PHP 魔術方法: __clone __toString

從php5以後的版本，類別就可以使用魔術方法了。 php規定以兩個底線（__）開頭的方法都保留為魔術方法，所以建議大家函數名最好不用__開 頭，除非是為了重載已有的魔術方法。

目前php已有的魔術方法有 __construct，__destruct，__call，__get，__set，__isset，__unset，__sleep，__wakeup，__toString，__set_state 和 __clone。

下面我們來看看兩個魔術方法：__clone()和__toString().

__clone()　　- 當物件複製的時候自動載入此方法

__toString()　- 當物件需要echo列印輸出的時候自動載入此方法

 

__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

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

 

php手冊給了我們一個例子有點難懂，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);

?>

 最後的結果

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

    [object2] </span>=> SubObject <span>Object</span><span> (
            [instance] </span>=> <span>2</span><span> )

)
Cloned </span><span>Object</span><span>:
MyCloneable </span><span>Object</span><span> (
    [object1] </span>=> SubObject <span>Object</span><span> (
            [instance] </span>=> <span>3 <span>/*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*/</span></span><span> )

    [object2] </span>=> SubObject <span>Object</span><span> (
            [instance] </span>=> <span>2</span><span> )

)</span>

 

 

__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

 

以上就介紹了PHP 魔術方法: __clone __toString，包括了PHP魔術方法方面的內容，希望對PHP教程有興趣的朋友有所幫助。