Re: need to convert C func -> closure within core (no stack usage, please..:)

[Mike Pall <mikelu-0503@...>]

Hi,

Asko Kauppi wrote:
> I'm modifying the 'luaT_gettmbyobj()' function within ltm.c (5.1w4) in 
> order to provide a couple of metamethod-like functions that are in fact 
> fixed within the core.
>
> The problem is.. how exactly to do that?
>
> I have the lua_CFunction pointers, of course, but creating a closure
> without touching the stack (if I touch the stack, well, BOOOM...)   Any
> ideas from harder-than-hard core programmers welcome.

Why not create them once during initialization? Creating them at runtime
for every metamethod access imposes a certain overhead (that will certainly
ruin the performance possibly gained by creating a new core type). I hope
you realize that closures are heap allocated ...

- Add a Table * pointer in the global_State struct.
- Create a table when opening the universe and store it there.
- Create the closures and add them to the table (__index = ..., ...).
- Use the pointer from the global_State in the switch statement in
  luaT_gettmbyobj when your new core type is referenced.


But this bears the question: Why do you want to extend the core with
a new type? Is USERDATA or LIGHTUSERDATA not good enough for your purpose?
Did you benchmark this? Care to explain in more detail?

I ask, because maybe there is a problem behind it that might be better
solved with a (new) generic meta-mechanism. Or maybe not.

Bye,
     Mike