lua的类似三目运算符用法
一般化的Lua三目运算为：(a and {b} or {c})[1]local v = (a and {b} or {c})[1]如果a为true，则 v = b
如果a为false，则 v = c原理解析：
https://blog.csdn.net/coffeecato/article/details/77546887
