Dependent Key Redundancy

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  foo: {
    bar: 'test'
  },
  
  lastUpdatedFoo: Ember.computed('foo', 'foo.bar', function () {
    return Date.now();
  }),
  
  lastUpdatedFooBar: Ember.computed('foo.bar', function () {
    return Date.now();
  }),
  
  actions: {
   	changeFoo() {
      this.set('foo', {
        bar: 'test'
      });
    },
               
		changeFooBar() {
      this.set('foo.bar', 'test2');
    }
  }
});

templates.application.hbs

<div>
  <code>'foo'</code>: {{lastUpdatedFoo}}
</div>
<div>
	<code>'foo.bar'</code>: {{lastUpdatedFooBar}}
</div>
<div>
	<button type="button" {{action 'changeFoo'}}>Change 'foo'</button>
  <button type="button" {{action 'changeFooBar'}}>Change 'foo.bar'</button>
</div>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}