How can I determine the type of lightuserdata?

I'm adding Lua Scripting to my game engine (C++) using the Lua C API.

I'm pushing my objects using lua_pushlightuserdata(lua_State *L, void *p) and when I want to get the objects I use lua_touserdata(lua_State *L, int idx), but I don't know what object I'm getting using lua_touserdata().

How can I check that?

Here's some example code:

bool LuaScript::InitScript(const char* code, GameObject * container)
{
   CloseLua();

   bool ret = false;
   luaState = LuaNewState();
   luaL_openlibs(luaState);
   RegisterAPI(luaState);

   /*Load the code inside .lua script and set "this" to reference the GameObject 
   containing the script and "renderer" referencing SpriteRenderer class (GameObject component)
   to show you the example.*/
   if (luaL_loadstring(luaState, code) == 0) {
       lua_pushlightuserdata(luaState, container);
       lua_setglobal(luaState, "this");

       SpriteRenderer* spr = new SpriteRenderer();
       lua_pushlightuserdata(luaState, spr);
       lua_setglobal(luaState, "renderer");
       ret = LuaUtils::CallFunction(luaState, NULL);
   }
   else {
       LOG_WARNING("Cannot load lua script of '%s': %s", container->name.c_str(), lua_tostring(luaState, -1));
   }
   return ret;
}    

void LuaScript::RegisterAPI(lua_State* luaState)
{
   luaL_Reg GameObjectAPI[] = 
   {
       { "SetActive", SetGameObjectActive },
       { NULL, NULL }
   };
   LuaUtils::RegisterLibrary(luaState, GameObjectAPI, "gameObject");
}

int LuaScript::SetGameObjectActive(lua_State * luaState)
{
   int arguments = lua_gettop(luaState);
   if (arguments != 2) {
       LOG_WARNING("SetActive(GameObject, bool) takes 2 arguments!");
   }
   else {
       if (lua_islightuserdata(luaState, 1)) {
/*---> Here it's the problem. I'm assuming that this data is a GameObject 
       but it can be other kind of data like SpriteRenderer.*/
           GameObject* go = (GameObject*)lua_touserdata(luaState, 1);
           bool active = lua_toboolean(luaState, 2);
           go->SetActive(active);
       }
   }
   return 0;
}

.lua Script:

function Start()
   gameObject.SetActive(this,false)
   gameObject.SetActive(renderer,false)
end

In the above example, gameObject.SetActive(this,false) works because this is a GameObject, but gameObject.SetActive(renderer,false) should not work because renderer is not a GameObject. But it works because I don't know a way to check if it's a GameObject or SpriteRenderer and the variable go at line GameObject* go = (GameObject*)lua_touserdata(luaState, 1); inside LuaScript::SetGameObjectActive(lua_State * luaState) is malformed (nullptr's, memory errors, etc.) because I'm assigning the data as a GameObject.