basic lua binding header helper

example.cpp

#include "lunatic.h"
#include <lua-5.1/lua.hpp>
#include <stdio.h>

class LuaTest {
public:
    LuaTest() {}
    LuaTest(lua_State * L) {}

    static const char className[];
    static Lunatic<LuaTest>::RegType methods[];

    int TestString(lua_State * L) {printf("this string is printed by c++\n");return 0;}
};

class LuaTest2 {
public:
    LuaTest2() {}
    LuaTest2(lua_State * L) {}

    static const char className[];
    static Lunatic<LuaTest2>::RegType methods[];

    int TestString(lua_State * L) {printf("this string is printed by c++\n");return 0;}
};


const char LuaTest::className[] = "LuaTest";

const char LuaTest2::className[] = "LuaTest2";

#define method(class, name) {#name, &class::name}

Lunatic<LuaTest>::RegType LuaTest::methods[] = {
    method(LuaTest, TestString), {nullptr, nullptr}
};

Lunatic<LuaTest2>::RegType LuaTest2::methods[] = {
    method(LuaTest2, TestString), {nullptr, nullptr}
};

int main() {
    lua_State * L = luaL_newstate();
    luaL_openlibs(L);
    // ok to bind multiple classes
    Lunatic<LuaTest>::Register(L);
    Lunatic<LuaTest2>::Register(L);
    // do_file better to use a absolute path
    luaL_dofile(L, "/Users/******************/test.lua");
    lua_close(L);

    return 0;
}

/*
test.lua

test = LuaTest()
test:TestString()
print("test string in lua")

*/

lunatic.h

#pragma once
#include <lua-5.1/lua.hpp>

template <typename T>
class Lunatic {
    typedef struct {T * pt;} userDataType;
public:
    typedef int (T::*mfp)(lua_State * L);
    typedef struct{const char * name; mfp mfunc;} RegType;


    static void Register(lua_State * L) {
        // 用一个tabble 保存栈索引，这个方法表就是要用来保存要导出的成员函数
        lua_newtable(L);
        int methods = lua_gettop(L);

        // 在注册表中新建一个元素, metatable保存其栈索引
        
        luaL_newmetatable(L, T::className);
        int metatable = lua_gettop(L);

        // 全局表(T::className)=methods表
        lua_pushstring(L, T::className);
        lua_pushvalue(L, methods);
        lua_settable(L, LUA_GLOBALSINDEX);

        // 设置metatable 的_metatable元事件
        // 将metatable封装起来，防止外部的获取和修改
        lua_pushliteral(L, "__metatable");
        lua_pushvalue(L, methods);
        lua_settable(L, metatable);

        lua_pushliteral(L, "__index");
        lua_pushvalue(L, methods);
        lua_settable(L, metatable);

        // 设置元表 __tostring和__gc (gc暂且不实现, 我们希望对象的生命周期完全在c++)
        lua_pushliteral(L, "__tostring");
        lua_pushcfunction(L, tostring_T);
        lua_settable(L, metatable);

        lua_pushliteral(L, "__gc");
        lua_pushcfunction(L, gc_T);
        lua_settable(L ,metatable);


        // 设置mt的_call metamethod a()时触发
        lua_newtable(L);
        int mt = lua_gettop(L);
        lua_pushliteral(L, "__call");
        lua_pushcfunction(L, new_T);
        lua_pushliteral(L, "new");
        lua_pushvalue(L, -2);
        lua_settable(L, methods);
        lua_settable(L, mt);
        lua_setmetatable(L, methods);
        
        // fill method table with methods from class T
        for(RegType *l = T::methods; l->name; l++) {
            lua_pushstring(L, l->name);
            lua_pushlightuserdata(L, (void*)l);
            lua_pushcclosure(L, thunk, 1); // 创建closure
            lua_settable(L, methods);
        }

        lua_pop(L, 2); // drop metatabke abd method table
    }

    static T * check(lua_State * L, int narg) {
        userDataType * ud = static_cast<userDataType*> (luaL_checkudata(L, narg, T::className));
        if(nullptr == ud) {
            luaL_typerror(L, narg, T::className);
        }
        return ud->pt;
    }

private:
    Lunatic();

    static int thunk(lua_State * L) {
        T * obj = check(L, 1);
        lua_remove(L, 1);   //remove self
        RegType * l = static_cast<RegType*>(lua_touserdata(L, lua_upvalueindex(1)));
        return (obj->*(l->mfunc))(L);   //call member function
    }
    static int new_T(lua_State * L) {
        lua_remove(L, 1);
        T * obj = new T(L);
        userDataType *ud = static_cast<userDataType*>(lua_newuserdata(L, sizeof(userDataType)));
        ud->pt = obj; // store pointer to object in userdata
        luaL_getmetatable(L, T::className);
        lua_setmetatable(L, -2);
        return 1;
    }
    static int tostring_T (lua_State * L) {
        char buff[32];
        userDataType * ud = static_cast<userDataType*>(lua_touserdata(L, 1));
        T * obj = ud->pt;
        sprintf(buff, "%p", obj);
        lua_pushfstring(L, "%s (%s)", T::className, buff);
        return 1;
    }

    static int gc_T(lua_State * L) {
        userDataType * ud = static_cast<userDataType*>(lua_touserdata(L, 1));
        T * obj = ud->pt;
        delete obj; // call dtor
        return 0;
    }
};