title: Determining, if a variable is a valid closure in PHP
body: <p>Using the following function:</p>
  
  <p><code>function is_closure($t) { return ( !is_string($t)  &amp;&amp; is_callable($t)); }</code></p>
  
  <p>Can this return true for anything else, than an anonymous closure function? If so, what would be the correct way to determine, if a variable is a closure?</p>
  
  <p>Many thanks</p>