Merger.h

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#ifndef UtilAlgos_Merger_h
#define UtilAlgos_Merger_h

#include "FWCore/Framework/interface/global/EDProducer.h"
#include "FWCore/Framework/interface/Event.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"
#include "FWCore/Utilities/interface/transform.h"
#include "FWCore/Utilities/interface/InputTag.h"
#include "DataFormats/Common/interface/CloneTrait.h"
#include <vector>

template<typename InputCollection,
     typename OutputCollection = InputCollection,
     typename P = typename edm::clonehelper::CloneTrait<InputCollection>::type>
class Merger : public edm::global::EDProducer<> {
public:
  explicit Merger( const edm::ParameterSet& );
  ~Merger() override;

private:
  void produce( edm::StreamID, edm::Event&, const edm::EventSetup&) const override;
  typedef std::vector<edm::EDGetTokenT<InputCollection> > vtoken;
  vtoken srcToken_;
};

template<typename InputCollection, typename OutputCollection, typename P>
Merger<InputCollection, OutputCollection, P>::Merger( const edm::ParameterSet& par ) :
  srcToken_( edm::vector_transform(par.template getParameter<std::vector<edm::InputTag> >( "src" ), [this](edm::InputTag const & tag){return consumes<InputCollection>(tag);} ) ) {
  produces<OutputCollection>();
}

template<typename InputCollection, typename OutputCollection, typename P>
Merger<InputCollection, OutputCollection, P>::~Merger() {
}

template<typename InputCollection, typename OutputCollection, typename P>
void Merger<InputCollection, OutputCollection, P>::produce( edm::StreamID, edm::Event& evt, const edm::EventSetup&) const {
  std::unique_ptr<OutputCollection> coll( new OutputCollection );
  for( typename vtoken::const_iterator s = srcToken_.begin(); s != srcToken_.end(); ++ s ) {
    edm::Handle<InputCollection> h;
    evt.getByToken( * s, h );
    for( typename InputCollection::const_iterator c = h->begin(); c != h->end(); ++c ) {
      coll->push_back( P::clone( * c ) );
    }
  }
  evt.put(std::move(coll));
}

#endif