ResultWrapper.h

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#ifndef RDFAnalysis_ResultWrapper_H
#define RDFAnalysis_ResultWrapper_H

// ROOT includes
#include <ROOT/RDF/InterfaceUtils.hxx>

// STL includes
#include <type_traits>
#include <functional>

namespace RDFAnalysis {
  template <typename T>
    class ResultWrapper  {
      public:
        ~ResultWrapper() {}

        template <typename U, 
                 typename = std::enable_if_t<std::is_base_of<T, U>{} || std::is_same<T, U>{}, void>>
          /* ResultWrapper(const ROOT::RDF::RResultPtr<U>& ptr) : */
          ResultWrapper(ROOT::RDF::RResultPtr<U> ptr) :
            m_holder([ptr] () mutable -> T* {return ptr.GetPtr();}) {}

        template <typename U,
                 typename = std::enable_if_t<
                   std::is_base_of<T, U>{} && !std::is_same<T, U>{}, void>>
          ResultWrapper(ResultWrapper<U> other) :
            m_holder([other] () mutable -> T* { return other.get(); }) {}

        template <typename U,
                 typename = std::enable_if_t<
                   std::is_base_of<T, U>{} && !std::is_same<T, U>{}, void>>
          ResultWrapper(ResultWrapper<U>&& other) :
            m_holder([other] () { return other.get(); }) {}

        ResultWrapper(const ResultWrapper&) = default;
        ResultWrapper(ResultWrapper&&) = default;

        T* get() {
          return m_holder();
        }
      private:
        std::function<T*()> m_holder;


    }; //> end class ResultWrapper
} //> end namespace RDFAnalysis
#endif //> !RDFAnalysis_ResultWrapper_H