Perhaps Future should have a static Future.cancelable method (similar to
Proxy.revocable):
let { future, cancel } = Future.cancelable(function(resolver) { .. do future
stuff .. });
You would still need a means to hook cancellation, possibly by replacing cancel
to the caller:
function getJSON() {
var xhr = new XMLHttpRequest();
...
let { future, cancel } = Future.cancelable(...);
return { future, cancel: function() { cancel(); xhr.abort(); } };
}
Ron
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Brendan Eich
Sent: Tuesday, April 23, 2013 6:41 PM
To: Tab Atkins Jr.
Cc: es-discuss
Subject: Re: Futures
Tab Atkins Jr. wrote:
> On Sat, Apr 20, 2013 at 6:17 AM, Brendan Eich<[email protected]> wrote:
>> Tab Atkins Jr. wrote:
>>> It would be so nice if JS had multiple return values, so we could
>>> let cancellable future-returning APIs just return a naked resolver
>>> as their second value,
>> Hello, destructuring:
>>
>> let{ proxy, revoke} = Proxy.revocable(target, handler);
>>
>>
>> from
>> http://wiki.ecmascript.org/doku.php?id=strawman:revokable_proxies. Or use an
>> array pattern if you prefer.
>>
>> JIT'ing VMs can optimize these pretty easily to avoid object allocation.
>
> Yeah, that's fine when you're explicitly invoking something that needs
> to return two objects.
You didn't grok what I wrote. The object is erased, and the value(s) are
returned to the caller depending on the pattern it uses.
> It's less fine when you have something like a hypothetical getJSON()
> (future-returning XHR sugar), which can reasonably just return a
> future, but which we also want to make cancellable. Burdening *every*
> call site
No, you can use a smaller pattern, e.g.
let { future } = getJSON();
instead of
let { future, cancel } = getJSON();
> with the need to pull out the future from the returned object
No, see above.
> isn't great.
HTH.
/be
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