RelationRange.h

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#ifndef PODIO_RELATIONRANGE_H
#define PODIO_RELATIONRANGE_H
 
#include <iterator>
#include <vector>
 
namespace podio {
/**
 * A simple helper class that allows to return related objects in a way that
 * makes it possible to use the return type in a range-based for loop.
 */
template <typename ReferenceType>
class RelationRange {
public:
  using ConstIteratorType = typename std::vector<ReferenceType>::const_iterator;
 
  RelationRange() = delete;
 
  RelationRange(ConstIteratorType begin, ConstIteratorType end) :
      m_begin(begin), m_end(end), m_size(std::distance(m_begin, m_end)) {
  }
 
  /// begin of the range (necessary for range-based for loop)
  ConstIteratorType begin() const {
    return m_begin;
  }
  /// end of the range (necessary for range-based for loop)
  ConstIteratorType end() const {
    return m_end;
  }
  /// convenience overload for size
  size_t size() const {
    return m_size;
  }
  /// convenience overload to check if the range is empty
  bool empty() const {
    return m_begin == m_end;
  }
  /// Indexed access
  ReferenceType operator[](size_t i) const {
    auto it = m_begin;
    std::advance(it, i);
    return *it;
  }
  /// Indexed access with range check
  ReferenceType at(size_t i) const {
    if (i < m_size) {
      auto it = m_begin;
      std::advance(it, i);
      return *it;
    }
    throw std::out_of_range("index out of bounds for RelationRange");
  }
 
private:
  ConstIteratorType m_begin;
  ConstIteratorType m_end;
  size_t m_size{0};
};
} // namespace podio
 
#endif // PODIO_RELATIONRANGE_H