In Nashorn, we introduced __noSuchProperty__ as a means of overriding property
search when a property is not declared. Example;
jjs> var other = { a: 10, b: 20, c: 30 };
jjs> var obj = { delegate: other, __noSuchProperty__: function(name) { return
this.delegate[name]; } }
jjs> obj.b;
20
In the current version of Nashorn, we don't call the __noSuchProperty__ handler
when accessed using indexing. However, the question has come up as whether
this support should extend to indexing as well; providing symmetry between
property access and indexing. Thus continuing the example;
jjs> obj["b"];
20
Does this make sense to everyone?
The only argument I could come up against was using indexing for property
testing, as in;
jjs> if (obj["b"]) print(obj.b);
20
But that argument doesn't hold since there are alternatives;
jjs> obj.hasProperty("b");
false
or;
jjs> "b" in obj;
false
The reason I ask is that we have a bug where megamorphic call sites switch to
indexed access (to reduce the number of cases) and thus __noSuchProperty__ is
not invoked when it should.
If we change the behaviour, then we will provide symmetry and address the bug.
Comments?
-- Jim
