cppdraft_translate/cppdraft/mdspan/layout/left.md

[mdspan.layout.left]

23 Containers library [containers]

23.7 Views [views]

23.7.3 Multidimensional access [views.multidim]

23.7.3.4 Layout mapping [mdspan.layout]

23.7.3.4.5 Class template layout_left​::​mapping [mdspan.layout.left]

23.7.3.4.5.1 Overview [mdspan.layout.left.overview]

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layout_left provides a layout mapping where the leftmost extent has stride 1, and strides increase left-to-right as the product of extents.

namespace std {templateclass layout_left::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_left; // [mdspan.layout.left.cons], constructorsconstexpr mapping() noexcept = default; constexpr mapping(const mapping&) noexcept = default; constexpr mapping(const extents_type&) noexcept; templateconstexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(const mapping&) noexcept; templateconstexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(const layout_right::mapping&) noexcept; templateconstexpr explicit(!is_convertible_v<typename LayoutLeftPaddedMapping::extents_type, extents_type>) mapping(const LayoutLeftPaddedMapping&) noexcept; templateconstexpr explicit(extents_type::rank() > 0) mapping(const layout_stride::mapping&); constexpr mapping& operator=(const mapping&) noexcept = default; // [mdspan.layout.left.obs], observersconstexpr 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; templatefriend constexpr bool operator==(const mapping&, const mapping&) noexcept; private: extents_type extents_{}; // exposition only// [mdspan.sub.map], submdspan mapping specializationtemplate<class... SliceSpecifiers>constexpr auto submdspan-mapping-impl(SliceSpecifiers...) const // exposition only-> see below; template<class... SliceSpecifiers>friend constexpr auto submdspan_mapping(const mapping& src, SliceSpecifiers... slices) {return src.submdspan-mapping-impl(slices...); }};}

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If Extents is not a specialization of extents, then the program is ill-formed.

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layout_left​::​mapping 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.

23.7.3.4.5.2 Constructors [mdspan.layout.left.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_right::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 LayoutLeftPaddedMapping> constexpr explicit(!is_convertible_v<typename LayoutLeftPaddedMapping::extents_type, extents_type>) mapping(const LayoutLeftPaddedMapping&) noexcept;

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Constraints:

• (9.1)

  is-layout-left-padded-mapping-of is true.

• (9.2)

  is_constructible_v<extents_type, typename LayoutLeftPaddedMapping​::​extents_type>
  is true.

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Mandates: If

• (10.1)

Extents​::​rank() is greater than one,

• (10.2)

Extents​::​static_extent(0) does not equal dynamic_extent, and

• (10.3)

LayoutLeftPaddedMapping​::​static-padding-stride does not equal dynamic_extent,

then Extents​::​static_extent(0) equalsLayoutLeftPaddedMapping​::​static-padding-stride.

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Preconditions:

• (11.1)

  If extents_type​::​rank() > 1 is true, then other.stride(1) equals other.extents(0).

• (11.2)

  other.required_span_size() is representable as a value of type index_type.

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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);

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Constraints: is_constructible_v<extents_type, OtherExtents> is true.

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Preconditions:

• (14.1)

If extents_type​::​rank() > 0 is true, then for all r in the range [0, extents_type​::​rank()),other.stride(r) equalsother.extents().fwd-prod-of-extents(r), and

• (14.2)

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().

23.7.3.4.5.3 Observers [mdspan.layout.left.obs]

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constexpr 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 thatis_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().fwd-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();