title: Use static variables in Laravel Facades
body: <p>I have a Facade (in this case a singleton) and I register it using a <code>ServiceProvider</code>:</p>
  
  <p><strong>Service Provider</strong></p>
  
  <pre><code>use App;
  
  class FacilityServiceProvider extends ServiceProvider 
  {
  
      public function register()
      {  
          $this-&gt;app-&gt;singleton('Facility', function(){
              return new Facility();
          });
  
          // Shortcut so developers don't need to add an Alias in app/config/app.php
          $this-&gt;app-&gt;booting(function()
          {
              $loader = \Illuminate\Foundation\AliasLoader::getInstance();
              $loader-&gt;alias('Facility', 'CLG\Facility\Facades\FacilityFacade');
          });
      }
  }
  </code></pre>
  
  <p><strong>Facade</strong></p>
  
  <pre><code>use Illuminate\Support\Facades\Facade;
  
  class FacilityFacade extends Facade {
  
      /**
       * Get the registered name of the component.
       *
       * @return string
       */
      protected static function getFacadeAccessor() { return 'Facility'; }
  }
  </code></pre>
  
  <p>Now, I want to have static variables inside my <code>Facility</code> class:</p>
  
  <p><strong>Facility.php</strong></p>
  
  <pre><code>class Facility
  {
      public static $MODEL_NOT_FOUND = '-1';
  
      public function __construct() { ... }
  }
  </code></pre>
  
  <p>but when I use <code>Facility::$MODEL_NOT_FOUND</code>, I get <code>Access to undeclared static property</code>.</p>
  
  <p>What am I doing wrong? </p>