Hi Tom. On 2 July 2011 13:50, Tom Van Cutsem <[email protected]> wrote: > Hi Andreas, > First, you're right about the typing issue: > In ES5, for values of type Object, the signature for [[DefineOwnProperty]] > would be: > [[DefineOwnProperty]](P: a property name, Desc: an internal property > descriptor, Throw: a boolean) > On trapping proxies, that signature would need to change to: > [[DefineOwnProperty]](P: a property name, Desc: an Object, Throw: a boolean)
I don't think such a change is consistent. [[DefineOwnProperty]] is invoked in a number of places in the spec, and I think in many of them the type of the receiver is not distinguished and may well be a proxy, so a proxy may then receive both kinds of descriptors. Moreover, I think it would be a mistake to make the appropriate case distinction everywhere -- you really want the internal method to have the same signature in all cases. > With that, I believe the strawman is otherwise internally consistent. In > [[DefineOwnProperty]] step 5, what will be passed to the user-defined > "defineProperty" trap is a proper Object, not an internal descriptor. > I did clarify the note you referred to, to be more explicit in this regard. > I don't see an alternative to changing the signature of > [[DefineOwnProperty]]. It can't just receive an internal descriptor, as it > doesn't preserve any non-standard attributes. How about simply bypassing [[DefineOwnProperty]] in Object.defineProperty for proxies, as I suggested in my reply to David? That seems to be the only place where additional objects can occur, or am I wrong? Cheers, /Andreas > 2011/7/1 Andreas Rossberg <[email protected]> >> >> On 1 July 2011 12:12, Andreas Rossberg <[email protected]> wrote: >> > I believe there is some "type" confusion in the proxy proposal spec >> > wrt property descriptors and their reification into attributes >> > objects. >> > >> > 1. In a note on the def of [[DefineOwnProperty]] for proxies, the >> > proposal says: >> > >> > "The Desc argument to this trap is a property descriptor object >> > validated by ToPropertyDescriptor, except that it also retains any >> > non-standard attributes present in the original property descriptor >> > passed to Object.defineProperty. See the semantics of the modified >> > Object.defineProperty built-in, below." >> > >> > That seems fishy, since according to ES5 8.10: >> > >> > "Values of the Property Descriptor type are records composed of named >> > fields where each field‘s name is an attribute name and its value is a >> > corresponding attribute value as specified in 8.6.1." >> > >> > In particular, I take this to mean that property descriptors are not >> > objects (but abstract records), and that there cannot be any fields >> > whose name is not an attribute name. (In fact, in V8 we currently >> > encode property descriptors using objects, but the encoding is >> > different from the reified attributes object representation, and not >> > quite compatible with the idea of adding arbitrary other fields.) >> >> I forgot to say: step 5 of the definition invokes the defineProperty >> trap of the handler passing Desc as the second argument. But the >> handler expects a reified attributes object. >> >> > 2. In the modified definition of Object.defineProperty, the proposal >> > says in step 4.c: >> > >> > "Call the [[DefineOwnProperty]] internal method of O with arguments >> > name, descObj, and true." >> > >> > This is passing descObj, which in fact is _not_ a descriptor, but its >> > reification as an attributes object. >> > >> > /Andreas >> > >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss > > _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
