Re: Replacement for luaL_openlib in Lua 5.1

[Rici Lake <lua@...>]

On 2-Dec-05, at 9:46 PM, David Burgess wrote:

> On 12/3/05, Rici Lake <lua@ricilake.net> wrote:
> > As far as I know, lua_replace will not work with the LUA_ENVIRONINDEX
> > pseudo-index, [...]
> This can be done, as it is in loadlib.c and liolib.c. It requires that 
> the
> C function that is doing the lua_replace has its own lua stack (i.e. 
> has
> been lua_call()ed).

Right you are; there is a special check in lua_replace for that very 
case. So I take it back, you can set your own environment with 
LUA_ENVIRONINDEX

>  I do not understand why.

The io library uses an environment table for data shared between the 
various io methods: specifically, the current input and output file 
descriptors. I imagine that the package system has a similar need.

The 5.0.2 io library uses the "FILE" metatable for this purpose, but 
that makes the data non-private:

Lua 5.0.2  Copyright (C) 1994-2004 Tecgraf, PUC-Rio
> f = io.open"/dev/null"
> =f._input
file (0x8072170)
> =f._output
file (0x80721d0)
> =f
file (0x8072b10)
> io.output(f)
> =f._output
file (0x8072b10)

--> contrast (note that the fenv wouldn't be visible without the debug 
library, which is one of the reasons you shouldn't include the debug 
library in production builds)

Lua 5.1 (beta)  Copyright (C) 1994-2005 Lua.org, PUC-Rio
> for k, v in pairs(debug.getfenv(io.read)) do print(k,v) end
1       file (0x281eaf00)
2       file (0x281eaf58)
__close function: 0x8082900
> =io.stdin
file (0x281eaf00)
> =io.stdout
file (0x281eaf58)
>