Lua 语言介绍

Lua 语言介绍

罗进
luojinlj@gmail.com

简单、高效、易移植、易嵌入

C/C++

Objective-C

.Net

Awesome
Java
Fortan

LuaPerl

Erlang

RubyLuaBridge

Lunatic Python
Numeric Lua

了解从比较开始
Lua5.1 Python2.6 Ruby1.9
生日 1993 1989 1995
籍贯巴西荷兰日本
安装 http luarocks easyinstall gem
交互 console ilua ipython irb
注释 -- # #
程序库少多多多
类型数量 8 37 >50
虚拟机 VM 基于寄存器基于栈基于栈
体积 win dll 120k, 可裁剪 2.155M 1.983M
速度 mandelbrot GCC(0.41ms) Java(4.96ms) PHP(9.19ms)
( 分形图形 ) 1.94ms 11.85ms 29.71ms
JIT 即时编译 LuaJIT ~ x150 Pypy ~ x20 Rubinius ~ x20

简单： 8 种类型
• string ：” abcdfeg” ， 0 结尾
• nil ： null
• boolean ： true ， false
• number ：统一 short,integer,float 到 double
• function ：带有逻辑的变量
local f = function (x) return x*x, x*x*x end
f(2) --4, 8
• userdata ： C 指针，用户自定义类型
• thread ：非抢占式协程 coroutine
• table ： hash 表，统一了序列式和关联式容器，索引从 1 开始
t1 = {1,2,3} t2= {s=“abs”,n=1.2,f=function(x) return x end}
t1[2] --2 t2.s --abs t2.n --1.2 t2.f(2) –2
只有 string, table, function, thread4 中类型分配在堆上，需要 GC 回收，其他类型分配在栈上

简单：基于原型的面向对象
metatable
String = {}
function String:new(s)
return setmetatable({value = s or ''}, {__index = String})
end
function String:print() print(self.value) end
function String:print2() print(self.value) end
String:new(‘hello ’):print() --hello

-- inheritance
Child=String:new(‘inheritance’)
function Child:print() print(‘child of string: ’ .. self.value) end
c = setmetatable({}, {__index = Child}}
c:print() -- child of string: inheritance
c:print2() -- inheritance

简单： Coroutines 非抢占式多任务
下载文件从指定地址 test

threads = {} -- list of all live threads host = "www.w3.org"
function get (host, file) -- create coroutine
co = coroutine.create(function() get(host, "/…/html40.txt")
… get(host, "/…/xhtml1.pdf")
if status == "timeout" then get(host, "/../html.html")
coroutine.yield(connection)
end dispatch() -- main loop
end)
table.insert(threads, co)
end

function dispatch ()
while true do
if threads[i] == nil then -- no more threads? 将底层细节和多状态模式
… 屏蔽，使得逻辑流畅易懂
local status, res = coroutine.resume(threads[i])
提高了工业强度
if not res then table.remove(threads, i) end
end
调度可控，显式优于隐式
end

高效：基于寄存器 VM ， LuaJIT
基于寄存器 4 条指令基于栈 11 条指令
local a,t,i 1: LOADNIL 0 2 0 local a,t,i 1: PUSHNIL 3
a=a+i 2: ADD 0 0 2 a=a+i 2: GETLOCAL 0 ; a
3: GETLOCAL 2 ; i
4: ADD
5: SETLOCAL 0 ; a
a=a+1 3: ADD 0 0 250 a=a+1 6: GETLOCAL 0 ; a
7: ADDI 1
8: SETLOCAL 0 ; a
a=t[i] 4: GETTABLE 0 1 2 a=t[i] 9: GETLOCAL 1 ; t
10: GETINDEXED 2 ; i
11: SETLOCAL 0 ; a

