stl/inc/array

// array standard header

// Copyright (c) Microsoft Corporation.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#ifndef _ARRAY_
#define _ARRAY_
#include <yvals_core.h>
#if _STL_COMPILER_PREPROCESSOR
#include <xutility>

#pragma pack(push, _CRT_PACKING)
#pragma warning(push, _STL_WARNING_LEVEL)
#pragma warning(disable : _STL_DISABLED_WARNINGS)
_STL_DISABLE_CLANG_WARNINGS
#pragma push_macro("new")
#undef new

_STD_BEGIN
#if _ITERATOR_DEBUG_LEVEL != 0
struct _Iterator_base12_compatible { // TRANSITION, for binary compatibility
    _Container_proxy* _Myproxy{};
    _Iterator_base12* _Mynextiter{};
};
#endif // _ITERATOR_DEBUG_LEVEL != 0

template <class _Ty, size_t _Size>
class _Array_const_iterator
#if _ITERATOR_DEBUG_LEVEL != 0
    : private _Iterator_base12_compatible
#endif // _ITERATOR_DEBUG_LEVEL != 0
{
public:
#if _HAS_CXX20
    using iterator_concept = contiguous_iterator_tag;
#endif // _HAS_CXX20
    using iterator_category = random_access_iterator_tag;
    using value_type        = _Ty;
    using difference_type   = ptrdiff_t;
    using pointer           = const _Ty*;
    using reference         = const _Ty&;

    enum { _EEN_SIZE = _Size }; // helper for expression evaluator

#if _ITERATOR_DEBUG_LEVEL == 0
    _CONSTEXPR17 _Array_const_iterator() noexcept : _Ptr() {}

    _CONSTEXPR17 explicit _Array_const_iterator(pointer _Parg, size_t _Off = 0) noexcept : _Ptr(_Parg + _Off) {}

    _NODISCARD _CONSTEXPR17 reference operator*() const noexcept {
        return *_Ptr;
    }

    _NODISCARD _CONSTEXPR17 pointer operator->() const noexcept {
        return _Ptr;
    }

    _CONSTEXPR17 _Array_const_iterator& operator++() noexcept {
        ++_Ptr;
        return *this;
    }

    _CONSTEXPR17 _Array_const_iterator operator++(int) noexcept {
        _Array_const_iterator _Tmp = *this;
        ++_Ptr;
        return _Tmp;
    }

    _CONSTEXPR17 _Array_const_iterator& operator--() noexcept {
        --_Ptr;
        return *this;
    }

    _CONSTEXPR17 _Array_const_iterator operator--(int) noexcept {
        _Array_const_iterator _Tmp = *this;
        --_Ptr;
        return _Tmp;
    }

    _CONSTEXPR17 _Array_const_iterator& operator+=(const ptrdiff_t _Off) noexcept {
        _Ptr += _Off;
        return *this;
    }

    _CONSTEXPR17 _Array_const_iterator& operator-=(const ptrdiff_t _Off) noexcept {
        _Ptr -= _Off;
        return *this;
    }

    _NODISCARD _CONSTEXPR17 ptrdiff_t operator-(const _Array_const_iterator& _Right) const noexcept {
        return _Ptr - _Right._Ptr;
    }

    _NODISCARD _CONSTEXPR17 reference operator[](const ptrdiff_t _Off) const noexcept {
        return _Ptr[_Off];
    }

    _NODISCARD _CONSTEXPR17 bool operator==(const _Array_const_iterator& _Right) const noexcept {
        return _Ptr == _Right._Ptr;
    }

#if _HAS_CXX20
    _NODISCARD constexpr strong_ordering operator<=>(const _Array_const_iterator& _Right) const noexcept {
        return _Ptr <=> _Right._Ptr;
    }
#else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
    _NODISCARD _CONSTEXPR17 bool operator<(const _Array_const_iterator& _Right) const noexcept {
        return _Ptr < _Right._Ptr;
    }
#endif // ^^^ !_HAS_CXX20 ^^^

    using _Prevent_inheriting_unwrap = _Array_const_iterator;

