From Jason Turner

[mdspan.layout.right]

C++20 → C++23 6.3 KB 190 lines
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Archived: C++20 | C++23
Markdown: C++20 | C++23
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tmp/tmpbgf00d7z/{from.md → to.md} RENAMED
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+ ##### Class template `layout_right::mapping` <a id="mdspan.layout.right">[[mdspan.layout.right]]</a>
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+
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+ ###### Overview <a id="mdspan.layout.right.overview">[[mdspan.layout.right.overview]]</a>
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+
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+ `layout_right` provides a layout mapping where the rightmost extent is
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+ stride 1, and strides increase right-to-left as the product of extents.
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+
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+ ``` cpp
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+ namespace std {
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+ template<class Extents>
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+ class layout_right::mapping {
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+ public:
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+ using extents_type = Extents;
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+ using index_type = typename extents_type::index_type;
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+ using size_type = typename extents_type::size_type;
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+ using rank_type = typename extents_type::rank_type;
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+ using layout_type = layout_right;
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+
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+ // [mdspan.layout.right.cons], constructors
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+ constexpr mapping() noexcept = default;
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+ constexpr mapping(const mapping&) noexcept = default;
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+ constexpr mapping(const extents_type&) noexcept;
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+ template<class OtherExtents>
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+ constexpr explicit(!is_convertible_v<OtherExtents, extents_type>)
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+ mapping(const mapping<OtherExtents>&) noexcept;
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+ template<class OtherExtents>
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+ constexpr explicit(!is_convertible_v<OtherExtents, extents_type>)
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+ mapping(const layout_left::mapping<OtherExtents>&) noexcept;
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+ template<class OtherExtents>
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+ constexpr explicit(extents_type::rank() > 0)
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+ mapping(const layout_stride::mapping<OtherExtents>&) noexcept;
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+
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+ constexpr mapping& operator=(const mapping&) noexcept = default;
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+
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+ // [mdspan.layout.right.obs], observers
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+ constexpr const extents_type& extents() const noexcept { return extents_; }
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+
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+ constexpr index_type required_span_size() const noexcept;
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+
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+ template<class... Indices>
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+ constexpr index_type operator()(Indices...) const noexcept;
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+
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+ static constexpr bool is_always_unique() noexcept { return true; }
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+ static constexpr bool is_always_exhaustive() noexcept { return true; }
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+ static constexpr bool is_always_strided() noexcept { return true; }
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+
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+ static constexpr bool is_unique() noexcept { return true; }
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+ static constexpr bool is_exhaustive() noexcept { return true; }
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+ static constexpr bool is_strided() noexcept { return true; }
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+
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+ constexpr index_type stride(rank_type) const noexcept;
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+
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+ template<class OtherExtents>
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+ friend constexpr bool operator==(const mapping&, const mapping<OtherExtents>&) noexcept;
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+
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+ private:
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+ extents_type extents_{}; // exposition only
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+ };
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+ }
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+ ```
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+
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+ If `Extents` is not a specialization of `extents`, then the program is
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+ ill-formed.
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+
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+ `layout_right::mapping<E>` is a trivially copyable type that models
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+ `regular` for each `E`.
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+
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+ *Mandates:* If `Extents::rank_dynamic() == 0` is `true`, then the size
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+ of the multidimensional index space `Extents()` is representable as a
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+ value of type `typename Extents::index_type`.
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+
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+ ###### Constructors <a id="mdspan.layout.right.cons">[[mdspan.layout.right.cons]]</a>
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+
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+ ``` cpp
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+ constexpr mapping(const extents_type& e) noexcept;
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+ ```
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+
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+ *Preconditions:* The size of the multidimensional index space `e` is
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+ representable as a value of type `index_type` [[basic.fundamental]].
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+
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+ *Effects:* Direct-non-list-initializes *extents\_* with `e`.
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+
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+ ``` cpp
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+ template<class OtherExtents>
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+ constexpr explicit(!is_convertible_v<OtherExtents, extents_type>)
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+ mapping(const mapping<OtherExtents>& other) noexcept;
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+ ```
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+
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+ *Constraints:* `is_constructible_v<extents_type, OtherExtents>` is
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+ `true`.
