The __get overload method will be called on a declared public member of an object if that member has been unset.

<?php
class c {
  public $p ;
  public function __get($name) { return "__get of $name" ; }
}

$c = new c ;
echo $c->p, "\n" ;    // declared public member value is empty
$c->p = 5 ;
echo $c->p, "\n" ;    // declared public member value is 5
unset($c->p) ;
echo $c->p, "\n" ;    // after unset, value is "__get of p"
?>