    _NODISCARD constexpr pointer _Unwrapped() const noexcept {
        return _Ptr;
    }

    static constexpr bool _Unwrap_when_unverified = true;

    constexpr void _Seek_to(pointer _It) noexcept {
        _Ptr = _It;
    }

private:
    pointer _Ptr; // beginning of array

#else // ^^^ _ITERATOR_DEBUG_LEVEL == 0 / _ITERATOR_DEBUG_LEVEL != 0 vvv
    _CONSTEXPR17 _Array_const_iterator() noexcept : _Ptr(), _Idx(0) {}

    _CONSTEXPR17 explicit _Array_const_iterator(pointer _Parg, size_t _Off = 0) noexcept : _Ptr(_Parg), _Idx(_Off) {}

    _NODISCARD _CONSTEXPR17 reference operator*() const noexcept {
        return *operator->();
    }

    _NODISCARD _CONSTEXPR17 pointer operator->() const noexcept {
        _STL_VERIFY(_Ptr, "cannot dereference value-initialized array iterator");
        _STL_VERIFY(_Idx < _Size, "cannot dereference out of range array iterator");
        return _Ptr + _Idx;
    }

    _CONSTEXPR17 _Array_const_iterator& operator++() noexcept {
        _STL_VERIFY(_Ptr, "cannot increment value-initialized array iterator");
        _STL_VERIFY(_Idx < _Size, "cannot increment array iterator past end");
        ++_Idx;
        return *this;
    }

    _CONSTEXPR17 _Array_const_iterator operator++(int) noexcept {
        _Array_const_iterator _Tmp = *this;
        ++*this;
        return _Tmp;
    }

    _CONSTEXPR17 _Array_const_iterator& operator--() noexcept {
        _STL_VERIFY(_Ptr, "cannot decrement value-initialized array iterator");
        _STL_VERIFY(_Idx != 0, "cannot decrement array iterator before begin");
        --_Idx;
        return *this;
    }

    _CONSTEXPR17 _Array_const_iterator operator--(int) noexcept {
        _Array_const_iterator _Tmp = *this;
        --*this;
        return _Tmp;
    }

    constexpr void _Verify_offset(const ptrdiff_t _Off) const noexcept {
        if (_Off != 0) {
            _STL_VERIFY(_Ptr, "cannot seek value-initialized array iterator");
        }

        if (_Off < 0) {
            _STL_VERIFY(_Idx >= size_t{0} - static_cast<size_t>(_Off), "cannot seek array iterator before begin");
        }

        if (_Off > 0) {
            _STL_VERIFY(_Size - _Idx >= static_cast<size_t>(_Off), "cannot seek array iterator after end");
        }
    }

    _CONSTEXPR17 _Array_const_iterator& operator+=(const ptrdiff_t _Off) noexcept {
        _Verify_offset(_Off);
        _Idx += static_cast<size_t>(_Off);
        return *this;
    }

    _CONSTEXPR17 _Array_const_iterator& operator-=(const ptrdiff_t _Off) noexcept {
        return *this += -_Off;
    }

    _NODISCARD _CONSTEXPR17 ptrdiff_t operator-(const _Array_const_iterator& _Right) const noexcept {
        _Compat(_Right);
        return static_cast<ptrdiff_t>(_Idx - _Right._Idx);
    }

    _NODISCARD _CONSTEXPR17 reference operator[](const ptrdiff_t _Off) const noexcept {
        return *(*this + _Off);
    }

    _NODISCARD _CONSTEXPR17 bool operator==(const _Array_const_iterator& _Right) const noexcept {
        _Compat(_Right);
        return _Idx == _Right._Idx;
    }

#if _HAS_CXX20
    _NODISCARD constexpr strong_ordering operator<=>(const _Array_const_iterator& _Right) const noexcept {
        _Compat(_Right);
        return _Idx <=> _Right._Idx;
    }
#else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
    _NODISCARD _CONSTEXPR17 bool operator<(const _Array_const_iterator& _Right) const noexcept {
        _Compat(_Right);
        return _Idx < _Right._Idx;
    }
#endif // ^^^ !_HAS_CXX20 ^^^

    _CONSTEXPR17 void _Compat(const _Array_const_iterator& _Right) const noexcept { // test for compatible iterator pair
        _STL_VERIFY(_Ptr == _Right._Ptr, "array iterators incompatible");
    }

    using _Prevent_inheriting_unwrap = _Array_const_iterator;

