php的变量引用详解

 <?php
 class SimpleClass
 {
     // property declaration
     public $var = 'a default value';

     // method declaration
     public function displayVar() {
         echo $this->var;
     }
 }

 $instance = new SimpleClass();

 $assigned   =  $instance;
 $reference  =& $instance;

 $assigned->var = "aaaaaaa";

 $assigned = null;

 var_dump($instance);
 var_dump($reference);
 var_dump($assigned);

 /*
  输出内容:
  E:\php>php TestClass.php
 class SimpleClass#1 (1) {
   public $var =>
   string(7) "aaaaaaa"
 }
 class SimpleClass#1 (1) {
   public $var =>
   string(7) "aaaaaaa"
 }
 NULL

 总结:
 $assigned, $reference, $assigned三个变量引用的都是同一块内存地址，
 $assigned = null; 之后，断开了指向$assigned的指针,所以$assigned为空，其他的变量不变
  /