Yeah, I don't see how it's going to happen either. Now that I get you meant dynamic as in contrary to lexical scoping having scoped object extensions seems very counter intuitive - especially given the direction the language is heading.
Thanks for the discussion. On Mon, Oct 14, 2013 at 1:36 AM, Brendan Eich <bren...@mozilla.com> wrote: > Benjamin (Inglor) Gruenbaum <mailto:ing...@gmail.com> >> October 13, 2013 2:28 PM >> >> Thanks, this really helped me understand the underlying issue here >> forcing dynamic resolution of scope here. It sounds a lot harder than I >> initially thought >> >> I have to say the fact this is so deeply rooted in the language semantics >> is somewhat surprising to me. That said, I think I see why behavioral >> typing would be act like this and I expect this to still be a lot harder >> than I imagine. >> >> > Here is a counterexample based on the strawman's syntax: >> > ... >> >> When I pass a parameter `a` to a function and call `a.where` , whether or >> not it's an extension method - don't I still have to do dynamic scope >> resolution? >> > > That's not "dynamic scope", first ("dynamic scope" refers to scoping where > an *unqualified* name's meaning cannot be determined lexically -- e.g., > with or the global object in JS; inline event handlers in the DOM). > > > Doesn't it still have to walk the prototype chain until I find `.where` - >> just like if I pass an array-like with `.splice` and send it to a method >> using it and it has to figure out it's not Array.prototype.splice? >> > > Of course. The meaning a dot-qualified name in JS indeed depends on > prototype lookup. But the parameters to that lookup procedure are the > starting (directly referenced) object and the property name -- and not the > scope in addition, or any equivalent transformation (e.g., my ?: example -- > not also it used instanceof and did not work when a direct shadowing method > existed on the array). > > > Off the top of my head - what about for the duration of the scope of >> these methods we "have a prototype right after Array.prototype" - in this >> scenario. Doesn't this make `c` go to Object.prototype.where and then >> String.prototype.select and all `b` does is another prototype chain look up >> before reaching the extension? This is probably another naive suggestion >> though. >> > > It is, if you mean dynamically altering the prototype chain of standard > objects within a lexical extent. That does create dynamic scope, since the > call graph is not statically decidable in general in JS, and calls out of > the lexical extent would see the prototype chain extension too. Even if we > could pin down the call graph, we do not want arbitrary mutations going in > and out of scope of prototype chains. > > Anyway, I think at this point we've established what is required for any > "scoped object extensions". Please draw the conclusion. > > /be >
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