set a Lua table as metatable of a userdata?

["lists@..." <lists@...>]

Hi,

This doesn't seem to work in my code, but I wanted a sanity check - am I trying to do something illegal in Lua?

I want to create a fulluserdata, but assign a Lua table to it as metatable (mt1), and in turn assign a C++ created metatable (mt2) to the first (mt1)

Essentially, I want to be able to interact with a fulluserdata as if it were a table by treating mt1 as a proxy, and yet still inherit class methods from C functions in mt2.

The problem is that the userdata does not seem to be looking up values in the metatable mt1 - can anyone see what I'm doing wrong?

pseudocode:

registerClass {

luaL_newmetatable(L, classname)

luaL_openlib(L, NULL, methods, 0)

}

newInstance {

lua_newtable(L); // mt1

// create a test value

lua_pushstring(L, "half")

lua_pushnumber(L, 0.5)

lua_settable(L, -3) // mt1.half = 0.5

void * udata = (void *)lua_newuserdata (L, sizeof(void *));

udata = new Object();

// duplicate userdata at index 1 for returning later

lua_pushvalue(L, -1)

lua_insert(L, 1)

// udata.mt = mt1

lua_setmetatable(L, -2);

// get class metatable (mt2)

luaL_getmetatable(L, classname)

lua_setmetatable(L, -2); // mt1.mt = mt2

// remove mt1 from stack

lua_settop(L, 1)

// return userdata to Lua

return 1

}

Lua:

a = Class() -- calls newInstance in C

print(type(a)) -- userdata 

print(a.half) -- should print 0.5 by finding "half" in the metatable mt1, but triggers an error:

PANIC: unprotected error in call to Lua API: attempt to index global 'a' (a userdata value))

Why isn't my table mt1 acting as metatable to the lua object?

Thanks in advance!