Lua程序设计

s = [[this is a very long string.
could be multiple lines]]

printf = function(s, ...) return io.write(string.format(s,...)); end
a = {[1] = 10, [2] = 20, [10] = 10, x = 30, y = 40}
print("using ipairs to iterate")
for i, v in ipairs(a) do
   printf("i = %d, v = %d\n", i, v);
end
print("using pairs to iterate")
for k in pairs(a) do
   print("k = " .. k);
end
print(#a)

-- [[
➜  playbook lua test.lua
using ipairs to iterate
i = 1, v = 10
i = 2, v = 20
using pairs to iterate
k = x
k = 1
k = 2
k = 10
k = y
2
-- ]]

days = {'Sun', 'Mon', 'Tue'} -- 数组构造，下标从1开始
point = {x = 10, y = 20} -- 字典构造
days_and_point = {'Sun', 'Mon', 'Tue', x = 10, y = 20} -- 混合构造，毕竟数组下标只是一个key而已

-- 此外支持表达式做key. {[expr] = value}
days = {["*"] = mul} -- days["*"] 来引用
days = {[ 0 ] = 20} -- days[0] 来引用

function hello(a, b)
   print("a = " .. tostring(a) .. ", b = " .. tostring(b))
end

hello(10)
hello(10, 20)
hello(10, 20, 30)

-- [[
> dofile("test.lua")
a = 10, b = nil
a = 10, b = 20
a = 10, b = 20
-- ]]

print 'hello, world'
a, b = table.unpack{10, 20}
print(a, b)

function hello(a, b)
   print("a = " .. tostring(a) .. ", b = " .. tostring(b))
end

-- 一种table.unpack的实现方法
function unpack(t, i)
   -- 如果没有那么多参数的话，那么i=nil
   i = i or 1
   if t[i] then
      return t[i], unpack(t, i+1)
   end
end
params = {10, 20}
hello(params)
hello(unpack(params))

function test_vargs(a, b, ...)
   print('a = ' .. a .. " , b = " .. b)
   for i = 1, select('#', ...) do
      print('varg #' .. i .. " = " .. select(i, ...))
   end
end
test_vargs(10,20, table.unpack{30, 40 , 50})

-- [[ arg是一个空table. 没有绑定到...上. 非常奇怪
function test_vargs(a, b, ...)
   print('a = ' .. a .. " , b = " .. b)
   for i, v in ipairs(arg) do
      print('varg #' .. i .. " = " .. v)
   end
end
-- ]]

function get_named_args(args)
   keys = {"height", "width", "depth"}
   for i, k in ipairs(keys) do
      local arg = args[k]
      print(k .. ' = ' .. arg)
   end
end
get_named_args({height = 100, width = 200, depth = 50})

nums = {5,4,3,2,1}
table.sort(nums, function(a,b)
              return a < b
end)
for i, v in ipairs(nums) do
   print(v)
end

do
   local fact;
   fact = function(n)
         if (n == 0) then
            return 1
         end
         return n * fact(n-1)
   end

   print(fact(10))
end

for var_1, ..., var_n in explist do block end

-- 等价于下面这样的形式

do
  local _f, _s, _var = explist
  while true do
    local var_1, ... , var_n = _f(_s, _var)
    _var = var_1
    if _var == nil then break end
    block
  end
end

function values(t)
   local i = 0
   return function()
      i = i + 1
      return t[i]
   end
end

function my_ipairs(t)
   local iter = function(t, i)
      i = i + 1
      if t[i] then
         return i, t[i]
      end
   end
   return iter, t, 0
end

print('========== values ==========')
for v in values({10, 20, 30, 40}) do
   print(v)
end
print('========== my_ipairs ==========')
for i, v in my_ipairs({10, 20, 30, 40}) do
   print(i, v)
end

f = loadstring("i = i + 1")

-- 等价于下面的形式

f = function() i = i + 1 end

i = 10

function f()
   local i = 20

   f2 = loadfile("test2.lua") -- i = i + 1
   f2()

   print("f.i = " .. i)
end

f()
print("global i = " .. i)

