RSVP filter with promise that resolves to array

[miguelcobain]

I think it would be really beneficial if we allow the first argument of filter to be a promise, as well as an array of promises.

For example, this is possible:

RSVP.filter([1, 2, 3, 4, 5, 6], function(v) {
  return new RSVP.Promise(function(resolve) {
    setTimeout(function() {
      return v > 2 ? resolve(true) : resolve(false);
    }, 1000);
  });
}).then(function(r) {
  console.log(r);
});
//outputs [3, 4, 5, 6]

but this isn't:

RSVP.filter(Ember.RSVP.resolve([1, 2, 3, 4, 5, 6]), function(v) {
  return new RSVP.Promise(function(resolve) {
    setTimeout(function() {
      return v > 2 ? resolve(true) : resolve(false);
    }, 1000);
  });
}).then(function(r) {
  console.log(r);
});
//outputs "Error: Array Methods must be provided an Array"

Instead, I need to map to an array of promises:

RSVP.filter([1, 2, 3, 4, 5, 6].map(function(i){ return RSVP.resolve(i); }),
function(v) {
  return new RSVP.Promise(function(resolve) {
    setTimeout(function() {
      return v > 2 ? resolve(true) : resolve(false);
    }, 1000);
  });
}).then(function(r) {
  console.log(r);
});
//outputs [3, 4, 5, 6]

I think the filter function should also take a promise that eventually resolves to an array.
This would prove especially useful to Ember Data users and async relationships. One can just invoke filter as RSVP.filter(model.get('someRelationship'), ...). A simple RSVP.filter(this.store.find(...), ...) would be nice as well.

Of course, in my project I could just create a function that normalizes its arguments and then invokes the regular filter func, but I thought I should report in to make this available in core RSVP.

[stefanpenner]

This isn't a thing. Because it tries to work in the same spirit as all

[miguelcobain]

I would argue that filter is a bit higher level, i.e it would be strange to do RSVP.all(aPromiseWithArray) but not RSVP.filter(aPromiseWithArray, ...).
Actually, if I'd want the current behavior I could write:

RSVP.filter(RSVP.all(array), ...)

Much nicer than (supposing array is resolved before):

RSVP.filter(array.map(function(i){ return RSVP.resolve(i); }), ...)

even if arrow functions make this a little prettier:

RSVP.filter(array.map(i => RSVP.resolve(i)), ...)

I see filter as a "promisified" version of the regular array filter. With my suggestion, filter would accept both arguments as promises.

The bottom line is that I think filter (and possibly others) should also handle the simplest scenario which is a single promise. Converting from an array of promises to a single promise is already done by all.

However, as I said, it isn't difficult to write a solution yourself. Feel free to close the issue if you still think this is a non-issue.

[stefanpenner]

RSVP.filter(array.map(i => RSVP.resolve(i)), ...)

I'm not sure why you need this, this is the current behavior.
the first example demonstrates this.

[miguelcobain]

Oh, yes, you're right.

The thing is that this doesn't work:

this.store.find('model').then(models => {
  return Ember.RSVP.filter(models, ...);
})

Fails with Error: Array Methods must be provided an Array, possibly because RSVP's isArray isn't aware of Ember enumerables?

[stefanpenner]

Fails with Error: Array Methods must be provided an Array, possibly because RSVP's isArray isn't aware of Ember enumerables?

correct, sometime soon enumerables will become ES2015 @@iterables and RSVP Does still need to support those.

work around:

this.store.find('model').then(models => {
  return Ember.RSVP.filter(models.toArray(), ...);
});

[miguelcobain]

Great. Thank you. Sorry for my misunderstanding.

[stefanpenner]

Nice. Sorry for my misunderstanding.

no problem, we should make the switch to iterables sometime during 2.1 or 2.2 of ember

[miguelcobain]

Along with switching to ES2015 class, decorators, etc. The Ember developer experience will be hugely improved. Can't wait!