Let's expect two things: you are using strong typed variables and you need to overload a class with pure virtual method.
In this case you will need to specify all arguments as in C++ in the Qore source code. Example:
Example 2.3. Pure virtual method in QAbstractItemModel
class MyModel inherits QAbstractItemModel
{
# ... skipped some methods...
# reimplementation of
# virtual int columnCount ( const QModelIndex & parent = QModelIndex() ) const = 0
# is a must now - or the method will not be found correctly:
columnCount(QModelIndex $parent=new QModelIndex()) returns int
{
return 1;
}
}