GroupQueryResult.h

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#ifndef art_Persistency_Common_GroupQueryResult_h
#define art_Persistency_Common_GroupQueryResult_h

// ======================================================================
//
// GroupQueryResult: A pointer-to-const-Group satisfying a query, or an
//                   exception object explaining a failed query.
//
// ======================================================================

#include "canvas/Utilities/Exception.h"
#include "cetlib/exempt_ptr.h"
#include "cetlib_except/exception.h"

#include <memory>

namespace art {
  // defined below:
  class GroupQueryResult;

  // forward declaration:
  class Group;
}

// ======================================================================

class art::GroupQueryResult {
public:
  // c'tors:
  GroupQueryResult(cet::exempt_ptr<Group const>);
  GroupQueryResult(std::shared_ptr<art::Exception const>);

  // observers:
  bool
  succeeded() const
  {
    return static_cast<bool>(result_);
  }
  bool
  failed() const
  {
    return static_cast<bool>(whyFailed_);
  }

  // properties:
  cet::exempt_ptr<Group const>
  result() const
  {
    return result_;
  }
  std::shared_ptr<art::Exception const>
  whyFailed() const
  {
    return whyFailed_;
  }

private:
  cet::exempt_ptr<Group const> result_{nullptr};
  std::shared_ptr<art::Exception const> whyFailed_{nullptr};

  bool
  invariant() const
  {
    return succeeded() != failed();
  }

}; // GroupQueryResult

// ======================================================================

#endif /* art_Persistency_Common_GroupQueryResult_h */

// Local Variables:
// mode: c++
// End: