I was refactoring some code and removed multiple (apparently) useless calls to a method that basically was doing a new DateTime(). The code was then doing some computations on those DateTime, like setting the time, adding some durations…
After my modifications, nothing was working correctly anymore. Fortunately a comment on the DateTime.add method explained it all: yes, add and sub return a DateTime, but it’s not a new one! Great, so now I start adding some clone until I realize there’s a DateTimeImmutable. That sounds a lot more like what I would expect.
So I update the code to use DateTimeImmutable, but things are still not working correctly. I track the issue down to a call of IntlDateFormatter::formatObject. That function simply does not work on DateTimeImmutable
// The following returns what you would expect
IntlDateFormatter::formatObject(new DateTime(), IntlDateFormatter::LONG, 'en');
// While the following returns false...
IntlDateFormatter::formatObject(new DateTimeImmutable(), IntlDateFormatter::LONG, 'en');
It would have made sense to me that DateTime and DateTimeImmutable be interchangeable, especially as they both implement DateTimeInterface:
This class behaves the same as DateTime except it never modifies itself but returns a new object instead.
So now I need to convert my DateTimeImmutable to a DateTime. You have a CreateFromMutable but not the other way, so I guess I can just
$dateTime = new DateTime();
$dateTime->setTimestamp($dateTimeImmutable->getTimestamp());
$dateTime->setTimezone($dateTimeImmutable->getTimezone());