On Nov 21, 2012, at 12:42 PM, Tom Van Cutsem wrote: > 2012/11/21 Mark S. Miller <erig...@google.com> > On Wed, Nov 21, 2012 at 8:55 AM, Allen Wirfs-Brock > <al...@wirfs-brock.com> wrote: > > [...] Essentially we could internally turn the [[Extensible]] internal > > property into a four state value: open,non-extensible,sealed,frozen. [...] > > First, my apologies for not yet finding the time to catch up on this > thread. But I did want to encourage this particular idea. We may not > be able to make this work out, but it would have many benefits if we > could. For example, the "isFrozen" check in the Object.observe API > would make more sense if this were a simple state rather than a > pattern check. More later... > > A lot of the complexity of the current invariant checks derives from the fact > that Javascript objects have (too) fine-grained invariants (i.e. > non-configurability at the level of individual properties, non-extensibility > at the level of the object, and all possible combinations in between). This > means we have to account for weird cases such as a non-extensible object with > all but 1 property being non-configurable (an "almost-frozen" object). > > If JS objects could be in only one of four states, things would be a lot > simpler to reason about. That said, I don't see how we can get there without > radically breaking with ES5's view of object invariants.
Of course, I don't necessarily agree that ES5 has such a view of object invariants... ;-) However, everything we currently have in ES5 maps to one of those fours states. Do you actually care very much, form a reasoning perspective, about a open object with some non-configurable properties. Or an non-extensible object with with some configurable properties? Overall, I think having the four states makes the conceptual model clearer and might guide us in cleaning up the MOP. Allen > > Cheers, > Tom
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