In our implementation we are using a generic object. It has some overhead, and a specific internal "descriptor object" representation might be a bit faster, but such magic objects that don't allow expando properties are usually pretty surprising to programers. Most of the HTML5 DOM allows arbitrary expando properties. I think we should stick to that theme.
Andreas On Jul 1, 2011, at 5:54 AM, Andreas Rossberg wrote: > 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
