转自： -- 两个横线是单行注释（译者注：这跟 SQL 一样）--[[     增加两个 [ 和 ] 变成多行注释     我是多行注释：）--]]------------------------------------------------------ 1. 变量和程序流程控制 Variables and flow control.----------------------------------------------------num = 42  -- 所有的数值都是双精度的-- 别吓一跳，64位的双精度需要52位-- 存储，特别是 int 值，机器精度对小于 52 位的 ints 不是一个问题s = 'walternate'  -- 字符串常量，跟 Python 差不多t = "也可以用双引号"u = [[ 在开始和结束位置两个中括号       表示多行字符串]]t = nil  -- t 赋值为空，Lua 会进行垃圾收集-- 块使用关键字如 do/end 来表示：while num < 50 do  num = num + 1  -- Lua 没有 ++ 和 += 这样的操作符end-- If 语句:if num > 40 then  print('over 40')elseif s ~= 'walternate' then  -- ~= 是不等于的意思  -- == 是相等检查，类似 Python 和 Java; ok for strs.  io.write('not over 40\n')  -- 默认写到标准输出else  -- 变量默认是全局的  thisIsGlobal = 5  -- 常见的驼峰式大小写  -- 如何定义局部变量  local line = io.read()  -- 读入标准输入下一行  -- 使用 .. 操作符进行字符串连接  print('Winter is coming, ' .. line)end-- 未定义的变量返回 nil-- 这不是一个错误foo = anUnknownVariable  -- 现在 foo 的值为 nilaBoolValue = false-- 只有 nil 和 false 为假，'' 为真if not aBoolValue then print('twas false') end-- 'or' 和 'and' are short-circuited.-- 这个类似 C/Java/JavaScript 里的 a?b:c 操作符ans = aBoolValue and 'yes' or 'no'  --> 'no'karlSum = 0for i = 1, 100 do  -- 范围包括两端的值  karlSum = karlSum + iend-- 使用 "100, 1, -1" 进行数值递减fredSum = 0for j = 100, 1, -1 do fredSum = fredSum + j end-- 一般情况下，范围是 begin, end[, step].-- 另外一种循环的方式repeat  print('the way of the future')  num = num - 1until num == 0------------------------------------------------------ 2. 函数.----------------------------------------------------function fib(n)  if n < 2 then return 1 end  return fib(n - 2) + fib(n - 1)end-- 闭包和匿名函数function adder(x)  -- adder 被调用时才会创建返回函数，记住 x 的值  return function (y) return x + y endenda1 = adder(9)a2 = adder(36)print(a1(16))  --> 25print(a2(64))  --> 100-- 返回, 函数调用和赋值都可以工作-- 列表可能不匹配长度-- 无法匹配的接收者就是 nil-- 无法匹配的发送者被丢弃 x, y, z = 1, 2, 3, 4-- 现在 x = 1, y = 2, z = 3, 和 4 被丢弃function bar(a, b, c)  print(a, b, c)  return 4, 8, 15, 16, 23, 42endx, y = bar('zaphod')  --> 打印 "zaphod  nil nil"-- 现在 x = 4, y = 8, 而 15..42 被丢弃-- 函数可以是全局的也可以是局部的-- 下面是相同的function f(x) return x * x endf = function (x) return x * x end-- 局部函数local function g(x) return math.sin(x) endlocal g = function (x) return math.sin(x) end-- Trig funcs work in radians, by the way.-- 调用一个字符串参数无需括号print 'hello'  -- Works fine.------------------------------------------------------ 3. Tables.------------------------------------------------------ Tables = Lua's only compound data structure;--          they are associative arrays.-- Similar to php arrays or js objects, they are-- hash-lookup dicts that can also be used as lists.-- Using tables as dictionaries / maps:-- Dict literals have string keys by default:t = {key1 = 'value1', key2 = false}-- String keys can use js-like dot notation:print(t.key1)  -- Prints 'value1'.t.newKey = {}  -- Adds a new key/value pair.t.key2 = nil   -- Removes key2 from the table.-- Literal notation for any (non-nil) value as key:u = {['@!#'] = 'qbert', [{}] = 1729, [6.28] = 'tau'}print(u[6.28])  -- prints "tau"-- Key matching is basically by value for numbers-- and strings, but by identity for tables.a = u['@!#']  -- Now a = 'qbert'.b = u[{}]     -- We might expect 1729, but it's nil:-- b = nil since the lookup fails. It fails-- because the key we used is not the same object-- as the one used to store the original value. So-- strings & numbers are more portable keys.-- A one-table-param function call needs no parens:function h(x) print(x.key1) endh{key1 = 'Sonmi~451'}  -- Prints 'Sonmi~451'.for key, val in pairs(u) do  -- Table iteration.  print(key, val)end-- _G is a special table of all globals.print(_G['_G'] == _G)  -- Prints 'true'.