lib/defacc.hpp

The following code example is taken from the book
C++23 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2026
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

// raw code

#include <mdspan>
#include <type_traits>

template<typename ElemT>
struct DefAccessor
{
  static_assert(!std::is_array_v<ElemT>,
               "Accesssor element type must not be an array type");
  static_assert(!std::is_abstract_v<ElemT>,
                "Accesssor element type must not be an abstract class type");

  using offset_policy = DefAccessor;
  using element_type = ElemT;
  using reference = element_type&;
  using data_handle_type = element_type*;

  constexpr DefAccessor() noexcept = default;

  template<typename OtherElemT>
  requires std::is_convertible_v<OtherElemT(*)[], element_type(*)[]>
  constexpr DefAccessor(DefAccessor<OtherElemT>) noexcept {
  }

  constexpr reference access(data_handle_type p, size_t i) const noexcept {
    return p[i];
  }

  constexpr data_handle_type offset(data_handle_type p, size_t i) const noexcept {
    return p + i;
  }
};