Method get_object_identity

library/LuaWrapper.cpp:498–526

* Given a DF object reference or type, safely retrieve its identity pointer. */

 * Given a DF object reference or type, safely retrieve its identity pointer.
 */
const type_identity *LuaWrapper::get_object_identity(lua_State *state, int objidx,
                                               const char *ctx, bool allow_type,
                                               bool keep_metatable)
{
    if (allow_type && !keep_metatable && lua_isstring(state, objidx))
    {
        int idx = luaL_checkoption(state, objidx, NULL, primitive_types);
        return primitive_identities[idx];
    }

    if (!lua_getmetatable(state, objidx))
        luaL_error(state, "Invalid object in %s", ctx);

    if (!allow_type && !lua_isuserdata(state, objidx))
        luaL_error(state, "Object expected in %s", ctx);

    if (!is_valid_metatable(state, objidx, -1))
        luaL_error(state, "Invalid object metatable in %s", ctx);

    // Extract identity from metatable
    lua_rawgetp(state, -1, &DFHACK_IDENTITY_FIELD_TOKEN);

    type_identity *id = (type_identity*)lua_touserdata(state, -1);
    if (!id)
        luaL_error(state, "Invalid object identity in %s", ctx);

    lua_pop(state, keep_metatable ? 1 : 2);
    return id;
}

static bool check_type_compatible(lua_State *state, int obj1, int obj2,
                                  const type_identity **type1, const type_identity **type2,