Err I take it back. They can be implemented in terms of private symbols, but every access has to be guarded with a hasOwn check which would be observable to a Proxy.
On Sunday, January 20, 2013, Brandon Benvie wrote: > On Sunday, January 20, 2013, Allen Wirfs-Brock wrote: >> >> I'm not sure if you are getting at something other than what I've >> described above. If a @@DateValue private symbol is actually used as the >> implementation of [[DateValue]] then actuality that would happen. >> > > I explored implementing [[DateValue]], [[NumberValue]], etc. as symbols > e.g. @@DateValue, but this causes observably different behavior from what > is specified with a.) inheritance, and b.) interaction with proxies. > > Object.create(new Date).getDate(); // works but is specified to not > work > > new Proxy(new Date, {}).getDate(); // works but is specified to not > work > > Since Proxy is new in ES6 this of course can still be fixed, but to make > the first case work would be a (probably benign) backward incompatible > change and isn't going to work cross-engine unless the spec is changed to > explicitly allow/require it. >
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