<?php
class C
{
//三私一公
protected static $_instance = null;
protected function __construct() //protected方便继承 ,privated无法继承
{
throw new Exception("禁止实例化");
}
protected function __clone()
{
throw new Exception("禁止克隆")
}
public function getInstance()
{
if (static::$_instance === null) {
static::$_instance = new static;//后期静态绑定，以实现继承
}
return static::$_instance;
}
}
class D extends C
{
protected static $_instance = null;//继承之后能够实现两套不同的数据库链接方式
}
$c = C::getInstance();
$d = D::getInstance();
var_dump($c === $d);
