php__clone()克隆方法以及浅克隆和深克隆使用实例详解

可以在对象类中定义一个clone()方法来调整对象的克隆行为。此方法的代码将在克隆操作期间执行。除了将所有现有对象成员复制到目标对象之外，还会执行clone()方法指定的操作。下面修改Corporate_Drone类，增加以下方法：

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

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之后，创建一个新的Corporate_Drone对象，增加employeeid成员的值，克隆这个对象，然后输出一些数据，从而显示克隆对象的tiecolor确实是通过clone()方法设置的。示例代码：

<?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 />";
?>

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程序运行结果

drone1 employeeID: 12345
drone2 employeeID: 67890
drone2 tiecolor:

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再来一个小例子：

<?php
class Fruit {
 private $name = "水果";
 private $color = "颜色";
 
 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（对象被回收） <br />"; 
 }
}

$apple = new Fruit();
$apple->setName("大苹果");
$apple->setColor("红色");
echo $apple->showColor();

$clone_apple = $apple;
$clone_apple->setName("小苹果");
$clone_apple->setColor("青色");

echo $clone_apple->showColor();
?>

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上面只是将一个类赋值给另一个类，所以此时内存中仍是一个对象。

<?php
class Fruit {
 private $name = "水果";
 private $color = "颜色";
 
 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（对象被回收） <br />"; 
 }
 function clone(){
 $this->name = "克隆水果"; 
 }
}

$apple = new Fruit();
$apple->setName("大苹果");
$apple->setColor("红色");
echo $apple->showColor();

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

echo $clone_apple->showColor();
?>

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clone方法克隆出了一个新的类，所以此时内存中有两个对象。

php的clone()方法对一个对象实例进行的浅复制,对象内的基本数值类型进行的是传值复制，而对象内的对象型成员变量,如果不重写clone方法,显式的clone这个对象成员变量的话,这个成员变量就是传引用复制,而不是生成一个新的对象.如下面一个例子的第28行注释所说

<?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() {  #复制方法,可在里面定义再clone是进行的操作
      $this->id = 0;
      $this->account = clone $this->account;  #不加这一句,account在clone是会只被复制引用,其中一个account的balance被修改另一个也同样会被修改
    }
  }
  
  $person = new Person("peter", 15, new Account(1000));
  $person->setId(1);
  $person2 = clone $person;
  
  $person2->account->balance = 250;
  
  var_dump($person, $person2);
  
 ?>

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浅克隆：只是克隆对象中的非对象非资源数据，即对象中属性存储的是对象类型，则会出现克隆不完全

<?php
class B{
 public $val = 10;
}
class A{
 public $val = 20;
 public $b;
 public function construct(){
  $this->b = new B();
 }
}
$obj_a = new A();
$obj_b = clone $obj_a;
$obj_a->val = 30;
$obj_a->b->val = 40;
var_dump($obj_a);
echo '<br>';
var_dump($obj_b);

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运行结果如下：

object(A)[1]
 public 'val' => int 30
 public 'b' =>
 object(B)[2]
  public 'val' => int 40
 
object(A)[3]
 public 'val' => int 20
 public 'b' =>
 object(B)[2]
  public 'val' => int 40

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深克隆：一个对象的所有属性数据都彻底的复制，需要使用魔术方法clone()，并在里面实现深度克隆

<?php
class B{
 public $val = 10;
}
class A{
 public $val = 20;
 public $b;
 public function construct(){
  $this->b = new B();
 }
 public function clone(){
  $this->b = clone $this->b;
 }
}
$obj_a = new A();
$obj_b = clone $obj_a;
$obj_a->val = 30;
$obj_a->b->val = 40;
var_dump($obj_a);
echo '<br>';
var_dump($obj_b);

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运行结果如下：

object(A)[1]
 public 'val' => int 30
 public 'b' =>
 object(B)[2]
  public 'val' => int 40
 
object(A)[3]
 public 'val' => int 20
 public 'b' =>
 object(B)[4]
  public 'val' => int 10

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