PHP Convert to DateTimeImmutable

In PHP 5.5 the DateTimeImmutable class was introduced. Immutable objects are nice in that they can not be modified, which helps reduce the likelihood I make certain types of errors.

Type Hinting DateTime

When using type declarations (a.k.a. type hinting), you can use the DateTimeInterface, which accepts either a DateTime or a DateTimeImmutable object. This is great but it means I may now have a mutable DateTime object (instead of a DateTimeImmutable object).

Convert to DateTimeImmutable

The DateTimeImmutable class comes with a helper static function createFromMutable(), which takes a DateTime object and returns a DateTimeImmutable object. Unfortunately, DateTimeImmutable::createFromMutable() throws an error if you use a DateTime object as the parameter, therefore we need to do a check before calling this function.

This is the code I use to ensure my value is an instance of DateTimeImmutable.

function myFunction(DateTimeInterface $dt) {
    $dt = $dt instanceof DateTimeImmutable ?
          $dt :
          DateTimeImmutable::createFromMutable($dt);
    // Now $dt is definitely a DateTimeImmutable object.

    // Other code goes here.
}