acad join poly entities vshadow

void App::on_join()
{
    try
    {
        // Query user for two entities
        Polyline primary = user_select_entity(L"Select first entity\n").cast<Polyline::db_type>();
        // ...
        Polyline secondary = user_select_entity(L"Select second entity\n").cast<Polyline::db_type>();

        // Open or create layer
        Layer layer = Layer::open(L"test", true);

        // Create joined polyline
        Polyline joined = Polyline::create();
        joined->upgradeOpen();
        joined->setColorIndex(1);

        if (!primary.join(secondary, joined))
            return;

        // And add to layer
        layer.append(joined);
    } catch (std::logic_error &ex)
    {
        acutPrintf(L"Logic error: %s\n", wstring(ex.what()).c_str());
    } catch (std::runtime_error &ex)
    {
        acutPrintf(L"Runtime error: %s\n", wstring(ex.what()).c_str());
    } catch (std::bad_alloc &ex)
    {
        acutPrintf(L"Allocation error: %s\n", wstring(ex.what()).c_str());
    }
}