On Dec 7, 2013, at 11:26 AM, Mark S. Miller wrote: > On Sat, Dec 7, 2013 at 10:45 AM, Tom Van Cutsem <[email protected]> wrote: > As currently specified, [[OwnPropertyKeys]] doesn't have any particular > invariants on the values it generates from the returned iterator. > > Mark and I proposed to reintroduce [[GetOwnPropertyNames]] as a separate > internal method, which would return an array rather than an iterator, but > which would also be required to return at least the names (symbols or > strings) of all non-configurable properties. The switch to an array return > value is motivated partly by the reasons Jason stated, but also because > actually checking the invariant requires exhausting the iterator anyway. > > [[OwnPropertyKeys]] would continue to return an iterator (or iterable , as > Jason suggests, which seems to make more sense), but there would be no > invariants on its generated values. > > [[GetOwnPropertyNames]] would be the reliable way of querying an object for > its own properties, and would be used at least by Object.getOwnPropertyNames > and the abstract operations used by Object.{freeze,isFrozen,seal,isSealed}, > so that the result of these operations can in turn be made reliable. > > Hi Tom, when we talked I think we overlooked something crucial. The > requirement as stated, "return at least the names (symbols or strings) of all > non-configurable properties", is not actually sufficient for freeze, > isFrozen, etc. We must additionally state that, if the object has been > observed to be non-extensible, then it may not afterwards claim to have any > own properties not observed by [[GetOwnPropertyNames]]. Without this > additional requirement, a non-extensible object can "hide" non-configurable > own properties from freeze, isFrozen, etc. >
If the primary motivation is to ensure the integrity of freeze (and seal??) then a [[Freeze]] mop operations seems like a better solution to me. BTW, this seems like old territory, at one time we had a [[SetIntegrity]] mop operation that could be used to implement both Object.freeze and Object.seal. Why did we get rid of it? Allen
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