Promises/A+

[benjamingr]

Hi, I was wondering if this implementation complies (or intends to) with the Promises/A+ specification http://promisesaplus.com/

I think this is something worth clarifying too.

Looks like really nice work by the way, good luck.

P.S
I'm also wondering why you chose to use the 'old' promise construction style (Deferred) rather than the new one (Promise constructor), thanks.

[mxcl]

Thanks for the link, the specifications I have worked off of are less good. I'll make an assessment of our compliance.

Can you provide an example of the constructor style? I used Deferred as my research had not led to another way of doing it that I felt was adequate. I'm not sure I saw this new style.

[mxcl]

So, mostly yes.

The only significant difference is PromiseKit’s then does not take an error handler, instead we have a dedicated catch handler. This was an active decision, I believe it makes code using Promises clearer.

It does make the implementation trickier, but I believe we otherwise (except where the spec is clearly Javascript specific) comply.

There are a couple of points that we don't yet implement that we should, but there are (AFAICT) for sanity checking reasons:

I'll update the README with details.

[benjamingr]

Thanks.

In JavaScript, the deferred pattern is something like

    (function(){
    var d = lib.defer();
    var foo = bar();
    someUnpromisifiedThing(function(result){
           d.resolve(result);
    });
    return d.promise()
    }).then(...

Where the "promise constructor pattern" is something like:

    (function(){
    return new Promise(function(resolve,reject){
         var foo = bar();
         someUnpromisifiedThing(resolve);
     });
     }).then(...

The big difference IMO is that with the constructor pattern, if var foo = bar() throws synchronously, the exception is caught by the returned promise's catch.

I'm not sure how this applies to objective C though.

For what it's worth, I think not supporting onRejected in .then is a perfectly reasonable design choice, I find .then(a,b) rather "confusing" compared to .catch(b).then(a).

[benjamingr]

Sorry for the late reply, great work! Good luck with this project, will definitely use the next time I write ObjectiveC code.