title: Tell if the object is instantiated in a static method?
body: <p>When calling a static method in PHP, can one tell if the method is running in an instantiated object or not?</p>
  
  <p>Something like</p>
  
  <pre><code>public static function update( $value = NULL) {
    if ( self::is_instantiated() ) {
      update_db($this-&gt;value);
    } else {
      update_db($value);
    }
  }
  </code></pre>
  
  <p>I don't want to simply test <code>! is_null($value)</code> because the method can be called publicly without passing a value.</p>
  
  <p>I tried checking <code>isset()</code> for <code>$this</code> and <code>$this-&gt;property</code>, but that didn't work in the non-object context.</p>