Status: New
Owner: ----
New issue 2804 by [email protected]: Generic use of __proto__ accessor not
allowed
http://code.google.com/p/v8/issues/detail?id=2804
On v8 3.20.8.1 / Chrome v28, `__proto__` is reflected as an accessor, but
extracting the setter and calling it is prohibited:
{{{
var protoDesc =
Object.getOwnPropertyDescriptor(Object.prototype,'__proto__');
protoDesc.set.call({}, {}); // TypeError: Generic use of __proto__ accessor
not allowed
}}}
I hit this error because I'm maintaining a library that shims
Object.setPrototypeOf, a new primitive in ES6 (see
<https://github.com/tvcutsem/harmony-reflect/issues/18> for details)
My code tests whether a platform reflects `__proto__` as an accessor
property whose setter is a function and if so, uses the extracted setter to
implement Object.setPrototypeOf.
I updated my shim to take v8's throwing behavior into account, but I
wonder, since v8 supports mutable `__proto__` (by virtue of `obj.__proto__
= v` ), why disallow the generic setter? Especially as ES6 will add
`Object.setPrototypeOf` which is equivalent.
Finally, if a mutable generic setter is really undesirable, it would be
easier to feature-detect if `protoDesc.set` were set to `undefined`, which
is the standard way in which a property descriptor signals that the
property cannot be updated.
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