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. Allen _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
