PHP 魔术方法 __clone __toString(五)

__clone()　　- 当对象克隆的时候自动加载此方法

__toString()　- 当对象需要echo打印输出的时候自动加载此方法

__clone()

<?php
class example{
    public static $pa;
    public $pb;
    public function __construct(){
        $this->pb = ++self::$pa;
    }

    public function __clone(){
        $this->pb = ‘no zuo no die‘;
    }
}

$a = new example;
$b = new example;
$c = clone $b;
$b->pb = ‘I Love You So Much!‘;

echo $a->pb;
echo ‘<hr/>‘;
echo $b->pb;
echo ‘<hr/>‘;
echo $c->pb;
echo ‘<hr/>‘;
echo $b->pb;
?>

结果如下

1
------------------------------------------------------------------------------------
I Love You So Much!
------------------------------------------------------------------------------------
no zuo no die /*要不是有__clone()这个魔术方法，这边的结果应该是2*/
------------------------------------------------------------------------------------
I Love You So Much!

php手册给了我们一个例子有些难以看懂，如下

<?php
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()
    {

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

$obj = new MyCloneable();

$obj->object1 = new SubObject();
$obj->object2 = new SubObject();

$obj2 = clone $obj;

print("Original Object:\n");
print_r($obj);

print("Cloned Object:\n");
print_r($obj2);

?>

最后的结果

Original Object:
MyCloneable Object
(
    [object1] => SubObject Object
        (
            [instance] => 1
        )

    [object2] => SubObject Object
        (
            [instance] => 2
        )

)
Cloned Object:
MyCloneable Object
(
    [object1] => SubObject Object
        (
            [instance] => 3  /*可能这里比较难以理解，其实就是$obj2当克隆的时候将最后的instance为2的结果克隆，并且再执行SubObject::__clone方法*/
        )

    [object2] => SubObject Object
        (
            [instance] => 2
        )

)

__toString()

<?php
// Declare a simple class
class TestClass
{
    public $foo;

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

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

$class = new TestClass(‘Hello‘);
echo $class;
?>

结果

Hello