STL：std::array 和基本数组类型array 浅谈一二三

发布时间：2023年12月26日

一、优缺点比较

在C++中，std::array是标准库提供的数组容器，相比于基础数据类型的数组，它具有以下优点和缺点：

优点：

1. 安全性：std::array提供了边界检查，可以避免数组越界访问的问题。
1. 可以作为函数参数：std::array可以作为函数的参数和返回值，而基础数据类型的数组不能直接作为函数参数传递。
1. 支持STL算法：std::array可以直接使用STL算法，如std::sort、std::find等，而基础数据类型的数组需要手动实现这些算法。

缺点：

1. 大小固定：std::array的大小在编译时就需要确定，无法动态改变大小，而基础数据类型的数组可以使用new和delete动态分配和释放内存。
1. 初始化复杂：相比于基础数据类型的数组，std::array的初始化语法可能更加繁琐。std::array 不支持参数列表的初始化形式。

总的来说，std::array相比于基础数据类型的数组更加安全和方便，但在某些情况下可能会有一些额外的开销和限制。

二、代码示例

#include <any>
#include <iostream>
#include <vector>
#include <map>
#include <list>
#include <array>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
using namespace std;

#define NOUSE(x) (void)x;

// test array
template <typename _Ty,size_t N>
void array_test_func(std::array<_Ty,N>& arr)
{
    /// 通过迭代器遍历
    auto traver_1 = [&](){
#if 0
        auto iter = arr.begin();
        for(;iter != arr.end();++iter)
            cout << *iter << " ";
#else
        std::copy(arr.cbegin(), arr.cend(), std::ostream_iterator<_Ty>(std::cout, " "));
#endif
        cout << endl;
    };
    traver_1();

    cout << "back  ==> " << arr.back() << endl;     // 首字符
    cout << "front ==> " << arr.front() << endl;    // 尾字符

    size_t n =  arr.size(); // 长度
    /// 通过数组指针遍历
    auto traver_2 = [&](){
        _Ty* dptr = arr.data(); // 首地址

        for(size_t i = 0; i < n ;++i){
            cout << *(dptr+i) << " ";
        }
        cout << endl;
    };
    traver_2();


    /// 通过下标遍历
    auto traver_3 = [&](){
       for(size_t i = 0; i < n;++i){
           cout << arr.at(i) << " ";
       }
       cout << endl;
    };
    traver_3();
}

int main(int argc, char *argv[])
{
    NOUSE(argc);
    NOUSE(argv);

    std::array<int,3> arr = {2,6,4};
    array_test_func<int,3>(arr);

    // array_test_func<int,3>({2,4,6}); // error : 不支持 initializer_list

    std::sort(arr.begin(),arr.end()); // 支持STL算法
    array_test_func<int,3>(arr);

    return 0;
}

三、源码赏析

// array standard header

// Copyright (c) Microsoft Corporation.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#pragma once
#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

 定于数组的const迭代器
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:
#ifdef __cpp_lib_concepts
    using iterator_concept = contiguous_iterator_tag;
#endif // __cpp_lib_concepts
    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;
    }

    _NODISCARD _CONSTEXPR17 _Array_const_iterator operator+(const ptrdiff_t _Off) const noexcept {
        _Array_const_iterator _Tmp = *this;
        return _Tmp += _Off;
    }

    _CONSTEXPR17 _Array_const_iterator& operator-=(const ptrdiff_t _Off) noexcept {
        _Ptr -= _Off;
        return *this;
    }

    _NODISCARD _CONSTEXPR17 _Array_const_iterator operator-(const ptrdiff_t _Off) const noexcept {
        _Array_const_iterator _Tmp = *this;
        return _Tmp -= _Off;
    }

    _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 ^^^ / vvv !_HAS_CXX20 vvv
    _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 _Ptr < _Right._Ptr;
    }

