[FEATURE] if helper inline form

[marcioj]

Adds a basic version of if helper in inline form. In the moment ids aren't support.
Bindings are supported, @mmun helped me to add it.
I added this behind a feature flag, not sure if it's needed, though.

[mixonic]

Feature flag is absolutely needed! :-)

[mmun]

I discussed a bit with Kris and we decided to want a slightly different implementation of the ConditionalStream.

Basically, we should store this._lastCondition on the stream with initial value undefined. Inside of the valueFn we will check if this.condition.value() is different from this._lastCondition. If its different, we will subscribe to the new valueStream and unsubscribe from the old valueStream (except when this._lastCondition is undefined).

[mmun]

Here's what I had in mind (I changed the variable names to match the spider monkey API):

import Stream from "ember-metal/streams/stream";
import { read } from "ember-metal/streams/read";
import { create as o_create } from "ember-metal/platform";

function ConditionalStream(test, consequent, alternate) {
  this._super(conditionalValueFn);
  this.oldTest = undefined;
  this.test = test;
  this.consequent = consequent;
  this.alternate = alternate;
}

ConditionalStream.prototype = o_create(Stream.prototype);
ConditionalStream.prototype._super = Stream;

function conditionalValueFn() {
  var test = !!read(this.test);

  if (test !== this.oldTest) {
    if (this.oldTest === true) {
      this.consequent.unsubscribe(this.notify, this);
    }
    if (this.oldTest === false) {
      this.alternate.unsubscribe(this.notify, this);
    }
    if (test === true) {
      this.consequent.subscribe(this.notify, this);
    }
    if (test === false) {
      this.alternate.subscribe(this.notify, this);
    }
    this.oldTest = test;
  }

  return test ? read(this.consequent) : read(this.alternate);
}

export default ConditionalStream;

[marcioj]

Hi @mmun, I updated the code based on your example

[mmun]

Thanks. I'm going to do a little touch up later.

[mixonic]

return value is not needed.

[mmun]

what do you mean? the return here is essential.

[mixonic]

Ah, this is a sub expression, not the if helper.

And return values now append a simple view: https://github.com/emberjs/ember.js/blob/master/packages/ember-htmlbars/lib/hooks/content.js#L13

New to me!