    _NODISCARD constexpr pointer _Unwrapped() const noexcept {
        return _Ptr + _Idx;
    }

    constexpr void _Verify_with(const _Array_const_iterator& _Last) const noexcept {
        // note _Compat check inside operator<=
        _STL_VERIFY(*this <= _Last, "array iterator range transposed");
    }

    friend constexpr void _Verify_range(
        const _Array_const_iterator& _First, const _Array_const_iterator& _Last) noexcept {
        _First._Verify_with(_Last);
    }

    constexpr void _Seek_to(pointer _It) noexcept {
        _Idx = static_cast<size_t>(_It - _Ptr);
    }

private:
    pointer _Ptr; // beginning of array
    size_t _Idx; // offset into array
#endif // ^^^ _ITERATOR_DEBUG_LEVEL != 0 ^^^

public:
    _NODISCARD _CONSTEXPR17 _Array_const_iterator operator+(const ptrdiff_t _Off) const noexcept {
        _Array_const_iterator _Tmp = *this;
        _Tmp += _Off;
        return _Tmp;
    }

    _NODISCARD _CONSTEXPR17 _Array_const_iterator operator-(const ptrdiff_t _Off) const noexcept {
        _Array_const_iterator _Tmp = *this;
        _Tmp -= _Off;
        return _Tmp;
    }

    _NODISCARD friend _CONSTEXPR17 _Array_const_iterator operator+(
        const ptrdiff_t _Off, _Array_const_iterator _Next) noexcept {
        _Next += _Off;
        return _Next;
    }

#if !_HAS_CXX20
    _NODISCARD _CONSTEXPR17 bool operator!=(const _Array_const_iterator& _Right) const noexcept {
        return !(*this == _Right);
    }

    _NODISCARD _CONSTEXPR17 bool operator>(const _Array_const_iterator& _Right) const noexcept {
        return _Right < *this;
    }

    _NODISCARD _CONSTEXPR17 bool operator<=(const _Array_const_iterator& _Right) const noexcept {
        return !(_Right < *this);
    }

    _NODISCARD _CONSTEXPR17 bool operator>=(const _Array_const_iterator& _Right) const noexcept {
        return !(*this < _Right);
    }
#endif // !_HAS_CXX20
};

#if _HAS_CXX20
template <class _Ty, size_t _Size>
struct pointer_traits<_Array_const_iterator<_Ty, _Size>> {
    using pointer         = _Array_const_iterator<_Ty, _Size>;
    using element_type    = const _Ty;
    using difference_type = ptrdiff_t;

    _NODISCARD static constexpr element_type* to_address(const pointer _Iter) noexcept {
        return _Iter._Unwrapped();
    }
};
#endif // _HAS_CXX20

template <class _Ty, size_t _Size>
class _Array_iterator : public _Array_const_iterator<_Ty, _Size> {
public:
    using _Mybase = _Array_const_iterator<_Ty, _Size>;

#if _HAS_CXX20
    using iterator_concept = contiguous_iterator_tag;
#endif // _HAS_CXX20
    using iterator_category = random_access_iterator_tag;
    using value_type        = _Ty;
    using difference_type   = ptrdiff_t;
    using pointer           = _Ty*;
    using reference         = _Ty&;

    enum { _EEN_SIZE = _Size }; // helper for expression evaluator

    _CONSTEXPR17 _Array_iterator() noexcept {}

    _CONSTEXPR17 explicit _Array_iterator(pointer _Parg, size_t _Off = 0) noexcept : _Mybase(_Parg, _Off) {}

    _NODISCARD _CONSTEXPR17 reference operator*() const noexcept {
        return const_cast<reference>(_Mybase::operator*());
    }

    _NODISCARD _CONSTEXPR17 pointer operator->() const noexcept {
        return const_cast<pointer>(_Mybase::operator->());
    }

    _CONSTEXPR17 _Array_iterator& operator++() noexcept {
        _Mybase::operator++();
        return *this;
    }

    _CONSTEXPR17 _Array_iterator operator++(int) noexcept {
        _Array_iterator _Tmp = *this;
        _Mybase::operator++();
        return _Tmp;
    }

    _CONSTEXPR17 _Array_iterator& operator--() noexcept {
        _Mybase::operator--();
        return *this;
    }

    _CONSTEXPR17 _Array_iterator operator--(int) noexcept {
        _Array_iterator _Tmp = *this;
        _Mybase::operator--();
        return _Tmp;
    }

