use PerlQt5::QtCore;
use PerlQt5::QtGui;
use PerlQt5::QtWidgets;

package MyApp;
use base qw(PerlQt5::QtCore::QCoreApplication);

package MyPushButton;
use base qw(PerlQt5::QtWidgets::QPushButton);

package main;
my $app = MyApp->new(scalar @ARGV, \@ARGV);

$app = PerlQt5::QtWidgets::QApplication->new( 'Hello, World!', undef);

# but crash here with error ... QWidget: Cannot create a QWidget without QApplication
my $button = PerlQt5::QtWidgets::QPushButton->new( 'Hello, World!', undef);