On Sep 19, 2013, at 8:25 AM, Tom Van Cutsem wrote: > 2013/9/19 Brendan Eich <[email protected]> > Refactoring [[Get]]+[[Call]] to [[Get]]+[[Invoke]] seems fine by me. It > better expresses the intent, and the change should only be observable to > proxies. > > Is this so? Wouldn't an ordinary object with a getter be able to observe the > two lookups? Indeed wouldn't the spec require this? > > You're right. The change would lead to observably different behavior for > conditionally invoked getters. > > Not sure how much of a backwards compat issue that would be. Allen previously > wrote upstream in this thread: > > There are currently 6 such places (not counting the Proxy trap invocators): > 3 in ToPrimitive (ie toSrting/valueOf) > 1 in instanceof to access @@hasInstance (legacy conpat. for missing > @@hasInstance) > 1 in [ ].toString to conditionally invoke 'join' method > 1 in JSON.stringify conditionally invoke 'toJSON' > > How likely is it that these are getters with side-effects?
Seems very unlikely. The @@hasInstance access is new so it isn't a backwards compat issue. BTW, these are static counts. For example, a typical call to ToPrimitive will only make a single such conditional invoke. Arguably allowing a String or Number wrapper to be transparently proxied and hence work like a unproxied wrapper WRT ToPrimitive is one the reasons we need to do this. Allen
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