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So as far as I've seen, most C code uses the Lua manual's example code
structure to iterate tables. Namely:

while (lua_next(L, idx) != 0) {
  /* code here */
  lua_pop(L, 1); /* pop value */

This structure goes back to the Lua 4.0 manual [1].

I noticed that the C for loop results in a more natural construction:

for (lua_pushnil(L); lua_next(L, idx); lua_pop(L, 1)) {
   /* code here always has the key/value pair on the stack */

One of the advantages I see is that the for loop code block must
follow good stack discipline (not leaving anything on the stack or
incidentally removing the value) because the lua_pop must always pop
the value. For example, this code is not very flexible to future

while (lua_next(L, idx)) {
  lua_pushboolean(L, 1);
  lua_rawset(L, someidx); /* value removed by rawset */

So does anyone use the for loop construct? I appreciate the manual
version is more clear in how it works but it is taken as the idiomatic
way to iterate tables. (In fact, the Lua source code uses that style
in the base libraries.)


Patrick Donnelly