FAQ addition: can you explain joint & join

[dgaedcke]

I'd like to understand what they represent and how they work....
I read the reference material but that only show's how to call them...not what they actually do...

[mxcl]

The join resolves the promise.

[dgaedcke]

Why would I use join instead of just fulfill? Can you show an example?

I've also been looking for docs re: dangers/best practices for saving a pending promise in an instance variable. I have a Social login SDK that opens the Facebook App & asks the user to authenticate, and then returns the results to my AppDelegate external URL handler. It's after that callback from the URL handler that I want to either fulfill or reject my stored promise..

[mxcl]

Joint exists to replace:

let (foo, fulfill, reject) = Promise.pending()
promise.then(fulfill).catch(reject)

// with

let (foo, joint) = Promise.joint()
promise.join(joint)

So for your situation you probably want just .pending().

I'm not improving the docs on Joint as it was an experimental feature we intend to remove due to insufficient value and we have a different way to do it for PMK5.

[dgaedcke]

sure....if it's going away, I don't need to understand it....
that "pending" pattern makes much more sense to me anyway...
at least the way I've been using it....but your example is quite a bit more concise....
I think (line #2) is saying:
if "promise" succeeds, then "foo" succeeds, else "foo" fails

this teaches me something....so you can pass the completion functions any place another promise is expected.....

[mxcl]

PromiseKit 5 abandons this construct.