to_string.php

<?php
class FooThing
{
  var $message = 'foo';

  function to_s() {
    return $message;
  }

  function __toString() {
    return $message;
  }
}

$foo = new FooThing();
echo $foo->to_s(); // prints "message"
('foo' == $foo->to_s()) // evaluates true

echo $foo;  // prints "message"
('foo' == $foo)  // evaluates false