// In header: <boost/stl_interfaces/view_interface.hpp>

template<typename Derived, element_layout Contiguity> 
struct view_interface {

  // public member functions
  template<typename D = Derived> 
    decltype(std::declval< D & >().begin()==std::declval< D & >().end()) 
    empty();
  template<typename D = Derived> 
    decltype(std::declval< D const & >().begin()==std::declval< D const & >().end()) 
    empty() const;
  template<typename D = Derived, 
           typename R = decltype(std::declval<D &>().empty())> 
    explicit constexpr operator bool();
  template<typename D = Derived, 
           typename R = decltype(std::declval<D const &>().empty())> 
    explicit constexpr operator bool() const;
  template<typename D = Derived, element_layout C = Contiguity, 
           typename Enable = std::enable_if_t<C == element_layout::contiguous> > 
    decltype(std::addressof(*std::declval< D & >().begin())) data();
  template<typename D = Derived, element_layout C = Contiguity, 
           typename Enable = std::enable_if_t<C == element_layout::contiguous> > 
    decltype(std::addressof(*std::declval< D const & >().begin())) 
    data() const;
  template<typename D = Derived> 
    decltype(std::declval< D & >().end() - std::declval< D & >().begin()) 
    size();
  template<typename D = Derived> 
    decltype(std::declval< D const & >().end() - std::declval< D const & >().begin()) 
    size() const;
  template<typename D = Derived> 
    decltype(*std::declval< D & >().begin()) front();
  template<typename D = Derived> 
    decltype(*std::declval< D const & >().begin()) front() const;
  template<typename D = Derived, 
           typename Enable = std::enable_if_t< v1_dtl::decrementable_sentinel<D>::value && v1_dtl::common_range<D>::value> > 
    decltype(*std::prev(std::declval< D & >().end())) back();
  template<typename D = Derived, 
           typename Enable = std::enable_if_t< v1_dtl::decrementable_sentinel<D>::value && v1_dtl::common_range<D>::value> > 
    decltype(*std::prev(std::declval< D const & >().end())) back() const;
  template<typename D = Derived> 
    decltype(std::declval< D & >().begin()[n]) 
    operator[](v1_dtl::range_difference_t< D >);
  template<typename D = Derived> 
    decltype(std::declval< D const & >().begin()[n]) 
    operator[](v1_dtl::range_difference_t< D >) const;
};