Re: General questions.

[Jamie Webb <j@...>]

On Tue, Jul 06, 2004 at 10:32:00AM -0700, William Roper wrote:
> "If you know how to export your object's functionality to Lua then you
> know how to do it whether the object already exists or not.  The only
> difference is that, rather than allocating the object's memory via
> lua_newuserdata, you will allocate space for a pointer to the object
> and store the pointer in the userdata."
> 
> I just reread this statement, could you elaborate on that a little?
> All the examples I can find both in the book and on the wiki deal with
> creating new instances of a class in lua, not handling existing
> instances of a class from C++.

// Create your class instance
MyClass* instance = new MyClass();

// Create a Lua userdata to point to your object
MyClass** ptr = (MyClass**) lua_newuserdata(L, sizeof(MyClass*));

// Make ptr point to your object
*ptr = instance;

Now you have a userdata representing a pointer to your object sitting
on the Lua stack. You'll need to set its metatable using the
techniques described in the book and wiki, and then return that value
to Lua.

Your methods will be created exatly is described in the book and wiki,
except that you will need to extract the pointer from the userdata and
dereference it in order to get your object, rather than the userdata
itself being the object.

-- Jamie Webb