lua - Lua 中的多个返回值

Question

之前遇到过这个问题。
对于多返回值函数

fn=function() return 'a','b' end

电话
print(fn())返回 a b
但电话
print(fn() or nil)仅返回 a
为什么？ or既然第一次调用成功应该没关系吧？

Answer 1

引自 Programming in Lua §5.1 – Multiple Results

Lua always adjusts the number of results from a function to the circumstances of the call. When we call a function as a statement, Lua discards all results from the function. When we use a call as an expression, Lua keeps only the first result. We get all results only when the call is the last (or the only) expression in a list of expressions.

在您的示例中，返回值 fn()用作表达式( or 运算符的左操作数)，因此只保留第一个值。