Array Computed without arrayComputed?

controllers.application.js

import Ember from 'ember';

const { computed, get, set } = Ember;

export default Ember.Controller.extend({
  appName:'Ember Twiddle',
  parts: computed('appName', {
    get() {
      return get(this, 'appName').split(' ');
    },
    set(key, value) {
      Ember.Logger.log('Setting parts...', arguments);
      set(this, 'appName', value.join(' '));
      return this;
    }
  }),
  newPart: '',
  actions: {
    add(part) {
      get(this, 'parts').addObject(part);
      set(this, 'newpart', '');
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
<ul>
	{{#each parts as |part|}}
  	<li>{{part}}</li>
  {{/each}}
</ul>
<br>
<br>
{{input value=newPart}}
<button {{action "add" newPart}}>Add Name Part</button>
<br>
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.4.7",
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.6/ember.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/1.13.7/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.6/ember-template-compiler.js"
  }
}