php魔術方法——屬性重載方法，php魔術屬性重載_PHP教程

php魔術方法——屬性重載方法，php魔術屬性重載

php有一類很神奇的方法，這些方法是保留方法，通常不會在外部被顯式調用，他們使用雙底線(__)開頭，他們被稱為魔術方法(Magic Methods)。php官方也不建議定義其他雙底線開頭的方法。

這次介紹屬性重載方法：get/set/isset/unset

public void __set ( string $name , mixed $value )public mixed __get ( string $name )public bool __isset ( string $name )public void __unset ( string $name )

這些方法觸發的時機，都是在訪問不可訪問的屬性的時候。

如以下：

 1 php 2  3 class Cls{ 4  5     private $a = 0; 6     protected $b = 1; 7     public $c = 2; 8     var $d = 3; 9 10     private $_properties = array(0);11 12     public function __set($name, $value){13         echo __METHOD__ . ' is called! ' . json_encode(func_get_args()) . "\n";14         return $this->_properties[$name] = $value;15     }16 17     public function __get($name){18         echo __METHOD__ . ' is called! ' . json_encode(func_get_args()) . "\n";19         return $this->_properties[$name];20     }21 22     public function __isset($name){23         echo __METHOD__ . ' is called! ' . json_encode(func_get_args()) . "\n";24         return isset($this->_properties[$name]);25     }26 27     public function __unset($name){28         echo __METHOD__ . ' is called! ' . json_encode(func_get_args()) . "\n";29         unset($this->_properties[$name]);30     }31 32     public function dump(){33         echo "====================== DUMP START ====================\n";34         echo <<<STR35     a: $this->a36     b: $this->b37     c: $this->c38     d: $this->d\n39 STR;40         foreach($this->_properties as $k => $v){41             echo <<<STR42     Property $k: $v\n43 STR;44         }45     46         echo "====================== DUMP STOP =====================\n";47         48     }49 }50 $string = 'abcdef';51 $obj = new Cls();52 53 $list = array('isset', 'get', 'set', 'isset', 'unset', 'isset');54 $obj->dump();55 foreach($list as $method){56     for($i = 0 ; $i < strlen($string) ; $i ++){57         $char = $string{$i};58         echo "------ $method : $char ------\n";59         switch($method){60             case 'isset':61                 echo json_encode($tmp = isset($obj->$char)) . "\n";62                 break;63             case 'get':64                 echo json_encode($tmp = $obj->$char) . "\n";65                 break;66             case 'set':67                 echo json_encode($tmp = $obj->$char = $char . "-val") . "\n";68                 break;69             case 'unset':70                 unset($obj->$char);71                 break;72             default:73                 break;74         }75     }76     $obj->dump();77 }

結果輸出：

====================== DUMP START ====================    a: 0    b: 1    c: 2    d: 3    Property 0: 0====================== DUMP STOP =====================------ isset : a ------Cls::__isset is called! ["a"]false------ isset : b ------Cls::__isset is called! ["b"]false------ isset : c ------true------ isset : d ------true------ isset : e ------Cls::__isset is called! ["e"]false------ isset : f ------Cls::__isset is called! ["f"]false====================== DUMP START ====================    a: 0    b: 1    c: 2    d: 3    Property 0: 0====================== DUMP STOP =====================------ get : a ------Cls::__get is called! ["a"]null------ get : b ------Cls::__get is called! ["b"]null------ get : c ------2------ get : d ------3------ get : e ------Cls::__get is called! ["e"]null------ get : f ------Cls::__get is called! ["f"]null====================== DUMP START ====================    a: 0    b: 1    c: 2    d: 3    Property 0: 0====================== DUMP STOP =====================------ set : a ------Cls::__set is called! ["a","a-val"]"a-val"------ set : b ------Cls::__set is called! ["b","b-val"]"b-val"------ set : c ------"c-val"------ set : d ------"d-val"------ set : e ------Cls::__set is called! ["e","e-val"]"e-val"------ set : f ------Cls::__set is called! ["f","f-val"]"f-val"====================== DUMP START ====================    a: 0    b: 1    c: c-val    d: d-val    Property 0: 0    Property a: a-val    Property b: b-val    Property e: e-val    Property f: f-val====================== DUMP STOP =====================------ isset : a ------Cls::__isset is called! ["a"]true------ isset : b ------Cls::__isset is called! ["b"]true------ isset : c ------true------ isset : d ------true------ isset : e ------Cls::__isset is called! ["e"]true------ isset : f ------Cls::__isset is called! ["f"]true====================== DUMP START ====================    a: 0    b: 1    c: c-val    d: d-val    Property 0: 0    Property a: a-val    Property b: b-val    Property e: e-val    Property f: f-val====================== DUMP STOP =====================------ unset : a ------Cls::__unset is called! ["a"]------ unset : b ------Cls::__unset is called! ["b"]------ unset : c ------------ unset : d ------------ unset : e ------Cls::__unset is called! ["e"]------ unset : f ------Cls::__unset is called! ["f"]====================== DUMP START ====================Cls::__get is called! ["c"]Cls::__get is called! ["d"]    a: 0    b: 1    c:     d:     Property 0: 0====================== DUMP STOP =====================------ isset : a ------Cls::__isset is called! ["a"]false------ isset : b ------Cls::__isset is called! ["b"]false------ isset : c ------Cls::__isset is called! ["c"]false------ isset : d ------Cls::__isset is called! ["d"]false------ isset : e ------Cls::__isset is called! ["e"]false------ isset : f ------Cls::__isset is called! ["f"]false====================== DUMP START ====================Cls::__get is called! ["c"]Cls::__get is called! ["d"]    a: 0    b: 1    c:     d:     Property 0: 0====================== DUMP STOP =====================

特彆強調，當這個屬性不存在(基於當前存取權限)的時候，才會觸發這些方法。因此嚴重建議使用確定的索引值進行get/set處理，特別是對應的索引值不要有存取權限問題，如上例中的a和b，會導致在類內部、類外部、子類內處理的方式不同，開發時產生不可預知的傳回值，極易產生bug。

empty方法不能調用屬性重載方法。

$tmp = $obj->$char = $char . "-val"

此例中，__set自身的傳回值將被忽略，同樣__get也不會被調用。

此外：屬性重載方法必須聲明為public，同時參數不能使用引用傳遞，靜態屬性不能通過這些方法重載，這些方法也不能被聲明為static。

當然，使用魔術方法的時候，也會對反射系統造成影響。

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