Passing a C++ struct and use its method within a Lua function

[dazzabaijan]

Currently I have a Msg class that I'm looking to pass into a Lua function, and within the function it'll call setters/getters or other methods of the Msg class based on certain rules i.e. if-else statements. As a prototype, here's the Msg class that I've been using to test the binding

class Msg
{
public:
  Msg()  { }
  ~Msg() { }
  void setField( int fVal, const std::string& str ) { this->_msgMap[fVal] = str; }
  std::string getField( int fVal )
  {
    std::map<int, std::string>::iterator itField = this->_msgMap.begin();

    for ( ; itField != this->_msgMap.end() ; itField++ )
    {
      if ( itField->first == fVal )
      {
        return this->_msgMap[fVal];
      }
    }
    return( "" );
  }
  void removeField( int fVal )
  {
    std::map<int, std::string>::iterator itField = this->_msgMap.begin();

    for ( ; itField != this->_msgMap.end() ; itField++ )
    {
      if ( itField->first == fVal )
      {
        this->_msgMap.erase( itField );
        return;
      }
    }
  }

private:
  std::map <int, std::string>  _msgMap;
};

The Lua script e.g. test_function.lua may look something like

function test_function( Msg )
  msgType = Msg:getField( 35 )
  if msgType == "D" then
    Msg:setField( 40, "Y" )
  end
end

In the main of my test code, I've been able to make it work using

int main()
{
  lua_State* s = luaL_newstate();
  luaL_openlibs(s);

  luaaa::LuaClass<Msg> luaMsg(s, "Msg");
  luaMsg.ctor();
  luaMsg.fun("setField", &Msg::setField);
  luaMsg.fun("getField", &Msg::getField);

  luaL_dofile(myLua, "test_function.lua");

  Msg* msg = new Msg();
  msg->setField( 35, "D" );

  lua_getglobal( s, "test_function" );

  Msg** msgPtr = (Msg **) lua_newuserdata(s, sizeof( Msg*));
  *msgPtr = msg;
  luaL_setmetatable( s, "Msg" );

  lua_call( s, 1, 0 );

  lua_close(s);
  delete msg;
}

Now, this works for now, within this test code. My first question would be could you comment on whether that's the correct way to do it? If not what's the better way to do it?

In my actual code, it'd simply look in directories for other different Lua files and load the bindings so they can be used. However, once I started to incorporate the changes above, it'd seem that the luaaa::LuaClass constructor does work sometimes, but often times it'd hit the following error(shown on gdb):

ProgrammeName: .../include/luaaa/luaaa.hpp:979: luaaa::LuaClass< <template-parameter-1-1> >::LuaClass(lua_State*, const char*, const luaL_Reg*) [with TCLASS = Msg; lua_State = lua_State; luaL_Reg = luaL_Reg]: Assertion `klassName == nullptr' failed.

So for whatever reason, it looks like whatever string name I've given to the LuaClass object would sometimes be assigned to the klassName variable, and from there it would fail the assert(klassName == nullptr); line since klassName is no longer a nullptr. Any ideas why this might be happening? Is my usage of your binder incorrect?