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
 /