ES6 doesn't need opt-in

Herby Vojčík herby at
Tue Jan 10 12:07:22 PST 2012


so I looked up the spec. I never remembered the exact [[Put]], [[Get]] 
machinery but now it is obvious that ES has in fact "amalgamate" mental 
model of "shared-part always-use-setter-for-assignment having shadowing 
default setter" (well, I figured that out before looking at spec by just 
reverse engineering actual state, but then I looked up). So, really, is 
not an error. But so is not the Object.defineProperty that is able to create 
own property. Assignment is assignment, setting own property is different, 
low-level thing. At least as I see it.


P.S.: I would bet 99% of developers thinks the model is in fact "fallback 
delegation". :-/ It is simpler model that works most of the time. Always 
write locally, always read locally and then look up the prototype chain.

-----Pôvodná správa----- 
From: Herby Vojčík
Sent: Tuesday, January 10, 2012 6:39 PM
To: John J Barton
Cc: Mark S. Miller ; Brendan Eich ; es-discuss Steen
Subject: Re: ES6 doesn't need opt-in


So, to sum, either we have "self shared part" mental model, in which foo.x
is shared part of bar.x, but then you _cannot_ have "own" shadowing
preoperties and plain "bar.x = 5" behaviour of current implementations is
or we have "own overlaying properties with property chain search" (which I
dubbed "fallback delegation") mental model, in which bar.x = 5 make perfect
sense, but alas not only in writable foo.x scenario, but every time (even if
foo.x does not exist or if foo.x is read-only), so prohibiting it for
read-only foo.x is inconstitency.

So, we have inconsistency anyway, the question is which one to fix (and I am
pretty sure not the first one).


P.S.: Yes, you can construct a complicated mental model amalgamate, like
"shared part with explicit allowance for per-child-subtree-shadowing". Let
someone like Allen or Brendan tells exactly what is the mental model, then.
It seems none of simple, consistent models of "shared part" or "fallback
delegate" is true.

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