<?php // new static 得到的单例分别为D，E和F。 class D { protected static $_instance = null; protected function __construct(){} protected function __clone() { //disallow clone } static public function getInstance() { if (static::$_instance === null) { static::$_instance = new static(); } return static::$_instance; } } class E extends D { protected static $_instance = null; } class F extends D{ protected static $_instance = null; } $d = D::getInstance(); $e = E::getInstance(); $f = F::getInstance(); var_dump($d); var_dump($e); var_dump($f); 运行结果： E:\code\php_test\apply\static.php:35: class D#1 (0) { } E:\code\php_test\apply\static.php:36: class E#2 (0) { } E:\code\php_test\apply\static.php:37: class F#3 (0) { }
可以看到，使用static可以解决self时出现的单例继承问题。
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