Qt objects. Q_PRIVATE_SLOT: qobjectdefs. h; Q_REQUIRED_RPCNDR_H_VERSION: [HOST]; Q_RETURN_ARG. h; Q_Q: qglobal. h; Q_QNAN: qnumeric. . Main Page · Related Pages · Namespaces · Namespace List Qt::ConnectionType callbackType() const;. Q_PRIVATE_SLOT(d_func(), void. h; Q_REQUIRED_RESULT: qglobal. Similar to Q_PRIVATE_PROPERTY, Q_PRIVATE_SLOT is used when you have a slot in a private class that you want to be considered part of the API [HOST]e.