From Jason Turner

[span.cons]

C++17 → C++20 5.1 KB 154 lines
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Archived: C++17 | C++20
Markdown: C++17 | C++20
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tmp/tmpvrp2j0kj/{from.md → to.md} RENAMED
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+ #### Constructors, copy, and assignment <a id="span.cons">[[span.cons]]</a>
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+
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+ ``` cpp
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+ constexpr span() noexcept;
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+ ```
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+
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+ *Constraints:* `Extent == dynamic_extent || Extent == 0` is `true`.
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+
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+ *Ensures:* `size() == 0 && data() == nullptr`.
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+
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+ ``` cpp
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+ template<class It>
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+ constexpr explicit(extent != dynamic_extent) span(It first, size_type count);
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+ ```
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+
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+ *Constraints:* Let `U` be `remove_reference_t<iter_reference_t<It>>`.
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+
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+ - `It` satisfies `contiguous_iterator`.
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+ - `is_convertible_v<U(*)[], element_type(*)[]>` is `true`.
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+ \[*Note 1*: The intent is to allow only qualification conversions of
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+ the iterator reference type to `element_type`. — *end note*]
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+
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+ *Preconditions:*
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+
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+ - \[`first`, `first + count`) is a valid range.
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+ - `It` models `contiguous_iterator`.
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+ - If `extent` is not equal to `dynamic_extent`, then `count` is equal to
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+ `extent`.
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+
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+ *Effects:* Initializes `data_` with `to_address(first)` and `size_` with
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+ `count`.
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+
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+ *Throws:* Nothing.
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+
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+ ``` cpp
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+ template<class It, class End>
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+ constexpr explicit(extent != dynamic_extent) span(It first, End last);
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+ ```
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+
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+ *Constraints:* Let `U` be `remove_reference_t<iter_reference_t<It>>`.
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+
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+ - `is_convertible_v<U(*)[], element_type(*)[]>` is `true`.
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+ \[*Note 2*: The intent is to allow only qualification conversions of
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+ the iterator reference type to `element_type`. — *end note*]
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+ - `It` satisfies `contiguous_iterator`.
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+ - `End` satisfies `sized_sentinel_for<It>`.
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+ - `is_convertible_v<End, size_t>` is `false`.
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+
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+ *Preconditions:*
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+
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+ - If `extent` is not equal to `dynamic_extent`, then `last - first` is
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+ equal to `extent`.
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+ - \[`first`, `last`) is a valid range.
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+ - `It` models `contiguous_iterator`.
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+ - `End` models `sized_sentinel_for<It>`.
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+
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+ *Effects:* Initializes `data_` with `to_address(first)` and `size_` with
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+ `last - first`.
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+
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+ *Throws:* When and what `last - first` throws.
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+
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+ ``` cpp
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+ template<size_t N> constexpr span(type_identity_t<element_type> (&arr)[N]) noexcept;
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+ template<class T, size_t N> constexpr span(array<T, N>& arr) noexcept;
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+ template<class T, size_t N> constexpr span(const array<T, N>& arr) noexcept;
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+ ```
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+
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+ *Constraints:* Let `U` be `remove_pointer_t<decltype(data(arr))>`.
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+
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+ - `extent == dynamic_extent || N == extent` is `true`, and
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+ - `is_convertible_v<U(*)[], element_type(*)[]>` is `true`.
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+ \[*Note 3*: The intent is to allow only qualification conversions of
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+ the array element type to `element_type`. — *end note*]
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+
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+ *Effects:* Constructs a `span` that is a view over the supplied array.
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+
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+ [*Note 1*: `type_identity_t` affects class template argument
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+ deduction. — *end note*]
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+
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+ *Ensures:* `size() == N && data() == data(arr)` is `true`.
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+
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+ ``` cpp
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+ template<class R> constexpr explicit(extent != dynamic_extent) span(R&& r);
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+ ```
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+
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+ *Constraints:* Let `U` be
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+ `remove_reference_t<ranges::range_reference_t<R>>`.
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+
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+ - `R` satisfies `ranges::contiguous_range` and `ranges::sized_range`.
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+ - Either `R` satisfies `ranges::borrowed_range` or
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+ `is_const_v<element_type>` is `true`.
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+ - `remove_cvref_t<R>` is not a specialization of `span`.
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+ - `remove_cvref_t<R>` is not a specialization of `array`.
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+ - `is_array_v<remove_cvref_t<R>>` is `false`.
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+ - `is_convertible_v<U(*)[], element_type(*)[]>` is `true`.
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+ \[*Note 4*: The intent is to allow only qualification conversions of
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+ the range reference type to `element_type`. — *end note*]
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+
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+ *Preconditions:*
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+
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+ - If `extent` is not equal to `dynamic_extent`, then `ranges::size(r)`
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+ is equal to `extent`.
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+ - `R` models `ranges::contiguous_range` and `ranges::sized_range`.
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+ - If `is_const_v<element_type>` is `false`, `R` models
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+ `ranges::borrowed_range`.
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+
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+ *Effects:* Initializes `data_` with `ranges::data(r)` and `size_` with
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+ `ranges::size(r)`.
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+
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+ *Throws:* What and when `ranges::data(r)` and `ranges::size(r)` throw.
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+
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+ ``` cpp
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+ constexpr span(const span& other) noexcept = default;
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+ ```
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+
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+ *Ensures:* `other.size() == size() && other.data() == data()`.
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+
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+ ``` cpp
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+ template<class OtherElementType, size_t OtherExtent>
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+ constexpr explicit(see below) span(const span<OtherElementType, OtherExtent>& s) noexcept;
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+ ```
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+
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+ *Constraints:*
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+
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+ - `extent == dynamic_extent` `||` `OtherExtent == dynamic_extent` `||`
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+ `extent == OtherExtent` is `true`, and
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+ - `is_convertible_v<OtherElementType(*)[], element_type(*)[]>` is
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+ `true`. \[*Note 5*: The intent is to allow only qualification
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+ conversions of the `OtherElementType` to
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+ `element_type`. — *end note*]
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+
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+ *Preconditions:* If `extent` is not equal to `dynamic_extent`, then
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+ `s.size()` is equal to `extent`.
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+
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+ *Effects:* Constructs a `span` that is a view over the range
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+ \[`s.data()`, `s.data() + s.size()`).
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+
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+ *Ensures:* `size() == s.size() && data() == s.data()`.
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+
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+ *Remarks:* The expression inside `explicit` is equivalent to:
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+
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+ ``` cpp
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+ extent != dynamic_extent && OtherExtent == dynamic_extent
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+ ```
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+
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+ ``` cpp
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+ constexpr span& operator=(const span& other) noexcept = default;
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+ ```
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+
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+ *Ensures:* `size() == other.size() && data() == other.data()`.
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+