need 'typename' before 'sigslot::has_slots<mt_policy>::sender_set::const_iterator' because 'sigslot::has_slots<mt_policy>::sender_set' 解法：复制里面的代码 https://www.cnblogs.com/choday/p/3429975.html 来源：https://my.oschina.net/u/4000302/blog/3106558 标签 sigslot
