data_default_record_trait.h

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#ifndef Framework_data_default_record_trait_h
#define Framework_data_default_record_trait_h
// -*- C++ -*-
//
// Package:     Framework
// Class  :     data_default_record_trait
//
//
// Author:      Chris Jones
// Created:     Thu Apr  7 07:59:56 CDT 2005
//

namespace edm {

  template <typename T>
  class ESHandle;

  // Special class to denote that the default record should be used.
  struct DefaultRecord {};

  namespace eventsetup {
    template <class T>
    struct MUST_GET_RECORD_FROM_EVENTSETUP_TO_GET_DATA;

    template <class DataT>
    struct data_default_record_trait {
      //NOTE: by default, a data item does not have a default record
      typedef MUST_GET_RECORD_FROM_EVENTSETUP_TO_GET_DATA<DataT> type;
    };

    template <typename T>
    struct default_record {
      using data_type = typename T::value_type;
      using RecordT = typename eventsetup::data_default_record_trait<data_type>::type;
    };

    template <typename T>
    using default_record_t = typename default_record<T>::RecordT;
  }  // namespace eventsetup

  template <typename T>
  struct ESHandleAdapter {
    using value_type = T;
  };
}  // namespace edm

#define EVENTSETUP_DATA_DEFAULT_RECORD(_data_, _record_) \
  namespace edm::eventsetup {                            \
    template <>                                          \
    struct data_default_record_trait<_data_> {           \
      typedef _record_ type;                             \
    };                                                   \
  }

#endif