    _CONSTEXPR17 _Array_iterator& operator+=(const ptrdiff_t _Off) noexcept {
        _Mybase::operator+=(_Off);
        return *this;
    }

    _NODISCARD _CONSTEXPR17 _Array_iterator operator+(const ptrdiff_t _Off) const noexcept {
        _Array_iterator _Tmp = *this;
        _Tmp += _Off;
        return _Tmp;
    }

    _NODISCARD friend _CONSTEXPR17 _Array_iterator operator+(const ptrdiff_t _Off, _Array_iterator _Next) noexcept {
        _Next += _Off;
        return _Next;
    }

    _CONSTEXPR17 _Array_iterator& operator-=(const ptrdiff_t _Off) noexcept {
        _Mybase::operator-=(_Off);
        return *this;
    }

    using _Mybase::operator-;

    _NODISCARD _CONSTEXPR17 _Array_iterator operator-(const ptrdiff_t _Off) const noexcept {
        _Array_iterator _Tmp = *this;
        _Tmp -= _Off;
        return _Tmp;
    }

    _NODISCARD _CONSTEXPR17 reference operator[](const ptrdiff_t _Off) const noexcept {
        return const_cast<reference>(_Mybase::operator[](_Off));
    }

    using _Prevent_inheriting_unwrap = _Array_iterator;

    _NODISCARD constexpr pointer _Unwrapped() const noexcept {
        return const_cast<pointer>(_Mybase::_Unwrapped());
    }
};

#if _HAS_CXX20
template <class _Ty, size_t _Size>
struct pointer_traits<_Array_iterator<_Ty, _Size>> {
    using pointer         = _Array_iterator<_Ty, _Size>;
    using element_type    = _Ty;
    using difference_type = ptrdiff_t;

    _NODISCARD static constexpr element_type* to_address(const pointer _Iter) noexcept {
        return _Iter._Unwrapped();
    }
};
#endif // _HAS_CXX20

_EXPORT_STD template <class _Ty, size_t _Size>
class array { // fixed size array of values
public:
    static_assert(is_object_v<_Ty>, "The C++ Standard forbids containers of non-object types "
                                    "because of [container.requirements].");

    using value_type      = _Ty;
    using size_type       = size_t;
    using difference_type = ptrdiff_t;
    using pointer         = _Ty*;
    using const_pointer   = const _Ty*;
    using reference       = _Ty&;
    using const_reference = const _Ty&;

    using iterator       = _Array_iterator<_Ty, _Size>;
    using const_iterator = _Array_const_iterator<_Ty, _Size>;

    using reverse_iterator       = _STD reverse_iterator<iterator>;
    using const_reverse_iterator = _STD reverse_iterator<const_iterator>;

    using _Library_defined = array;

#if _HAS_TR1_NAMESPACE
    _DEPRECATE_TR1_NAMESPACE void assign(const _Ty& _Value) {
        _STD fill_n(_Elems, _Size, _Value);
    }
#endif // _HAS_TR1_NAMESPACE

    _CONSTEXPR20 void fill(const _Ty& _Value) {
        _STD fill_n(_Elems, _Size, _Value);
    }

    _CONSTEXPR20 void swap(array& _Other) noexcept(_Is_nothrow_swappable<_Ty>::value) {
        _STD _Swap_ranges_unchecked(_Elems, _Elems + _Size, _Other._Elems);
    }

    _NODISCARD _CONSTEXPR17 iterator begin() noexcept {
        return iterator(_Elems, 0);
    }

    _NODISCARD _CONSTEXPR17 const_iterator begin() const noexcept {
        return const_iterator(_Elems, 0);
    }

    _NODISCARD _CONSTEXPR17 iterator end() noexcept {
        return iterator(_Elems, _Size);
    }

    _NODISCARD _CONSTEXPR17 const_iterator end() const noexcept {
        return const_iterator(_Elems, _Size);
    }

    _NODISCARD _CONSTEXPR17 reverse_iterator rbegin() noexcept {
        return reverse_iterator(end());
    }

    _NODISCARD _CONSTEXPR17 const_reverse_iterator rbegin() const noexcept {
        return const_reverse_iterator(end());
    }

    _NODISCARD _CONSTEXPR17 reverse_iterator rend() noexcept {
        return reverse_iterator(begin());
    }

