Proxies: get+fn vs. invoke

Brendan Eich brendan at mozilla.com
Thu Oct 14 12:35:51 PDT 2010


On Oct 14, 2010, at 12:33 PM, Brendan Eich wrote:

> Tom, thanks for this, assuming it is an accurate reading of Dmitry's post, your reply clarifies something for me. When we bridged Java to JS in the '90s, we had to deal with Java objects having overloaded members. A member o.m could be an int field or a String -> int method, say.

I meant "int -> String" there, as later context suggests.

/be

> And methods could be overloaded to take different argument types.
> 
> We implemented something like proxies in C code, and for any overloaded field, we returned a proxy that could access the int field or call the String-returning method, depending on context. If called, we tried the method. If got or set with a number value, we accessed the field. For overloaded methods we tried disambiguated by JS actual argument type, but this could fail. There was an elaborate property name, accessibly only via o["m(i):S"] or some such (I forget the syntax), by which one could unambiguously name a specific method in the overload.
> 
> But in no case would one want the overloaded member to test as if it were not present. This may be where Dmitry parts company from us on TC39. Whatever happens, having methods appear only when invoked is a bug in our view.

> . . .


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