Enum

<?php

use  Comquer\Enum\Enum;

class Colors extends Enum
{
    public const RED = 'red';
    public const GREEN = 'green';
    protected const INVISIBLE_COLOR = 'invisible_color';
}

<?php
// $red is instance of Enum with value 'red'
$red = Colors::RED();
$red->getValue(); // "red"
$red->getKey();// "RED"