All animals are ==, but some animals are === than others.

Equality comparators work differently when it comes to types. Arrays of different instances are always equal (see previous post), objects of different instances are ==-equal but not ===-equal. Funnily, comparing classes (or functions) to strings turns out to be equal again (because identifiers are nothing more than strings ).

<?

$a = array(1,2,3);
$b = array(2,3);

var_dump($a==$b); // false
var_dump($a===$b); // false
array_shift($a); // $a = (2,3)
var_dump($a==$b); // true
var_dump($a===$b); // true (!)

$x = new StdClass();
$y = new StdClass();

var_dump($x == $y); // true
var_dump($x === $y); // false

class X {};

$p = new X();
$q = new X();

var_dump($p == $q); // true
var_dump($p === $q); // false

$r = array();

var_dump($p == $r); // false
var_dump($p === $r); // false

var_dump("X" == X); // true
var_dump("X" === X); // true