    _NODISCARD _CONSTEXPR17 const_reverse_iterator rend() const noexcept {
        return const_reverse_iterator(begin());
    }

    _NODISCARD _CONSTEXPR17 const_iterator cbegin() const noexcept {
        return begin();
    }

    _NODISCARD _CONSTEXPR17 const_iterator cend() const noexcept {
        return end();
    }

    _NODISCARD _CONSTEXPR17 const_reverse_iterator crbegin() const noexcept {
        return rbegin();
    }

    _NODISCARD _CONSTEXPR17 const_reverse_iterator crend() const noexcept {
        return rend();
    }

    _CONSTEXPR17 _Ty* _Unchecked_begin() noexcept {
        return _Elems;
    }

    _CONSTEXPR17 const _Ty* _Unchecked_begin() const noexcept {
        return _Elems;
    }

    _CONSTEXPR17 _Ty* _Unchecked_end() noexcept {
        return _Elems + _Size;
    }

    _CONSTEXPR17 const _Ty* _Unchecked_end() const noexcept {
        return _Elems + _Size;
    }

    _NODISCARD _Ret_range_(==, _Size) constexpr size_type size() const noexcept {
        return _Size;
    }

    _NODISCARD constexpr size_type max_size() const noexcept {
        return _Size;
    }

    _NODISCARD_EMPTY_ARRAY_MEMBER constexpr bool empty() const noexcept {
        return false;
    }

    _NODISCARD _CONSTEXPR17 reference at(size_type _Pos) {
        if (_Size <= _Pos) {
            _Xran();
        }

        return _Elems[_Pos];
    }

    _NODISCARD constexpr const_reference at(size_type _Pos) const {
        if (_Size <= _Pos) {
            _Xran();
        }

        return _Elems[_Pos];
    }

    _NODISCARD _CONSTEXPR17 reference operator[](_In_range_(<, _Size) size_type _Pos) noexcept /* strengthened */ {
#if _MSVC_STL_HARDENING_ARRAY || _ITERATOR_DEBUG_LEVEL != 0
        _STL_VERIFY(_Pos < _Size, "array subscript out of range");
#endif

        return _Elems[_Pos];
    }

    _NODISCARD constexpr const_reference operator[](_In_range_(<, _Size) size_type _Pos) const noexcept
    /* strengthened */ {
#if _MSVC_STL_HARDENING_ARRAY || _ITERATOR_DEBUG_LEVEL != 0
        _STL_VERIFY(_Pos < _Size, "array subscript out of range");
#endif

        return _Elems[_Pos];
    }

    _NODISCARD _CONSTEXPR17 reference front() noexcept /* strengthened */ {
        return _Elems[0];
    }

    _NODISCARD constexpr const_reference front() const noexcept /* strengthened */ {
        return _Elems[0];
    }

    _NODISCARD _CONSTEXPR17 reference back() noexcept /* strengthened */ {
        return _Elems[_Size - 1];
    }

    _NODISCARD constexpr const_reference back() const noexcept /* strengthened */ {
        return _Elems[_Size - 1];
    }

    _NODISCARD _CONSTEXPR17 _Ty* data() noexcept {
        return _Elems;
    }

    _NODISCARD _CONSTEXPR17 const _Ty* data() const noexcept {
        return _Elems;
    }

    _Ty _Elems[_Size];

private:
    [[noreturn]] static void _Xran() {
        _Xout_of_range("invalid array<T, N> subscript");
    }
};

#if _HAS_CXX17
template <class _First, class... _Rest>
struct _Enforce_same {
    static_assert(
        conjunction_v<is_same<_First, _Rest>...>, "N4950 [array.cons]/2: Mandates: (is_same_v<T, U> && ...) is true.");
    using type = _First;
};

template <class _First, class... _Rest>
array(_First, _Rest...) -> array<typename _Enforce_same<_First, _Rest...>::type, 1 + sizeof...(_Rest)>;
#endif // _HAS_CXX17

struct _Empty_array_element {};

template <class _Ty>
class array<_Ty, 0> {
public:
    static_assert(is_object_v<_Ty>, "The C++ Standard forbids containers of non-object types "
                                    "because of [container.requirements].");

    using value_type      = _Ty;
    using size_type       = size_t;
    using difference_type = ptrdiff_t;
    using pointer         = _Ty*;
    using const_pointer   = const _Ty*;
    using reference       = _Ty&;
    using const_reference = const _Ty&;

    using iterator               = _Array_iterator<_Ty, 0>;
    using const_iterator         = _Array_const_iterator<_Ty, 0>;
    using reverse_iterator       = _STD reverse_iterator<iterator>;
    using const_reverse_iterator = _STD reverse_iterator<const_iterator>;

    using _Library_defined = array;

