c++ classes & lua

Question

I want to have C++ objects that I can read/write in both C++ & Lua.

I have looked at: http://www.lua.org/pil/28.html

However, I do not like that solution, since my objects have constructors & destructors (and they are important as I use RAII and these take care of reference counts).

What I don't like in the PIL solution is that the object is allocated in Lua's heap.

What i want instead, is to create hte C++ object on my own, and just have lua have a way to do get/set on them.

Does anyone have a good tutorial/link on this?

Tanks!

Answer 1

Seems like a factory is the way to go? E.g. instead of just dynamically creating your object in Lua via "standard" means, can you call a function for Create and Destroy?

Answer 2

Use the placement new. See here for a handy template:

template< typename T >
void my_newuserdata( lua_State * L ) {
   new ( reinterpret_cast< T * >( lua_newuserdata( L, sizeof( T ) ) ) ) T();
}

template< typename T >
int my_gc( lua_State * l ) {
   reinterpret_cast< T * >( lua_touserdata( L, 1 ) )->~T();
   return 0;
}

(Untested, see link above for details.)

Answer 3

I seem to remember a co-worker getting that kind of thing going, both Lua and C++ objects as 1st-class citizens and completely operable in both directions.

If memory serves me right it was based upon Lua++ but at this point I am not sure, sorry.