TRex\Core\Enum is an abstraction for a unique value in a finite list. This ensures you have a value among the constants of your class.

How to implement?

First you need to declare all of possible values in the constants of your class.

class Letter extends Enum{

    const A = 'a';
    const B = 'b';


And when you instantiate your class, you have to specify one of this possible values.

$a = new Letter(Letter::A);

$a->getValue(); //'a'
$a->is(Letter::A); //true

No other value is allowed.

new Letter(123); //UnexpectedValueException