pointersEqual.h

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#ifndef art_Utilities_pointersEqual_h
#define art_Utilities_pointersEqual_h
// Compare two pointers taking into account possible multiple inheritance

#include "canvas/Utilities/Exception.h"

#include <type_traits>

namespace art {
  template <typename T1, typename T2>
  inline std::enable_if_t<std::is_same<T1, T2>::value ||
                            std::is_base_of<T1, T2>::value ||
                            std::is_base_of<T2, T1>::value,
                          bool>
  pointersEqual(T1* t1, T2* t2)
  {
    return t1 == t2;
  }

  // Not compatible.
  template <typename T1, typename T2>
  std::enable_if_t<!std::is_same<T1, T2>::value &&
                     !std::is_base_of<T1, T2>::value &&
                     !std::is_base_of<T2, T1>::value,
                   bool>
  pointersEqual(T1*, T2*)
  {
    throw art::Exception(art::errors::LogicError)
      << "Tried to compare two incompatible pointers.\n";
  }
} // namespace art

#endif /* art_Utilities_pointersEqual_h */

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