RefItemGet.h

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#ifndef DataFormats_Common_RefItemGet_h
#define DataFormats_Common_RefItemGet_h

/*----------------------------------------------------------------------
  
RefItemGet: Free function to get pointer to a referenced item.


----------------------------------------------------------------------*/
#include "DataFormats/Common/interface/EDProductGetter.h"
#include "DataFormats/Common/interface/RefCore.h"
#include "DataFormats/Common/interface/RefCoreGet.h"

namespace edm {

  namespace refitem {

    template <typename C, typename T, typename F, typename K>
    inline void findRefItem(RefCore const& refCore, C const* container, K const& key) {
      F finder;
      T const* item = finder(*container, key);
      refCore.setProductPtr(item);
    }

    template <typename C, typename T, typename F, typename KEY>
    struct GetRefPtrImpl {
      static T const* getRefPtr_(RefCore const& product, KEY const& key) {
        T const* item = static_cast<T const*>(product.productPtr());
        if (item != nullptr) {
          return item;
        }
        auto prodGetter = product.productGetter();
        if (nullptr == prodGetter) {
          item = static_cast<T const*>(product.productPtr());
          if (item != nullptr) {
            //Another thread updated the value since we checked
            return item;
          }
        }
        C const* prod = edm::template getProductWithCoreFromRef<C>(product, prodGetter);
        /*
        typename C::const_iterator it = prod->begin();
         std::advance(it, item.key());
         T const* p = it.operator->();
        */
        F func;
        item = func(*prod, key);
        product.setProductPtr(item);
        return item;
      }
    };

    template <typename C, typename T, typename F>
    struct GetRefPtrImpl<C, T, F, unsigned int> {
      static T const* getRefPtr_(RefCore const& product, unsigned int key) {
        T const* item = static_cast<T const*>(product.productPtr());
        if (item != nullptr) {
          return item;
        }
        auto getter = product.productGetter();
        if (getter == nullptr) {
          auto prod = product.productPtr();
          if (prod != nullptr) {
            //another thread updated the value since we last checked.
            return static_cast<T const*>(prod);
          }
        }
        C const* prod = edm::template tryToGetProductWithCoreFromRef<C>(product, getter);
        if (prod != nullptr) {
          F func;
          item = func(*prod, key);
          product.setProductPtr(item);
          return item;
        }
        unsigned int thinnedKey;
        std::tie(prod, thinnedKey) = edm::template getThinnedProduct<C>(product, key, getter);
        F func;
        item = func(*prod, thinnedKey);
        product.setProductPtr(item);
        return item;
      }
    };
  }  // namespace refitem

  template <typename C, typename T, typename F, typename KEY>
  inline T const* getRefPtr(RefCore const& product, KEY const& iKey) {
    return refitem::GetRefPtrImpl<C, T, F, KEY>::getRefPtr_(product, iKey);
  }

  namespace refitem {
    template <typename C, typename KEY>
    struct IsThinnedAvailableImpl {
      static bool isThinnedAvailable_(RefCore const& product, KEY const& key) { return false; }
    };

    template <typename C>
    struct IsThinnedAvailableImpl<C, unsigned int> {
      static bool isThinnedAvailable_(RefCore const& ref, unsigned int key) {
        if (ref.productPtr() != nullptr) {
          return true;
        }
        if (ref.isTransient()) {
          return false;
        }
        auto getter = ref.productGetter();
        if (getter != nullptr) {
          return ref.isThinnedAvailable(key, getter);
        }
        //another thread may have updated the cache
        return nullptr != ref.productPtr();
      }
    };
  }  // namespace refitem

  template <typename C, typename KEY>
  inline bool isThinnedAvailable(RefCore const& product, KEY const& iKey) {
    return refitem::IsThinnedAvailableImpl<C, KEY>::isThinnedAvailable_(product, iKey);
  }

  //
  // The thinned may point to parent collection, in which case the Ref-to-parent is returned
  //
  // If thinned does not contain the element of the Ref-to-parent, a Null Ref is returned.
  //
  // If parent collection is not thinned, or there is no thinning relation between parent and thinned,
  // an exception is thrown
  template <typename C, typename T, typename F>
  Ref<C, T, F> thinnedRefFrom(Ref<C, T, F> const& parent,
                              RefProd<C> const& thinned,
                              edm::EDProductGetter const& prodGetter) {
    if (parent.id() == thinned.id()) {
      return parent;
    }

    auto thinnedKey = prodGetter.getThinnedKeyFrom(parent.id(), parent.key(), thinned.id());
    if (std::holds_alternative<unsigned int>(thinnedKey)) {
      return Ref<C, T, F>(thinned, std::get<unsigned int>(thinnedKey));
    } else if (std::holds_alternative<detail::GetThinnedKeyFromExceptionFactory>(thinnedKey)) {
      auto ex = std::get<detail::GetThinnedKeyFromExceptionFactory>(thinnedKey)();
      ex.addContext("Calling edm::thinnedRefFrom()");
      throw ex;
    }

    return Ref<C, T, F>();
  }

  //
  // The thinned may point to parent collection, in which case the Ref-to-parent is returned
  //
  // If thinned does not contain the element of the Ref-to-parent, a Null Ref is returned.
  //
  // If parent collection is not thinned, or there is no thinning relation between parent and thinned,
  // a Null Ref is returned
  template <typename C, typename T, typename F>
  Ref<C, T, F> tryThinnedRefFrom(Ref<C, T, F> const& parent,
                                 RefProd<C> const& thinned,
                                 edm::EDProductGetter const& prodGetter) {
    if (parent.id() == thinned.id()) {
      return parent;
    }

    auto thinnedKey = prodGetter.getThinnedKeyFrom(parent.id(), parent.key(), thinned.id());
    if (std::holds_alternative<unsigned int>(thinnedKey)) {
      return Ref<C, T, F>(thinned, std::get<unsigned int>(thinnedKey));
    }

    return Ref<C, T, F>();
  }
}  // namespace edm

#endif