produce_helpers.h

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#ifndef Framework_produce_helpers_h
#define Framework_produce_helpers_h
// -*- C++ -*-
//
// Package:     Framework
// Class  :     produce_helpers
//
//
// Author:      Chris Jones
// Created:     Fri Apr 15 10:25:20 EDT 2005
//

// system include files
#include <memory>
#include <optional>
// user include files

namespace edm::eventsetup {

  namespace produce {
    struct Null;
  }

  template <typename FromT, typename ToT>
  void moveFromTo(FromT& iFrom, ToT& iTo) {
    iTo = std::move(iFrom);
  }

  template <typename FromT, typename ToT>
  void moveFromTo(std::unique_ptr<FromT>& iFrom, ToT& iTo) {
    iTo = std::move(iFrom);
  }
  template <typename FromT, typename ToT>
  void moveFromTo(std::optional<FromT>& iFrom, ToT& iTo) {
    iTo = std::move(iFrom.value());
  }

  namespace produce {
    struct Null {};
    template <typename T>
    struct EndList {
      static_assert(
          (not std::is_pointer_v<T>),
          "use std::shared_ptr or std::unique_ptr to hold EventSetup data products, do not use bare pointers");
      using tail_type = T;
      using head_type = Null;
    };
    template <typename T>
    struct product_traits {
      using type = T;
    };
    template <typename T>
    struct product_traits<T*> {
      using type = EndList<T*>;
    };
    template <typename T>
    struct product_traits<std::unique_ptr<T>> {
      using type = EndList<std::unique_ptr<T>>;
    };
    template <typename T>
    struct product_traits<std::shared_ptr<T>> {
      using type = EndList<std::shared_ptr<T>>;
    };
    template <typename T>
    struct product_traits<std::optional<T>> {
      using type = EndList<std::optional<T>>;
    };

    template <typename T>
    struct size {
      using type = typename product_traits<T>::type;
      constexpr static int value = size<typename type::head_type>::value + 1;
    };
    template <>
    struct size<Null> {
      constexpr static int value = 0;
    };

    template <typename T>
    struct smart_pointer_traits {
      using type = typename T::element_type;
      static auto getPointer(T const& iPtr) -> decltype(&*iPtr) { return &*iPtr; }
    };

    template <typename T>
    struct smart_pointer_traits<std::unique_ptr<const T>> {
      using type = T;
      static auto getPointer(std::unique_ptr<const T> const& iPtr) -> decltype(&*iPtr) { return &*iPtr; }
    };

    template <typename T>
    struct smart_pointer_traits<std::shared_ptr<const T>> {
      using type = T;
      static auto getPointer(std::shared_ptr<const T> const& iPtr) -> decltype(&*iPtr) { return &*iPtr; }
    };

    template <typename T>
    struct smart_pointer_traits<std::optional<T>> {
      using type = T;
      static T const* getPointer(std::optional<T> const& iPtr) {
        if (iPtr.has_value()) {
          return &*iPtr;
        }
        return nullptr;
      }
    };

    template <typename T, typename FindT>
    struct find_index {
      using container_type = typename product_traits<T>::type;
      template <typename HeadT, typename TailT>
      constexpr static int findIndexOf() {
        if constexpr (not std::is_same_v<TailT, FindT>) {
          using container_type = typename product_traits<HeadT>::type;
          return findIndexOf<typename container_type::head_type, typename container_type::tail_type>() + 1;
        } else {
          return 0;
        }
      }
      constexpr static int value =
          findIndexOf<typename container_type::head_type, typename container_type::tail_type>();
    };
    namespace test {
      template <typename T>
      const char* name(const T*);
    }

  }  // namespace produce
}  // namespace edm::eventsetup

#endif