PHP 객체 비교

<?php
function bool2str($bool)
{
    if ($bool === false) {
        return &#39;FALSE&#39;;
    } else {
        return &#39;TRUE&#39;;
    }
}
function compareObjects(&$o1, &$o2)
{
    echo &#39;o1 == o2 : &#39; . bool2str($o1 == $o2) . "\n";
    echo &#39;o1 != o2 : &#39; . bool2str($o1 != $o2) . "\n";
    echo &#39;o1 === o2 : &#39; . bool2str($o1 === $o2) . "\n";
    echo &#39;o1 !== o2 : &#39; . bool2str($o1 !== $o2) . "\n";
}
class Flag
{
    public $flag;
    function Flag($flag = true) {
        $this->flag = $flag;
    }
}
class OtherFlag
{
    public $flag;
    function OtherFlag($flag = true) {
        $this->flag = $flag;
    }
}
$o = new Flag();
$p = new Flag();
$q = $o;
$r = new OtherFlag();
echo "Two instances of the same class\n";
compareObjects($o, $p);
echo "\nTwo references to the same instance\n";
compareObjects($o, $q);
echo "\nInstances of two different classes\n";
compareObjects($o, $r);
?>

Two instances of the same class
o1 == o2 : TRUE
o1 != o2 : FALSE
o1 === o2 : FALSE
o1 !== o2 : TRUE
Two references to the same instance
o1 == o2 : TRUE
o1 != o2 : FALSE
o1 === o2 : TRUE
o1 !== o2 : FALSE
Instances of two different classes
o1 == o2 : FALSE
o1 != o2 : TRUE
o1 === o2 : FALSE
o1 !== o2 : TRUE