EnumTrait.php

<?php
trait EnumTrait
{
    /** @var static[]  */
    private static $instance;

    /** @var mixed value of constant */
    private $value;

    /**
     * Enum constructor.
     *
     * @param mixed $value value of constant
     */
    private function __construct($value)
    {
        $ref = new ReflectionObject($this);
        $cons = $ref->getConstants();
        if (!in_array($value, $cons, true)) {
            throw new InvalidArgumentException("invalid constant value");
        }

        $this->value = $value;
    }

    /**
     * return value of constant
     *
     * @return mixed
     */
    final public function value()
    {
        return $this->value;
    }

    /**
     * return true if same constant
     *
     * @return bool
     */
    final public function is(self $lhs){
        return $this === $lhs;
    }

    /**
     * return enum constant with the specified value
     *
     * @param mixed $value
     * @return self
     */
    final public static function valueOf($value)
    {
        $cls = __CLASS__;
        foreach ((new ReflectionClass($cls))->getConstants() as $name => $const_value) {
            if ($const_value === $value) {
                return $cls::$name();
            }
        }
        
        throw new InvalidArgumentException("invalid constant value");
    }
    
    /**
     * @return self
     */
    private static function constant()
    {
        static $name = null;
        if ($name === null) {
            $name = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 1)[0]['function'];
        }

        if (!isset(self::$instance[$name])) {
            $cls = __CLASS__;
            self::$instance[$name] = new $cls(constant("{$cls}::{$name}"));
        }

        return self::$instance[$name];
    }
}