PHP单态的使用

1. [代码][PHP]代码    

<?php
	/*
		作者 : shyhero
		邮箱 : shyhero@outlook.com
		Q  Q : 1757424878
	 */
	class Demo{
		private static $ob=null;

		private $name;
		private $age;

		private function __construct(){

		}

		public static function makeOb(){
			var_dump($a);
			if(self::$ob == null){
				$c = __CLASS__;
				self::$ob = new $c();
		 	}
			return self::$ob;
		}

		public function __set($tName,$value){
			$this -> $tName = $value;
		}
	}

	$a = Demo::makeOb();
	var_dump($a);