Both Pure Enums and Backed Enums implement an internal interface named
UnitEnum. UnitEnum includes a static method
cases(). cases() returns a packed array of
all defined Cases in the order of declaration.
<?php
Suit::cases();
// Produces: [Suit::Hearts, Suit::Diamonds, Suit::Clubs, Suit:Spades]
?>
Manually defining a cases() method on an Enum will result in a fatal error.