance? Feel free to bounce to es-discuss. Thanks,
>
> /be
>
> Begin forwarded message:
>
>> *From:* schlegel.andr...@gmail.com
>> <mailto:schlegel.andr...@gmail.com>
>> *Date:* December 1, 2013 at 11:16:56 AM GMT
>> *To:* dev-tech-js-engine-internals@lists.mozilla.org
>> <mailto:dev-tech-js-engine-internals@lists.mozilla.org>
>> *Subject:* *[JS-internals] Transparency of JavaScript Proxies*
>>
>> Hello,
>>
>> I'm a student at the university of Freiburg.
>>
>> I write my master thesis about transparency of JavaScript proxies.
>>
>> The topic is, that the proxies are not really transparent,
>> because the Equal-Operators (== and ===) compare the references
>> of the proxies and not of the targets. Also the WeakMap uses the
>> proxy as key and don't allow the target also as key, if a proxy
>> was inserted.
>>
>> First Question:
>> ---------------
>> I should implement an addition for the Proxy API in form of a new
>> Handler Trap, which says if a proxy is really transparent or not.
>>
>> The trap should look like this:
>>
>> var handler = {
>> isTransparent: function(){
>> return true;
>> }
>> };
>>
>> With this trap I should change the operators for comparing either
>> the target or the proxy, dependent of the result of the trap.
>>
>> I've implemented the following Methods for the BaseProxyHandler
>> and Proxy:
>>
>> bool
>> BaseProxyHandler::isTransparent(JSContext *cx, HandleObject
>> proxy, bool *bp)
>> {
>> return Proxy::isTransparent(cx, proxy, bp);
>> }
>>
>> bool
>> Proxy::isTransparent(JSContext *cx, HandleObject proxy, bool *bp)
>> {
>> JS_CHECK_RECURSION(cx, return false);
>> return proxy->as<ProxyObject>().handler()->isTransparent(cx,
>> proxy, bp);
>> }
>>
>> How can I integrate the new trap into the proxy?
>> I've found the "const Class js::ObjectProxyObject::class_" must I
>> do an new entry for the trap?
>>
>>
>> Second Question:
>> ---------------
>> I've found the "static JSObject *
>> proxy_WeakmapKeyDelegate(JSObject *obj)". Can I make a trap to
>> use a Proxy as key in a WeakMap but use the target to get the
>> value with this method?
>>
>> Third Question:
>> ---------------
>> Is there a documentation for the Proxy API specific to the C++
>> implementation?
>>
>> Thanks a lot
>>
>> Andreas Schlegel
>> _______________________________________________
>> dev-tech-js-engine-internals mailing list
>> dev-tech-js-engine-internals@lists.mozilla.org
>> <mailto:dev-tech-js-engine-internals@lists.mozilla.org>
>> https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals
>
>
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