ThinnedRefSet.h

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#ifndef DataFormats_Common_ThinnedRefSet_h
#define DataFormats_Common_ThinnedRefSet_h
//
// Package:     DataFormats/Common
// Class  :     ThinnedRefSet
//
#include "DataFormats/Common/interface/Handle.h"
#include "DataFormats/Common/interface/Ref.h"
#include "DataFormats/Common/interface/RefItemGet.h"

#include <unordered_set>

namespace edm {
  class EDProductGetter;

  enum class ThinnedRefSetMode { throwOnInvalidParentRef, ignoreInvalidParentRef };

  template <typename C>
  class ThinnedRefSet {
  public:
    class Filler {
    public:
      explicit Filler(ThinnedRefSet<C>* set, RefProd<C> thinned, edm::EDProductGetter const& prodGetter)
          : set_(set), thinnedRefProd_(thinned), prodGetter_(prodGetter) {}

      template <typename T, typename F>
      void insert(Ref<C, T, F> const& ref) {
        if (ref.isNonnull()) {
          Ref<C, T, F> thinnedRef;
          if (set_->invalidParentRefMode_ == ThinnedRefSetMode::ignoreInvalidParentRef) {
            thinnedRef = tryThinnedRefFrom(ref, thinnedRefProd_, prodGetter_);
          } else {
            thinnedRef = thinnedRefFrom(ref, thinnedRefProd_, prodGetter_);
          }
          if (thinnedRef.isNonnull()) {
            set_->keys_.insert(thinnedRef.key());
          }
        }
      }

    private:
      ThinnedRefSet<C>* set_;
      RefProd<C> thinnedRefProd_;
      edm::EDProductGetter const& prodGetter_;
    };

    explicit ThinnedRefSet(ThinnedRefSetMode mode = ThinnedRefSetMode::throwOnInvalidParentRef)
        : invalidParentRefMode_(mode) {}

    Filler fill(RefProd<C> thinned, edm::EDProductGetter const& prodGetter) {
      return Filler(this, thinned, prodGetter);
    }

    void clear() { keys_.clear(); }

    bool contains(unsigned int key) const { return keys_.find(key) != keys_.end(); }

  private:
    std::unordered_set<unsigned int> keys_;
    ThinnedRefSetMode invalidParentRefMode_;
  };
}  // namespace edm

#endif