DateTimeInterface
DateTimeInterface is a PHP interface implemented by both DateTime and DateTimeImmutable. It defines the common API shared by both mutable and immutable date-time objects.
Using DateTimeInterface as a type in function signatures accepts either class, making code agnostic to mutability. It cannot be implemented by user-defined classes directly; it exists solely to type both built-in date-time classes.
DateTimeInterface exposes methods such as format(), getTimestamp(), getTimezone(), and diff().
<?php
function formatDate(DateTimeInterface $date): string {
return $date->format('Y-m-d');
}
// both classes satisfy the type
echo formatDate(new DateTime('2024-01-15'));
echo formatDate(new DateTimeImmutable('2024-06-03'));
?>