Control/AthenaKernel/AthenaKernel/ClassID_traits.h

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/*
  Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration
*/
 
#ifndef ATHENAKERNEL_CLASSID_TRAITS_H
#define ATHENAKERNEL_CLASSID_TRAITS_H
 
#include "AthenaKernel/ClassName.h"
#include "GaudiKernel/ClassID.h"
 
#include <string>
#include <typeinfo>
#include <type_traits>
#include <concepts>
 

#define MY_STATIC_ASSERT( B ) \
  static_assert (B, "You should use the CLASS_DEF macro to define CLID and VERSION")
class ClassID_trait_dummy{};

template <typename T>
struct ClassID_traits {
  // Always false, but needs to depend on T to prevent the assertions
  // from being instantiated too early.
  static const bool s_isDataObject = std::same_as<T, ClassID_trait_dummy>;
  using has_classID_tag = std::false_type;
  static const int s_version = 0;
 
  static constexpr CLID ID() {
    MY_STATIC_ASSERT(s_isDataObject);
    return CLID_NULL;
  }
 
  static const std::string& typeName() {
    MY_STATIC_ASSERT(s_isDataObject);
    static const std::string dummy;
    return dummy;
  }
 
  static const std::type_info& typeInfo() {
    MY_STATIC_ASSERT(s_isDataObject);
    return typeid(int);
  }
};
 

template <typename T>
requires requires () {
  { T::classID() } -> std::convertible_to<CLID>;
}
struct ClassID_traits<T> {
  static const bool s_isDataObject = true;

  static CLID ID() {
    return T::classID(); 
  }

  static const std::string& typeName() {
    static const std::string tname = Athena::typeinfoName(typeid(T));
    return tname;
  }

  static const std::type_info& typeInfo() {
    return typeid(T);
  }
 
  using has_version_tag = std::false_type;
  using has_classID_tag = std::false_type;
 
  static const int s_version = 0;
 
  // Is this is true, these types will automatically be made
  // const when added to StoreGate.
  static const bool s_isConst = false;
};
 
#undef MY_STATIC_ASSERT
 
#endif // not ATHENAKERNEL_CLASSID_TRAITS_H