Le 07/07/2011 18:24, David Bruant a écrit : > Le 07/07/2011 18:05, Andreas Rossberg a écrit : >> On 7 July 2011 17:58, Brendan Eich <[email protected]> wrote: >>> On Jul 7, 2011, at 8:32 AM, Andreas Rossberg wrote: >>> >>>> On 7 July 2011 16:12, David Bruant <[email protected]> wrote: >>>>>>> Derived traps as showed are written in JS for expository purposes. >>>>>>> Engines >>>>>>> will be free to optimize as they wish internally as long as the observed >>>>>>> behavior is the same. >>>>>> True, but optimizing that actually is more tricky than you might >>>>>> think, since in general it would change the semantics if an engine >>>>>> decided to call toString only once. It has to make sure that none of >>>>>> the names are objects, or at least none of their toString methods was >>>>>> modified and they are all free of side effects. >>>>> Interesting. >>>>> However, I'm not sure side-effects are a problem. >>>>> ----- >>>>> var o = {a:1, toString:function(){o.b = 12; return 'a'; }}; >>>>> console.log(o[o], o.b); // 1, 12 on Firefox 5 >>>>> ----- >>>>> Here, o[o] triggers a side effect and that sound like the normal behavior. >>>> I'm not sure I understand what your example is intended to show. But >>>> consider this: >>>> >>>> var i = 0 >>>> var o = {toString: function() { ++i; return "a" } >>>> var p = Proxy.create({getOwnPropertyNames: function() { return [o] }, ...}) >>>> var k = Object.keys(p) >>>> // What's the value of i now? >>> Fresh tracemonkey tip js shell: >>> >>> js> var i = 0 >>> js> var o = {toString: function() { ++i; return "a" }} >>> js> var p = Proxy.create({getOwnPropertyNames: function() { return [o] }, >>> getOwnPropertyDescriptor: function() { return >>> {value:42} }}) >>> js> var k = Object.keys(p) >>> js> i >>> 1 >>> >>> Where would there be a double-conversion? >> Well, with the canonical fix to the spec we discussed further up the >> thread (adding a conversion to string in the default trap for `keys') >> there would (have to) be. So my concern was that that is perhaps not >> the best fix, despite its simplicity. > No, with the current keys default trap (calling > this.getOwnPropertyNames()) there is no double conversion. Only one at > the exit of the keys trap. There would be 2 conversions if the "keys" > trap had the proxy argument (based on > http://wiki.ecmascript.org/doku.php?id=strawman:handler_access_to_proxy) > and if internally, the default keys trap was calling > "Object.getOwnPropertyNames(proxy)" (which would call the trap and do > type coercion). > > But the current implementation and a type coercion only when going out > of traps would do double-conversion. "not". "would not do double-conversion", sorry.
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