void lua_resizetable

["Sean Riley" <sean@...>]

Title: void lua_resizetable

Hello,

I have a situation where I am storing potentially 1000’s of lua tables that I need to reference quickly from C. One optimal way of doing this seemed to be to put them into the array portion of the global table, that way I can use LUA_GLOBALSINDEX to easily get at those tables by a single integer lookup. But… the global table doesn’t seem to have an array – just a hash table, and adding to it with rawseti even with an integer index just puts the new values in the hash table.

I couldn’t find a way to force the global table to have an array, so I made this function that lives in lapi.c:

LUA_API void lua_resizetable (lua_State *L, int idx, int n) {

  StkId o;

  lua_lock(L);

  api_checknelems(L, 1);

  o = index2adr(L, idx);

  api_check(L, ttistable(o));

  luaH_resizearray(L, hvalue(o), n);

  luaC_barriert(L, hvalue(o), L->top-1);

  L->top--;

  lua_unlock(L);

}

So I can then call:

lua_resizetable(ec.L, LUA_GLOBALSINDEX, 10000);

Now the global table has an array and I can use rawseti and rawgeti to access my tables in linear time with code like:

lua_rawgeti(ec.L, LUA_GLOBALSINDEX, m_value);

Sure, I could have used another non-global table, but then I would have to look that table up, push it on the stack at an appropriate index every time, instead of using LUA_GLOBALSINDEX which is always valid.

Is this the wrong thing to do?

-------------------

Sean Riley

Lead Programmer, Metaplace.

"All problems in computer science can be solved by another level of indirection", Butler Lampson, 1972