<?php
class BaseClass
{
    public function myMethod()
    {
         echo "BaseClass method called";
    }
}
?
class DerivedClass extends BaseClass
{
      public function myMethod()
      {
           echo "DerivedClass method called";
      }
}
?
function processClass(BaseClass $c)
{
      $c->myMethod();
}
?
$c = new DerivedClass();
processClass($c);? 
// // $c->myMethod();
?>