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Standard library header <span> (C++20)

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This header is part of the containers library.

Contents

Classes

(C++20)
a non-owning view over a contiguous sequence of objects
(class template) [edit]

Constants

a constant of type std::size_t signifying that the span has dynamic extent
(constant) [edit]

Functions

converts a span into a view of its underlying bytes
(function template) [edit]
Range access
(C++11)(C++14)
returns an iterator to the beginning of a container or array
(function template) [edit]
(C++11)(C++14)
returns an iterator to the end of a container or array
(function template) [edit]
returns a reverse iterator to the beginning of a container or array
(function template) [edit]
(C++14)
returns a reverse end iterator for a container or array
(function template) [edit]
(C++17)(C++20)
returns the size of a container or array
(function template) [edit]
(C++17)
checks whether the container is empty
(function template) [edit]
(C++17)
obtains the pointer to the underlying array
(function template) [edit]

[edit] Synopsis

namespace std {
  // constants
  inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max();
 
  template<class T>
    concept __integral_constant_like = /* see description */; // exposition only
 
  template<class T>
    constexpr size_t __maybe_static_ext = dynamic_extent;     // exposition only
 
  template<__integral_constant_like T>
    constexpr size_t __maybe_static_ext<T> = {T::value};      // exposition only
 
  // class template span
  template<class ElementType, size_t Extent = dynamic_extent>
    class span;
 
  template<class ElementType, size_t Extent>
    constexpr bool ranges::enable_view<span<ElementType, Extent>> = true;
  template<class ElementType, size_t Extent>
    constexpr bool ranges::enable_borrowed_range<span<ElementType, Extent>> = true;
 
  // views of object representation
  template<class ElementType, size_t Extent>
    span<const byte,
         Extent == dynamic_extent ? dynamic_extent : sizeof(ElementType) * Extent>
      as_bytes(span<ElementType, Extent> s) noexcept;
 
  template<class ElementType, size_t Extent>
    span<byte, Extent == dynamic_extent ? dynamic_extent : sizeof(ElementType) * Extent>
      as_writable_bytes(span<ElementType, Extent> s) noexcept;
}

[edit] Concept integral-constant-like

namespace std { // unspecified, for name lookup only
  template<class T>
    concept __integral_constant_like =        // exposition only
      is_integral_v<decltype(T::value)> &&
     !is_same_v<bool, remove_const_t<decltype(T::value)>> &&
      convertible_to<T, decltype(T::value)> &&
      equality_comparable_with<T, decltype(T::value)> &&
      bool_constant<T() == T::value>::value &&
      bool_constant<static_cast<decltype(T::value)>(T()) == T::value>::value;
}

[edit] Class template std::span

namespace std {
  template<class ElementType, size_t Extent = dynamic_extent>
  class span {
  public:
    // constants and types
    using element_type = ElementType;
    using value_type = remove_cv_t<ElementType>;
    using size_type = size_t;
    using difference_type = ptrdiff_t;
    using pointer = element_type*;
    using const_pointer = const element_type*;
    using reference = element_type&;
    using const_reference = const element_type&;
    using iterator = /* implementation-defined */;
    using const_iterator = std::const_iterator<iterator>;
    using reverse_iterator = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::const_iterator<reverse_iterator>;
    static constexpr size_type extent = Extent;
 
    // constructors, copy, and assignment
    constexpr span() noexcept;
    template<class It>
      constexpr explicit(extent != dynamic_extent) span(It first, size_type count);
    template<class It, class End>
      constexpr explicit(extent != dynamic_extent) span(It first, End last);
    template<size_t N>
      constexpr span(type_identity_t<element_type> (&arr)[N]) noexcept;
    template<class T, size_t N>
      constexpr span(array<T, N>& arr) noexcept;
    template<class T, size_t N>
      constexpr span(const array<T, N>& arr) noexcept;
    template<class R>
      constexpr explicit(extent != dynamic_extent) span(R&& r);
    constexpr span(const span& other) noexcept = default;
    template<class OtherElementType, size_t OtherExtent>
      constexpr explicit(/* see description */)
        span(const span<OtherElementType, OtherExtent>& s) noexcept;
 
    constexpr span& operator=(const span& other) noexcept = default;
 
    // subviews
    template<size_t Count>
      constexpr span<element_type, Count> first() const;
    template<size_t Count>
      constexpr span<element_type, Count> last() const;
    template<size_t Offset, size_t Count = dynamic_extent>
      constexpr span<element_type, /* see description */> subspan() const;
 
    constexpr span<element_type, dynamic_extent> first(size_type count) const;
    constexpr span<element_type, dynamic_extent> last(size_type count) const;
    constexpr span<element_type, dynamic_extent> subspan(
      size_type offset, size_type count = dynamic_extent) const;
 
    // observers
    constexpr size_type size() const noexcept;
    constexpr size_type size_bytes() const noexcept;
    [[nodiscard]] constexpr bool empty() const noexcept;
 
    // element access
    constexpr reference operator[](size_type idx) const;
    constexpr reference front() const;
    constexpr reference back() const;
    constexpr pointer data() const noexcept;
 
    // iterator support
    constexpr iterator begin() const noexcept;
    constexpr iterator end() const noexcept;
    constexpr const_iterator cbegin() const noexcept { return begin(); }
    constexpr const_iterator cend() const noexcept { return end(); }
    constexpr reverse_iterator rbegin() const noexcept;
    constexpr reverse_iterator rend() const noexcept;
    constexpr const_reverse_iterator crbegin() const noexcept { return rbegin(); }
    constexpr const_reverse_iterator crend() const noexcept { return rend(); }
 
  private:
    pointer data_;   // exposition only
    size_type size_; // exposition only
  };
 
  template<class It, class EndOrSize>
    span(It, EndOrSize) -> span<remove_reference_t<iter_reference_t<It>>,
                                __maybe_static_ext<EndOrSize>>;
  template<class T, size_t N>
    span(T (&)[N]) -> span<T, N>;
  template<class T, size_t N>
    span(array<T, N>&) -> span<T, N>;
  template<class T, size_t N>
    span(const array<T, N>&) -> span<const T, N>;
  template<class R>
    span(R&&) -> span<remove_reference_t<ranges::range_reference_t<R>>>;
}