Data structures are difficult to handle

Current code design makes difficult to handle data structures, e.g. in TRestHits.h

class TRestHits : public TObject {
   public:
    Int_t fNHits;         ///< Number of punctual energy depositions, it is the length
                          ///< for all the array
    Double_t fTotEnergy;  ///< Event total energy

    std::vector<Float_t> fX;          // [fNHits] Position on X axis for each punctual
                                      // deposition (units mm)
    std::vector<Float_t> fY;          // [fNHits] Position on Y axis for each punctual
                                      // deposition (units mm)
    std::vector<Float_t> fZ;          // [fNHits] Position on Z axis for each punctual
                                      // deposition (units mm)
    std::vector<Float_t> fT;          // [fNHits] Absolute time information for each punctual deposition
                                      // (units us, 0 is time of decay)
    std::vector<Float_t> fEnergy;     // [fNHits] Energy deposited at each
                                      // 3-coordinate position (units keV)
    std::vector<REST_HitType> fType;  //

Y would suggest to move to a different data structure e.g.

  class TRestHit : public TObject {
    Float_t fX;
    Float_t fY;
    Float_t fZ;
    Float_t fT;
    Float_t fEnergy;
    REST_HitType fType;
   enum REST_HitType { unknown = -1, X = 2, Y = 3, Z = 5, XY = 6, XZ = 10, YZ = 15, XYZ = 30 };
  };

 class TRestHits : public TObject {
   public:
     //fNHits is not needed anymore, it is just hitArray.size( );
     Double_t fTotEnergy;  ///< Event total energy
     std::vector<TRestHit> hitArray;          // Array of hits
 

This would simplify the handling of TRestHits using standard std iterators, for instance this part of the code mimic std iterators:

  class TRestHits_Iterator : public std::iterator<std::random_access_iterator_tag, TRestHits_Iterator> {

The implementatio of this proposal would imply a lot of changes in the code and perhaps the root files might loose the backward compatibility, but it will be a big improvement that would simplify the code.

Let me know what do you think, I can help with the migration.