Re: Deprecating Future's .then()

On Tue, Jun 4, 2013 at 9:48 AM, Anne van Kesteren <> wrote:
> On Tue, Jun 4, 2013 at 8:55 AM, Sam Tobin-Hochstadt <> wrote:
>> Thinking about this more, I'm now unsure why both `fulfill` and
>> `resolve` are needed given the semantics of `.chain()` and `.then()`
>> described below.
>> In particular, if `.then()` chains recursively *before* calling the
>> callback, then there's no difference between:
>>     Future.resolve(x).then(v => ...)
>> and
>>     Future.fulfill(x).then(v => ...)
>> even when `x` is a promise.  The only way to observe this is with `.chain()`.
>> Thoughts?
> I'm just going to try to repeat what you said here to make sure I understand.
> Promise.resolve(val) creates a promise of val, regardless of whether
> val is a promise, has a callable then property, or anything like that.
> (In that sense it is equivalent to Future.accept() today.)
> promise.then() keeps unwrapping promise's internal value until it no
> longer has a callable then property at which point it invokes the
> relevant callback passed to promise.then(). (Exact algorithm TBD after
> broader agreement.)
> promise.chain() invokes its relevant callback with promise's internal value.
> promise.then() and promise.chain() return value (newPromise) is
> resolved with the return value of their callbacks after it has been
> unwrapped once.

That's exactly right.


Received on Tuesday, 4 June 2013 13:56:08 UTC