[Rivet] chaining projections together in analysis code

[William Hamish Bell]

Hi,

I would like to chain together two projections that both inherit from FinalState.  Ideally, one would like to produce a projection from the combination of the requirements in the analysis code, e.g.:

    // Projection to find the electrons
    std::vector<std::pair<double, double> > eta_elec;
    eta_elec.push_back(make_pair(-2.5,2.5));
    IdentifiedFinalState el_id(eta_elec, 25.0*GeV);
    el_id.acceptIdPair(PID::ELECTRON);
    FinalState *fs = dynamic_cast<FinalState*>(&el_id);
    assert(fs);
    FromElectroweakDecay elecs(*fs);
    addProjection(elecs, "elecs");

Since the constructor expects a reference to a FinalState instance, there is a dynamic_cast on a pointer to the instance.  The code compiles and runs, but it is safe in terms of the Rivet design?  (I am using Rivet 2.0.0)

Thanks and best regards,

Will