How to implement enumeration using PHP?

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Enumeration

In mathematics and computer science theory, an enumeration of a set is a program that lists all the members of some finite set of sequences, or A count of objects of a specific type. The two types often (but not always) overlap.

An enumeration is a named collection of integer constants. Enumerations are very common in daily life. For example, SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, and SATURDAY representing the week are an enumeration. ——Wikipedia

Business Scenario

In the actual development process, it is very easy for us to come into contact with enumeration types, but because PHP’s native support for enumerations is not very good, so Many times developers do not pay attention to the use of enumerations, but use global constants or class constants instead. In principle, these two data are still strings and cannot be used for type judgment.

Business

• Order Status Pending Payment/Pending Shipment/Pending Receipt/Pending Evaluation
• Member Status Activated/Inactive
• . ...

Wait, many times we will use simple 1/2/3/4 or 0/1 to represent it, and then specify these things in documents or comments.

The more advanced thing is to define it as a constant, and then facilitate unified access, but the value of the constant is still a string, and the type cannot be judged.

Here we need to take a look at PHP’s support for enumerations. Although PHP does not have perfect support for enumerations, there is still a basic enumeration class in SPL

SPL Enumeration

SplEnum extends SplType {/ Constants /
const NULL __default = NULL ;
/ 方法 /
public getConstList ([ bool $include_default = FALSE ] ) : array
/ 继承的方法 /
SplType::__construct ( [mixed $initial_value [, bool $strict ]] )
}

But! This requires additional installation of PECL. Use PECL to install Spl_Types, which unintentionally increases the cost of use. Are there any other solutions? The answer is yes.

Write one directly by hand.

Start preparation

First define an enumeration

class Enum
{
    // 默认值
    const __default = self::WAIT_PAYMENT;
    // 待付款
    const WAIT_PAYMENT = 0;
    // 待发货
    const WAIT_SHIP = 1;
    // 待收货
    const WAIT_RECEIPT = 2;
    // 待评价
    const WAIT_COMMENT = 3;
}

This seems to be completed, we can directly use Enum::WAIT_PAYMENT to get it It's worth it, but we can't verify it where the parameters are passed.

function setStatus(Enum $status){
    // TODO
}
setStatus(Enum::WAIT_PAYMENT);
// Error 显然这是不行的 因为上面常量的值时一个 int 并不是 Enum 类型。

Here we need to use a magic method __toString() in PHP object-oriented

public __toString (void): string

__toString() method is used How a class should respond when treated as a string. For example, echo $obj; should display something. This method must return a string, otherwise a fatal error of level E_RECOVERABLE_ERROR will be issued.

Now let’s improve this method.

class OrderStatus extends Enum
{
    // 默认值
    const __default = self::WAIT_PAYMENT;
    // 待付款
    const WAIT_PAYMENT = 0;
    // 待发货
    const WAIT_SHIP = 1;
    // 待收货
    const WAIT_RECEIPT = 2;
    // 待评价
    const WAIT_COMMENT = 3;

    public function __toString()
    {
        return '233';
    }
}
// object
echo gettype($orderStatus) . PHP_EOL;
// boolean true
var_dump($orderStatus instanceof Enum);
// 233
echo $orderStatus;

Initially taking shape

It seems that part of it has been achieved, so how should we make him do better? Let’s revamp it again.

class OrderStatus extends Enum
{
    // 默认值
    const __default = self::WAIT_PAYMENT;
    // 待付款
    const WAIT_PAYMENT = 0;
    // 待发货
    const WAIT_SHIP = 1;
    // 待收货
    const WAIT_RECEIPT = 2;
    // 待评价
    const WAIT_COMMENT = 3;
    /**
     * @var string
     */
    protected $value;

    public function __construct($value = null)
    {
        $this->value = is_null($value) ? self::__default : $value;
    }

    public function __toString()
    {
        return (string)$this->value;
    }
}

// 1️⃣
$orderStatus = new OrderStatus(OrderStatus::WAIT_SHIP);

// object
echo gettype($orderStatus) . PHP_EOL;
// boolean true
var_dump($orderStatus instanceof Enum);
// 1
echo $orderStatus . PHP_EOL;
// 2️⃣
$orderStatus = new OrderStatus();
// object
echo gettype($orderStatus) . PHP_EOL;
// boolean true
var_dump($orderStatus instanceof Enum);
// 0
echo $orderStatus;
// 3️⃣
$orderStatus = new OrderStatus('意外的参数');
// object
echo gettype($orderStatus) . PHP_EOL;
// boolean true
var_dump($orderStatus instanceof Enum);
// 意外的参数
echo $orderStatus;

This time, we added the constructor and allowed him to pass in an optional value, which is then used as the output value of the __toString method. This time It looks good, the functions have been implemented, if the parameters passed in are not what we expected. But what if it doesn’t match? Look, at the 3️⃣ point, it has already become an accident. Is there any way to remedy it? The answer is of course Yes. Here we will use another good thing of PHP, the reflection class. Of course, this is not unique to PHP and is also available in other languages.
Of course, in addition to reflection, we will also use another thing Method overloading inside the __callStatic method.