    _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

    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;
    }

    _NODISCARD _CONSTEXPR17 _Array_const_iterator operator+(const ptrdiff_t _Off) const noexcept {
        _Array_const_iterator _Tmp = *this;
        return _Tmp += _Off;
    }

    _CONSTEXPR17 _Array_const_iterator& operator-=(const ptrdiff_t _Off) noexcept {
        return *this += -_Off;
    }

    _NODISCARD _CONSTEXPR17 _Array_const_iterator operator-(const ptrdiff_t _Off) const noexcept {
        _Array_const_iterator _Tmp = *this;
        return _Tmp -= _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 ^^^ / vvv !_HAS_CXX20 vvv
    _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 {
        _Compat(_Right);
        return _Idx < _Right._Idx;
    }

    _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

    _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");
    }

    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
};

#if _ITERATOR_DEBUG_LEVEL != 0
template <class _Ty, size_t _Size>
constexpr void _Verify_range(
    const _Array_const_iterator<_Ty, _Size>& _First, const _Array_const_iterator<_Ty, _Size>& _Last) noexcept {
    // TRANSITION, CUDA
    _First._Verify_with(_Last);
}
#endif // _ITERATOR_DEBUG_LEVEL != 0

/// 迭代器模板特化
template <class _Ty, size_t _Size>
_NODISCARD _CONSTEXPR17 _Array_const_iterator<_Ty, _Size> operator+(
    const ptrdiff_t _Off, _Array_const_iterator<_Ty, _Size> _Next) noexcept {
    return _Next += _Off;
}

#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

/// 定义子类：非常迭代器
template <class _Ty, size_t _Size>
class _Array_iterator : public _Array_const_iterator<_Ty, _Size> {
public:
    using _Mybase = _Array_const_iterator<_Ty, _Size>;

#ifdef __cpp_lib_concepts
    using iterator_concept = contiguous_iterator_tag;
#endif // __cpp_lib_concepts
    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->());  // 去常
    }

	// 前++ 重载
    _CONSTEXPR17 _Array_iterator& operator++() noexcept {
        _Mybase::operator++();
        return *this;
    }

	// 后加加重载
    _CONSTEXPR17 _Array_iterator operator++(int) noexcept {
        _Array_iterator _Tmp = *this;
        _Mybase::operator++();
        return _Tmp;
    }

	// 前减减重载 
    _CONSTEXPR17 _Array_iterator& operator--() noexcept {
        _Mybase::operator--();
        return *this;
    }

	// 后减减重载
    _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;
        return _Tmp += _Off;
    }

    _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;
        return _Tmp -= _Off;
    }

	// 下标操作符重载
    _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());
    }
};

template <class _Ty, size_t _Size>
_NODISCARD _CONSTEXPR17 _Array_iterator<_Ty, _Size> operator+(
    const ptrdiff_t _Off, _Array_iterator<_Ty, _Size> _Next) noexcept {
    return _Next += _Off;
}

#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


/// 定义数组模板
template <class _Ty, size_t _Size>
class array { // fixed size array of values
public:
    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>;

#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) {
        _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 constexpr size_type size() const noexcept {
        return _Size;
    }

    _NODISCARD constexpr size_type max_size() const noexcept {
        return _Size;
    }

    _NODISCARD 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_(0, _Size - 1) size_type _Pos) noexcept /* strengthened */ {
#if _CONTAINER_DEBUG_LEVEL > 0
        _STL_VERIFY(_Pos < _Size, "array subscript out of range");
#endif // _CONTAINER_DEBUG_LEVEL > 0

        return _Elems[_Pos];
    }

    _NODISCARD constexpr const_reference operator[](_In_range_(0, _Size - 1) size_type _Pos) const noexcept
    /* strengthened */ {
#if _CONTAINER_DEBUG_LEVEL > 0
        _STL_VERIFY(_Pos < _Size, "array subscript out of range");
#endif // _CONTAINER_DEBUG_LEVEL > 0

