Re: table.remove problem

[Doug Rogers <rogers@...>]

Patrick Donnelly wrote:

> I've found something I believe is undocumented in the manual about the
> behavior of table.remove. If you have a table (as an array) with n
> elements and you call table.remove(t, n+1) or with anything greater
> than n, you remove the last element.

Wow. I hadn't noticed that:

$ /usr/local/bin/lua -e "t={1,2,3} table.remove(t,4) print(#t)"
2

I don't know whether this was the intended behavior, but I don't like
it. I would prefer that it do nothing if the index is invalid.

Here's a one-line patch that checks the index first:

----------------
*** ltablib-orig.c      2007-11-13 08:00:18.000000000 -0500
--- ltablib.c   2007-11-13 08:21:15.000000000 -0500
***************
*** 118,124 ****
  static int tremove (lua_State *L) {
    int e = aux_getn(L, 1);
    int pos = luaL_optint(L, 2, e);
!   if (e == 0) return 0;  /* table is `empty' */
    luaL_setn(L, 1, e - 1);  /* t.n = n-1 */
    lua_rawgeti(L, 1, pos);  /* result = t[pos] */
    for ( ;pos<e; pos++) {
--- 118,124 ----
  static int tremove (lua_State *L) {
    int e = aux_getn(L, 1);
    int pos = luaL_optint(L, 2, e);
!   if ((pos > e) || (pos <= 0)) return 0;  /* check index and size */
    luaL_setn(L, 1, e - 1);  /* t.n = n-1 */
    lua_rawgeti(L, 1, pos);  /* result = t[pos] */
    for ( ;pos<e; pos++) {
----------------

After patch:

$ ./lua -e "t={1,2,3} table.remove(t,4) print(#t)"
3

Doug

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