#if _HAS_TR1_NAMESPACE
    _DEPRECATE_TR1_NAMESPACE void assign(const _Ty&) {}
#endif // _HAS_TR1_NAMESPACE

    _CONSTEXPR20 void fill(const _Ty&) {}

    _CONSTEXPR20 void swap(array&) noexcept {}

    _NODISCARD _CONSTEXPR17 iterator begin() noexcept {
        return iterator{};
    }

    _NODISCARD _CONSTEXPR17 const_iterator begin() const noexcept {
        return const_iterator{};
    }

    _NODISCARD _CONSTEXPR17 iterator end() noexcept {
        return iterator{};
    }

    _NODISCARD _CONSTEXPR17 const_iterator end() const noexcept {
        return const_iterator{};
    }

    _NODISCARD _CONSTEXPR17 reverse_iterator rbegin() noexcept {
        return reverse_iterator(end());
    }

    _NODISCARD _CONSTEXPR17 const_reverse_iterator rbegin() const noexcept {
        return const_reverse_iterator(end());
    }

    _NODISCARD _CONSTEXPR17 reverse_iterator rend() noexcept {
        return reverse_iterator(begin());
    }

    _NODISCARD _CONSTEXPR17 const_reverse_iterator rend() const noexcept {
        return const_reverse_iterator(begin());
    }

    _NODISCARD _CONSTEXPR17 const_iterator cbegin() const noexcept {
        return begin();
    }

    _NODISCARD _CONSTEXPR17 const_iterator cend() const noexcept {
        return end();
    }

    _NODISCARD _CONSTEXPR17 const_reverse_iterator crbegin() const noexcept {
        return rbegin();
    }

    _NODISCARD _CONSTEXPR17 const_reverse_iterator crend() const noexcept {
        return rend();
    }

    _CONSTEXPR17 _Ty* _Unchecked_begin() noexcept {
        return nullptr;
    }

    _CONSTEXPR17 const _Ty* _Unchecked_begin() const noexcept {
        return nullptr;
    }

    _CONSTEXPR17 _Ty* _Unchecked_end() noexcept {
        return nullptr;
    }

    _CONSTEXPR17 const _Ty* _Unchecked_end() const noexcept {
        return nullptr;
    }

    _NODISCARD constexpr size_type size() const noexcept {
        return 0;
    }

    _NODISCARD constexpr size_type max_size() const noexcept {
        return 0;
    }

    _NODISCARD_EMPTY_ARRAY_MEMBER constexpr bool empty() const noexcept {
        return true;
    }

    [[noreturn]] reference at(size_type) {
        _Xran();
    }

    [[noreturn]] const_reference at(size_type) const {
        _Xran();
    }

    _NODISCARD reference operator[](size_type) noexcept /* strengthened */ {
#if _MSVC_STL_HARDENING_ARRAY || _ITERATOR_DEBUG_LEVEL != 0
        _STL_REPORT_ERROR("array<T, 0> subscript is invalid");
#endif

        return *data();
    }

    _NODISCARD const_reference operator[](size_type) const noexcept /* strengthened */ {
#if _MSVC_STL_HARDENING_ARRAY || _ITERATOR_DEBUG_LEVEL != 0
        _STL_REPORT_ERROR("array<T, 0> subscript is invalid");
#endif

        return *data();
    }

    _NODISCARD reference front() noexcept /* strengthened */ {
#if _MSVC_STL_HARDENING_ARRAY || _ITERATOR_DEBUG_LEVEL != 0
        _STL_REPORT_ERROR("array<T, 0>::front() is invalid");
#endif

        return *data();
    }

    _NODISCARD const_reference front() const noexcept /* strengthened */ {
#if _MSVC_STL_HARDENING_ARRAY || _ITERATOR_DEBUG_LEVEL != 0
        _STL_REPORT_ERROR("array<T, 0>::front() is invalid");
#endif

