SwitchProducer.cc

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#include "FWCore/Framework/interface/global/EDProducer.h"
#include "FWCore/Framework/interface/MakerMacros.h"
#include "FWCore/ParameterSet/interface/ConfigurationDescriptions.h"

namespace edm {
  class SwitchProducer : public global::EDProducer<> {
  public:
    explicit SwitchProducer(ParameterSet const& iConfig);
    ~SwitchProducer() override = default;
    static void fillDescriptions(ConfigurationDescriptions& descriptions);
    void produce(StreamID, Event& e, EventSetup const& c) const final {}
  };

  SwitchProducer::SwitchProducer(ParameterSet const& iConfig) {
    auto const& moduleLabel = iConfig.getParameter<std::string>("@module_label");
    auto const& chosenLabel = iConfig.getUntrackedParameter<std::string>("@chosen_case");
    callWhenNewProductsRegistered([=](edm::BranchDescription const& iBranch) {
      if (iBranch.moduleLabel() == chosenLabel) {
        if (iBranch.branchType() != InEvent) {
          throw Exception(errors::UnimplementedFeature)
              << "SwitchProducer does not support non-event branches. Got " << iBranch.branchType()
              << " for SwitchProducer with label " << moduleLabel << " whose chosen case is " << chosenLabel << ".";
        }

        // With consumes, create the connection to the chosen case EDProducer for prefetching
        this->consumes(edm::TypeToGet{iBranch.unwrappedTypeID(), PRODUCT_TYPE},
                       edm::InputTag{iBranch.moduleLabel(), iBranch.productInstanceName(), iBranch.processName()});
        // With produces, create a producer-like BranchDescription
        // early-enough for it to be flagged as non-OnDemand in case
        // the SwithcProducer is on a Path
        this->produces(iBranch.unwrappedTypeID(), iBranch.productInstanceName()).setSwitchAlias(iBranch.moduleLabel());
      }
    });
  }

  void SwitchProducer::fillDescriptions(ConfigurationDescriptions& descriptions) {
    ParameterSetDescription desc;
    desc.add<std::vector<std::string>>("@all_cases");
    desc.addUntracked<std::string>("@chosen_case");
    descriptions.addDefault(desc);
  }
}  // namespace edm

using edm::SwitchProducer;
DEFINE_FWK_MODULE(SwitchProducer);