Standard library header <deque>

#include <compare>
#include <initializer_list>
namespace std {
  // 类模板 deque
  template<class T, class Allocator = allocator<T>>
  class deque;
  template<class T, class Allocator>
  bool operator==(const deque<T, Allocator>& x, const deque<T, Allocator>& y);
  template<class T, class Allocator>
  /*synth-three-way-result*/<T> operator<=>(const deque<T, Allocator>& x,
                                            const deque<T, Allocator>& y);
  template<class T, class Allocator>
  void swap(deque<T, Allocator>& x, deque<T, Allocator>& y) noexcept(noexcept(x.swap(y)));
  // 擦除操作
  template<class T, class Allocator, class U = T>
  typename deque<T, Allocator>::size_type erase(deque<T, Allocator>& c, const U& value);
  template<class T, class Allocator, class Predicate>
  typename deque<T, Allocator>::size_type erase_if(deque<T, Allocator>& c,
                                                   Predicate pred);
  namespace pmr {
    template<class T>
    using deque = std::deque<T, polymorphic_allocator<T>>;
  }
}

namespace std {
  template<class T, class Allocator = allocator<T>>
  class deque
  {
  public:
    // 类型定义
    using value_type             = T;
    using allocator_type         = Allocator;
    using pointer                = typename allocator_traits<Allocator>::pointer;
    using const_pointer          = typename allocator_traits<Allocator>::const_pointer;
    using reference              = value_type&;
    using const_reference        = const value_type&;
    using size_type              = /* 实现定义 */;
    using difference_type        = /* 实现定义 */;
    using iterator               = /* 实现定义 */;
    using const_iterator         = /* 实现定义 */;
    using reverse_iterator       = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
    // 构造/复制/销毁
    deque()
      : deque(Allocator())
    {
    }
    explicit deque(const Allocator&);
    explicit deque(size_type n, const Allocator& = Allocator());
    deque(size_type n, const T& value, const Allocator& = Allocator());
    template<class InputIter>
    deque(InputIter first, InputIter last, const Allocator& = Allocator());
    template<container-compatible-range<T> R>
    deque(from_range_t, R&& rg, const Allocator& = Allocator());
    deque(const deque& x);
    deque(deque&&);
    deque(const deque&, const type_identity_t<Allocator>&);
    deque(deque&&, const type_identity_t<Allocator>&);
    deque(initializer_list<T>, const Allocator& = Allocator());
    ~deque();
    deque& operator=(const deque& x);
    deque& operator=(deque&& x) noexcept(
      allocator_traits<Allocator>::is_always_equal::value);
    deque& operator=(initializer_list<T>);
    template<class InputIter>
    void assign(InputIter first, InputIter last);
    template<container-compatible-range<T> R>
    void assign_range(R&& rg);
    void assign(size_type n, const T& t);
    void assign(initializer_list<T>);
    allocator_type get_allocator() const noexcept;
    // 迭代器
    iterator begin() noexcept;
    const_iterator begin() const noexcept;
    iterator end() noexcept;
    const_iterator end() const noexcept;
    reverse_iterator rbegin() noexcept;
    const_reverse_iterator rbegin() const noexcept;
    reverse_iterator rend() noexcept;
    const_reverse_iterator rend() const noexcept;
    const_iterator cbegin() const noexcept;
    const_iterator cend() const noexcept;
    const_reverse_iterator crbegin() const noexcept;
    const_reverse_iterator crend() const noexcept;
    // 容量
    bool empty() const noexcept;
    size_type size() const noexcept;
    size_type max_size() const noexcept;
    void resize(size_type sz);
    void resize(size_type sz, const T& c);
    void shrink_to_fit();
    // 元素访问
    reference operator[](size_type n);
    const_reference operator[](size_type n) const;
    reference at(size_type n);
    const_reference at(size_type n) const;
    reference front();
    const_reference front(