SplittingMergingTransformer.h

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* (c) Copyright 2022-2026 CERN for the benefit of the LHCb Collaboration      *
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#pragma once
#include "details.h"
#include "utilities.h"
#include <optional>
#include <vector>
 
namespace Gaudi::Functional {
  template <typename Container>
  using vector_of_ = std::vector<Container>;
  template <typename Container>
  using vector_of_optional_ = std::vector<std::optional<Container>>;
  using details::vector_of_const_;
 
  namespace details {
 
    template <typename Signature, typename Traits_>
    struct SplittingMergingTransformer;
 
    template <typename Out, typename... Args, typename Traits_>
      requires has_handle_vector_input<Args...>
    struct SplittingMergingTransformer<vector_of_<Out>( const Args&... ), Traits_>
        : DataHandleVectorMixin<type_list<vector_of_output_<Out>>, Traits_, Args...> {
      using DataHandleVectorMixin<type_list<vector_of_output_<Out>>, Traits_, Args...>::DataHandleVectorMixin;
 
      // derived classes can NOT implement execute
      StatusCode execute( const EventContext& ctx ) const override final {
        return details::execute_single_output( *this, ctx, this->m_outputs );
      }
 
      // TODO/FIXME: how does the callee know in which order to produce the outputs?
      //             (note: 'missing' items can be specified by making Out an std::optional<Out>,
      //              and only those entries which contain an Out are stored)
      virtual vector_of_<Out> operator()( const Args&... ) const = 0;
    };
 
  } // namespace details
 
  template <typename Signature, typename Traits_ = Traits::useDefaults>
  using SplittingMergingTransformer = details::SplittingMergingTransformer<Signature, Traits_>;
 
} // namespace Gaudi::Functional