The result of array_unique - php

Question

Working with DateTime in projects again have a problem with duplicating if use array_unique to array which have a elemts of object,(but probles only with DateTime), see code:
class simpleClass
{
public $dt;
function __construct($dt)
{
$this->dt = $dt;
}
}
$dateObj = new simpleClass(new DateTime);
$std = new stdClass;
$arr = [$dateObj, $dateObj, $std, $std, $std, $std];
var_dump(array_unique($arr, SORT_REGULAR));
Expected 1 element with dateObj
But actually there 2

Answer 1

Function array_unique() will compare strings, so objects will be casted to strings. Solution to that would be to use __toString() magic method to return full date identifier:
class simpleClass
{
public $dt;
function __construct(DateTime $dt) {
$this->dt = $dt;
}
public function __toString() {
return $this->dt->format('r');
}
}
$dateObj1 = new simpleClass(new DateTime);
$dateObj2 = new simpleClass(new DateTime);
$dateObj3 = new simpleClass(new DateTime('today'));
$arr = [$dateObj1, $dateObj2, $dateObj3];
print_r(array_unique($arr));
Demo.

Answer 2

I still can't understand. Setting the array with:
$arr = [$dateObj, $dateObj, $std, $std];
returns:
array (size=2)
0 =>
object(simpleClass)[1]
public 'dt' =>
object(DateTime)[2]
public 'date' => string '2013-11-14 14:37:08' (length=19)
public 'timezone_type' => int 3
public 'timezone' => string 'Europe/Rome' (length=11)
2 =>
object(stdClass)[3]
This way, array_unique seems to work...