Go further

public static __callStatic ( string $name , array $arguments ) : mixed

When calling an inaccessible method in a static context , __callStatic() will be called. The

$name parameter is the name of the method to be called. The $arguments parameter is an enumeration array containing the parameters to be passed to the method $name.

Continue to transform.

class Enum
{
    const __default = null;
    /**
     * @var string
     */
    protected static $value;

    // 注意这里 将构造函数的 修饰符改成了 受保护的 即 外部无法直接 new
    protected function __construct($value = null)
    {
        // 很常规
        self::$value = is_null($value) ? static::__default : $value;
    }

    /**
     * @param $name
     * @param $arguments
     * @return mixed
     * @throws ReflectionException
     */
    public static function __callStatic($name, $arguments)
    {
        // 实例化一个反射类 static::class 表示调用者
        $reflectionClass = new ReflectionClass(static::class);
        // 这里我们要有一个约定， 就是类常量成员的名字必须的大写。
        // 这里就是取出来调用的静态方法名对应的常量值 虽然这里有个 getValue 方法
        // 但是因为其返回值不可靠 我们就依赖于他原本的隐式的 __toString 方法来帮我们输出字符串即可。
        $constant = $reflectionClass->getConstant(strtoupper($name));
        // 获取调用者的 构造方法
        $construct = $reflectionClass->getConstructor();
        // 设置成可访问 因为我们把修饰符设置成了受保护的 这里需要访问到，所以就需要设置成可访问的。
        $construct->setAccessible(true);
        // 因为现在类已经是可以访问的了所以我们直接实例化即可，实例化之后 PHP 会自动调用 __toString 方法 使得返回预期的值。
        $static = new static($constant);
        return $static;
    }

    public function __toString()
    {
        return (string)self::$value;
    }

}

class OrderStatus extends Enum
{
    // 默认值
    const __default = self::WAIT_PAYMENT;
    // 待付款
    const WAIT_PAYMENT = 0;
    // 待发货
    const WAIT_SHIP = 1;
    // 待收货
    const WAIT_RECEIPT = 2;
    // 待评价
    const WAIT_COMMENT = 3;

}

$WAIT_SHIP = OrderStatus::WAIT_SHIP();
var_dump($WAIT_SHIP . '');
var_dump($WAIT_SHIP instanceof Enum);

Here, a simple enumeration class is completed.

End

What if we have other needs, such as determining whether a value is within the enumeration range? Get all enumeration values? Get all enumeration keys and determine whether the enumeration keys are valid? Automatic formatting "Because the __toString method only allows returning strings, but sometimes we force the need for integer, bool and other types"

class Enum
{
    const __default = null;
    /**
     * @var string
     */
    protected static $value;
    /**
     * @var ReflectionClass
     */
    protected static $reflectionClass;

    // 注意这里 将构造函数的 修饰符改成了 受保护的 即 外部无法直接 new
    protected function __construct($value = null)
    {
        // 很常规
        self::$value = is_null($value) ? static::__default : $value;
    }

    /**
     * @param $name
     * @param $arguments
     * @return mixed
     */
    public static function __callStatic($name, $arguments)
    {
        // 实例化一个反射类 static::class 表示调用者
        $reflectionClass = self::getReflectionClass();
        // 这里我们要有一个约定， 就是类常量成员的名字必须的大写。
        // 这里就是取出来调用的静态方法名对应的常量值 虽然这里有个 getValue 方法
        // 但是因为其返回值不可靠 我们就依赖于他原本的隐式的 __toString 方法来帮我们输出字符串即可。
        $constant = $reflectionClass->getConstant(strtoupper($name));
        // 获取调用者的 构造方法
        $construct = $reflectionClass->getConstructor();
        // 设置成可访问 因为我们把修饰符设置成了受保护的 这里需要访问到，所以就需要设置成可访问的。
        $construct->setAccessible(true);
        // 因为现在类已经是可以访问的了所以我们直接实例化即可，实例化之后 PHP 会自动调用 __toString 方法 使得返回预期的值。
        $static = new static($constant);
        return $static;
    }