        return *data();
    }

    _NODISCARD reference back() noexcept /* strengthened */ {
#if _MSVC_STL_HARDENING_ARRAY || _ITERATOR_DEBUG_LEVEL != 0
        _STL_REPORT_ERROR("array<T, 0>::back() is invalid");
#endif

        return *data();
    }

    _NODISCARD const_reference back() const noexcept /* strengthened */ {
#if _MSVC_STL_HARDENING_ARRAY || _ITERATOR_DEBUG_LEVEL != 0
        _STL_REPORT_ERROR("array<T, 0>::back() is invalid");
#endif

        return *data();
    }

    _NODISCARD _CONSTEXPR17 _Ty* data() noexcept {
        return nullptr;
    }

    _NODISCARD _CONSTEXPR17 const _Ty* data() const noexcept {
        return nullptr;
    }

    conditional_t<disjunction_v<is_default_constructible<_Ty>, _Is_implicitly_default_constructible<_Ty>>, _Ty,
        _Empty_array_element>
        _Elems[1]{};

private:
    [[noreturn]] static void _Xran() {
        _Xout_of_range("invalid array<T, 0> subscript");
    }
};

_EXPORT_STD template <class _Ty, size_t _Size, enable_if_t<_Size == 0 || _Is_swappable<_Ty>::value, int> = 0>
_CONSTEXPR20 void swap(array<_Ty, _Size>& _Left, array<_Ty, _Size>& _Right) noexcept(noexcept(_Left.swap(_Right))) {
    _Left.swap(_Right);
}

_EXPORT_STD template <class _Ty, size_t _Size>
_NODISCARD _CONSTEXPR20 bool operator==(const array<_Ty, _Size>& _Left, const array<_Ty, _Size>& _Right) {
    return _STD equal(_Left.data(), _Left.data() + _Size, _Right.data());
}

#if _HAS_CXX20
_EXPORT_STD template <class _Ty, size_t _Size>
_NODISCARD constexpr _Synth_three_way_result<_Ty> operator<=>(
    const array<_Ty, _Size>& _Left, const array<_Ty, _Size>& _Right) {
    return _STD lexicographical_compare_three_way(
        _Left.data(), _Left.data() + _Size, _Right.data(), _Right.data() + _Size, _Synth_three_way{});
}
#else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
template <class _Ty, size_t _Size>
_NODISCARD bool operator!=(const array<_Ty, _Size>& _Left, const array<_Ty, _Size>& _Right) {
    return !(_Left == _Right);
}

template <class _Ty, size_t _Size>
_NODISCARD _CONSTEXPR20 bool operator<(const array<_Ty, _Size>& _Left, const array<_Ty, _Size>& _Right) {
    return _STD lexicographical_compare(_Left.data(), _Left.data() + _Size, _Right.data(), _Right.data() + _Size);
}

template <class _Ty, size_t _Size>
_NODISCARD _CONSTEXPR20 bool operator>(const array<_Ty, _Size>& _Left, const array<_Ty, _Size>& _Right) {
    return _Right < _Left;
}

template <class _Ty, size_t _Size>
_NODISCARD _CONSTEXPR20 bool operator<=(const array<_Ty, _Size>& _Left, const array<_Ty, _Size>& _Right) {
    return !(_Right < _Left);
}

template <class _Ty, size_t _Size>
_NODISCARD _CONSTEXPR20 bool operator>=(const array<_Ty, _Size>& _Left, const array<_Ty, _Size>& _Right) {
    return !(_Left < _Right);
}
#endif // ^^^ !_HAS_CXX20 ^^^

#if _HAS_CXX20
template <class _Ty, size_t _Size, size_t... _Idx>
_NODISCARD constexpr array<remove_cv_t<_Ty>, _Size> _To_array_lvalue_impl(
    _Ty (&_Array)[_Size], index_sequence<_Idx...>) {
    return {{_Array[_Idx]...}};
}

template <class _Ty, size_t _Size, size_t... _Idx>
_NODISCARD constexpr array<remove_cv_t<_Ty>, _Size> _To_array_rvalue_impl(
    _Ty (&&_Array)[_Size], index_sequence<_Idx...>) {
    return {{_STD move(_Array[_Idx])...}};
}

