UnitEnum
The UnitEnum interface identifies any enumeration. It works on both enumerations and backed-enumerations.
This interface is only available for type checks, and cannot be implemented by another class.
This interface ensure the enum::cases() method is available, that lists all cases in that enumeration.
<?php
enum E { case A;}
enum F: int { case B = 1;}
var_dump(E::A instanceof UnitEnum); // true
var_dump(F::B instanceof UnitEnum); // true
?>