        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;
    }

    [[noreturn]] void _Xran() const {
        _Xout_of_range("invalid array<T, N> subscript");
    }

    _Ty _Elems[_Size];
};

#if _HAS_CXX17
template <class _First, class... _Rest>
struct _Enforce_same {
    static_assert(conjunction_v<is_same<_First, _Rest>...>,
        "N4687 26.3.7.2 [array.cons]/2: "
        "Requires: (is_same_v<T, U> && ...) is true. Otherwise the program is ill-formed.");
    using type = _First;
};

/// 检查数组中元素类型与第一个要严格一致
template <class _First, class... _Rest>
array(_First, _Rest...) -> array<typename _Enforce_same<_First, _Rest...>::type, 1 + sizeof...(_Rest)>;
#endif // _HAS_CXX17


/// 数组模板偏特化
template <class _Ty>
class array<_Ty, 0> {
public:
    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>;

#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 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 _CONTAINER_DEBUG_LEVEL > 0
        _STL_REPORT_ERROR("array subscript out of range");
#endif // _CONTAINER_DEBUG_LEVEL > 0

        return _Elems[0];
    }

    _NODISCARD const_reference operator[](size_type) const noexcept /* strengthened */ {
#if _CONTAINER_DEBUG_LEVEL > 0
        _STL_REPORT_ERROR("array subscript out of range");
#endif // _CONTAINER_DEBUG_LEVEL > 0

        return _Elems[0];
    }

    _NODISCARD reference front() noexcept /* strengthened */ {
#if _CONTAINER_DEBUG_LEVEL > 0
        _STL_REPORT_ERROR("array<T, 0>::front() invalid");
#endif // _CONTAINER_DEBUG_LEVEL > 0

        return _Elems[0];
    }

    _NODISCARD const_reference front() const noexcept /* strengthened */ {
#if _CONTAINER_DEBUG_LEVEL > 0
        _STL_REPORT_ERROR("array<T, 0>::front() invalid");
#endif // _CONTAINER_DEBUG_LEVEL > 0

        return _Elems[0];
    }

    _NODISCARD reference back() noexcept /* strengthened */ {
#if _CONTAINER_DEBUG_LEVEL > 0
        _STL_REPORT_ERROR("array<T, 0>::back() invalid");
#endif // _CONTAINER_DEBUG_LEVEL > 0

        return _Elems[0];
    }

    _NODISCARD const_reference back() const noexcept /* strengthened */ {
#if _CONTAINER_DEBUG_LEVEL > 0
        _STL_REPORT_ERROR("array<T, 0>::back() invalid");
#endif // _CONTAINER_DEBUG_LEVEL > 0

        return _Elems[0];
    }

    _NODISCARD _CONSTEXPR17 _Ty* data() noexcept {
        return nullptr;
    }

    _NODISCARD _CONSTEXPR17 const _Ty* data() const noexcept {
        return nullptr;
    }

    [[noreturn]] void _Xran() const {
        _Xout_of_range("invalid array<T, 0> subscript");
    }

    _Ty _Elems[1];
};

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))) {
    return _Left.swap(_Right);
}

template <class _Ty, size_t _Size>
_NODISCARD _CONSTEXPR20 bool operator==(const array<_Ty, _Size>& _Left, const array<_Ty, _Size>& _Right) {
#ifdef __EDG__ // TRANSITION, VSO-1161663
    return _STD equal(_Left.begin(), _Left.end(), _Right.begin());
#else // ^^^ workaround / no workaround vvv
    return _STD equal(_Left._Unchecked_begin(), _Left._Unchecked_end(), _Right._Unchecked_begin());
#endif // ^^^ no workaround ^^^
}

#if !_HAS_CXX20
template <class _Ty, size_t _Size>
_NODISCARD bool operator!=(const array<_Ty, _Size>& _Left, const array<_Ty, _Size>& _Right) {
    return !(_Left == _Right);
}
#endif // !_HAS_CXX20

