PHP 魔術方法 __clone __toString(五)，__clone__tostring

PHP 魔術方法 __clone __toString(五)，__clone__tostring

__clone()　　- 當對象克隆的時候自動加載此方法

__toString()　- 當對象需要echo打印輸出的時候自動加載此方法

__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;
?>

 結果如下

1
------------------------------------------------------------------------------------
I Love You So Much!
------------------------------------------------------------------------------------
no zuo no die /*要不是有__clone()這個魔術方法，這邊的結果應該是2*/
------------------------------------------------------------------------------------
I Love You So Much!

php手冊給了我們一個例子有些難以看懂，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()
    {
      
        // 強制復制一份this->object， 否則仍然指向同一個對象
        $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);

?>

 最後的結果

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

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

)
Cloned Object:
MyCloneable Object
(
    [object1] => SubObject Object
        (
            [instance] => 3  /*可能這裡比較難以理解，其實就是$obj2當克隆的時候將最後的instance為2的結果克隆，並且再執行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;
?>

 結果

Hello