-- Using tables as lists / arrays:-- List literals implicitly set up int keys:v = {'value1', 'value2', 1.21, 'gigawatts'}for i = 1, #v do  -- #v is the size of v for lists.  print(v[i])  -- Indices start at 1 !! SO CRAZY!end-- A 'list' is not a real type. v is just a table-- with consecutive integer keys, treated as a list.------------------------------------------------------ 3.1 Metatables and metamethods.------------------------------------------------------ A table can have a metatable that gives the table-- operator-overloadish behavior. Later we'll see-- how metatables support js-prototypey behavior.f1 = {a = 1, b = 2}  -- Represents the fraction a/b.f2 = {a = 2, b = 3}-- This would fail:-- s = f1 + f2metafraction = {}function metafraction.__add(f1, f2)  sum = {}  sum.b = f1.b * f2.b  sum.a = f1.a * f2.b + f2.a * f1.b  return sumendsetmetatable(f1, metafraction)setmetatable(f2, metafraction)s = f1 + f2  -- call __add(f1, f2) on f1's metatable-- f1, f2 have no key for their metatable, unlike-- prototypes in js, so you must retrieve it as in-- getmetatable(f1). The metatable is a normal table-- with keys that Lua knows about, like __add.-- But the next line fails since s has no metatable:-- t = s + s-- Class-like patterns given below would fix this.-- An __index on a metatable overloads dot lookups:defaultFavs = {animal = 'gru', food = 'donuts'}myFavs = {food = 'pizza'}setmetatable(myFavs, {__index = defaultFavs})eatenBy = myFavs.animal  -- works! thanks, metatable-- Direct table lookups that fail will retry using-- the metatable's __index value, and this recurses.-- An __index value can also be a function(tbl, key)-- for more customized lookups.-- Values of __index,add, .. are called metamethods.-- Full list. Here a is a table with the metamethod.-- __add(a, b)                     for a + b-- __sub(a, b)                     for a - b-- __mul(a, b)                     for a * b-- __div(a, b)                     for a / b-- __mod(a, b)                     for a % b-- __pow(a, b)                     for a ^ b-- __unm(a)                        for -a-- __concat(a, b)                  for a .. b-- __len(a)                        for #a-- __eq(a, b)                      for a == b-- __lt(a, b)                      for a < b-- __le(a, b)                      for a <= b-- __index(a, b)  
    
       for a.b-- __newindex(a, b, c)             for a.b = c-- __call(a, ...)                  for a(...)------------------------------------------------------ 3.2 Class-like tables and inheritance.------------------------------------------------------ Classes aren't built in; there are different ways-- to make them using tables and metatables.-- Explanation for this example is below it.Dog = {}                                   -- 1.function Dog:new()                         -- 2.  newObj = {sound = 'woof'}                -- 3.  self.__index = self                      -- 4.  return setmetatable(newObj, self)        -- 5.endfunction Dog:makeSound()                   -- 6.  print('I say ' .. self.sound)endmrDog = Dog:new()                          -- 7.mrDog:makeSound()  -- 'I say woof'         -- 8.-- 1. Dog acts like a class; it's really a table.-- 2. function tablename:fn(...) is the same as--    function tablename.fn(self, ...)--    The : just adds a first arg called self.--    Read 7 & 8 below for how self gets its value.-- 3. newObj will be an instance of class Dog.-- 4. self = the class being instantiated. Often--    self = Dog, but inheritance can change it.