Hi,
This is an idea naturally derived of all the current discussions about
WeakMaps and Private symbols. The proposal is easily summarized by these
lines of code:
var wm = new WeakMap();
var o = {};
o[wm] = 12 // desugars to wm.set(o, 12)
var a = o[wm]; // desugars to wm.get(o);
wm in o // desugars to wm.has(o);
delete o[wm] // desugars to wm.delete(o);
# Benefits
## Private symbols are out
No need for the specific freeze behavior.
No need for the unknownPrivateSymbol trap.
Unique symbols do remain though
## MarkM's hint
The use of a different syntax for a different usage would be the hint.
It's possible that both syntax will be used, but in all likelihood, only
one syntax will be used per weakmap, clearly indicating to the engine
which storage and implementation characteristics should be preferred.
Worst case, the performance of unclear code is a bit worse.
## Inheritance
Both "o[wm]" and "wm in o" could desugar to a slightly more useful
algorithm involving proto-climbing thus emulating inheritance as we know it.
var w = new WeakMap();
var o = {};
o[w] = 37;
var o2 = Object.create(o);
console.log(o2[w]); // w.has(o2) returns false, w.has(o) return
true. w.get(o); logs 37.
# Downsides
## Object.defineProperty & friends don't work with weakmap as property name
No getter/setter, no configurability, no hasOwnProperty. I see that as a
benefit actually. YMMV
It makes weakmaps-as-private-symbol inconsistent with unique symbol. I'm
also ok with this.
## Confusion?
Maybe people will be confused by this bi-use of the same feature. Maybe
the sugar will result in everyone using it and not caring of
WeakMap.prototype methods, defeating the "hint" point above.
# Open question
## What happens when the WeakMap is wrapped?
var w = new WeakMap();
var ww = new Proxy(w, {});
var o = {};
o[ww] = 12; // ww.set(o) calling the ww's set trap?
// should a/4 new trap(s) be created for internal weakmap methods?
David
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