2. Basic Concepts

本文主要参考自官方文档中的 Basic Concepts 一章.

• https://www.lua.org/manual/5.3/manual.html

• https://cloudwu.github.io/lua53doc/manual.html

在开始学习之前, 我们先来看一下怎么 debug lua 脚本. 下面给出了一个例子, 展示了如何在 lua 中写 comment, 以及如何将值打印出来. 打印值将是我们最常用的 debug 方式.

how_to_debug.lua

--[[
this is multi-line comment
line1
line2
line3
]]--

-- this is single-line comment
a = 1 -- this is single-line comment
print(a) -- your can print a value to console
-- you can use string format to print a better message
print(string.format("a = %s", a))

import subprocess

subprocess.run(["lua", "how_to_debug.lua"]);

1
a = 1

2.1 值与类型

value_and_types_1.lua

local a_nil
print(string.format("a_nil = %s", a_nil))

local a_boolean = true
print(string.format("a_boolean = %s", a_boolean))

local a_number = 42
print(string.format("a_number = %s", a_number))

local a_string = "Hello World!"
print(string.format("a_string = %s", a_string))

local a_table = { 1, 2, 3 }
print(string.format("a_table = %s", a_table))

local a_function = function()
    print("this is a function!")
end
a_function()

subprocess.run(["lua", "value_and_types_1.lua"]);

a_nil = nil
a_boolean = true
a_number = 42
a_string = Hello World!
a_table = table: 0x600000c34000
this is a function!

2.2 环境与全局环境

local_and_global_variable.lua

#!/usr/bin/env lua

a = 1 -- global variable
function func1()
    a = 2 -- you can change the value of global variable inside of a function
    print(string.format("inside function a = %s", a)) -- should be 2
end
func1()
print(string.format("outside function a = %s", a)) -- should be 2


b = 1
function func2()
    local b = 2 -- this is NOT the global variable b
    print(string.format("inside function b = %s", b)) -- should be 2
end
func2()
print(string.format("outside function b = %s", b)) -- should be 1


local c = 1
function func3()
    c = 2 -- this is the global variable c
    print(string.format("inside function c = %s", c)) -- should be 2
end
func3()
print(string.format("outside function c = %s", c)) -- should be 2, the local c got overwritten


local d = 1
function func4()
    local d = 2 -- this is local variable d
    print(string.format("inside function d = %s", d)) -- should be 2
end
func4()
print(string.format("outside function d = %s", d)) -- should be 1

subprocess.run(["lua", "local_and_global_variable.lua"]);

inside function a = 2
outside function a = 2
inside function b = 2
outside function b = 1
inside function c = 2
outside function c = 2
inside function d = 2
outside function d = 1