On Mon, Jul 19, 2010 at 2:35 PM, Allen Wirfs-Brock < allen.wirfs-br...@microsoft.com> wrote:
> > -----Original Message----- > > From: Mark S. Miller [mailto:erig...@google.com] > > Sent: Monday, July 19, 2010 2:02 PM > > > > >> Do we?? What do you think "host object" means? > > > > Objects that are not native objects. I.e., the categories are disjoint > and Garrett's > > isHostObject method is correct. > > > > Ok, I think we generally agree. "host object" as used in the ES5 spec. in > essentially all cases means "not native object". Garrett's isHostObject > test would arguably almost be valid if used within a perfectly conforming > and unextended ES5 implementation. However, a conforming implementation is > allowed to "provide additional types, values, objects,..." and such > extensions might include the use of new [[Class]] values. For example, the > JSON object is semantically a perfectly normal native object but has a > distinct [[Class]] value. If an implementation included a different but > similar extension isHostObject would classify it as a "host object". > Whether or not you are happy with that result probably depends upon your > isHostObject use case. > I agree. FWIW, I am happy with that result. By the definition of ES5 "native object", such an object is not an *ES5* native object, since it has a [[Class]] value not defined by the ES5 spec. By the note on the host object definition, it is therefore (to ES5) a host object. Perhaps Garrett's function should be renamed isES5HostObject for clarity. With that new name, I would feel comfortable using and recommending use of that function. > > The starting point of this discussion seems to be the desire to find a > reliable way to discriminate "host objects". ES5 wasn't intentionally > trying to provide such a mechanism and I don't believe that it accidently > did so. > I agree that we did not intend to provide such a discrimination mechanism. But I do think we accidentally did so. > > Allen > -- Cheers, --MarkM
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