TTreeReaderArray.h

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// @(#)root/tree:$Id$
// Author: Axel Naumann, 2010-08-02
// Author: Vincenzo Eduardo Padulano CERN 02/2025
 
/*************************************************************************
 * Copyright (C) 1995-2013, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/
 
#ifndef ROOT_TTreeReaderArray
#define ROOT_TTreeReaderArray
 
#include "TTreeReaderValue.h"
#include "TTreeReaderUtils.h"
#include <type_traits>
#include <cstddef>
 
namespace ROOT {
namespace Internal {
 
/** \class TTreeReaderArrayBase
Base class of TTreeReaderArray.
*/
 
class TTreeReaderArrayBase : public TTreeReaderValueBase {
   struct StreamerElementArrayInfo {
      int fArrayNDims{};               // Number of dimensions of the n-dim array
      int fArrayCumulativeLength{};    // Total length of the n-dim array as if it were flattened
      int fTDataTypeCode{};            // A number representing the value type of the array, queried via TDataType.
      std::array<int, 5> fArrayDims{}; // Length of each dimension of the n-dim array. Max 5 dimensions, aligned with
                                       // TStreamerElement::fMaxIndex
   };
   StreamerElementArrayInfo FillStreamerElementArrayInfo(TStreamerElement *elem);
 
public:
   TTreeReaderArrayBase(TTreeReader *reader, const char *branchname, TDictionary *dict)
      : TTreeReaderValueBase(reader, branchname, dict)
   {
   }
 
   std::size_t GetSize() const { return fImpl ? fImpl->GetSize(GetProxy()) : 0; }
   bool IsEmpty() const { return !GetSize(); }
 
   EReadStatus GetReadStatus() const override { return fImpl ? fImpl->fReadStatus : kReadError; }
 
   bool IsContiguous() const { return fImpl->IsContiguous(GetProxy()); }
 
   /// Returns the `sizeof` of the collection value type. Returns 0 in case the value size could not be retrieved.
   std::size_t GetValueSize() const { return fImpl ? fImpl->GetValueSize(GetProxy()) : 0; }
 
protected:
   void *UntypedAt(std::size_t idx) const { return fImpl->At(GetProxy(), idx); }
   void CreateProxy() override;
   bool GetBranchAndLeaf(TBranch *&branch, TLeaf *&myLeaf, TDictionary *&branchActualType,
                         bool suppressErrorsForMissingBranch = false);
   void SetImpl(TBranch *branch, TLeaf *myLeaf);
   const char *GetBranchContentDataType(TBranch *branch, TString &contentTypeName, TDictionary *&dict,
                                        StreamerElementArrayInfo &arrInfo);
 
   std::unique_ptr<TVirtualCollectionReader> fImpl; // Common interface to collections
 
   // FIXME: re-introduce once we have ClassDefInline!
   // ClassDefOverride(TTreeReaderArrayBase, 0);//Accessor to member of an object stored in a collection
};
 
class R__CLING_PTRCHECK(off) TTreeReaderUntypedArray final : public TTreeReaderArrayBase {
   std::string fArrayElementTypeName;
 
public:
   TTreeReaderUntypedArray(TTreeReader &tr, std::string_view branchName, std::string_view innerTypeName)
      : TTreeReaderArrayBase(&tr, branchName.data(), TDictionary::GetDictionary(innerTypeName.data())),
        fArrayElementTypeName(innerTypeName)
   {
   }
 
   std::byte *At(std::size_t idx) const { return reinterpret_cast<std::byte *>(UntypedAt(idx)); }
 
protected:
   const char *GetDerivedTypeName() const final { return fArrayElementTypeName.c_str(); }
};
 
} // namespace Internal
} // namespace ROOT
 
// clang-format off
/**
 * \class TTreeReaderArray
 * \ingroup treeplayer
 * \brief An interface for reading collections stored in ROOT columnar datasets
 *
 * The TTreeReaderArray is a type-safe tool to be used in association with a TTreeReader
 * to access the collections stored in TTree, TNtuple and TChain datasets.
 * In order to access values which are not collections, the TTreeReaderValue class can
 * be used.
 *
 * See the documentation of TTreeReader for more details and examples.
*/
// clang-format on
 
template <typename T>
class R__CLING_PTRCHECK(off) TTreeReaderArray final : public ROOT::Internal::TTreeReaderArrayBase {
   // R__CLING_PTRCHECK is disabled because pointer / types are checked by CreateProxy().
 
public:
   /// Random access iterator to the elements of a TTreeReaderArray.
   // The template parameter is there to allow distinguishing between the `const` and `non-const` cases.
   template <typename ReaderArrayType>
   class Iterator_t {
   public:
      // iterators must define the following types
      using iterator_category = std::random_access_iterator_tag;
      using value_type = T;
      using difference_type = std::ptrdiff_t;
      using pointer = std::conditional_t<std::is_const<ReaderArrayType>::value, const T *, T *>;
      using reference = std::conditional_t<std::is_const<ReaderArrayType>::value, const T &, T &>;
 
   private:
      TTreeReaderArray *fArray; ///< The array iterated over; nullptr if invalid/past-the-end.
      std::size_t fIndex;       ///< Current index in the array.
      std::size_t fSize;        ///< Size of the TTreeReaderArray
   public:
      /// Default ctor: constructs a past-the-end iterator
      Iterator_t() : fArray(nullptr), fIndex(0u), fSize(0u) {}
 
