const YES = '是';

const NO = '否';

class BoolEnum {

  const YES = '是';

  const NO = '否';

}

BoolEnum::YES(); // 是

BoolEnum::NO(); // 否

BoolEnum::toArray(); // ['Yes' => '是', 'No' => '否']

abstract class Enum

{  

  // 获取所有枚举类型

  public static function toArray(){

    // 通过反射获取常量

    $reflection = new \ReflectionClass(static::class);

    $contants = $reflection->getConstants();

    // 返回对应的常量

    return $contants;

  }

  // 动态调用属性

  public static function __callStatic($name, $arguments)

  {

    $arr = static::toArray();

    if(isset($arr[$name])){

      return $arr[$name];

    }

    throw new \BadMethodCallException("找不到对应的枚举值 {$name}");

  }

}

class BoolEnum extends Enum

{

  const YES = '是';

  const NO = '否';

}

abstract class Enum

{  

  protected static $cache = [];

  public static function toArray(){

    $class = static::class;

    // 第一次获取，就通过反射来获取

    if(! isset(static::$cache[$class])){

      $reflection = new \ReflectionClass(static::class);

      static::$cache[$class] = $reflection->getConstants();

    }

    return static::$cache[$class];

  }

}

$yes = new BoolEnum("是");

echo $yes; // "是"

abstract Enum 

{

  protected $value;

  public function __construct($value)

  {  

    if ($value instanceof static) {

      $value = $value->getValue();

    }

    if(! $this->isValid($value)){

      throw new \UnexpectedValueException("$value 不属于该枚举值" . static::class);

    }

    $this->value = $value;

  }

  // 获取实例对应的键

  public function getKey(){

    return array_search($this->value, static::toArray(), true);

  }

  // 获取实例对应的值

  public function getValue()

  {

    return $this->value;

  }

  // 允许字符串形式输出

  public function __toString()

  {

    return $this->value;

  }

  // 验证值是否合法

  public function isValid($value)

  {

   $arr = static::toArray();

   return in_array($value, $arr, true);

  }

  // 验证键是否合法

  public function isValidKey($key)

  {

   $arr = static::toArray();

   return array_key_exists($key, $arr);

  }

}

$user->banned = '非法值'; // 可能不会报错

$yes = new BoolEnum("非法值"); // 将会抛出异常

$user->banned = $yes;

function setUserStatus(BoolEnum $boolEnum){

  $user->banned = $boolEnum;

}