如何检查Lua中的值是否为空? [英] How to check if a value is empty in Lua?

问题描述

在Lua中使条件检查哪些内容为空或不为空的正确方法是什么? if x == ""和f x ~= ""似乎无效.

What is the proper way to make a conditional which checks of something is or is not empty in Lua? if x == "" and f x ~= "" does not seem to work.

推荐答案

Lua是一种基于动态类型的语言.
任何变量都可以包含以下类型之一: nil ， boolean ， number ， string ，表，功能，线程或用户数据.
索引时，表中的任何变量(包括_G，即全局变量所在的表)中都没有值，其值将为nil.将表变量设置为nil时，它实际上会取消声明"它(将条目从内存中完全删除).
声明local变量时，如果未立即分配该变量，则将为其赋予nil值.与表变量不同，将local变量设置为nil时，它不会不取消声明"它(它只是具有nil的值).

Lua is a dynamically type-based language.
Any variable can hold one of the following types: nil, boolean, number, string, table, function, thread, or userdata.
Any variable in a table (including _G, the table where globals reside) without a value gives a value of nil when indexed. When you set a table variable to nil, it essentially "undeclares" it (removing the entry from memory entirely).
When a local variable is declared, if it is not assigned immediately it is given a value of nil. Unlike table variable, when you set a local variable to nil, it does not "undeclare" it (it just has a value of nil).

在Lua中，空字符串("")仍然是值"，它只是大小为零的字符串.

In Lua, an empty string ("") is still a "value" - it's simply a string of size zero.

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