CbmStructLooper.h

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/* Copyright (C) 2025 GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt
   SPDX-License-Identifier: GPL-3.0-only
   Authors: Sergei Zharko [committer] */

 
#ifndef CbmStructLooper_h
#define CbmStructLooper_h 1
 
#include "CbmTypeTraits.h"
 
#include <functional>
#include <optional>
#include <tuple>
 
namespace cbm::util
{
  template<class Handler, class... Variables>
  class StructLooper {
   public:
    constexpr StructLooper(Variables Handler::*... vars)
      : fVariableTuple(std::make_tuple(std::forward<decltype(vars)>(vars)...))
    {
    }

    template<typename HandlerPtr, class Visitor, std::enable_if_t<is_pointer_to_v<HandlerPtr, Handler>, bool> = true>
    constexpr void ForEachValue(HandlerPtr handler, Visitor&& visitor) const
    {
      std::apply([&](auto&&... v) { ((VisitValue(handler, std::forward<Visitor>(visitor), v)), ...); }, fVariableTuple);
    }

    template<typename HandlerPtr, class Visitor, std::enable_if_t<is_pointer_to_v<HandlerPtr, Handler>, bool> = true>
    constexpr void ForEachVariable(HandlerPtr handler, Visitor&& visitor) const
    {
      std::apply([&](auto&&... v) { ((std::invoke(std::forward<Visitor>(visitor), handler->*v)), ...); },
                 fVariableTuple);
    }
 
   private:
    const std::tuple<Variables Handler::*...> fVariableTuple;  

    template<class Visitor, class VarPtrType, typename HandlerPtr,
             std::enable_if_t<is_pointer_to_v<HandlerPtr, Handler>, bool> = true>
    constexpr void VisitValue(HandlerPtr handler, Visitor&& visitor, VarPtrType&& varAddr) const
    {
      using VarType = std::remove_const_t<std::remove_reference_t<decltype(handler->*varAddr)>>;
      // TODO: add other single-value contain types
      if constexpr (is_std_optional_v<VarType>) {
        // Invoke a visitor, if the variable contains a value
        if ((handler->*varAddr).has_value()) {
          std::invoke(std::forward<Visitor>(visitor), *(handler->*varAddr));
        }
      }
      else {
        std::invoke(std::forward<Visitor>(visitor), handler->*varAddr);
      }
    }
  };
}  // namespace cbm::util
 
#endif  // CbmStructLooper_h