static constexpr rank_type dynamic-index(rank_type i) noexcept;
static constexpr rank_type dynamic-index-inv(rank_type i) noexcept;
constexpr size_t fwd-prod-of-extents(rank_type i) const noexcept;
constexpr size_t rev-prod-of-extents(rank_type i) const noexcept;
template<class OtherIndexType>
static constexpr auto index-cast(OtherIndexType&& i) noexcept;
template<class OtherIndexType, size_t... OtherExtents>
constexpr explicit(see below)
extents(const extents<OtherIndexType, OtherExtents...>& other) noexcept;
template<class... OtherIndexTypes>
constexpr explicit extents(OtherIndexTypes... exts) noexcept;
template<class OtherIndexType, size_t N>
constexpr explicit(N != rank_dynamic())
extents(span<OtherIndexType, N> exts) noexcept;
template<class OtherIndexType, size_t N>
constexpr explicit(N != rank_dynamic())
extents(const array<OtherIndexType, N>& exts) noexcept;
template<class... Integrals>
explicit extents(Integrals...) -> see below;
static constexpr size_t static_extent(rank_type i) noexcept;
constexpr index_type extent(rank_type i) const noexcept;
template<class OtherIndexType, size_t... OtherExtents>
friend constexpr bool operator==(const extents& lhs,
const extents<OtherIndexType, OtherExtents...>& rhs) noexcept;
template<class IndexType, size_t Rank>
using dextents = see below;