Lua 速查表

本文根据 Devhints / Lua 翻译。代码示例及版本范围沿用原文。

基础示例

参考资料

• https://www.lua.org/pil/13.html
• http://lua-users.org/wiki/ObjectOrientedProgramming

注释

-- comment
--[[ Multiline
     comment ]]

调用函数

print()
print("Hi")

-- You can omit parentheses if the argument is one string or table literal
print "Hello World"     <-->     print("Hello World")
dofile 'a.lua'          <-->     dofile ('a.lua')
print [[a multi-line    <-->     print([[a multi-line
 message]]                        message]])
f{x=10, y=20}           <-->     f({x=10, y=20})
type{}                  <-->     type({})

表 / 数组

t = {}
t = { a = 1, b = 2 }
t.a = function() ... end

t = { ["hello"] = 200 }
t.hello

-- Remember, arrays are also tables
array = { "a", "b", "c", "d" }
print(array[2])       -- "b" (one-indexed)
print(#array)         -- 4 (length)

循环

while condition do
end

for i = 1,5 do
end

for i = start,finish,delta do
end

for k,v in pairs(tab) do
end

repeat
until condition

-- Breaking out:
while x do
  if condition then break end
end

条件判断

if condition then
  print("yes")
elseif condition then
  print("maybe")
else
  print("no")
end

变量

local x = 2
two, four = 2, 4

函数

function myFunction()
  return 1
end

function myFunctionWithArgs(a, b)
  -- ...
end

myFunction()

anonymousFunctions(function()
  -- ...
end)

-- Not exported in the module
local function myPrivateFunction()
end

-- Splats
function doAction(action, ...)
  print("Doing '"..action.."' to", ...)
  --> print("Doing 'write' to", "Shirley", "Abed")
end

doAction('write', "Shirley", "Abed")

查找

mytable = { x = 2, y = function() .. end }

-- The same:
mytable.x
mytable['x']

-- Syntactic sugar, these are equivalent:
mytable.y(mytable)
mytable:y()

mytable.y(mytable, a, b)
mytable:y(a, b)

function X:y(z) .. end
function X.y(self, z) .. end

更多概念

元表

mt = {}

-- A metatable is simply a table with functions in it.
mt.__tostring = function() return "lol" end
mt.__add      = function(b) ... end       -- a + b
mt.__mul      = function(b) ... end       -- a * b
mt.__index    = function(k) ... end       -- Lookups (a[k] or a.k)
mt.__newindex = function(k, v) ... end    -- Setters (a[k] = v)

-- Metatables allow you to override behavior of another table.
mytable = {}
setmetatable(mytable, mt)

print(myobject)

类

Account = {}

function Account:new(balance)
  local t = setmetatable({}, { __index = Account })

  -- Your constructor stuff
  t.balance = (balance or 0)
  return t
end

function Account:withdraw(amount)
  print("Withdrawing "..amount.."...")
  self.balance = self.balance - amount
  self:report()
end

function Account:report()
  print("Your current balance is: "..self.balance)
end

a = Account:new(9000)
a:withdraw(200)    -- method call

常量

nil
false
true

运算符（及其对应的元表名称）

关系运算符

-- Relational (binary)
-- __eq  __lt  __gt  __le  __ge
   ==    <     >     <=    >=
~=   -- Not equal, just like !=

-- Arithmetic (binary)
-- __add  __sub  __muv  __div  __mod  __pow
   +      -      *      /      %      ^

-- Arithmetic (unary)
-- __unm (unary minus)
   -

逻辑运算符

-- Logic (and/or)
nil and false  --> nil
false and nil  --> false
not true       --> false
0 and 20       --> 20
10 and 20      --> 20

表

-- Length
-- __len(array)
#array


-- Indexing
-- __index(table, key)
t[key]
t.key

-- __newindex(table, key, value)
t[key]=value

-- String concat
-- __concat(left, right)
"hello, "..name

-- Call
-- __call(func, ...)

API

API：全局函数

dofile("hello.lua")
loadfile("hello.lua")

assert(x)    -- x or (raise an error)
assert(x, "failed")

type(var)   -- "nil" | "number" | "string" | "boolean" | "table" | "function" | "thread" | "userdata"

-- Does /not/ invoke meta methods (__index and __newindex)
rawset(t, index, value)    -- Like t[index] = value
rawget(t, index)           -- Like t[index]

_G  -- Global context
setfenv(1, {})  -- 1: current function, 2: caller, and so on -- {}: the new _G

pairs(t)     -- iterable list of {key, value}
ipairs(t)    -- iterable list of {index, value}

tonumber("34")
tonumber("8f", 16)

API：字符串

'string'..'concatenation'

s = "Hello"
s:upper()
s:lower()
s:len()    -- Just like #s

s:find()
s:gfind()

s:match()
s:gmatch()

s:sub()
s:gsub()

s:rep()
s:char()
s:dump()
s:reverse()
s:byte()
s:format()

API：表

table.foreach(t, function(row) ... end)
table.setn
table.insert(t, 21)          -- append (--> t[#t+1] = 21)
table.insert(t, 4, 99)
table.getn
table.concat
table.sort
table.remove(t, 4)

API：数学

math.abs     math.acos    math.asin       math.atan    math.atan2
math.ceil    math.cos     math.cosh       math.deg     math.exp
math.floor   math.fmod    math.frexp      math.ldexp   math.log
math.log10   math.max     math.min        math.modf    math.pow
math.rad     math.random  math.randomseed math.sin     math.sinh
math.sqrt    math.tan     math.tanh

math.sqrt(144)
math

API：杂项

io.output(io.open("file.txt", "w"))
io.write(x)
io.close()

for line in io.lines("file.txt")

file = assert(io.open("file.txt", "r"))
file:read()
file:lines()
file:close()