Special indices (was Re: Simple C++ wrapper)

[Mark Hamburg <mark@...>]

This reminds me of an issue I ran into when considering a Lua patch to  
provide fast access to the environment table for userdata objects  
(more below), LUA_REGISTRYINDEX is both the index used to access the  
registry and the boundary for the special indices. It would be nice to  
have a separate #define for the latter -- e.g., LUA_MINSTACKINDEX-- so  
that when adding new special indices code that needs to know where the  
stack indices end (particularly the negative indices) would be updated  
on a recompile. With that in place, the below code would become:

	if(index < 0 && index >= LUA_MINSTACKINDEX)
		index -= 1;

Actually, it might be useful to simply pre-reserve some expansion  
space though that assumes that nothing else in a release would force a  
recompile.

Mark

P.S. The specific case that triggered this thinking for me was around  
adding LUA_UDENVINDEX which is defined as pointing to the environment  
table of the userdata value at index 1. It results in an error if  
index 1 does not contain a full userdata. Its intended use is to make  
it easier to create userdata objects that use their environment tables  
to store references to other Lua objects -- e.g., lua_getfield(L,  
LUA_UDENVINDEX, "on_click").

On Apr 24, 2009, at 1:17 PM, TNHarris wrote:

> Hello,
>
> I'd like to wrap the Lua API in a C++ class to take advantage of
> overloading and default arguments, etc. I looked at Paolo Capriotti's
> library but it seems to be oriented for using C++ objects on the  
> stack.
> I don't need that so much as just a more convenient way to use Lua.
>
> I think something like this would be favorable:
>
> namespace luaxx
> {
>        class State
>        {
>                void getTable(int index = -2)
>                        { lua_gettable(m_L, index); };
>                void getTable(int index = -2, int key = -1)
>                {
>                        if (index < 0 && index > LUA_REGISTRYINDEX)
>                                index -= 1;
>                        push(key);
>                        lua_gettable(m_L, index);
>                };
>        };
> }
>
> Does anyone have a library already made?
>
> -- tom
> telliamed@whoopdedo.org