Wt

 this->setTheme(new Wt::WBootstrapTheme);
 Wt::WContainerWidget* root = this->root();
 Wt::WDateEdit* dte1 = new Wt::WDateEdit(root);
 dte1->setPlaceholderText("EmptyText");
 new Wt::WBreak(root);
 Wt::WDateEdit* dte2 = new Wt::WDateEdit(root);
 new Wt::WBreak(root);
 Wt::WPushButton* evaluate = new Wt::WPushButton("Evaluate",root);
 evaluate->clicked().connect(
    std::bind([=]()  {
    std::cout << dte1->date().isValid() << std::endl; //expected valid result, returns false
    std::cout << dte2->date().isValid() << std::endl; //expected valid result, returns true
   } )
 );