php7新特性

：-}

参考文档

http://php.net/manual/zh/migration70.new-features.php

https://zhuanlan.zhihu.com/guagua

https://coyee.com/article/11569-what-s-new-and-exciting-in-php-7-1

https://www.cnblogs.com/linlin-php/p/7297618.html

https://segmentfault.com/a/1190000006910600