22 Containers library [containers]

22.3 Sequence containers [sequences]

22.3.7 Class template array [array] Overview [array.overview]

The header <array> defines a class template for storing fixed-size sequences of objects.
An array is a contiguous container.
An instance of array<T, N> stores N elements of type T, so that size() == N is an invariant.
An array is an aggregate that can be list-initialized with up to N elements whose types are convertible to T.
An array meets all of the requirements of a container and of a reversible container ([container.requirements]), except that a default constructed array object is not empty and that swap does not have constant complexity.
An array meets some of the requirements of a sequence container.
Descriptions are provided here only for operations on array that are not described in one of these tables and for operations where there is additional semantic information.
array<T, N> is a structural type ([temp.param]) if T is a structural type.
Two values a1 and a2 of type array<T, N> are template-argument-equivalent ([temp.type]) if and only if each pair of corresponding elements in a1 and a2 are template-argument-equivalent.
The types iterator and const_­iterator meet the constexpr iterator requirements ([iterator.requirements.general]).
namespace std {
  template<class T, size_t N>
  struct array {
    // types
    using value_type             = T;
    using pointer                = T*;
    using const_pointer          = const T*;
    using reference              = T&;
    using const_reference        = const T&;
    using size_type              = size_t;
    using difference_type        = ptrdiff_t;
    using iterator               = implementation-defined; // see [container.requirements]
    using const_iterator         = implementation-defined; // see [container.requirements]
    using reverse_iterator       = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;

    // no explicit construct/copy/destroy for aggregate type

    constexpr void fill(const T& u);
    constexpr void swap(array&) noexcept(is_nothrow_swappable_v<T>);

    // iterators
    constexpr iterator               begin() noexcept;
    constexpr const_iterator         begin() const noexcept;
    constexpr iterator               end() noexcept;
    constexpr const_iterator         end() const noexcept;

    constexpr reverse_iterator       rbegin() noexcept;
    constexpr const_reverse_iterator rbegin() const noexcept;
    constexpr reverse_iterator       rend() noexcept;
    constexpr const_reverse_iterator rend() const noexcept;

    constexpr const_iterator         cbegin() const noexcept;
    constexpr const_iterator         cend() const noexcept;
    constexpr const_reverse_iterator crbegin() const noexcept;
    constexpr const_reverse_iterator crend() const noexcept;

    // capacity
    [[nodiscard]] constexpr bool empty() const noexcept;
    constexpr size_type size() const noexcept;
    constexpr size_type max_size() const noexcept;

    // element access
    constexpr reference       operator[](size_type n);
    constexpr const_reference operator[](size_type n) const;
    constexpr reference       at(size_type n);
    constexpr const_reference at(size_type n) const;
    constexpr reference       front();
    constexpr const_reference front() const;
    constexpr reference       back();
    constexpr const_reference back() const;

    constexpr T *       data() noexcept;
    constexpr const T * data() const noexcept;

  template<class T, class... U>
    array(T, U...) -> array<T, 1 + sizeof...(U)>;