24 Containers library [containers]

24.7 Views [views]

24.7.3 Multidimensional access [views.multidim]

24.7.3.4 Layout mapping [mdspan.layout]

24.7.3.4.6 Class template layout_right​::​mapping [mdspan.layout.right]

24.7.3.4.6.1 Overview [mdspan.layout.right.overview]

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layout_right provides a layout mapping where the rightmost extent is stride 1, and strides increase right-to-left as the product of extents.
namespace std { template<class Extents> class layout_right::mapping { public: using extents_type = Extents; using index_type = typename extents_type::index_type; using size_type = typename extents_type::size_type; using rank_type = typename extents_type::rank_type; using layout_type = layout_right; // [mdspan.layout.right.cons], constructors constexpr mapping() noexcept = default; constexpr mapping(const mapping&) noexcept = default; constexpr mapping(const extents_type&) noexcept; template<class OtherExtents> constexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(const mapping<OtherExtents>&) noexcept; template<class OtherExtents> constexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(const layout_left::mapping<OtherExtents>&) noexcept; template<class OtherExtents> constexpr explicit(extents_type::rank() > 0) mapping(const layout_stride::mapping<OtherExtents>&) noexcept; constexpr mapping& operator=(const mapping&) noexcept = default; // [mdspan.layout.right.obs], observers constexpr const extents_type& extents() const noexcept { return extents_; } constexpr index_type required_span_size() const noexcept; template<class... Indices> constexpr index_type operator()(Indices...) const noexcept; static constexpr bool is_always_unique() noexcept { return true; } static constexpr bool is_always_exhaustive() noexcept { return true; } static constexpr bool is_always_strided() noexcept { return true; } static constexpr bool is_unique() noexcept { return true; } static constexpr bool is_exhaustive() noexcept { return true; } static constexpr bool is_strided() noexcept { return true; } constexpr index_type stride(rank_type) const noexcept; template<class OtherExtents> friend constexpr bool operator==(const mapping&, const mapping<OtherExtents>&) noexcept; private: extents_type extents_{}; // exposition only }; }
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If Extents is not a specialization of extents, then the program is ill-formed.
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layout_right​::​mapping<E> is a trivially copyable type that models regular for each E.
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Mandates: If Extents​::​rank_dynamic() == 0 is true, then the size of the multidimensional index space Extents() is representable as a value of type typename Extents​::​index_type.

24.7.3.4.6.2 Constructors [mdspan.layout.right.cons]

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constexpr mapping(const extents_type& e) noexcept;
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Preconditions: The size of the multidimensional index space e is representable as a value of type index_type ([basic.fundamental]).
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Effects: Direct-non-list-initializes extents_ with e.
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template<class OtherExtents> constexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(const mapping<OtherExtents>& other) noexcept;
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Constraints: is_constructible_v<extents_type, OtherExtents> is true.
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Preconditions: other.required_span_size() is representable as a value of type index_type ([basic.fundamental]).
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Effects: Direct-non-list-initializes extents_ with other.extents().
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template<class OtherExtents> constexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(const layout_left::mapping<OtherExtents>& other) noexcept;
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Constraints:
  • (6.1)
    extents_type​::​rank() <= 1 is true, and
  • (6.2)
    is_constructible_v<extents_type, OtherExtents> is true.
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Preconditions: other.required_span_size() is representable as a value of type index_type ([basic.fundamental]).
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Effects: Direct-non-list-initializes extents_ with other.extents().
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template<class OtherExtents> constexpr explicit(extents_type::rank() > 0) mapping(const layout_stride::mapping<OtherExtents>& other) noexcept;
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Constraints: is_constructible_v<extents_type, OtherExtents> is true.
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Preconditions:
  • (10.1)
    If extents_type​::​rank() > 0 is true, then for all r in the range [0, extents_type​::​rank()), other.stride(r) equals other.extents().rev-prod-of-extents(r).
  • (10.2)
    other.required_span_size() is representable as a value of type index_type ([basic.fundamental]).
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Effects: Direct-non-list-initializes extents_ with other.extents().

24.7.3.4.6.3 Observers [mdspan.layout.right.obs]

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index_type required_span_size() const noexcept;
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Returns: extents().fwd-prod-of-extents(extents_type​::​rank()).
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template<class... Indices> constexpr index_type operator()(Indices... i) const noexcept;
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Constraints:
  • (2.1)
    sizeof...(Indices) == extents_type​::​rank() is true,
  • (2.2)
    (is_convertible_v<Indices, index_type> && ...) is true, and
  • (2.3)
    (is_nothrow_constructible_v<index_type, Indices> && ...) is true.
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Preconditions: extents_type​::​index-cast(i) is a multidimensional index in extents_ ([mdspan.overview]).
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Effects: Let P be a parameter pack such that is_same_v<index_sequence_for<Indices...>, index_sequence<P...>> is true.
Equivalent to: return ((static_cast<index_type>(i) * stride(P)) + ... + 0);
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constexpr index_type stride(rank_type i) const noexcept;
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Constraints: extents_type​::​rank() > 0 is true.
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Preconditions: i < extents_type​::​rank() is true.
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Returns: extents().rev-prod-of-extents(i).
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template<class OtherExtents> friend constexpr bool operator==(const mapping& x, const mapping<OtherExtents>& y) noexcept;
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Constraints: extents_type​::​rank() == OtherExtents​::​rank() is true.
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Effects: Equivalent to: return x.extents() == y.extents();