PHP中魔术方法的用法

/** PHP把所有以__（两个下划线）开头的类方法当成魔术方法。所以你定义自己的类方法时，不要以 __为前缀。 * */

// __toString、__set、__get__isset()、__unset()
/*
  The __toString method allows a class to decide how it will react when it is converted to a string.
  __set() is run when writing data to inaccessible members.
  __get() is utilized for reading data from inaccessible members.
  __isset() is triggered by calling isset() or empty() on inaccessible members.
  __unset() is invoked when unset() is used on inaccessible members.
 */
class TestClass {

    private $data = array();
    public $foo;

    public function __construct($foo) {
        $this->foo = $foo;
    }

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

    public function __set($name, $value) {
        echo "__set, Setting '$name' to '$value'\n";
        $this->data[$name] = $value;
    }

    public function __get($name) {
        echo "__get, Getting '$name'\n";
        if (array_key_exists($name, $this->data)) {
            return $this->data[$name];
        }
    }

    /** As of PHP 5.1.0 */
    public function __isset($name) {
        echo "__isset, Is '$name' set?\n";
        return isset($this->data[$name]);
    }

    /** As of PHP 5.1.0 */
    public function __unset($name) {
        echo "__unset, Unsetting '$name'\n";
        unset($this->data[$name]);
    }

}

$obj = new TestClass('Hello');
echo "__toString, $obj\n";
$obj->a = 1;
echo $obj->a . "\n\n";
var_dump(isset($obj->a));
unset($obj->a);
var_dump(isset($obj->a));
echo "\n\n"; 
/**
  输出结果如下：
  __toString, Hello
  __set, Setting 'a' to '1'
  __get, Getting 'a'
  __isset, Is 'a' set?
  bool(true)
  __unset, Unsetting 'a'
  __isset, Is 'a' set?
  bool(false)
 **/



// __call  __callStatic
/*
  mixed __call ( string $name , array $arguments )
  mixed __callStatic ( string $name , array $arguments )
  __call() is triggered when invoking inaccessible methods in an object context.
  __callStatic() is triggered when invoking inaccessible methods in a static context.
  The $name argument is the name of the method being called.
  The $arguments argument is an enumerated array containing the parameters passed to the $name'ed method.
 */
class MethodTest {
    public function __call($name, $arguments) {
        // Note: value of $name is case sensitive.
        echo "__call, Calling object method '$name' " . implode(', ', $arguments) . "\n";
    }

    /** As of PHP 5.3.0 */
    public static function __callStatic($name, $arguments) {
        // Note: value of $name is case sensitive.
        echo "__callStatic, Calling static method '$name' " . implode(', ', $arguments) . "\n";
    }

}

$obj = new MethodTest;
$obj->runTest('in object context', 'param2', 'param3');
//MethodTest::runTest('in static context'); // As of PHP 5.3.0
echo "\n\n"; 
/**
 输出结果如下：
 __call, Calling object method 'runTest' in object context, param2, param3
  string(10) "__invoke: "
 */



// __invoke
/* 
  The __invoke method is called when a script tries to call an object as a function.
  Note: This feature is available since PHP 5.3.0.
*/
class CallableClass {
    function __invoke($x) {
        var_dump($x);
    }
}

$obj = new CallableClass;
//$obj(5);
var_dump('__invoke: ' . is_callable($obj));
echo "\n\n"; 





// __sleep  __wakeup
/*
  串行化serialize可以把变量包括对象,转化成连续bytes数据. 你可以将串行化后的变量存在一个文件里或在网络上传输. 
  然后再反串行化还原为原来的数据. 你在反串行化类的对象之前定义的类,PHP可以成功地存储其对象的属性和方法. 
  有时你可能需要一个对象在反串行化后立即执行. 为了这样的目的,PHP会自动寻找__sleep和__wakeup方法.
  当一个对象被串行化,PHP会调用__sleep方法(如果存在的话). 在反串行化一个对象后,PHP 会调用__wakeup方法. 
  这两个方法都不接受参数. __sleep方法必须返回一个数组,包含需要串行化的属性. PHP会抛弃其它属性的值. 
  如果没有__sleep方法,PHP将保存所有属性.下面的例子显示了如何用__sleep和__wakeup方法来串行化一个对象. 
  Id属性是一个不打算保留在对象中的临时属性. __sleep方法保证在串行化的对象中不包含id属性. 
  当反串行化一个User对象,__wakeup方法建立id属性的新值. 这个例子被设计成自我保持. 
  在实际开发中,你可能发现包含资源(如图像或数据流)的对象需要这些方法
 */

