PHP对象相关知识总结

对象传递：一种说法是“PHP对象是通过引用传递的”，更准确的说法是别名(标识符)传递，即它们都保存着同一个标识符(ID)的拷贝，这个标识符指向同一个对象的真正内容。

 <?php
 class A {
   public $foo = 1;
 } 
 
 $a = new A;
 $b = $a;   // $a ,$b都是同一个标识符的拷贝
       // ($a) = ($b) = <id>
 $b->foo = 2;
 echo $a->foo."n";//2

 $c = new A;
 $d = &$c;  // $c ,$d是引用
       // ($c,$d) = <id>
 
 $d->foo = 2;
 echo $c->foo."n";//2
 
 $e = new A;
 
 function foo($obj) {
   // ($obj) = ($e) = <id>
   $obj->foo = 2;
 }
 
 foo($e);
 echo $e->foo."n";//2

•对象复制：对象复制可以通过 clone 关键字来完成，如果原对象定义了 __clone() 方法，则新对象中的 __clone() 方法将在复制完后被调用，__clone() 方法可用于修改复制对象属性的值。当对象被复制后，会对对象的所有属性执行一个浅复制(shallow copy)，但所有的引用属性仍然会是一个指向原来的变量的引用。

 <?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;
   }
   
   function cloneTest()
   {
     echo 'cloneTest';
   }
 }
 
 $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);
 echo $obj2->cloneTest().":n";
 echo (new Reflectionclass($obj2));

上例输出结果：

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

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

)
Cloned Object:
MyCloneable Object
(
  [object1] => SubObject Object
    (
      [instance] => 3
    )

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

)
cloneTest:
Class [ <user> class MyCloneable ] {
 @@ /public/t.php 18-33

 - Constants [0] {
 }

 - Static properties [0] {
 }

 - Static methods [0] {
 }

 - Properties [2] {
  Property [ <default> public $object1 ]
  Property [ <default> public $object2 ]
 }

 - Methods [2] {
  Method [ <user> public method __clone ] {
   @@ /public/t.php 23 - 27
  }

  Method [ <user> public method cloneTest ] {
   @@ /public/t.php 29 - 32
  }
 }
}

•对象遍历： foreach只能遍历对象的可见属性，无法遍历其方法，实现起来比较容易；另外，也可通过实现Iterator接口或IteratorAggregate接口的方法遍历对象属性。