Benjamin (Inglor) Gruenbaum <mailto:ing...@gmail.com>
October 13, 2013 11:00 AM
Brendan Eich<bren...@mozilla.com <mailto:bren...@mozilla.com>> wrote:
> No, object detection, polyfilling, and even "prollyfilling" are
common and successful adaptationsp on the Web.
Polyfilling is great _after_ the method has already been added to the
spec.
Prollyfilling is great too (perhaps you disagree?), and as its name
suggests it happens *before* the method is added to the spec.
I'm completely fine with adding an Array.prototype.map shim to IE8,
the problem with adding a method that's not on the prototype yet is
that it'll fail in case the spec is different from the implementation
I chose. If you mentioned PrototypeJS, its `.bind` method is one such
example.
How exactly did that example "fail"? The differences in detail hardly
matter; PrototypeJS trod a cow-path that ES5 paved. Most users don't
worry about the edge case differences.
> Your subject recalls a defunct proposal to add lexically-scoped but
heap-based -- therefore object property-lookup performance hindering
-- extension properties.
I have to say this surprises me, a performance issue is the last thing
I expected. What about attaching a prototype as a closure variable,
something (and this is a syntax I __don't__ like) like:
```
(function(use Array){
Array.prototype.contains = function() { ...
...
// any code here has access to .contains, code that did not
originate here does not have such access, much like a closure.
// other code is free to use Array without any collisions.
})()
```
Again, I __don't__ like this sort of syntax and I'm __not__ sure about
the semantics here, I just noticed I have this problem - I'm probably
not the most qualified for coming up with the solution out of the
amazing minds right here.
Don't worry about syntax yet. The issue in any such semantic extension
is the required extra lookup parameter: not just contains on the right
of dot, but the enclosing closure scope.
Unqualified identifiers (ones not used after dot) indeed require lookup
via closure environments, to the global (let's ignore 'with' and DOM
inline event handlers).
Dot-qualified identifiers and equivalent bracketed computed property
name accesses require prototype chain lookup.
No matter the syntax, and independent of details of how one specs it,
you're proposing a hybrid of the two schemes. This must cost, and it
does cost.
/be
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