Le 10/02/2012 09:23, Gavin Barraclough a écrit :
On Feb 9, 2012, at 7:18 PM, Allen Wirfs-Brock wrote:
I would expect Gavin's approach to ultimately be even worse than mine
from a semantic analysis perspective. It expose (via
Object.getOwnPropertyDescriptor) functions that have the ability to
mutate any object's [[Prototype]] property and one those functions
are exposed they can be installed as methods or explicitly called at
any time. I think that tame them is likely to have even greater
impact than what I have done. Certainly, for the ES5 language level
(which is what my current spec. addresses) there is no way to talk
about frames or the association of one of these functions or any
other object with a frame. With my approach there is no need to
match the proto mutator function's frame with the target object's
frame, because there is no mutator function.
Hi Allen,
I completely agree with you that frame-based checks should not be a
part of the solution, however they are no more necessary if __proto__
is an accessor property then if it is a data descriptor. The solution
I proposed was that the [[ProtoSetter]] should hold a private
reference to the Object Prototype upon which it is initially assigned,
and that upon being invoked it should walk the this object's prototype
chain to see if it any entry matches the stored value. With a check
such as this in place (I expect there are other ways we could achieve
this), it would not be possible to apply a given [[ProtoSetter]] to
any object other than those upon which it would initially have been
available to operate via the Object Prototype.
Maybe I'm missing something, but what you're proposing is *exactly* a
frame-based check.
By assuming there can exist several [[ProtoSetter]] and several
Object.prototype, you're implicitely saying that there are several
frames. You do not name them, but I can't see the difference between a
frame and "a context where objects inherit from a particular
Object.prototype".
What you're doing is identifying a frame to the identity of its
Object.prototype.
David
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