root/ROOT/RNTupleCollectionWriter.hxx

0001 /// \file ROOT/RNTupleCollectionWriter.hxx
0002 /// \ingroup NTuple ROOT7
0003 /// \author Jakob Blomer <jblomer@cern.ch>
0004 /// \date 2024-02-22
0005 /// \warning This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback
0006 /// is welcome!
0007
0008 /*************************************************************************
0009  * Copyright (C) 1995-2024, Rene Brun and Fons Rademakers.               *
0010  * All rights reserved.                                                  *
0011  *                                                                       *
0012  * For the licensing terms see $ROOTSYS/LICENSE.                         *
0013  * For the list of contributors see $ROOTSYS/README/CREDITS.             *
0014  *************************************************************************/
0015
0016 #ifndef ROOT7_RNTupleCollectionWriter
0017 #define ROOT7_RNTupleCollectionWriter
0018
0019 #include <ROOT/REntry.hxx>
0020 #include <ROOT/RNTupleUtil.hxx>
0021
0022 #include <cstddef>
0023 #include <memory>
0024 #include <utility>
0025
0026 namespace ROOT {
0027 namespace Experimental {
0028
0029 // clang-format off
0030 /**
0031 \class ROOT::Experimental::RNTupleCollectionWriter
0032 \ingroup NTuple
0033 \brief A virtual ntuple used for writing untyped collections that can be used to some extent like an RNTupleWriter
0034 *
0035 * This class is between a field and a ntuple.  It carries the offset column for the collection and the default entry
0036 * taken from the collection model.  It does not, however, own an ntuple model because the collection model has been
0037 * merged into the larger ntuple model.
0038 */
0039 // clang-format on
0040 class RNTupleCollectionWriter {
0041    friend class RCollectionField;
0042
0043 private:
0044    std::size_t fBytesWritten = 0;
0045    ClusterSize_t fOffset;
0046    std::unique_ptr<REntry> fDefaultEntry;
0047
0048 public:
0049    explicit RNTupleCollectionWriter(std::unique_ptr<REntry> defaultEntry)
0050       : fOffset(0), fDefaultEntry(std::move(defaultEntry))
0051    {
0052    }
0053    RNTupleCollectionWriter(const RNTupleCollectionWriter &) = delete;
0054    RNTupleCollectionWriter &operator=(const RNTupleCollectionWriter &) = delete;
0055    ~RNTupleCollectionWriter() = default;
0056
0057    std::size_t Fill() { return Fill(*fDefaultEntry); }
0058    std::size_t Fill(REntry &entry)
0059    {
0060       const std::size_t bytesWritten = entry.Append();
0061       fBytesWritten += bytesWritten;
0062       fOffset++;
0063       return bytesWritten;
0064    }
0065
0066    ClusterSize_t *GetOffsetPtr() { return &fOffset; }
0067 }; // class RNTupleCollectionWriter
0068
0069 } // namespace Experimental
0070 } // namespace ROOT
0071
0072 #endif // ROOT7_RNTupleCollectionWriter