php7静态方法的链式调用

A::aa()::bb()::cc();

 1 class A
 2 {
 3     public static $a = 0;
 4     
 5     public static function aa()
 6     {
 7         self::$a++;
 8         return self::class;
 9     }
10     
11     public static function bb()
12     {
13         self::$a++;
14         return self::class;
15     }
16     
17     public static function cc()
18     {
19         echo self::$a;
20     }
21 }
22 
23 
24 A::aa()::bb()::cc(); //2