使用直接 Lua，如何公开现有的 C++ 类对象以在 Lua 脚本中使用?

Let's start off the top, that is by registering PersonManager in Lua. Since it's a singleton, we'll register it as a global.

void registerPersonManager(lua_State *lua)
{
    //First, we create a userdata instance, that will hold pointer to our singleton
    PersonManager **pmPtr = (PersonManager**)lua_newuserdata(
        lua, sizeof(PersonManager*));
    *pmPtr = PersonManager::getInstance();  //Assuming that's the function that 
                                            //returns our singleton instance

    //Now we create metatable for that object
    luaL_newmetatable(lua, "PersonManagerMetaTable");
    //You should normally check, if the table is newly created or not, but 
    //since it's a singleton, I won't bother.

    //The table is now on the top of the stack.
    //Since we want Lua to look for methods of PersonManager within the metatable, 
    //we must pass reference to it as "__index" metamethod

    lua_pushvalue(lua, -1);
    lua_setfield(lua, -2, "__index");
    //lua_setfield pops the value off the top of the stack and assigns it to our 
    //field. Hence lua_pushvalue, which simply copies our table again on top of the stack.
    //When we invoke lua_setfield, Lua pops our first reference to the table and 
    //stores it as "__index" field in our table, which is also on the second 
    //topmost position of the stack.
    //This part is crucial, as without the "__index" field, Lua won't know where 
    //to look for methods of PersonManager

    luaL_Reg personManagerFunctions[] = {
         'get', lua_PersonManager_getPerson,
          nullptr, nullptr
    };

    luaL_register(lua, 0, personManagerFunctions);

    lua_setmetatable(lua, -2);

    lua_setglobal(lua, "PersonManager");
}

现在我们处理PersonManager的get方法:

int lua_PersonManager_getPerson(lua_State *lua)
{
    //Remember that first arbument should be userdata with your PersonManager 
    //instance, as in Lua you would call PersonManager:getPerson("Stack Overflower");
    //Normally I would first check, if first parameter is userdata with metatable 
    //called PersonManagerMetaTable, for safety reasons

    PersonManager **pmPtr = (PersonManager**)luaL_checkudata(
        lua, 1, "PersonManagerMetaTable");
    std::string personName = luaL_checkstring(lua, 2);

    Person *person = (*pmPtr)->getPerson(personName);
    if (person)
        registerPerson(lua, person);    //Function that registers person. After 
                //the function is called, the newly created instance of Person 
                //object is on top of the stack
    else
        lua_pushnil(lua);

    return 1;
}

void registerPerson(lua_State *lua, Person *person)
{
    //We assume that the person is a valid pointer
    Person **pptr = (Person**)lua_newuserdata(lua, sizeof(Person*));
    *pptr = person; //Store the pointer in userdata. You must take care to ensure 
                    //the pointer is valid entire time Lua has access to it.

    if (luaL_newmetatable(lua, "PersonMetaTable")) //This is important. Since you 
        //may invoke it many times, you should check, whether the table is newly 
        //created or it already exists
    {
        //The table is newly created, so we register its functions
        lua_pushvalue(lua, -1);
        lua_setfield(lua, -2, "__index");

        luaL_Reg personFunctions[] = {
            "getAge", lua_Person_getAge,
            nullptr, nullptr
        };
        luaL_register(lua, 0, personFunctions);
    }

    lua_setmetatable(lua, -2);
}

最后处理Person的getAge.

int lua_Person_getAge(lua_State *lua)
{
    Person **pptr = (Person**)lua_checkudata(lua, 1, "PersonMetaTable");

    lua_pushnumber(lua, (*pptr)->getAge());
    return 1;
}

您现在应该在执行 Lua 代码之前调用 registerPersonManager，最好在您创建新的 Lua 状态并打开所需的库之后调用.

local person = PersonManager:getPerson("Stack Overflower");
print(person:getAge());