void MyApp::CastradosMenu(Bar& bar)
{
    bar.Add(my_name, [=] { PromptOK("something") });
    if(should_have_something)
       bar.Add("something", ...);
....
}

MyApp::MyApp() {
    menup.Set([=](Bar& bar) {
        bar.Sub("Cadastros", [=](Bar& bar) { CastradosMenu(bar); });
    });
}