2009/11/2 Brendan Eich <[email protected]>: > On Nov 2, 2009, at 10:47 AM, Mike Samuel wrote: > >> What do getters and setters do around with? >> >> var flipFlop; >> with ({ get test: function () { return (flipFlop = !flipFlop) ? >> 'flip' : 'flop'; } }) { >> for (var i = 0; i < 10; ++i) { alert(test); } >> } >> >> The with block invokes NewObjectEnvironment with O being the binding >> object. >> But I'm unclear on whether line 4 in GetBindingValue below would >> invoke a getter. > > It ought to, because ES3 with anything like getters, including a native or > host object cooperating [[HasProperty]] and [[Get]] implementations -- but > also Mozilla's getter and setter implementation of ten years' standing, > would invoke the getter. > > ES3 spec sections are 12.10, 10.1.4, and 11.1.2 which feeds into GetValue > when the Identifier is used as a rvalue; GetValue does call [[Get]]. > > Indeed ES5 is correctly compatible with ES3 + getters or internal > [[HasProperty]]/[[Get]] implementations. > >> 10.2.1.1.4 GetBindingValue(N,S) >> The concrete Environment Record method GetBindingValue for declarative >> environment records simply >> returns the value of its bound identifier whose name is the value of >> the argument N. The binding must already >> exist. If S is true and the binding is an uninitialized immutable >> binding throw a ReferenceError exception. >> 1. Let envRec be the declarative environment record for which the >> method was invoked. >> 2. Assert: envRec has a binding for N. >> 3. If the binding for N in envRec is an uninitialized immutable binding, >> then >> a. If S is false, return the value undefined, otherwise throw a >> ReferenceError exception. >> 4. Else, return the value currently bound to N in envRec. >> === end quote === > > Wrong section. The concrete type of envRec for a 'with' statement is an > object environment record, so you want: > > 10.2.1.2.4 GetBindingValue(N,S)
Ah thanks. > The concrete Environment Record method GetBindingValue for object > environment records returns the value of its associated binding object‘s > property whose name is the String value of the argument identifier N. The > property should already exist but if it does not the result depends upon the > value of the S argument: > > 1. Let envRec be the object environment record for which the method was > invoked. > 2. Let bindings be the binding object for envRec. > 3. Let value be the result of calling the [[HasProperty]] internal method of > bindings, passing N as the property name. > 4. If value is false, then > a. If S is false, return the value undefined, otherwise throw a > ReferenceError exception. > 5. Return the result of calling the [[Get]] internal method of bindings, > passing N for the argument. > > /be _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