    /**
     * 实例化一个反射类
     * @return ReflectionClass
     * @throws ReflectionException
     */
    protected static function getReflectionClass()
    {
        if (!self::$reflectionClass instanceof ReflectionClass) {
            self::$reflectionClass = new ReflectionClass(static::class);
        }
        return self::$reflectionClass;
    }

    /**
     * @return string
     */
    public function __toString()
    {
        return (string)self::$value;
    }

    /**
     * 判断一个值是否有效 即是否为枚举成员的值
     * @param $val
     * @return bool
     * @throws ReflectionException
     */
    public static function isValid($val)
    {
        return in_array($val, self::toArray());
    }

    /**
     * 转换枚举成员为键值对输出
     * @return array
     * @throws ReflectionException
     */
    public static function toArray()
    {
        return self::getEnumMembers();
    }

    /**
     * 获取枚举的常量成员数组
     * @return array
     * @throws ReflectionException
     */
    public static function getEnumMembers()
    {
        return self::getReflectionClass()
            ->getConstants();
    }

    /**
     * 获取枚举成员值数组
     * @return array
     * @throws ReflectionException
     */
    public static function values()
    {
        return array_values(self::toArray());
    }

    /**
     * 获取枚举成员键数组
     * @return array
     * @throws ReflectionException
     */
    public static function keys()
    {
        return array_keys(self::getEnumMembers());
    }

    /**
     * 判断 Key 是否有效 即存在
     * @param $key
     * @return bool
     * @throws ReflectionException
     */
    public static function isKey($key)
    {
        return in_array($key, array_keys(self::getEnumMembers()));
    }

    /**
     * 根据 Key 去获取枚举成员值
     * @param $key
     * @return static
     */
    public static function getKey($key)
    {
        return self::$key();
    }

    /**
     * 格式枚举结果类型
     * @param null|bool|int $type 当此处的值时什么类时 格式化输出的即为此类型
     * @return bool|int|string|null
     */
    public function format($type = null)
    {
        switch (true) {
            // 当为纯数字 或者类型处传入的为 int 值时 转为 int
            case ctype_digit(self::$value) || is_int($type):
                return (int)self::$value;
                break;
            // 当 type 传入 true 时 返回 bool 类型
            case $type === true:
                return (bool)filter_var(self::$value, FILTER_VALIDATE_BOOLEAN);
                break;
            default:
                return self::$value;
                break;
        }
    }

}

class OrderStatus extends Enum
{
    // 默认值
    const __default = self::WAIT_PAYMENT;
    // 待付款
    const WAIT_PAYMENT = 0;
    // 待发货
    const WAIT_SHIP = 1;
    // 待收货
    const WAIT_RECEIPT = 2;
    // 待评价
    const WAIT_COMMENT = 3;

}

$WAIT_SHIP = OrderStatus::WAIT_SHIP();
// 直接输出是字符串
echo $WAIT_SHIP;
// 判断类型是否存在
var_dump($WAIT_SHIP instanceof OrderStatus);
// 格式化输出一下 是要 字符串 、还是 bool 还是整形
// 自动
var_dump($WAIT_SHIP->format());
// 整形
var_dump($WAIT_SHIP->format(1));
// bool
var_dump($WAIT_SHIP->format(true));
// 判断这个值是否有效的枚举值
var_dump(OrderStatus::isValid(2));
// 判断这个值是否有效的枚举值
var_dump(OrderStatus::isValid(8));
// 获取所有枚举成员的 Key
var_dump(OrderStatus::keys());
// 获取所有枚举成员的值
var_dump(OrderStatus::values());
// 获取枚举成员的键值对
var_dump(OrderStatus::toArray());
// 判断枚举 Key 是否有效
var_dump(OrderStatus::isKey('WAIT_PAYMENT'));
// 判断枚举 Key 是否有效
var_dump(OrderStatus::isKey('WAIT_PAYMENT_TMP'));
// 根据 Key 取去 值 注意 这里取出来的已经不带有类型了
// 更加建议直接使用 取类常量的方式去取 或者在高版本的 直接使用类常量修饰符 
// 将类常量不可见最佳，但是需要额外处理了
var_dump(OrderStatus::getKey('WAIT_PAYMENT')
    ->format(1));

As of now, a complete enumeration is completed ~

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