[Rivet] Rivet Analysis Class 'Gotcha'

[David Bjergaard]

Hi,

I'm using rivet to do analysis for the BOOST group.  There are a few
idioms that I thought were sensible, but weren't, and they stem from the
same issue.  

Can someone explain why my histogram pointer is set to null:
src/Core/Analysis.cc, Analysis::scale()
>558:    // Set histo pointer to null - it can no longer be used.
>559:    histo = 0;

I didn't allocate the pointer, but it is a member of my class.  This
means I can't do things like: 
   normalize(myHisto,1.0);
   double mean=myHisto->mean();
   double rms=myHisto->rms();
But:
   double mean=myHisto->mean();
   double rms=myHisto->rms();
   normalize(myHisto,1.0);
Is valid.  

I know std::maps are expensive, but I would rather express things
succinctly and then change it later if it becomes a performance issue.
What I have in mind is:
    typedef std::map<std::string,AIDA::IHistogramID*> BookedHistos;
    class MyAnalysis : public Analysis {
      ...
      public:
      void init() {
	Histos["MyHisto"]=bookHistogram1D(...);
      }
      void analyze() {
	Histos["MyHisto"]->fill();
      }
      void finalize(){
	foreach(BookedHistos::value_type h, Histos){
	  //calculate/store statistics for each histo
	  normalize(h);
	}
      }
    private:
      BookedHistos Histos;
    }
But this code will segfault when finalize() is called because the
default destructer will try to delete stuff that is set to NULL by
normalize. 

Sincerely,

    Dave