_EXPORT_STD template <class _Ty, size_t _Size>
_NODISCARD constexpr array<remove_cv_t<_Ty>, _Size> to_array(_Ty (&_Array)[_Size]) {
    static_assert(!is_array_v<_Ty>, "N4950 [array.creation]/1: "
                                    "to_array does not accept multidimensional arrays.");
    static_assert(is_constructible_v<_Ty, _Ty&>, "N4950 [array.creation]/1: "
                                                 "to_array requires copy constructible elements.");
    return _STD _To_array_lvalue_impl(_Array, make_index_sequence<_Size>{});
}

_EXPORT_STD template <class _Ty, size_t _Size>
_NODISCARD constexpr array<remove_cv_t<_Ty>, _Size> to_array(_Ty (&&_Array)[_Size]) {
    static_assert(!is_array_v<_Ty>, "N4950 [array.creation]/4: "
                                    "to_array does not accept multidimensional arrays.");
    static_assert(is_move_constructible_v<_Ty>, "N4950 [array.creation]/4: "
                                                "to_array requires move constructible elements.");
    return _STD _To_array_rvalue_impl(_STD move(_Array), make_index_sequence<_Size>{});
}
#endif // _HAS_CXX20

template <class _Ty, class _Enable = void>
constexpr bool _Is_library_defined = false;
template <class _Ty>
constexpr bool _Is_library_defined<_Ty, enable_if_t<is_same_v<typename _Ty::_Library_defined, _Ty>>> = true;

_EXPORT_STD template <size_t _Idx, class _Ty, size_t _Size>
_NODISCARD constexpr _Ty& get(array<_Ty, _Size>& _Arr) noexcept {
    static_assert(_Idx < _Size, "array index out of bounds");
    if constexpr (_Is_library_defined<array<_Ty, _Size>>) {
        return _Arr._Elems[_Idx];
    } else {
#if _HAS_CXX17
        return _Arr[_Idx];
#else // ^^^ _HAS_CXX17 / !_HAS_CXX17 vvv
        return const_cast<_Ty&>(_STD as_const(_Arr)[_Idx]);
#endif // ^^^ !_HAS_CXX17 ^^^
    }
}

_EXPORT_STD template <size_t _Idx, class _Ty, size_t _Size>
_NODISCARD constexpr const _Ty& get(const array<_Ty, _Size>& _Arr) noexcept {
    static_assert(_Idx < _Size, "array index out of bounds");
    if constexpr (_Is_library_defined<array<_Ty, _Size>>) {
        return _Arr._Elems[_Idx];
    } else {
        return _Arr[_Idx];
    }
}

_EXPORT_STD template <size_t _Idx, class _Ty, size_t _Size>
_NODISCARD constexpr _Ty&& get(array<_Ty, _Size>&& _Arr) noexcept {
    static_assert(_Idx < _Size, "array index out of bounds");
    if constexpr (_Is_library_defined<array<_Ty, _Size>>) {
        return _STD move(_Arr._Elems[_Idx]);
    } else {
#if _HAS_CXX17
        return _STD move(_Arr[_Idx]);
#else // ^^^ _HAS_CXX17 / !_HAS_CXX17 vvv
        return const_cast<_Ty&&>(_STD move(_STD as_const(_Arr)[_Idx]));
#endif // ^^^ !_HAS_CXX17 ^^^
    }
}

_EXPORT_STD template <size_t _Idx, class _Ty, size_t _Size>
_NODISCARD constexpr const _Ty&& get(const array<_Ty, _Size>&& _Arr) noexcept {
    static_assert(_Idx < _Size, "array index out of bounds");
    if constexpr (_Is_library_defined<array<_Ty, _Size>>) {
        return _STD move(_Arr._Elems[_Idx]);
    } else {
        return _STD move(_Arr[_Idx]);
    }
}

#if _HAS_TR1_NAMESPACE
namespace _DEPRECATE_TR1_NAMESPACE tr1 {
    using _STD array;
    using _STD get;
} // namespace _DEPRECATE_TR1_NAMESPACE tr1
#endif // _HAS_TR1_NAMESPACE
_STD_END

#pragma pop_macro("new")
_STL_RESTORE_CLANG_WARNINGS
#pragma warning(pop)
#pragma pack(pop)
#endif // _STL_COMPILER_PREPROCESSOR
#endif // _ARRAY_