lua hacking wondering

[Jeffrey Drake <wackysteak@...>]

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I am trying to install an '__existingindex' metatable method. But not 
quite working.

The code I am trying to do: (excuse the lack of a patch, but I am using 
a custom directory arrangement for my lua framework (osx))

ltm.c @ 28
void luaT_init (lua_State *L) {
  static const char *const luaT_eventname[] = {  /* ORDER TM */
    "__index", "__existingindex", "__newindex", "__usedindex",

ltm.h @ 18
typedef enum {
  TM_INDEX,
  TM_EXISTINGINDEX,
  TM_NEWINDEX,

lvm.c @ 147

/*
** Function to index a table.
** Receives the table at `t' and the key at `key'.
** leaves the result at `res'.
*/
const TObject *luaV_gettable (lua_State *L, const TObject *t, TObject 
*key,
                              int loop) {
  if (loop > MAXTAGLOOP)
    luaG_runerror(L, "loop in gettable");
  if (ttistable(t)) {  /* `t' is a table? */
    Table *h = hvalue(t);

    /* start EXISTINGINDEX HACK  */
    const TObject *tm = fasttm(L, h->metatable, TM_EXISTINGINDEX);
    if (tm != NULL)
    {
        if (ttisfunction(tm))
        {
            callTMres(L, tm, t, key);
            return L->top;
        }
    }

    /* end HACK */

    const TObject *v = luaH_get(h, key);  /* do a primitive get */
    if (!ttisnil(v)) return v;
    else return luaV_index(L, t, key, loop+1);
  }
  else return luaV_getnotable(L, t, key, loop+1);
}


I do not claim to understand lua internals very well, but I basically 
could figure out all of it but how the loops were working.

This is how it works:

Anubis:~/.tmp/lua-5.0.2/src/lua jdrake$ rlwrap lua
Lua 5.0.2  Copyright (C) 1994-2004 Tecgraf, PUC-Rio
> blah = {}
> blah.x = 5
> print (blah.x)
5
> ximp = {}
> function ximp.__existingindex(t,k) print("existing index: ", k); 
return k end
> setmetatable(blah, ximp)
> print (blah.x)
5
>

From what I can tell the function definitely isn't being called.

An example of __index being called:

> function ximp.__index(t,k) print("index: ", k); return 0 end
> print (blah.y)
index:  y
0


Any ideas here?


"Reportedly, he remarked to one of his Christian missionary friends: 
'What you teach us to do is admirable, but what you teach us to believe 
is foolish'."
- - Referring to King Mongkut of Siam
http://en.wikipedia.org/wiki/Mongkut
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