#ifdef __cpp_lib_concepts
template <class _Ty, size_t _Size>
_NODISCARD constexpr _Synth_three_way_result<_Ty> operator<=>(
    const array<_Ty, _Size>& _Left, const array<_Ty, _Size>& _Right) {
#ifdef __EDG__ // TRANSITION, VSO-1161663
    return _STD lexicographical_compare_three_way(
        _Left.begin(), _Left.end(), _Right.begin(), _Right.end(), _Synth_three_way{});
#else // ^^^ workaround / no workaround vvv
    return _STD lexicographical_compare_three_way(_Left._Unchecked_begin(), _Left._Unchecked_end(),
        _Right._Unchecked_begin(), _Right._Unchecked_end(), _Synth_three_way{});
#endif // ^^^ no workaround ^^^
}
#else // ^^^ defined(__cpp_lib_concepts) / !defined(__cpp_lib_concepts) vvv
template <class _Ty, size_t _Size>
_NODISCARD _CONSTEXPR20 bool operator<(const array<_Ty, _Size>& _Left, const array<_Ty, _Size>& _Right) {
#ifdef __EDG__ // TRANSITION, VSO-1161663
    return _STD lexicographical_compare(_Left.begin(), _Left.end(), _Right.begin(), _Right.end());
#else // ^^^ workaround / no workaround vvv
    return _STD lexicographical_compare(
        _Left._Unchecked_begin(), _Left._Unchecked_end(), _Right._Unchecked_begin(), _Right._Unchecked_end());
#endif // ^^^ no workaround ^^^
}

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 // ^^^ !defined(__cpp_lib_concepts) ^^^

#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])...}};
}

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>, "N4830 [array.creation]/1: "
                                    "to_array does not accept multidimensional arrays.");
    static_assert(is_constructible_v<_Ty, _Ty&>, "N4830 [array.creation]/1: "
                                                 "to_array requires copy constructible elements.");
    return _To_array_lvalue_impl(_Array, make_index_sequence<_Size>{});
}

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>, "N4830 [array.creation]/4: "
                                    "to_array does not accept multidimensional arrays.");
    static_assert(is_move_constructible_v<_Ty>, "N4830 [array.creation]/4: "
                                                "to_array requires move constructible elements.");
    return _To_array_rvalue_impl(_STD move(_Array), make_index_sequence<_Size>{});
}
#endif // _HAS_CXX20

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");
    return _Arr._Elems[_Idx];
}

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");
    return _Arr._Elems[_Idx];
}

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");
    return _STD move(_Arr._Elems[_Idx]);
}

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");
    return _STD move(_Arr._Elems[_Idx]);
}

#if _HAS_TR1_NAMESPACE
namespace _DEPRECATE_TR1_NAMESPACE tr1 {
    using _STD array;
    using _STD get;
} // 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_

从源码来看，非常经典而简洁，在我们平时自己使用元编程技巧时，有不错的借鉴意义。而且这一段难度比较低，基本上大家应该都能看得懂。
std::array 在底层实现上，还是依赖于基础数组这一数据类型,以下源码可以佐证。

template <class _Ty, size_t _Size>
class array { // fixed size array of values
    _Ty _Elems[_Size];  // 数组
};

个人喜欢std::array 的OOP ，不过std::array 也有觉得可以优化的地方，譬如不支持弹性数组的特性，不支持扩容，不支持参数化列表初始化等，不过，这也许正是设计者设计std::array如此简洁优雅之意图。
编程，不只是技术，深入去思考，会觉得简直就是艺术~
在这里插入图片描述

文章来源:https://blog.csdn.net/weixin_39568531/article/details/135216575
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STL：std::array 和 基本数组类型array 浅谈一二三

一、优缺点比较

二、代码示例

三、源码赏析

STL：std::array 和基本数组类型array 浅谈一二三