constexpr mapping(const extents_type& e) noexcept;
template<class OtherExtents>
constexpr explicit(!is_convertible_v<OtherExtents, extents_type>)
mapping(const mapping<OtherExtents>& other) noexcept;
template<class OtherExents>
constexpr explicit(!is_convertible_v<OtherExtents, extents_type>)
mapping(const layout_right::mapping<OtherExtents>& other) noexcept;
template<class LayoutLeftPaddedMapping>
constexpr explicit(!is_convertible_v<typename LayoutLeftPaddedMapping::extents_type,
extents_type>)
mapping(const LayoutLeftPaddedMapping&) noexcept;
template<class OtherExtents>
constexpr explicit(extents_type::rank() > 0)
mapping(const layout_stride::mapping<OtherExtents>& other);