ConstIter.h

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/*
  Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
*/
 
#ifndef TRIGCONFDATA_CONSTITER_H
#define TRIGCONFDATA_CONSTITER_H

 
#include "CxxUtils/CachedValue.h"
#include <iterator> //std::forward_iterator_tag
#include <functional>
 
namespace TrigConf {

   template<typename V, typename T>
   class ConstIter final {
   public:
      ConstIter( const V & buf, size_t offset = 0, 
                 std::function<T(const typename V::value_type &)> f = [](auto & x)->T{return {x};}) :
         m_buf(buf),
         m_offset(offset),
         m_data(),
         m_f(std::move(f)),
         m_bufIt(buf.begin())
      {}

      bool operator==(const ConstIter &i) const {
         return &i.m_buf == &m_buf && i.m_offset == m_offset;
      }
 

      ConstIter & operator++() {
         ++m_offset;
         ++m_bufIt;
         m_data.reset();
         return *this;
      }

      const T & operator*() const {
         if( ! m_data.isValid() ) {
            m_data.set (m_f(*m_bufIt));
         }
         return *m_data.ptr();
      }
 
   private:
      const V & m_buf; 
      std::size_t m_offset; 
      CxxUtils::CachedValue<T> m_data; 
      std::function<T(const typename V::value_type &)> m_f; 
      typename V::const_iterator m_bufIt; 
 
   };
 
}

namespace std {
    template<typename V, typename T>
    class iterator_traits<TrigConf::ConstIter<V,T> >
    {
    public:
        using difference_type = std::ptrdiff_t;
        using size_type = std::size_t;
        using value_type = const T;
        using pointer = const T*;
        using reference = const T&;
        using iterator_category = std::forward_iterator_tag;
    };
}
 
#endif