in src/annoyluamodule.cc [275:285]
static void createNew(lua_State* L, int f) {
void* self = lua_newuserdata(L, sizeof(Impl));
if (luaL_newmetatable(L, typeAsString())) {
compat_setfuncs(L, getMetatable());
lua_newtable(L);
compat_setfuncs(L, getMethods());
lua_setfield(L, -2, "__index");
}
new (self) Impl(f);
lua_setmetatable(L, -2);
}