Hi Allen,
On Jan 29, 2012, at 4:25 PM, Allen Wirfs-Brock wrote:
> There are no rules that constrain [[Put]] in this manner you are suggesting.
Sorry, perhaps my comments were unclear. The observation I was intending to
highlight was only that the current behaviour of [[Put]] will be to call
[[DefineOwnProperty]] on a base object that is not the object that logically
contains the 'magic' property, if the __proto__ is specified as a data
descriptor.
E.g.
> Object.prototype.__p__ = 1;
> var a = {};
> a.__p__ = 2;
The [[Put]] of '2' will call the [[DefineOwnProperty]] trap of 'a', not the
object that currently contains a data descriptor for __p__.
Hence (as I think you recognize in your comments), it would not simply be
sufficient to provide an overridden implementation for [[DefineOwnProperty]]
for the object prototype. This does mean that the 'magic' behaviour cannot be
as easily and cleanly encapsulated as it can for Array, where the 'magic'
properties are directly on the base object passed to [[DefineOwnProperty]].
> This seems like a perfectly reasonable way to specify this. As __proto__
> does indeed affect the property access semantics for every object. Of
> course, I'm only talking specification. How you accomplish it in your
> implementation is up to you.
>
> There are other, alternatives.
I'm not questioning for a minute that this is possible – it certainly is – I'm
just stating that it seems to be completely unnecessary, confusing, and not a
good idea to do so. :-) Seriously, why are we doing this? – __proto__ is an
accessor, it's much simpler to just spec it as such, why are we trying to set
up hoops for ourselves to jump through to avoid doing so?
cheers,
G.
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