FindManyInChainP.h

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#ifndef LARDATA_UTILITIES_FINDMANYINCHAINP_H
#define LARDATA_UTILITIES_FINDMANYINCHAINP_H

// framework
#include "canvas/Persistency/Common/Ptr.h"
#include "canvas/Utilities/InputTag.h"

// C/C++ standard library
#include <cstdlib> // std::size_t
#include <initializer_list>
#include <utility> // std::forward()
#include <vector>

namespace lar {

  namespace details {

    template <typename T, typename R = void>
    struct enable_if_type_exists;

    template <typename T, typename R = void>
    using enable_if_type_exists_t = typename enable_if_type_exists<T, R>::type;

    template <typename H, typename R = void>
    using enable_if_is_handle_t = enable_if_type_exists_t<typename std::decay_t<H>::HandleTag, R>;

  } // namespace details

  struct SameAsDataTag {};

  constexpr SameAsDataTag SameAsData;

  template <typename Target, typename... Intermediate>
  class FindManyInChainP {

  public:
    using Target_t = Target;                
    using TargetPtr_t = art::Ptr<Target_t>; 

    using TargetPtrCollection_t = std::vector<TargetPtr_t>;

    template <typename Source, typename Event, typename... InputTags>
    FindManyInChainP(Source&& source, Event const& event, InputTags... tags)
      : results(find(std::forward<Source>(source), event, tags...))
    {}

    std::size_t size() const noexcept;

    TargetPtrCollection_t const& at(std::size_t i) const;

    template <typename Source, typename Event, typename... InputTags>
    static std::vector<TargetPtrCollection_t> find(Source&& source,
                                                   Event const& event,
                                                   InputTags... tags);

  private:
    std::vector<TargetPtrCollection_t> results; 

  }; // class FindManyInChainP<>

} // namespace lar

//------------------------------------------------------------------------------
//---  template implementation
//---
#include "FindManyInChainP.tcc" // expected in the same directory as this file

//------------------------------------------------------------------------------

#endif // LARDATA_UTILITIES_FINDMANYINCHAINP_H