- From: Sam Tobin-Hochstadt <samth@ccs.neu.edu>
- Date: Tue, 4 Jun 2013 09:55:15 -0400
- To: Anne van Kesteren <annevk@annevk.nl>
- Cc: "Tab Atkins Jr." <jackalmage@gmail.com>, "Mark S. Miller" <erights@google.com>, Sean Hogan <shogun70@westnet.com.au>, "www-dom@w3.org" <www-dom@w3.org>, "public-script-coord@w3.org" <public-script-coord@w3.org>, Alex Russell <slightlyoff@google.com>
On Tue, Jun 4, 2013 at 9:48 AM, Anne van Kesteren <annevk@annevk.nl> wrote: > On Tue, Jun 4, 2013 at 8:55 AM, Sam Tobin-Hochstadt <samth@ccs.neu.edu> 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. Sam
Received on Tuesday, 4 June 2013 13:56:02 UTC