PHPにおける配列とオブジェクトの同一性

配列 オブジェクト
class test{
 var $a;
}
$a = array();
$b = array();
$a==$b
$a = new test();
$b = new test();
$a==$b
$a[1] = 1;
$a != $b
$a->a = 1;
$a != $b
$a[1] = 1;
$b[1] = 1;
$a==$b
$a->a = 1;
$b->a = 1;
$a==$b
$a[1] = 1;
$b[2] = 1;
$a!=$b
$a->a = 1;
$b->b = 1;
$a!=$b
$a = array();
$b = array();
$a[1] = array();
$b[1] = array();
$a==$b
$a = new test();
$b = new test();
$a->a = new test();
$b->a = new test();
$a==$b
$a[1][1] = 1;
$b[1][1] = 0;
$a!=$b
$a->a->a = 1;
$b->a->a = 0;
$a!=$b
$a[1][1] = 1;
$b[1][1] = 1;
$a==$b
$a->a->a = 1;
$b->a->a = 1;
$a==$b
class test2{
  var $a;
}
$a = new test();
$b = new test2();
$a!=$b

=== でも == でも結果は同じ。では、オブジェクトの同一性(リファレンスがどうか)を見るにはどうすればよいのだろう?