Lua C Functions in C++ class

[Tim Conkling <tconkling@...>]

I have a C++ class that exports some functions to a Lua environment. 
These functions are, of course, static, but they need to access member 
functions/variables of the class. The only way to do this (that I can 
think of) is to make those class members static as well, because 
there's no way to associate any sort of user data with the exported 
functions -- they only receive the lua_State* parameter, so I can't 
tell them which class they belong to when they're called. This wouldn't 
be such a problem, except that it's possible I might want multiple 
instances of this class at once, and clearly if they're both 
manipulating the same static members, there'll be problems, since these 
members really shouldn't be static.

I can't think of a great way to solve this problem that doesn't involve 
jumping through hoops every time a function of the class gets called. 
Is there a design pattern I'm missing here? What do other people do in 
this situation?

Tim