<?php
class B {
  public function __toString() {
    return "w3cschool.cn!\n";
  }
}  

$b = new B();
$a = "w3cschool.cn!\n";
print(is_string($a) ? 'true' : 'false'); //true
print('<br/>');
print(is_string($b) ? 'true' : 'false'); //false
?>