(PHP 8 >= 8.1.0)
Enumerations are a restricting layer on top of classes and class constants, intended to provide a way to define a closed set of possible values for a type.
<?phpenum Suit{ case Hearts; case Diamonds; case Clubs; case Spades;}function do_stuff(Suit $s){ // ...}do_stuff(Suit::Spades);?>
For a full discussion, see the Enumerations chapter.