Fun with serializing Lua functions (was Re: Sharing userdata among stats.)

[Sean Conner <sean@...>]

It was thus said that the Great Sean Conner once stated:
> 
>   Functions are an interesting problem.  Yes, you can get the bytecode
> (string.dump()) but there are issues:  1) the default serialization of
> functions will only work on the same architecture and 2) does not contain
> the current values of any upvalues.  1) is not an issue with your usecase,
> but 2) is.  Again, that can be worked around by not only encoding the
> function (via string.dump()) but also including any upvalues, which can get
> quite interesting (oh, an upvalue might be math.floor() or _G itself!).

  So I played around with this today, and I created a github repository for
those interested:

	https://github.com/spc476/LuaFunctionSerialize

  Right now, the code only supports Lua 5.1, and is not meant for any real
production (it's just a "proof-of-concept" right now).  But it works.  At
least, for the one complicated recursive function I've tested so far.  

	1) It uses string.dump() to get the bytecode
	2) It serializes any upvalues [1]
	3) It only serializes the environment if it's the global environment
	4) It can handle any normal Lua global value (like io.stdin or getmetatable)
	5) It will probably fail horribly if given a Lua function written in
           C (I did not check for this condition)

  So there you have it.  Something to play around with.

  -spc

[1]	bools, numbers, tables and functions.  Tables can have cycles.