DateTime VS DateTimeImmutable example

DateTimeImmutabilityExample.php

<?php

class DateTimeImmutabilityExample
{
    private $date;

    /**
     * Intentionaly no type hinting so you can test with both DateTime and DateTimeImmutable
     */
    public function __construct($date)
    {
        $this->date = $date;
    }

    public function dump()
    {
        var_dump($this->date->format('Y-m-d'));
    }
}


$today = new DateTime();

$bad = new DateTimeImmutabilityExample($today);
$bad->dump(); // string(10) "2016-11-08"

// Modify internal state of DateTimeImmutabilityExample instance
$today->add(DateInterval::createFromDateString('10 days'));

$bad->dump(); // string(10) "2016-11-18" <-- this is BAD!

$today = new DateTimeImmutable();

$good = new DateTimeImmutabilityExample($today);
$good->dump(); // string(10) "2016-11-08"

$today->add(DateInterval::createFromDateString('10 days'));
$good->dump(); // string(10) "2016-11-08" <-- original $date is not changed

At line you could have used DateTimeInterface as type.

public function __construct(DateTimeInterface  $date)
    {
        $this->date = $date;
    }

Awesome

Can anyone tell me, i don't get it. So when we use DateTimeImmutable() instead of using DateTime() i mean in real case or scenario?

@agungsugiarto here https://www.nikolaposa.in.rs/blog/2019/07/01/stop-using-datetime/ the autor quite good explained the problem.

But related to above example. As you see, you was able to change a Date from outside of DateTimeImmutabilityExample class. Thats extreme dangerous!!