-- [[ 结果如下

➜  playbook lua test.lua
f.i = 20
global i = 11

-- ]]

printf=function (fmt, ...) print(string.format(fmt, ...)) end

function my_func(v)
   if v == 10 then
      error("value == 10")
   else
      return "good"
   end
end

function test_pcall()
   print("========== test_pcall ==========")
   local bad_func = function ()
      print('calling bad_func')
      return my_func(10)
   end
   local good_func = function ()
      print('calling good_func')
      return my_func(20)
   end

   local status, err = pcall(bad_func)
   printf("status = %s, err = '%s'", tostring(status), tostring(err))

   local status, value = pcall(good_func)
   printf("status = %s, value = %s", tostring(status), tostring(value))
end

function test_xpcall()
   print("========== test_xpcall ==========")
   local bad_func = function ()
      print('calling bad_func')
      return my_func(10)
   end
   local good_func = function ()
      print('calling good_func')
      return my_func(20)
   end
   local on_failed_fn = function(err)
      printf("on failed. err = '%s'", tostring(err))
      print(debug.traceback())
   end

   xpcall(bad_func, on_failed_fn)
   xpcall(good_func, on_failed_fn)
end

test_pcall()
test_xpcall()

-- [[ output
➜  playbook lua test.lua
========== test_pcall ==========
calling bad_func
status = false, err = 'test.lua:5: value == 10'
calling good_func
status = true, value = good
========== test_xpcall ==========
calling bad_func
on failed. err = 'test.lua:5: value == 10'
stack traceback:
    test.lua:41: in function <test.lua:39>
    [C]: in function 'error'
    test.lua:5: in function 'my_func'
    (...tail calls...)
    [C]: in function 'xpcall'
    test.lua:44: in function 'test_xpcall'
    test.lua:49: in main chunk
    [C]: in ?
calling good_func
-- ]]

producer = coroutine.create(
   function()
      local send = function(x)
         last_command = coroutine.yield(x)
         return last_command
      end

      while true do
         local x = io.read()
         last_command = send(x)
         if last_command == 'quit' then
            break
         end
      end
   end
)

function consumer()
   local last_command = nil

   local receive = function(x)
      local status, value = coroutine.resume(producer, last_command)
      last_command = value
      return value
   end

   while true do
      local x = receive()
      if x == nil then
         break
      end
      io.write("ECHO ", x, "\n")
   end
   assert(last_command == nil)
end

consumer()

-- main.lua
function Entry(t)
   fields = {"author", "book_name", "publisher", "year"}
   print("----- Entry -----")
   for i, v in ipairs(fields) do
      print(string.format("%s = %s", v, tostring(t[i])))
   end
end

dofile("datafile")


-- datafile

Entry{"Donald E. Knuth",
"Literate Programming",
"CSLI",
1992}

Entry{"Jon Bentley",
"More Programming Pearls",
"Addison-Wesley",
1990}


-- [[ output
➜  playbook lua test.lua
----- Entry -----
author = Donald E. Knuth
book_name = Literate Programming
publisher = CSLI
year = 1992
----- Entry -----
author = Jon Bentley
book_name = More Programming Pearls
publisher = Addison-Wesley
year = 1990
-- ]]

local _m = {
   __tostring = function ()
      return o.c
   end,
   __add = function (a, b)
      return a.c + b.c
   end,
   __index = function (t, k)
      -- t是调用对象，而非metatable
      print(t == obj1, t == obj2, t == _m)
      print('request key = ' .. k)
      if k == 'e' then
         return 10
      else
         return 20
      end
   end
}

local function make_obj(c)
   o = {c = c}
   setmetatable(o, _m)
   return o
end

local function inspect_obj(o)
   for k,v in pairs(o) do
      print('key = ' .. k .. ', value = ' .. v)
   end
end

obj1 = make_obj(10)
obj2 = make_obj(20)
print(obj1 + obj2)

inspect_obj(obj1)
print(obj1.e, obj1.f)
print(rawget(obj1, 'e'), rawget(obj1, 'c'))

-- [[ output
➜  workspace lua test.lua
30
key = c, value = 10
true	false	false
request key = e
true	false	false
request key = f
10	20
nil	10
-- ]]