--    newObj gets self's functions when we set both--    newObj's metatable and self's __index to self.-- 5. Reminder: setmetatable returns its first arg.-- 6. The : works as in 2, but this time we expect--    self to be an instance instead of a class.-- 7. Same as Dog.new(Dog), so self = Dog in new().-- 8. Same as mrDog.makeSound(mrDog); self = mrDog.------------------------------------------------------ Inheritance example:LoudDog = Dog:new()                           -- 1.function LoudDog:makeSound()  s = self.sound .. ' '                       -- 2.  print(s .. s .. s)endseymour = LoudDog:new()                       -- 3.seymour:makeSound()  -- 'woof woof woof'      -- 4.-- 1. LoudDog gets Dog's methods and variables.-- 2. self has a 'sound' key from new(), see 3.-- 3. Same as LoudDog.new(LoudDog), and converted to--    Dog.new(LoudDog) as LoudDog has no 'new' key,--    but does have __index = Dog on its metatable.--    Result: seymour's metatable is LoudDog, and--    LoudDog.__index = LoudDog. So seymour.key will--    = seymour.key, LoudDog.key, Dog.key, whichever--    table is the first with the given key.-- 4. The 'makeSound' key is found in LoudDog; this--    is the same as LoudDog.makeSound(seymour).-- If needed, a subclass's new() is like the base's:function LoudDog:new()  newObj = {}  -- set up newObj  self.__index = self  return setmetatable(newObj, self)end------------------------------------------------------ 4. Modules.------------------------------------------------------[[ I'm commenting out this section so the rest of--   this script remains runnable.-- Suppose the file mod.lua looks like this:local M = {}local function sayMyName()  print('Hrunkner')endfunction M.sayHello()  print('Why hello there')  sayMyName()endreturn M-- Another file can use mod.lua's functionality:local mod = require('mod')  -- Run the file mod.lua.-- require is the standard way to include modules.-- require acts like:     (if not cached; see below)local mod = (function ()  
     
      end)()-- It's like mod.lua is a function body, so that-- locals inside mod.lua are invisible outside it.-- This works because mod here = M in mod.lua:mod.sayHello()  -- Says hello to Hrunkner.-- This is wrong; sayMyName only exists in mod.lua:mod.sayMyName()  -- error-- require's return values are cached so a file is-- run at most once, even when require'd many times.-- Suppose mod2.lua contains "print('Hi!')".local a = require('mod2')  -- Prints Hi!local b = require('mod2')  -- Doesn't print; a=b.-- dofile is like require without caching:dofile('mod2')  --> Hi!dofile('mod2')  --> Hi! (runs again, unlike require)-- loadfile loads a lua file but doesn't run it yet.f = loadfile('mod2')  -- Calling f() runs mod2.lua.-- loadstring is loadfile for strings.g = loadstring('print(343)')  -- Returns a function.g()  -- Prints out 343; nothing printed before now.--]]------------------------------------------------------ 5. References.------------------------------------------------------[[I was excited to learn Lua so I could make gameswith the Löve 2D game engine. That's the why.I started with BlackBulletIV's Lua for programmers.Next I read the official Programming in Lua book.That's the how.It might be helpful to check out the Lua shortreference on lua-users.org.The main topics not covered are standard libraries: * string library * table library * math library * io library * os libraryBy the way, this entire file is valid Lua; save itas learn.lua and run it with "lua learn.lua" !This was first written for tylerneylon.com, and isalso available as a github gist. Have fun with Lua!--]]