Return value of G4VSensitiveDetector::ProcessHits

G4VSensitiveDetector's method ProcessHits must be implemented by the user. nain4 provides n4::sensitive_detector to ease implementing G4VSensitiveDetector subclasses. Because ProcessHits is mandatory, nain4 obliges the user to provide an implementation as a construction argument to n4::sensitive_detector.

The aforementioned method returns bool for historical reasons. (This seems to be undocumented, but see this Geant4 forum comment.)

The summary is:

• The actual value returned doesn't matter: it is ignored by G4.
• One day the Geant4 developers may decide to change the return type to void at which point old code will give compilation errors.