Set = {} -- 数据结构类
Set.mt = {} -- 类的metatable
-- 类字段
Set.version = "1.0.0"
Set.name = "yan"

function Set.new(t)
   local inst = {}
   for i, v in ipairs(t) do
      inst[v] = true
   end
   setmetatable(inst, Set.mt)
   return inst
end

Set.mt.__tostring = function (obj)
   local tmp = {}
   for k in pairs(obj) do
      table.insert(tmp, k)
   end
   return "{" .. table.concat(tmp, ",") .. "}"
end

Set.mt.__add = function(a, b)
   local tmp = Set.new({})
   assert (getmetatable(a) == Set.mt)
   assert (getmetatable(b) == Set.mt)
   for k in pairs(a) do
      tmp[k] = true
   end
   for k in pairs(b) do
      tmp[k] = true
   end
   return tmp
end

a = Set.new({1,2,3,4})
b = Set.new({5,6,7})
print("a = " .. tostring(a))
print("b = " .. tostring(b))
c = a + b
print("c = " .. tostring(c))

local pk = function () end -- 使用函数对象可以作为key.
-- local pk = {} -- 或者是空表（空表地址）

function track(t)
   local proxy = {}
   proxy[pk] = t
   setmetatable(proxy, mt)
   return proxy
end

mt = {
   __index = function(proxy, k)
      t = proxy[pk]
      print(string.format("access table %s field %s ...", tostring(t), tostring(k)))
      return t[k]
   end
}


t = { a= 10, b = 20}
pt = track(t)
print(pt.a)
for k in pairs(pt) do
   print(k)
end

-- [[ 扫描下面所有的keys的话，这个pk还是可以看到的
> dofile("test.lua")
access table table: 0x7fc62c407030 field a ...
10
function: 0x7fc62c402bd0
-- ]]

-- /usr/bin/env lua
-- coding:utf-8
-- Copyright (C) dirlt

local _M = {}           -- 局部的变量
_M._VERSION = '1.0'     -- 模块版本

local mt = { __index = _M }

function _M.new(self, width, height)
    return setmetatable({ width=width, height=height }, mt)
end

function _M.get_square(self)
    return self.width * self.height
end

function _M.get_circumference(self)
    return (self.width + self.height) * 2
end

return _M

local rect = require 'kv' -- 上面module命名为kv.lua

obj = rect:new(10, 20)
print(obj:get_square(), obj:get_circumference())

for k in pairs(obj) do
   print(k)
end

Account = {balance = 0}

function Account:new (o) -- same as Account.new(self, o), self = Account
  o = o or {}
  setmetatable(o, self)
  self.__index = self -- 这样可以找到类字段
  return o
end

function Account:add_balance(value)
   self.balance = self.balance + value
   return self
end

account = Account:new()
print(rawget(account, 'balance'), account.balance) -- nil, 0
account:add_balance(10)
account:add_balance(20)
print(account.balance)

SubAccount = Account:new()

function SubAccount:add_level(value)
   self.level = self.level + value
   return self
end

sub_account = SubAccount:new({level = 10})
sub_account:add_balance(10)
sub_account:add_level(50)
print(sub_account.balance, sub_account.level)

local function search(k, plist)
   for i = 1, #plist do
      local v = plist[i][k]
      if v then return v end
   end
end

function createClass(...)
   local c = {}
   local parents = { ... }
   setmetatable(c, {__index = function(t, k)
                       return search(k, parents)
   end})
   c.__index = c

   function c:new(o)
      o = o or {}
      setmetatable(o, c)
      return o
   end
   return c
end

t = {}
mt = getmetatable(t)
if mt == nil then
   mt = {}
   setmetatable(t, mt)
end
mt.__mode = "k" -- 设置成为弱引用

key = function() end
t[key] = 10

key = function() end -- 原来的key被gc, 所以(key, 10)这个entry会被删除
t[key] = 20

-- 现在还有两个entries.
print('===== before gc =====')
for k in pairs(t) do; print(k, t[k]); end

print('===== after gc =====')
collectgarbage()
-- 现在只有(key, 20)这个entry
for k in pairs(t) do; print(k, t[k]); end