PHP 魔术方法

2018-01-18 约 1748 字预计阅读 4 分钟

魔术方法是一种特殊的方法，当对对象执行某些操作时会覆盖 PHP 的默认操作。

魔术方法

PHP 将所有以 __（两个下划线）开头的类方法保留为魔术方法。所以在定义类方法时，除了心下魔术方法，建议不要以 __ 为前缀。

名称	说明	备注
`__construct()`	类的构造函数
`__destruct()`	类的析构函数
`__call()`	在对象中调用一个不可访问方法时调用
`__callStatic()`	用静态方式中调用一个不可访问方法时调用
`__get()`	获得一个类的成员变量时调用
`__set()`	设置一个类的成员变量时调用
`__isset()`	当对不可访问属性调用 `isset()` 或 `empty()` 时调用
`__unset()`	当对不可访问属性调用 `unset()` 时被调用
`__sleep()`	执行 `serialize()` 时，先会调用这个函数
`__wakeup()`	执行 `unserialize()` 时，先会调用这个函数
`__toString()`	用于一个类被当成字符串时应怎样回应
`__invoke()`	当尝试以调用函数的方式调用一个对象时，`__invoke()` 方法会被自动调用
`__set_state()`	调用 `var_export()` 导出类时，此静态方法会被调用
`__clone()`	当复制完成时，如果定义了 `__clone()` 方法，则新创建的对象（复制生成的对象）中的 `__clone()` 方法会被调用，可用于修改属性的值（如果有必要的话）
`__debugInfo()`	当打印一个对象以获取显示的属性时，此方法被 `var_dump()` 调用。如果此方法未在对象上定义，则将显示所有公开的，受保护的和私有的属性

方法实例

`construct()` 和 `destruct()`

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<?php

class Object
{
	public function __construct()
	{
		echo __METHOD__ . PHP_EOL;
	}

	public function __destruct()
	{
		echo __METHOD__ . PHP_EOL;
	}
}

class Test extends Object
{
	public function __construct()
	{
		echo __METHOD__ . PHP_EOL;
		parent::__construct();
	}

	public function __destruct()
	{
		echo __METHOD__ . PHP_EOL;
		parent::__destruct();
	}
}

new Test();

// 结果
Test::__construct
Object::__construct
Test::__destruct
Object::__destruct

`call()` 和 `callStatic()`

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<?php

class Object
{
	public function __call($name, $arguments)
	{
		echo "Calling object method '$name' " . implode(', ', $arguments) . PHP_EOL;
	}

	public static function __callStatic($name, $arguments)
	{
		echo "Calling static method '$name' " . implode(', ', $arguments) . PHP_EOL;
	}
}

$object = new Object();
$object->getCall('in object context');
Object::getCallStatic('in static context');

// 结果
Calling object method 'getCall' in object context
Calling static method 'getCallStatic' in static context

`get()`, `set()`, `isset()`, `unset()`

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<?php

class Object
{
	private $data = [];

	public function __set($key, $val)
	{
		echo __METHOD__ . PHP_EOL;
		$this->data[$key] = $val;
	}

	public function __get($key)
	{
		if (array_key_exists($key, $this->data)) {
			echo __METHOD__ . PHP_EOL;
			return $this->data[$key];
		}

		return null;
	}

	public function __isset($key)
	{
		echo __METHOD__ . PHP_EOL;
		return isset($this->data[$key]);
	}

	public function __unset($key)
	{
		echo __METHOD__ . PHP_EOL;
		unset($this->data[$key]);
	}
}

$object = new Object();
$object->property = 'This is the property of the object.';
$object->property;
isset($object->property);
unset($object->property);

// 结果
Object::__set
Object::__get
Object::__isset
Object::__unset

`sleep()` 和 `wakeup`

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<?php

class Object
{
    protected $link;
    private $server, $username, $password, $database;

    public function __construct($server, $username, $password, $database)
    {
        echo __METHOD__ . PHP_EOL;
        $this->server = $server;
        $this->username = $username;
        $this->password = $password;
        $this->database = $database;
    }

    public function __sleep()
    {
        echo __METHOD__ . PHP_EOL;

        return ['server', 'username', 'password', 'database'];
    }

    public function __wakeup()
    {
        echo __METHOD__ . PHP_EOL;
        $this->connect();
    }

    private function connect()
    {
        echo __METHOD__ . PHP_EOL;
        $this->link = mysqli_connect(
            $this->server,
            $this->username,
            $this->password
        );
    }
}

$object = new Object('localhost', 'root', '', 'test');
$serialize = serialize($object);
unserialize($serialize);

// 结果
Object::__construct
Object::__sleep
Object::__wakeup
Object::connect

`__toString()`

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<?php

class Object
{
	public function __toString()
	{
		return __METHOD__;
	}
}

$object = new Object();
echo $object;

// 结果
Object::__toString

`__invoke()`

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<?php

class Object
{
	public function __invoke()
	{
		echo __METHOD__ . PHP_EOL;
	}
}

$object = new Object();
var_dump(is_callable($object()));

// 结果
Object::__invoke
bool(false)

