Membranes need shadow targets, because of non-extensibility of objects and non-configurability of properties. This special case of no-invariants-anywhere is not JavaScript. Trying to do membranes without shadow targets is a useless exercise.
On Thu, Sep 12, 2013 at 8:03 AM, David Bruant <[email protected]> wrote: > Le 12/09/2013 15:35, Mark S. Miller a écrit : > > On Thu, Sep 12, 2013 at 4:14 AM, Tom Van Cutsem <[email protected]>wrote: > >> [+markm, allenwb] >> >> But more generally, you're right that it's odd [[GetInheritance]] is >> doing an invariant check on an otherwise extensible/configurable object. I >> think it's simply a remnant of the time before we fully embraced >> setPrototypeOf. >> > > agreed > > >> >> Now that Object.setPrototypeOf is part of ES6, there doesn't seem to be >> a point in guaranteeing the stability of Object.getPrototypeOf for >> extensible objects. >> >> The important invariant is that getPrototypeOf remain stable for >> non-extensible objects. >> >> Hence, it seems we could replace steps 8-10 of Proxy.[[GetInheritance]] >> <https://people.mozilla.org/%7Ejorendorff/es6-draft.html#sec-9.3.1> with: >> >> 8. Let extensibleTarget be the result of IsExtensible(target). >> 9. ReturnIfAbrupt(extensibleTarget). >> 10. If extensibleTarget is true, then return handlerProto. >> // steps below identical to the old steps 8-10: >> 11. Let targetProto be the result of calling the [[GetInheritance]] >> internal method of target. >> 12. ReturnIfAbrupt(targetProto). >> 13. If SameValue(handlerProto, targetProto) is false, then throw a >> TypeError exception. >> >> Mark, Allen, does that seem right? >> > > yes. > > Based on this new fresh agreement and assuming it sticks, the answer to > Boris initial question changes a bit then: > if B.isPrototypeOf(A) and A' = new Proxy(A, handler), then the > handler.getPrototypeOf can return any object (including B', a > membrane-proxy to B) as long as A is extensible. If the code that runs > against your membrane is not expected to be allowed to change > extensiveness, you don't need a shadow target. > > David > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > > -- Cheers, --MarkM
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