Why not use the identity-preserving membrane pattern?
On Mon, Dec 2, 2013 at 10:36 AM, Andreas Schlegel < [email protected]> wrote: > 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 <[email protected]> > >> 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:* [email protected] >> *Date:* December 1, 2013 at 11:16:56 AM GMT >> *To:* [email protected] >> *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 >> [email protected] >> https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals >> >> > > -- Cheers, --MarkM _______________________________________________ dev-tech-js-engine-internals mailing list [email protected] https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals
