Re: [ANNOUNCE] Lua 5.0 (alpha) now available
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- Subject: Re: [ANNOUNCE] Lua 5.0 (alpha) now available
- From: John Belmonte <jvb@...>
- Date: 2002年8月17日 12:23:01 +0900
Roberto wrote:
I'd like to see a generator in the library for lists that doesn't
include the index as ipairs does:
for v in list(t) do ... end
Such generator would have to keep its own state, and so would be more
expensive than `ipairs'...
I'm a curious guy so I decided to test out your theory. In my simple
timing tests I couldn't see a significant performance difference between
ipairs and a list generator I implemented (below).
While doing this excercise, I ran into a few other issues:
* use of var_1 in for loop
The passing of var_1 to the generator function in the for loop seems
arbitrary. Indeed, I didn't need it in the list implementation, and
could likewise picture situations where more than var_1 are
needed. Why not just rely on closures?
Even passing the table to the generator seems dubious, as a
generator may simply synthesize a sequence of numbers, for example,
and not require a table at all.
* use of rawgeti in table generators
Use of raw accessors precludes array and list proxies.
-John
----
static int list (lua_State *L) {
lua_Number i = lua_tonumber(L, lua_upvalueindex(1));
luaL_check_type(L, 1, LUA_TTABLE);
i++; /* next value */
lua_pushnumber(L, i);
lua_replace(L, lua_upvalueindex(1));
lua_rawgeti(L, 1, (int)i);
return 1;
}
static int luaB_list (lua_State *L) {
luaL_check_type(L, 1, LUA_TTABLE);
lua_pushnumber(L, 0); /* initial value */
lua_pushcclosure(L, list, 1); /* return generator */
lua_pushvalue(L, 1); /* and state */
return 2;
}
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