Harmonize const-ness in relation navigation return types

[dudarboh]

BEGINRELEASENOTES

• Make getRelatedToMaxWeightAndObject(), getRelatedToMaxWeightObject(), getRelatedFromMaxWeightObject() return non-const LCObject pointer.

ENDRELEASENOTES

[tmadlener]

Is there a use case where you would need to modify the pointed-to contents? If symmetry is the main argument, I would rather add const to other methods than removing them here.

[dudarboh]

My goal would be that people can easily switch from getRelatedToObjects() to getRelatedToMaxWeightAndObject() by intuitively updating their code, without any extra debugging of const correctness.

For example, I switched from using

EVENT::MCParticle* getMcFromTrack(EVENT::Track* track, const UTIL::LCRelationNavigator& trk2mc){
        auto& objects = trk2mc.getRelatedToObjects(track);
        auto& weights = trk2mc.getRelatedToWeights(track);
        if ( weights.empty() ) return nullptr;
        auto maxWeightIdx = std::max_element(weights.begin(), weights.end()) - weights.begin();
        return static_cast <EVENT::MCParticle*> (objects[maxWeightIdx]);
}

to this

EVENT::MCParticle* getMcFromTrack(EVENT::Track* track, const UTIL::LCRelationNavigator& trk2mc){
    return static_cast <EVENT::MCParticle*> ( trk2mc.getRelatedToMaxWeightObject(track) );
}

and it immediately broke because if I use getRelatedToMaxWeightObject() I had to do this instead:

const EVENT::MCParticle* getMcFromTrack(EVENT::Track* track, const UTIL::LCRelationNavigator& trk2mc){
    return static_cast <const EVENT::MCParticle*> ( trk2mc.getRelatedToMaxWeightObject(track) );
}

or what I do right now to keep everything as it previously was:

EVENT::MCParticle* getMcFromTrack(EVENT::Track* track, const UTIL::LCRelationNavigator& trk2mc){
    return static_cast <EVENT::MCParticle*> ( const_cast<EVENT::LCObject*> (trk2mc.getRelatedToMaxWeightObject(track) ));
}

so I wouldn't mind switching everything to const, if we also switch the old getRelatedToObjects() to returning const.
However, then the whole MarlinReco is broken, because I assume nobody did static_cast to const, and it should be fixed everywhere these methods are used.

[tmadlener]

Thanks for the detailed explanation. Given that, I think this is indeed the quickest and easiest solution.