      /// Construct iterator
      Iterator_t(std::size_t index, TTreeReaderArray *array)
         : fArray(array), fIndex(index), fSize(fArray ? fArray->GetSize() : 0u)
      {
         if (fIndex >= fSize)
            fArray = nullptr; // invalidate iterator
      }
 
      /// Construct iterator from a const TTreeReaderArray
      Iterator_t(std::size_t index, const TTreeReaderArray *array)
         : Iterator_t(index, const_cast<TTreeReaderArray *>(array))
      {
      }
 
      Iterator_t(Iterator_t &&) = default;
      Iterator_t(const Iterator_t &) = default;
      Iterator_t &operator=(Iterator_t &&) = default;
      Iterator_t &operator=(const Iterator_t &) = default;
 
      reference operator*() const
      {
         R__ASSERT(fArray && "invalid iterator!");
         return fArray->At(fIndex);
      }
 
      pointer operator->() const { return IsValid() ? &fArray->At(fIndex) : nullptr; }
 
      bool operator==(const Iterator_t &other) const
      {
         // Follow C++14 requiring two past-the-end iterators to be equal.
         if (!IsValid() && !other.IsValid())
            return true;
         return fArray == other.fArray && fIndex == other.fIndex;
      }
 
      bool operator!=(const Iterator_t &other) const { return !(*this == other); }
 
      /// Pre-increment operator
      Iterator_t &operator++()
      {
         if (IsValid())
            ++fIndex;
         if (fIndex >= fSize)
            fArray = nullptr; // invalidate iterator
         return *this;
      }
 
      /// Post-increment operator
      Iterator_t operator++(int)
      {
         auto ret = *this;
         this->operator++();
         return ret;
      }
 
      /// Pre-decrement operator
      Iterator_t &operator--()
      {
         if (fIndex == 0u)
            fArray = nullptr; // invalidate iterator
         else
            --fIndex;
         return *this;
      }
 
      /// Post-decrement operator
      Iterator_t operator--(int)
      {
         auto ret = *this;
         this->operator--();
         return ret;
      }
 
      Iterator_t operator+(std::ptrdiff_t n) const { return Iterator_t(fIndex + n, fArray); }
      friend auto operator+(std::ptrdiff_t n, const Iterator_t &it) -> decltype(it + n) { return it + n; }
 
      Iterator_t operator-(std::ptrdiff_t n) const
      {
         const auto index = std::ptrdiff_t(fIndex);
         const auto newIndex = index >= n ? index - n : std::numeric_limits<decltype(fIndex)>::max();
         return Iterator_t(newIndex, fArray);
      }
 
      std::ptrdiff_t operator-(const Iterator_t &other) const { return fIndex - other.fIndex; }
 
      Iterator_t &operator+=(std::ptrdiff_t n) { return (*this = *this + n); }
 
      Iterator_t &operator-=(std::ptrdiff_t n) { return (*this = *this - n); }
 
      bool operator<(const Iterator_t &other) const { return fIndex < other.fIndex; }
      bool operator>(const Iterator_t &other) const { return fIndex > other.fIndex; }
      bool operator<=(const Iterator_t &other) const { return !(*this > other); }
      bool operator>=(const Iterator_t &other) const { return !(*this < other); }
 
      reference operator[](std::size_t index) const { return *(*this + index); }
 
      operator pointer() { return &fArray->At(fIndex); }
 
      bool IsValid() const { return fArray != nullptr; }
   };
 
   using iterator = Iterator_t<TTreeReaderArray<T>>;
   using const_iterator = Iterator_t<const TTreeReaderArray<T>>;
 
   /// Create an array reader of branch "branchname" for TTreeReader "tr".
   TTreeReaderArray(TTreeReader &tr, const char *branchname)
      : TTreeReaderArrayBase(&tr, branchname, TDictionary::GetDictionary(typeid(T)))
   {
   }
 
   T &At(std::size_t idx) { return *static_cast<T *>(UntypedAt(idx)); }
   const T &At(std::size_t idx) const { return *static_cast<T *>(UntypedAt(idx)); }
   T &operator[](std::size_t idx) { return At(idx); }
   const T &operator[](std::size_t idx) const { return At(idx); }
 
   iterator begin() { return iterator(0u, this); }
   iterator end() { return iterator(GetSize(), this); }
   const_iterator begin() const { return cbegin(); }
   const_iterator end() const { return cend(); }
   const_iterator cbegin() const { return const_iterator(0u, this); }
   const_iterator cend() const { return const_iterator(GetSize(), this); }
 
protected:
#define R__TTreeReaderArray_TypeString(T) #T
   const char *GetDerivedTypeName() const override { return R__TTreeReaderArray_TypeString(T); }
#undef R__TTreeReaderArray_TypeString
   // FIXME: re-introduce once we have ClassDefTInline!
   // ClassDefT(TTreeReaderArray, 0);//Accessor to member of an object stored in a collection
};
 
namespace cling {
template <typename T>
std::string printValue(TTreeReaderArray<T> *val)
{
   return printValue(static_cast<ROOT::Internal::TTreeReaderValueBase *>(val));
}
} // namespace cling
 
#endif // ROOT_TTreeReaderArray