Why is their mainwindow:arguments twice? What does this mean?

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C++

QT

Why is their MainWindow:Arguments twice? What does this mean?
MainWindow::Arguments MainWindow::arguments()
{
bool ok1, ok2;
float a1 = ui->argument1Input->text().toFloat(&ok1);
float a2 = ui->argument2Input->text().toFloat(&ok2);
if (!ok1 || !ok2)
{
QMessageBox messageBox;
messageBox.setIconPixmap(QPixmap(":/icon.png"));
messageBox.setText("One of your entries is not a valid
number.");
messageBox.setWindowTitle("Error");
messageBox.exec();
}
return Arguments(a1, a2);
}

What I have tried:

Why is their MainWindow:Arguments twice? What does this mean?
MainWindow::Arguments MainWindow::arguments()
{
 bool ok1, ok2;
 float a1 = ui->argument1Input->text().toFloat(&ok1);
 float a2 = ui->argument2Input->text().toFloat(&ok2);
 if (!ok1 || !ok2)
 {
 QMessageBox messageBox;
 messageBox.setIconPixmap(QPixmap(":/icon.png"));
 messageBox.setText("One of your entries is not a valid
number.");
 messageBox.setWindowTitle("Error");
 messageBox.exec();
 }
 return Arguments(a1, a2);
}