callfunc関数、および関数伝達値

<?php

function foo()
{
      echo "
foot()";
}

function callfunc($x, $y='')
{
      if($y == '')
      {
            if($x == ''){
                echo "
empty";
            }else{
                $x();
            }
      }else{
            $y->$x();
      }
}

class cbar
{
     public function fcatch()
     { 
        echo "
fcatch";
     }

}

$x = '';
callfunc($x);  //empty

$x = "foo";
callfunc($x);  //  foot()    

$o = new cbar();
$x = 'fcatch';
callfunc($x, $o);  //fcatch
?>