Thanks! I forgot about unwrapping.
> On 22 Nov 2015, at 00:32, Mark S. Miller <[email protected]> wrote: > > Answering the question in the subject line, no. The key is the difference > between a standalone proxy and a membrane. With a membrane, the key is that > the: > > * Countdown class > * Countdown.prototype > * Countdown.prototype.dec > * instances of the Countdown class > * the WeakMaps used by the Countdown class to store it private state > (_counter, _action) > > are all on one side of the membrane. As is conventional, let's call that the > wet side, and the other side the dry side. Say both a Countdown instance c > and the WeakMap _action get passed through the membrane. Let's name the > corresponding dry proxies dry_c and dry_action. If, on the dry side, someone > does > > dry_action.get(dry_c) > > then this would trap on dry_action, passing dry_c back through the membrane, > resulting in the dry_action handler performing, on the wet side > > const r = _action.get(c) > > The wet result, r, of this invocation would get passed back through the > membrane, leading to the original expression returning dry_r. > > Alternatively, let's say that someone on the dry side does > > dry_c.dec() > > This traps on dry_c, which looks up c's inherited "dec" method, passes that > back through the membrane, resulting in a dry_dec proxy for that method. When > that is invoked with dry_c as its this, it traps, invoking the wet dec method > with c as its this. > > Conclusion: it all works fine. > > > On Sat, Nov 21, 2015 at 3:02 PM, Axel Rauschmayer <[email protected] > <mailto:[email protected]>> wrote: > Take, for example, the following class, which uses WeakMaps for its private > data: > > ```js > let _counter = new WeakMap(); > let _action = new WeakMap(); > class Countdown { > constructor(counter, action) { > _counter.set(this, counter); > _action.set(this, action); > } > dec() { > let counter = _counter.get(this); > if (counter < 1) return; > counter--; > _counter.set(this, counter); > if (counter === 0) { > _action.get(this)(); > } > } > } > ``` > > If you wrap an instance of `Countdown` with a revocable Proxy (e.g. when it > is returned by a method inside a membrane) that resets its private state, > because its `this` changes. > > Right? If yes then I’d expect that to cause problems for code that uses > WeakMaps for private data. -- Dr. Axel Rauschmayer [email protected] rauschma.de
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