VariantAccessor.h

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/*
  Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
*/
 
 
 
#ifndef COLUMNAR_VARIANT_VARIANT_ACCESSOR_H
#define COLUMNAR_VARIANT_VARIANT_ACCESSOR_H
 
#include <ColumnarCore/ColumnAccessor.h>
#include <ColumnarVariant/VariantDef.h>
#include <boost/mp11/tuple.hpp>
 
namespace columnar
{
  // the column accessor for variant objects in ColumnarModeArray
  //
  // This internally contains a tuple of accessors, one for each
  // variant. This is probably not the best way to implement it, but it
  // fits best with the current accessor infrastructure.
  template<ContainerIdConcept CIBase,ContainerIdConcept... CIList,typename CT,ColumnAccessMode CAM>
    requires requires { AccessorTemplate<CIBase,CT,CAM,ColumnarModeArray>{}; }
  class AccessorTemplate<VariantContainerId<CIBase,CIList...>,CT,CAM,ColumnarModeArray> final
  {
  public:
 
    static_assert (!std::is_const_v<CT>, "CT must not be const");
 
    using CI = VariantContainerId<CIBase,CIList...>;
    using CM = ColumnarModeArray;
    using ColumnType = typename ColumnAccessModeTraits<CAM>::template ColumnType<typename ColumnTypeTraits<CT,ColumnarModeArray>::ColumnType>;
    using AccessorTuple = std::tuple<AccessorTemplate<CIList,CT,CAM,CM>...>;
 
    AccessorTemplate () noexcept = default;
 
    AccessorTemplate (ColumnarTool<CM>& columnarTool, const std::string& name, ColumnInfo&& info = {})
    {
      boost::mp11::tuple_for_each (m_accessors, [&columnarTool,&name,&info] (auto& accessor)
      {
        resetAccessor (accessor, columnarTool, name, ColumnInfo(info));
      });
    }
 
    AccessorTemplate (AccessorTemplate&& that)
    {
      m_accessors = std::move (that.m_accessors);
    }
 
    AccessorTemplate& operator = (AccessorTemplate&& that)
    {
      if (this != &that)
        m_accessors = std::move (that.m_accessors);
      return *this;
    }
 
    AccessorTemplate (const AccessorTemplate&) = delete;
    AccessorTemplate& operator = (const AccessorTemplate&) = delete;
 
    void reset (ColumnarTool<CM>& columnarTool, const std::string& name, ColumnInfo&& info = {})
    {
      boost::mp11::tuple_for_each (m_accessors, [&columnarTool,&name,&info] (auto& accessor)
      {
        resetAccessor (accessor, columnarTool, name, ColumnInfo(info));
      });
    }
 
    [[nodiscard]] decltype(auto) operator () (ObjectId<CI,CM> id) const noexcept
    {
      return internalGet<0> (id);
    }
 
    [[nodiscard]] bool isAvailable (ObjectId<CI,CM> id) const noexcept
    {
      return internalIsAvailable<0> (id);
    }
 
  private:
 
    AccessorTuple m_accessors;
 
    template<unsigned Index>
    void internalInit (ColumnarTool<CM>& columnarTool, const std::string& name, const ColumnInfo& info)
    {
      resetAccessor (std::get<Index>(m_accessors), columnarTool, name, ColumnInfo(info));
      if constexpr (Index + 1 < CI::numVariants)
        internalInit<Index + 1>(columnarTool, name, info);
    }
 
    template<unsigned Index>
    decltype(auto) internalGet (const ObjectId<CI,CM>& id) const noexcept
    {
      if (id.getVariantIndex() == Index)
      {
        using CI2 = std::tuple_element_t<Index,std::tuple<CIList...>>;
        ObjectId<CI2,CM> objId {id.getData(), id.getObjectIndex()};
        return std::get<Index>(m_accessors)(objId);
      } else if constexpr (Index+1 < CI::numVariants)
        return internalGet<Index + 1>(id);
      else
      {
        std::cerr << "Invalid variant index: " << id.getVariantIndex() << std::endl;
        std::abort ();
      }
    }
 
    template<unsigned Index>
    bool internalIsAvailable (const ObjectId<CI,CM>& id) const noexcept
    {
      if (id.getVariantIndex() == Index)
      {
        using CI2 = std::tuple_element_t<Index,std::tuple<CIList...>>;
        ObjectId<CI2,CM> objId {id.getData(), id.getObjectIndex()};
        return std::get<Index>(m_accessors).isAvailable(objId);
      } else if constexpr (Index+1 < CI::numVariants)
        return internalIsAvailable<Index + 1>(id);
      else
      {
        std::cerr << "Invalid variant index: " << id.getVariantIndex() << std::endl;
        std::abort ();
      }
    }
  };
}
 
#endif