static_cast<void(QButtonGroup::*)(QAbstractButton *, bool)>(&QButtonGroup::m_buttonGroup)
Starting from the wrong end look at whatever is in the parentheses:
is a static object, in the
class. And the
means use the address of this object. So that is the original item that is to be cast, to whatever is in the angle brackets (
). The angle brackets contain:
void(QButtonGroup::*)(QAbstractButton *, bool)
Which is a function pointer definition. The
part says this is a pointer to something in the
class. The parentheses around this tell us it's a function rather than a data pointer. The following parentheses contain the definition of the parameters to be passed to the function, and the preceding
part tells us that the function does not have a return type.
Without more context it's not possible to say more.