How about *optional* property fixing as a compromise? We could replace the configurability check of the "defineProperty" trap return value with a check of whether the return value is an object, in which case it would be treated as a property descriptor to fix the property to, otherwise the return value would just be ignored.
On Thu, Jun 16, 2011 at 4:18 AM, David Bruant <[email protected]> wrote: > Le 16/06/2011 00:53, Mark S. Miller a écrit : > > On Wed, Jun 15, 2011 at 2:10 PM, David Bruant <[email protected]> wrote: > >> >> In a way, the fixed properties proposal make proxies bicephal. For some >> inputs (property names), they plug their handler-provided MOP-brain and >> for some others, they plug a native object MOP-brain (ES5 - 8.12). These >> brains cannot communicate. This is why changing .length in the "native >> object brain" has no effect in the other brain (which handles numeric >> properties(...unless some of these are non-configurable)). And I think >> it has been said before, but there would be no logging possible for >> non-configurable properties in the context of the fixed properties >> strawman since native MOP-brain doesn't allow that. > > > Cute metaphor. But as Tom's code showed, the proxy can create fixed > (non-configurable) accessor properties whose getters and setters form a > corpus callosum ;). > > Interactions with getter/setter is already a good thing, but I think it's > not enough. ES5 offers a very fine-grained API to study objects. If we > pretend to be able to emulate arrays based on proxies, we should be able to > emulate everything including answering correctly when it comes to "is it a > data or an accessor property descriptor?". > For instance, for a data property descriptor, even if non-configurable, > "writable" can be changed from true to false (then it cannot be changed > afterward). This behavior is not possible when dealing with getter/setters. > With fixed properties Tom's code, it is not possible to change an array's > length from writable to not writable. Trying to do so would throw an error > (because the property is non-configurable and any attempt to switch from > accessor to data property descriptor throw an error (or just reject?)). > > I'd like to insist on the ability for proxies to be able to emulate native > arrays (and new ES5 Object.* API interaction in particular) especially > because currently, SpiderMonkey has a problem with redefining ".length" on > arrays. See https://bugzilla.mozilla.org/show_bug.cgi?id=598996 > I wish proxies to be able to compensate if there is such a bug (in any ES > implementation) and I need this level of spec conformance. > This discredits the current fixed properties proposal (especially the > getter/setter compensation code), I think. > > David > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > > -- Sean Eagan _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
