PHP編程中的__clone()方法使用詳解

可以在對象類中定義一個__clone()方法來調整對象的克隆行為。此方法的代碼將在克隆操作期間執行。除了將所有現有對象成員復制到目標對象之外，還會執行__clone()方法指定的操作。下面修改Corporate_Drone類，增加以下方法：

function __clone() { 
 $this->tiecolor = "blue";
}

之後，創建一個新的Corporate_Drone對象，增加employeeid成員的值，克隆這個對象，然後輸出一些數據，從而顯示克隆對象的tiecolor確實是通過__clone()方法設置的。示例代碼：

<?php
 // Create new corporatedrone object
  $drone1 = new corporatedrone();
 
 // Set the $drone1 employeeid member
  $drone1->setEmployeeID("12345");
 
 // Clone the $drone1 object
  $drone2 = clone $drone1;
 
 // Set the $drone2 employeeid member
  $drone2->setEmployeeID("67890");
 
 // Output the $drone1 and $drone2 employeeid members
  echo "drone1 employeeID: ".$drone1->getEmployeeID()."<br />";
  echo "drone2 employeeID: ".$drone2->getEmployeeID()."<br />";
  echo "drone2 tiecolor: ".$drone2->getTiecolor()."<br />";
?>

程序運行結果

drone1 employeeID: 12345
drone2 employeeID: 67890
drone2 tiecolor:

再來一個小例子：

<?php
class Fruit {
 private $name = "水果";
 private $color = "顏色";
 
 public function setName($name){
 $this->name = $name;
 }
 
 public function setColor($color){
 $this->color = $color;
 }
 
 function showColor(){
 return $this->color.'的'.$this->name."<br />";
 }
 
 function __destruct(){
 echo "被吃掉了（對象被回收） <br />"; 
 }
}

$apple = new Fruit();
$apple->setName("大蘋果");
$apple->setColor("紅色");
echo $apple->showColor();

$clone_apple = $apple;
$clone_apple->setName("小蘋果");
$clone_apple->setColor("青色");

echo $clone_apple->showColor();
?>

上面只是將一個類賦值給另一個類，所以此時內存中仍是一個對象。

<?php
class Fruit {
 private $name = "水果";
 private $color = "顏色";
 
 public function setName($name){
 $this->name = $name;
 }
 
 public function setColor($color){
 $this->color = $color;
 }
 
 function showColor(){
 return $this->color.'的'.$this->name."<br />";
 }
 
 function __destruct(){
 echo "被吃掉了（對象被回收） <br />"; 
 }
 function __clone(){
 $this->name = "克隆水果"; 
 }
}

$apple = new Fruit();
$apple->setName("大蘋果");
$apple->setColor("紅色");
echo $apple->showColor();

$clone_apple = clone $apple;
$clone_apple->setColor("青色");

echo $clone_apple->showColor();
?>

clone方法克隆出了一個新的類，所以此時內存中有兩個對象。

php的__clone()方法對一個對象實例進行的淺復制,對象內的基本數值類型進行的是傳值復制，而對象內的對象型成員變量,如果不重寫__clone方法,顯式的clone這個對象成員變量的話,這個成員變量就是傳引用復制,而不是生成一個新的對象.如下面一個例子的第28行注釋所說

<?php
  class Account {
    public $balance;
    
    public function __construct($balance) {
      $this->balance = $balance;
    }
  }
 
  class Person {
    private $id;
    private $name;
    private $age;
    public $account;
    
    public function __construct($name, $age, Account $account) {
      $this->name = $name;
      $this->age = $age;
      $this->account = $account;
    }
    
    public function setId($id) {
      $this->id = $id;
    }
    
    public function __clone() {  #復制方法,可在裡面定義再clone是進行的操作
      $this->id = 0;
      $this->account = clone $this->account;  #不加這一句,account在clone是會只被復制引用,其中一個account的balance被修改另一個也同樣會被修改
    }
  }
  
  $person = new Person("peter", 15, new Account(1000));
  $person->setId(1);
  $person2 = clone $person;
  
  $person2->account->balance = 250;
  
  var_dump($person, $person2);
  
 ?>

輸出:
復制代碼 代碼如下:
object(Person)#1 (4) { ["id":"Person":private]=> int(1) ["name":"Person":private]=> string(5) "peter" ["age":"Person":private]=> int(15) ["account"]=> object(Account)#2 (1) { ["balance"]=> int(1000) } } object(Person)#3 (4) { ["id":"Person":private]=> int(0) ["name":"Person":private]=> string(5) "peter" ["age":"Person":private]=> int(15) ["account"]=> object(Account)#4 (1) { ["balance"]=> int(250) } }