`__set_state()`

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<?php

class Object
{
	public $a;
	public $b;

	public static function __set_state(array $array)
	{
		echo __METHOD__ . PHP_EOL;
		$object = new Object();
		$object->a = $array['a'];
		$object->b = $array['b'];

		return $object;
	}
}

$object = new Object();
$object->a = 'this is a';
$object->b = 'this is b';

eval('$b = ' . var_export($object, true) . ';');
var_dump($b);

// 结果
Object::__set_state
object(Object)#2 (2) {
  ["a"]=>
  string(9) "this is a"
  ["b"]=>
  string(9) "this is b"
}

`__clone()`

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<?php

class Object
{
	public static $count = 0;
	public $instance;

	public function __construct()
	{
        echo __METHOD__ . PHP_EOL;
        $this->instance = ++self::$count;
	}

	public function __clone()
	{
        echo __METHOD__ . PHP_EOL;
		$this->instance = ++self::$count;
	}
}

class Cloneable
{
	public $object1;
    public $object2;

    public function __construct()
    {
        echo __METHOD__ . PHP_EOL;
    }

	public function __clone()
	{
        echo __METHOD__ . PHP_EOL;

        // 强制复制一份 this->object，否则仍然指向同一个对象
		$this->object1 = clone $this->object1;
	}
}

$cloneable = new Cloneable();
$cloneable->object1 = new Object();
$cloneable->object2 = new Object();

$clone = clone $cloneable;

print "Original Object:\n";
var_dump($cloneable);

print "Cloned Object:\n";
var_dump($clone);

// 结果
Cloneable::__construct
Object::__construct
Object::__construct
Cloneable::__clone
Object::__clone
Original Object:
class Cloneable#1 (2) {
  public $object1 =>
  class Object#2 (1) {
    public $instance =>
    int(1)
  }
  public $object2 =>
  class Object#3 (1) {
    public $instance =>
    int(2)
  }
}
Cloned Object:
class Cloneable#4 (2) {
  public $object1 =>
  class Object#5 (1) {
    public $instance =>
    int(3)
  }
  public $object2 =>
  class Object#3 (1) {
    public $instance =>
    int(2)
  }
}

`__debugInfo()`

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<?php

date_default_timezone_set('PRC');

class Object
{
	public $year, $month, $day, $hour, $minute, $second;

	public function __debugInfo()
	{
		$date = $this->year . '-' . $this->month . '-' . $this->day;
		$time = $this->hour . ':' . $this->minute . ':' . $this->second;
		$datetime = $date . ' ' . $time;
		return [
			'date' => $date,
			'time' => $time,
			'datetime' => $datetime,
			'property' => call_user_func('get_object_vars', $this),
		];
	}
}

$object = new Object();
$object->year = date('Y');
$object->month = date('m');
$object->day = date('d');
$object->hour = date('H');
$object->minute = date('i');
$object->second = date('s');
var_dump($object);

// 结果
class Object#1 (4) {
  public $date =>
  string(10) "2018-01-18"
  public $time =>
  string(8) "17:27:45"
  public $datetime =>
  string(19) "2018-01-18 17:27:45"
  public $property =>
  array(6) {
    'year' =>
    string(4) "2018"
    'month' =>
    string(2) "01"
    'day' =>
    string(2) "18"
    'hour' =>
    string(2) "17"
    'minute' =>
    string(2) "27"
    'second' =>
    string(2) "45"
  }
}

魔术常量

名称	说明	备注
`__LINE__`	文件中的当前行号
`__FILE__`	文件的完整路径和文件名
`__DIR__`	文件所在的目录
`__FUNCTION__`	函数名称
`__CLASS__`	类的名称
`__TRAIT__`	`Trait` 的名字
`__METHOD__`	类的方法名
`__NAMESPACE__`	当前命名空间的名称

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<?php

namespace App;

trait ObjectTrait
{
    public function getTrait()
    {
        echo __TRAIT__ . PHP_EOL;
    }
}

class Object
{
    use ObjectTrait;

    public function __construct()
    {
        echo __LINE__ . PHP_EOL;
        echo __FILE__ . PHP_EOL;
        echo __DIR__ . PHP_EOL;
        echo __FUNCTION__ . PHP_EOL;
        echo __CLASS__ . PHP_EOL;
        echo $this->getTrait();
        echo __METHOD__ . PHP_EOL;
    }
}

$object = new Object();

// 结果
19
/Users/xxx/Downloads/test/vscode.php
/Users/xxx/Downloads/test
__construct
App\Object
App\ObjectTrait
App\Object::__construct

目录

PHP 魔术方法

魔术方法

方法实例

__construct() 和 __destruct()

__call() 和 __callStatic()

__get(), __set(), __isset(), __unset()

__sleep() 和 __wakeup

__toString()

__invoke()

__set_state()

__clone()

__debugInfo()

魔术常量

`construct()` 和 `destruct()`

`call()` 和 `callStatic()`

`get()`, `set()`, `isset()`, `unset()`

`sleep()` 和 `wakeup`

`__toString()`

`__invoke()`

`__set_state()`

`__clone()`

`__debugInfo()`