title: How to tell if optional parameter in PHP method/function was set or not?
body: <p>Assume I have a method/function with the following signature:</p>
  
  <pre><code>foo($bar = 0)
  </code></pre>
  
  <p>Inside <strong><em>foo</em></strong>, how do I tell if <strong>$bar</strong> was set or not? <strong><em>isset</em></strong> will alway return a <strong><em>TRUE</em></strong> since <strong><em>$bar</em></strong> is assigned <strong><em>0</em></strong> in the event nothing is passed to <strong><em>foo</em></strong>.</p>
  
  <p>Checking for 0 is not an option. I need to know the difference between the parameter explicitly being set to 0 or defaulting to 0.</p>