in src/annoyluamodule.cc [105:113]
static int tostring(lua_State* L) {
Impl* self = getAnnoy(L, 1);
lua_pushfstring(
L,
"annoy.AnnoyIndex object (%dx%d, %s distance)",
self->get_n_items(), self->get_f(), Distance::name()
);
return 1;
}