empty_sequence_iterator.h

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#ifndef MYSQL_ITERATORS_EMPTY_SEQUENCE_ITERATOR_H
#define MYSQL_ITERATORS_EMPTY_SEQUENCE_ITERATOR_H
 
/// @file
/// Experimental API header
 
#include <cassert>                               // assert
#include <iterator>                              // random_access_iterator_tag
#include "mysql/iterators/iterator_interface.h"  // Iterator_interface
 
/// @addtogroup GroupLibsMysqlIterators
/// @{
 
namespace mysql::iterators {
 
/// Iterator over an empty sequence.
///
/// @tparam Value_tp Type of values returned from the iterator. Although no
/// values are returned, this is required in order to define the return type for
/// the dereference iterator.
template <class Value_tp>
class Empty_sequence_iterator
    : public Iterator_interface<Empty_sequence_iterator<Value_tp>> {
 public:
  using Value_t = Value_tp;
 
  [[nodiscard]] constexpr Value_t get() const {
    Value_t *tmp{};  // default-constructed = null
    assert(false);
    return *tmp;
  }
 
  constexpr void advance(std::ptrdiff_t) {}
 
  [[nodiscard]] constexpr std::ptrdiff_t distance_from(
      const Empty_sequence_iterator &) const {
    return 0;
  }
 
  [[nodiscard]] constexpr std::ptrdiff_t distance_from_sentinel() const {
    return 0;
  }
};
 
}  // namespace mysql::iterators
 
// addtogroup GroupLibsMysqlIterators
/// @}
 
#endif  // ifndef MYSQL_ITERATORS_EMPTY_SEQUENCE_ITERATOR_H