LuaJIT
解释器使用自定义字节码格式
直接派发，替代了以前的 switch
用汇编重写

易移植易嵌入： Lua 虚拟机快
照
lua_State lua_State
stack stack
callinfo callinfo

global_State MM GC

易移植易嵌入： Lua 虚拟机结
构
C Library

易嵌入： Lua 虚拟机的栈与宿主程序交互

struct lua_State {
C API 正逆栈 lua_State
global_State *l_G; 索索 statck
引引
StkId stack; lua_pushlightuserdata 6 -1 <…>
StkId top;
lua_getglobal 5 -2 (cfunction)
StkId base;
… lua_pushcfunction 0x20120729
}; lua_newtable 4 -3 (table)
lua_rawseti {‘lua,’ ’pyton’,’ruby’}
/*Function Prototypes*/ lua_pushstring 3 -4 (string)
struct Proto { lua_tostring “script language”
TValue *k; /*constants */ lua_pushboolean 2 -5 true
Instruction *code;
lua_pushnumber 1 -6 123
Tstring **upvalues; lua_tonumber
/*inside funcs*/
function(Lua)
struct Proto **p;
…
};

嵌入示例在栈上交互调用
C 宿主程序 test.c Lua 嵌入脚本 test.lua
#include <lua.h> function lua_func(x)
static int c_func (lua_State *L) { if x<= 1 then
double d = lua_tonumber(L, 1); /* get argument */ return 1
lua_pushnumber(L, sqrt(d)); /* push result */ end
return 1; /* number of results */ return ((lua_func(x-2))+
} lua_func((x-1)))
static int register_c_func (lua_State *L, const char *func_name) { end
lua_pushcfunction(l, c_func);
lua_setglobal(l, func_name); function lua_call_c(x)
} return c_func(x)
static int call_lua_func (lua_State *L, const char *func_name) { end
lua_getglobal(L, func_name);/*get lua function by name*/
lua_pushnumber(L, 1); /*push argument in local stack*/ --test
lua_pcall(L, 1, 1, 0); /*call function*/ local fibonacci = lua_func
return lua_tointeger(L, 1); /*get result from local stack*/ for i = 0, 10 do
} print(fibonacci (i))
int main(int argc, char* argv[]) { end
lua_State *L = luaL_newstate(); /*1.create interpreter*/
luaL_openlibs(L); /*2.register standard libs*/ local sqrt= lua_call_c
register_c_func (L, “c_func“); /*3.register callback function*/ for i = 0, 10 do
luaL_dofile(L, “test.lua”); /*4.load script file*/ print(sqrt(i))
call_lua_func (L, “lua_func”); /*5. call lua function*/ end
lua_close(L); /*6. bye Lua*/
}

嵌入示例 Lua and C array 共享同一内
存
struct CArray { CArray * new_CArray (lua_State *L, …){
size_t size; …
size_t elemsize;//1:char,2;short,4:int,8:double CArray *a = (CArray*) lua_newuserdata(L, nbytes);
float values[1]; …
}; luaL_newmetatable(L, "CArray");
static int getarray (lua_State *L) { luaL_register(L, NULL, arraylib_m);
CArray *a = (CArray*)luaL_checkudata(L, 1, “CArray"); lua_setmetatable(L, -2);
size_t idx= luaL_checkint(L, 2) - 1; lua_setglobal(L, array_name);
luaL_argcheck(L, 0 <= idx …, 2, “error …"); return a;
… }
lua_pushinteger(L, (int*)(a->values)[index]); CArray *a1 = new_CArray(L, “a1", 200, “int”);
return 1; CArray *a2 = new_CArray(L, “a2", 100, “double”);
}
--------------------------------------------------
static const struct luaL_Reg arraylib_m [] = { Test.lua
{"__newindex", setarray}, for i = 1, 10 do
{"__index", getarray}, print(a1(i), a2[i])
{"__call", array_call}, a1[i] , a2[i] = i, i
{NULL, NULL} print(a1(i), a2[i])
}; end

将新建的 userdata 附上 metatable(struct luaL_Reg) ，
就可以在 Lua 中基于对象编程了，实际使用的是宿主函数

Lua 语言介绍

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