Re: Adding lightuserdatas that are invisible to scripts

[Ignacio Burgueño <ignaciob@...>]

Peter Pimley wrote:
> Hello Lua enthusiasts :)
>
> I've been making quite light use of lua (from C/C++) on and off for a
> couple of years now and I love it to bits :)
>
> There are two things that I always wanted, but have never quite figured
> out how to do.  I'm sure they're probably quite easy.  Here's the first;
> I'll put the other in a separate mail.
>
> Quite often I'll create a lua_State, and at the same time I'll create
> some C structures or C++ objects.  Something along the lines of:
>
> lua_State * lua = luaL_newstate ();
> MyThing * thing = new MyThing ();
>
> Semantically, the C++ objects 'belong' to the lua_State.  I have more
> than one lua_State in my program, and I'd like each one to carry its
> associated C++ structures around with it.  However (and this is the
> important bit) I don't want any scripts that the lua_State executes to
> be able to access or modify the objects.  The C++ objects should be
> invisible to any lua scripts.

EHm, if I understood right, you want to access MyThing objects only from 
C functions called by Lua. You can have it available as an upvalue of 
the function. You do that when registering the functions in Lua:

lua_pushlightuserdata(L, thing);
lua_pushcclosure(L, your_C_function, 1);
lua_setglobal(L, "yourFunctionName");


Regards,
Ignacio Burgueño