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+
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+ *Preconditions:* `other.required_span_size()` is representable as a
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+ value of type `index_type` [[basic.fundamental]].
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+
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+ *Effects:* Direct-non-list-initializes *extents\_* with
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+ `other.extents()`.
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+
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+ ``` cpp
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+ template<class OtherExtents>
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+ constexpr explicit(!is_convertible_v<OtherExtents, extents_type>)
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+ mapping(const layout_left::mapping<OtherExtents>& other) noexcept;
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+ ```
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+
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+ *Constraints:*
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+
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+ - `extents_type::rank() <= 1` is `true`, and
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+ - `is_constructible_v<extents_type, OtherExtents>` is `true`.
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+
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+ *Preconditions:* `other.required_span_size()` is representable as a
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+ value of type `index_type` [[basic.fundamental]].
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+
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+ *Effects:* Direct-non-list-initializes *extents\_* with
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+ `other.extents()`.
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+
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+ ``` cpp
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+ template<class OtherExtents>
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+ constexpr explicit(extents_type::rank() > 0)
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+ mapping(const layout_stride::mapping<OtherExtents>& other) noexcept;
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+ ```
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+
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+ *Constraints:* `is_constructible_v<extents_type, OtherExtents>` is
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+ `true`.
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+
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+ *Preconditions:*
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+
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+ - If `extents_type::rank() > 0` is `true`, then for all r in the range
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+ [0, `extents_type::rank()`), `other.stride(`r`)` equals
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+ `other.extents().`*`rev-prod-of-extents`*`(`r`)`.
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+ - `other.required_span_size()` is representable as a value of type
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+ `index_type` [[basic.fundamental]].
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+
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+ *Effects:* Direct-non-list-initializes *extents\_* with
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+ `other.extents()`.
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+
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+ ###### Observers <a id="mdspan.layout.right.obs">[[mdspan.layout.right.obs]]</a>
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+
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+ ``` cpp
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+ index_type required_span_size() const noexcept;
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+ ```
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+
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+ *Returns:* `extents().`*`fwd-prod-of-extents`*`(extents_type::rank())`.
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+
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+ ``` cpp
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+ template<class... Indices>
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+ constexpr index_type operator()(Indices... i) const noexcept;
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+ ```
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+
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+ *Constraints:*
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+
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+ - `sizeof...(Indices) == extents_type::rank()` is `true`,
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+ - `(is_convertible_v<Indices, index_type> && ...)` is `true`, and
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+ - `(is_nothrow_constructible_v<index_type, Indices> && ...)` is `true`.
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+
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+ *Preconditions:* `extents_type::`*`index-cast`*`(i)` is a
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+ multidimensional index in *extents\_*[[mdspan.overview]].
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+
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+ *Effects:* Let `P` be a parameter pack such that
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+
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+ ``` cpp
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+ is_same_v<index_sequence_for<Indices...>, index_sequence<P...>>
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+ ```
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+
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+ is `true`. Equivalent to:
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+
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+ ``` cpp
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+ return ((static_cast<index_type>(i) * stride(P)) + ... + 0);
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+ ```
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+
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+ ``` cpp
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+ constexpr index_type stride(rank_type i) const noexcept;
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+ ```
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+
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+ *Constraints:* `extents_type::rank() > 0` is `true`.
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+
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+ *Preconditions:* `i < extents_type::rank()` is `true`.
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+
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+ *Returns:* `extents().`*`rev-prod-of-extents`*`(i)`.
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+
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+ ``` cpp
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+ template<class OtherExtents>
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+ friend constexpr bool operator==(const mapping& x, const mapping<OtherExtents>& y) noexcept;
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+ ```
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+
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+ *Constraints:* `extents_type::rank() == OtherExtents::rank()` is `true`.
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+
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+ *Effects:* Equivalent to: `return x.extents() == y.extents();`
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+