Array index access from metatable field/method - c++

Question

I have some metatables that reflect some C++ classes/structs. I usually rely on __index to get called for any fields/methods for the object and resolve them in one function.
The difficulty I'm having is when I want to pass parameters to a field, like so:
anim = playerInfo.animations
while anim do
print (anim)
numstates = anim.numstates
for i = 1, numstates do
state = anim.states(i) <--- This line right here is the issue
print(state)
end
anim = anim.next
end
Here is the relevant C code:
static const struct luaL_Reg objanimationlib_m[] = {
{"__tostring", objanimation2string},
{"__index", objanimationget},
{"__newindex", objanimationset},
{NULL, NULL}
};
luaL_newmetatable(L, "objanimation");
lua_pushvalue(L, -1); // duplicates the metatable
luaL_setfuncs(L, objanimationlib_m, 0);
Inside the __index function:
else if (!strcmp(field, "states"))
{
int number = (int)luaL_checknumber(L, 3) - 1; // -1 cuz Lua is not 0-based
if (number >= anim->numstates)
return 0;
PushUserdata(&anim->states[number], "objstate");
}
Running the script, I get an error:
Warning: [string "test.lua"]:13: bad argument #3 to '__index' (number expected, got no value)
I feel like I'm missing something stupidly simple. What is it?
Edit: Here's my solution, inside the __index function:
else if (!strcmp(field, "states"))
{
lua_newtable(L);
int i;
for (i = 0; i < anim->numstates; i++)
{
PushUserdata(&anim->states[i], "objstate");
lua_rawseti(L, -2, i+1);
}
}
This returns a table full of userdata elements. Might be expensive, so this would also increase performance:
anim = playerInfo.animations
while anim do
print (anim)
numstates = anim.numstates
states = anim.states
for i = 1, numstates do
print(states[i])
end
anim = anim.next
end

Answer 1

state = anim.states(i)
is equivalent to
do local f=anim.states; state=f(i) end
and so your metamethod never sees i.
In other words, the index metamethod receives two arguments, the table and the key. What it returns is not necessarily subject to any metamethods, unless you make it explicitly so.
I'd go for defining __len returning numstates and for __call to handle anim.states(i), so that you code can be written
for i = 1, #anim do
state = anim(i)
print(state)
end