New Twiddle

controllers.application.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  @service('currentUser') currentUser;
	constructor() {
    super(...arguments);
    this.appName = 'foo';
  }
}

services.current-user.js

import Service from '@ember/service';

export default class CurrentUserService extends Service {
  constructor() {
    super();
    this.email = '[email protected]';
  }
}

templates.application.hbs

<h1>Welcome to {{appName}}, {{currentUser.email}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0",
    "ember-decorators": "*"
  }
}