EnumTrait.php

<?php

/**
 * Trait EnumTrait
 * @author Philipp Dahse <ph.dahse@gmail.com>
 */
trait EnumTrait
{
    /**
     * @return array
     */
    public static function toArray()
    {
        return (new \ReflectionClass(self::class))->getConstants();
    }
    /**
     * @param $const
     *
     * @return null|mixed
     */
    public static function get($const)
    {
        return defined($constant = self::class . "::$const") ? constant($constant) : null;
    }
    /**
     * @param $const
     * @return bool
     */
    public static function has($const)
    {
        return self::get($const) !== null;
    }
  
    /**
     * Get enum as fliped array
     * @notice maybe you will lose entries if values are not unique
     */
    public static function reverseArray()
    {
      return array_flip(self::toArray()));
    }
  
    /**
     * Find key by value
     *
     * @notice not consistent for ambiguous values
     * @param $value
     *
     * @return null
     */
    public static function reverseLookup($value)
    {
        return array_key_exists($value,$reverse = self::reverseArray()) ? $reverse[$value] : null;
    }
}

// EXAMPLE USAGE

/**
 * Class BillingStateEnum
 */
abstract class BillingStateEnum
{
    use EnumTrait;
  
    const BILLED = 'billed';
    const CANCELED = 'canceled';
    const FAILED = 'failed';
    const PAID = 'paid';   
}

BillingStateEnum::toArray(); // ['BILLED' => 'billed', 'CANCELED' => 'canceled', 'FAILED' => 'failed', 'PAID' => 'paid']
BillingStateEnum::get('BILLED'); // billed
BillingStateEnum::has('TEST'); // false
BillingStateEnum::reverseArray(); // ['billed' => 'BILLED', 'canceled' => 'CANCELED', 'failed' => 'FAILED', 'paid' => 'PAID']
BillingStateEnum::reverseLookup('failed'); //FAILED