title: Instance as a static class property
body: <p>Is it possible to declare an instance of a class as a property in PHP?</p>
  
  <p>Basically what I want to achieve is:</p>
  
  <pre><code>abstract class ClassA() 
  {
    static $property = new ClassB();
  }
  </code></pre>
  
  <p>Well, I know I can't do that, but is there any workaround beside always doing something like this:</p>
  
  <pre><code>if (!isset(ClassA::$property)) ClassA::$property = new ClassB();
  </code></pre>