On 22.8.09 14:00 , Allen Wirfs-Brock wrote:
15.2.3.7 Object.defineProperties “atomic†processing clarified.
This still needs further clarification on how to address definition of properties on
objects with custom [[DefineOwnProperty]] hooks, as earlier alluded to by David-Sarah
Hopwood. I think a restriction on what custom definitions of [[DefineOwnProperty]] may
do is in order, so that atomicity can actually be implemented; I'm not sure what that
restriction should be, precisely. Simply saying [[DefineOwnProperty]] must not have side
effects would directly contradict the JSClass.addProperty hook in SpiderMonkey by which
property definitions may be "censored", such that the value that was set can be
changed by the hook. I don't know whether this is a problem inherent to any DOM
properties, but I would be surprised if it isn't. On the other hand, this hook supports
arbitrary actions, which seem entirely out of the question as supportable. (I'm
considering an ex post facto restriction that the only immediately observable side effect
must be a modification of the property's value
as an immediate stopgap. This would allow observable side effects after Object.defineProperties returns, but I care about this only insofar as it makes partial rollback impossible to implement, and this invalidates as little previously-permissible hook behavior as possible.)
In any case, featureful implementations which in one form or another support
modification of the effective behavior of [[DefineOwnProperty]] can't really
implement Object.defineProperties as currently written, not without violating
the atomicity requirement or making assumptions about potential custom
behaviors.
Jeff
_______________________________________________
es-discuss mailing list
[email protected]
https://mail.mozilla.org/listinfo/es-discuss
