Type-safe enumeration class.

DirectionEnum.php

<?php
class DirectionEnum extends Enum
{
    const NORTH     = 'NORTH';
    const SOUTH     = 'SOUTH';
    const EAST      = 'EAST';
    const WEST      = 'WEST';

    /**
     * @return boolean
     */
    public function isCold()
    {
      return $this === self::NORTH();
    }
}


class MyNavigator
{
    public function setDirection(DirectionEnum $direction)
    {
        echo "Going to : " . $direction . PHP_EOL;

        if ($direction->isCold()) {
            echo "It's could !!" . PHP_EOL;
        }
    }
}



$south = DirectionEnum::SOUTH();

var_dump($south === DirectionEnum::SOUTH());
// bool(true)

var_dump((string)$south === DirectionEnum::SOUTH);
// bool(true)

var_dump($south->valueOf() === DirectionEnum::SOUTH);
// bool(true)


$navigator = new MyNavigator();

$navigator->setDirection(DirectionEnum::EAST());
// Going to : EAST

$navigator->setDirection(DirectionEnum::NORTH());
// Going to : NORTH
// It's could !!

Enum.php

<?php

/**
 * Enum
 * 
 * Type-safe enumerations.
 * An alternative to the simple string or integer constants to represent sets of related items.
 *
 * @author Fabio B. Silva <fabio.bat.silva@gmail.com>
 */
class Enum
{
    /**
     * Enumeration value
     *
     * @var mixed
     */
    protected $value;

    /**
     * @var Enumeration instances
     */
    static protected $instances;

    /**
     * Enumeration construct
     *
     * @param mixed $value
     */
    protected function __construct($value)
    {
        $this->value = $value;
    }

    /**
     * Returns the enumeration value as string
     *
     * @return string
     */
    public function __toString()
    {
        return (string) $this->value;
    }

    /**
     * Returns the enumeration value
     *
     * @return string
     */
    public function valueOf()
    {
        return $this->value;
    }

    /**
     * Returns an enumeration instance
     *
     * @param   string  $name   Literal enumeration declaration
     * @param   array   $args   Unused method args
     * @return  Enum
     *
     * @throws  \InvalidArgumentException
     */
    public static function __callStatic($name, $args)
    {
        if (isset(self::$instances[$name])) {
            return self::$instances[$name];
        }

        $class = get_called_class();

        if ( ! defined($class . '::' . $name)) {
            throw new \InvalidArgumentException("Undefined enumeration value \"{$name}\"");
        }

        if ( ! empty($args)) {
            throw new \InvalidArgumentException("Enumeration method for \"{$name}\" does not accept any value");
        }

        return self::$instances[$name] = new $class(constant($class . '::' . $name));
    }
}