On Sep 11, 2013, at 7:17 AM, Tom Van Cutsem wrote:
> 2013/9/11 David Bruant <[email protected]>
> Le 11/09/2013 06:10, Boris Zbarsky a écrit :
>
> Hey all,
>
> I was looking at implementing a membrane using ES6 proxies and ran into a
> snag. Consider a situation where object A has prototype B. A' is a proxy
> implementing the membrane, whose target is A.
>
> But now if Object.getPrototypeOf(A') is invoked the return value will be B
> (unless it just throws). There's no way for A' to return a new proxy B'
> whose target is B in this situation.
> In essence yes. In practice, you can do:
> // trap:
> getPrototypeOf: function(target){
> target.__proto__ = B';
> return B';
> }
> But of course, it changes A [[Prototype]], which is probably not desirable.
> And of course, although to-be-standard, __proto__ is bad taste...
>
> Indeed, this is also the pattern I used, except it doesn't set the
> `__proto__` of the real target, but of a shadow target:
> <https://github.com/tvcutsem/harmony-reflect/blob/master/examples/membrane.js#L246>.
>
> Setting `__proto__` may be bad taste in general, but this is a case where
> using this capability is necessary.
At least if the ES6 spec. is fully implemented, Object.setPrototypeOf would be
preferable to assigning to __proto__. EG,
// trap:
getPrototypeOf: function(target){
Object.setPrototypeOf(target, B');
return B';
}
There's nothing magic about __proto__=. Both dunder proto and
Object.setPrototypeOf are defined in terms of [[SetInheritance]]. The only
difference is that the functionality of dunder protois dependent upon the
current [[Prototype]][ value of target while setPrototypeOf doesn't have that
dependency.
>
> Ps: btw, wasn't "GetInheritance" supposed to be renamed "GetPrototype"?
>
> I think we had agreement on that. Allen?
I'm willing to call them [[GetPrototypeOf]] and [[SetPrototypeOf]] to match the
trap names. I prefer avoiding a direct connotation with the [[Prototype]]
internal data property as an exotic object is not required to have one.
Allen
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