On Tue, Sep 10, 2013 at 8:35 PM, Allen Wirfs-Brock <[email protected]>wrote:
> > On Sep 10, 2013, at 10:45 AM, Jason Orendorff wrote: > > > On Tue, Sep 10, 2013 at 11:11 AM, Allen Wirfs-Brock > > <[email protected]> wrote: > >> Having to create a new bound function on every method call seems too > expensive. > > > > Only for proxy method calls, and it's easily optimized away in the > > default case (i.e. there is no .getMethod handler method). > > > > (As an aside, exchanges like the above have gotten so frequent they > > are beginning to feel a bit pro forma. I don't mean to sweep all > > performance concerns into one pile here.) > > > >> But what about: > >> > >> 6. Let method = O.[[Get]](P). > >> 7. ReturnIfAbrupt(method). > >> 8. If IsCallable(method) is false, throw a TypeError. > >> 9. Return O.[[InvokeFunction]](method,O, args). > >> > >> Using [[InvokeFunction]] the Proxy still mediates the [[Call]] to > method but it is assume the [[Get]] step has already been performed and has > produced method. > > > > This is appealing. There are a few things [[GetMethod]] can do that > > this can't: [[InvokeFunction]] can't be used to make a proxy that > > mimics the behavior of __noSuchMethod__, for example. I don't think it > > can mimic ActionScript 3 Proxy.callMethod either. > > Well, we didn't have those capabilities before we added [[Invoke]] and > neither were primary use cases that motivated [[Invoke]]. > > > > > If [[InvokeFunction]] is deemed powerful enough, I'm all for it. > > > > I was thinking we might only need to have [[InvokeFunction]] but if we had > both it and [[Invoke]] then then we'd only have we'd only those those > capability in situations that required a conditional invoke. However, that > would still create an anomalous edge case, for example toJSON not > triggering a __noSuchMethod__ emulator. Should it? > > I'm beginning to like a conditional option on [[Invoke]]. > > Consider: [[Invoke]](P, ArgumentsList, Receiver, conditional=false) > > If conditional is false, it works just like the current [[Invoke]] spec. > > If conditional is true and the [[Get]] value is not callable (this > includes undefined for a missing property) result is: [false, [[Get]] > result]. > if conditional is true and the [[Get]] value is callable, result is [true, > value returned from [[Call]] > > The conditional form would only be used in odd cases like the toJSON call. > > ES code can accomplish the same thing via Reflect.invoke with true as the > 4th argument. > > I like it. This gets around the issue of distinguishing a return value of `undefined` from "no callable property with that name found" and would be easy to implement for proxies, too.
_______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