class User {

    public $name;
    public $id;

    function __construct() {
        //give user a unique ID 赋予一个差别 的ID
        $this->id = uniqid();
    }

    //__sleep返回值的类型是数组，数组中的值是不需要串型化的字段id

    function __sleep() {
        //do not serialize this->id 不串行化id
        return(array("name"));
    }

    function __wakeup() {
        //give user a unique ID
        $this->id = uniqid();
    }

}

//create object 成立一个器材
$u = new User;
$u->name = "Leon"; //serialize it 串行化 留意不串行化id属性,id的值被遗弃
$s = serialize($u);
echo "__sleep, __wakeup, s: $s"; //unserialize it 反串行化 id被重新赋值
$u2 = unserialize($s); //$u and $u2 have different IDs $u和$u2有差别 的ID
print_r($u);
print_r($u2);
echo "\n\n"; 
/**
 输出结果如下：
  __sleep, __wakeup, s: O:4:"User":1:{s:4:"name";s:4:"Leon";}
  User Object
  (
  [name] => Leon
  [id] => 4db1b17640da1
  )
  User Object
  (
  [name] => Leon
  [id] => 4db1b17640dbc
  )
 */


// __set_state
/*
  This static method is called for classes exported by var_export() since PHP 5.1.0.
  The only parameter of this method is an array containing exported properties in the form array('property' => value, ...).
 */

class A {

    public $var1;
    public $var2;

    public static function __set_state($an_array) { // As of PHP 5.1.0
        //$an_array打印出来是数组，而不是调用时传递的对象
        print_r($an_array);
        $obj = new A;
        $obj->var1 = $an_array['var1'];
        $obj->var2 = $an_array['var2'];
        return $obj;
    }

}

$a = new A;
$a->var1 = 5;
$a->var2 = 'foo';
echo "__set_state:\n";
eval('$b = ' . var_export($a, true) . ';'); 
// $b = A::__set_state(array(
// 'var1' => 5,
// 'var2' => 'foo',
// ));
var_dump($b);
echo "\n\n"; 
/**
  输出结果如下：
  __set_state:
  Array
  (
  [var1] => 5
  [var2] => foo
  )
  object(A)#5 (2) {
  ["var1"]=>
  int(5)
  ["var2"]=>
  string(3) "foo"
  }
 */



// __clone
class SubObject {

    static $instances = 0;
    public $instance;

    public function __construct() {
        $this->instance = ++self::$instances;
    }

    public function __clone() {
        $this->instance = ++self::$instances;
    }

}

class MyCloneable {

    public $object1;
    public $object2;

    function __clone() {
        // Force a copy of this->object, otherwise
        // it will point to same object.
        $this->object1 = clone $this->object1;
    }

}

$obj = new MyCloneable();
$obj->object1 = new SubObject();
$obj->object2 = new SubObject();
$obj2 = clone $obj;
print("__clone, Original Object:\n");
print_r($obj);
print("__clone, Cloned Object:\n");
print_r($obj2);
echo "\n\n";
/**
 输出结果如下：
 __clone, Original Object:
  MyCloneable Object
  (
  [object1] => SubObject Object
  (
  [instance] => 1
  ) [object2] => SubObject Object
  (
  [instance] => 2
  ))
  __clone, Cloned Object:
  MyCloneable Object
  (
  [object1] => SubObject Object
  (
  [instance] => 3
  ) [object2] => SubObject Object
  (
  [instance] => 2
  )) 
 */