标准库标头 <inplace_vector> (C++26)

#include <compare>
#include <initializer_list>
 
namespace std {
  // 类模板 inplace_vector
  template<class T, std::size_t N>
    class inplace_vector; // partially freestanding
 
  // inplace_vector 的擦除
  template<class T, std::size_t N, class U>
  constexpr typename inplace_vector<T, N>::size_type
    erase(inplace_vector<T, N>& c, const U& value);
 
  template<class T, std::size_t N, class Predicate>
  constexpr typename inplace_vector<T, N>::size_type
    erase_if(inplace_vector<T, N>& c, Predicate pred);
}

namespace std {
  template<class T, std::size_t N>
  class inplace_vector {
  public:
    // 类型：
    using value_type             = T;
    using pointer                = T*;
    using const_pointer          = const T*;
    using reference              = value_type&;
    using const_reference        = const value_type&;
    using size_type              = std::size_t;                 
    using difference_type        = std::ptrdiff_t;             
    using iterator               = /* 由实现定义 */;
    using const_iterator         = /* 由实现定义 */;
    using reverse_iterator       = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 
    // 构造/复制/析构
    constexpr inplace_vector() noexcept;
    // freestanding-deleted
    constexpr explicit inplace_vector(size_type n); 
    // freestanding-deleted
    constexpr inplace_vector(size_type n, const T& value); 
    // freestanding-deleted
    template <class InputIterator>
      constexpr inplace_vector(InputIterator first, InputIterator last); 
    // freestanding-deleted
    template <container-compatible-range<T> R>
      constexpr inplace_vector(std::from_range_t, R&& rg); 
    constexpr inplace_vector(const inplace_vector&);
    constexpr inplace_vector(inplace_vector&&)
      noexcept(N == 0 || std::is_nothrow_move_constructible_v<T>);
    // freestanding-deleted
    constexpr inplace_vector(std::initializer_list<T> il); 
    constexpr ~inplace_vector();
    constexpr inplace_vector& operator=(const inplace_vector& other);
    constexpr inplace_vector& operator=(inplace_vector&& other)
      noexcept(N == 0 || 
              (std::is_nothrow_move_assignable_v<T> &&
               std::is_nothrow_move_constructible_v<T>));
    // freestanding-deleted
    constexpr inplace_vector& operator=(std::initializer_list<T>); 
    // freestanding-deleted
    template <class InputIterator>
      constexpr void assign(InputIterator first, InputIterator last); 
    template<container-compatible-range<T> R>
      constexpr void assign_range(R&& rg); // freestanding-deleted
    constexpr void assign(size_type n, const T& u); // freestanding-deleted
    constexpr void assign(std::initializer_list<T> il); // freestanding-deleted
 
    // 迭代器
    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;
 
    // 大小/容量
    constexpr bool empty() const noexcept;
    constexpr size_type size() const noexcept;
    static constexpr size_type max_size() noexcept;
    static constexpr size_type capacity() noexcept;
    constexpr void resize(size_type sz); // freestanding-deleted
    constexpr void resize(size_type sz, const T& c); // freestanding-deleted
    static constexpr void reserve(size_type n); // freestanding-deleted
    static constexpr void shrink_to_fit() noexcept;
 
    // 元素访问
    constexpr reference       operator[](size_type n);
    constexpr const_reference operator[](size_type n) const;
    constexpr const_reference at(size_type n) const; // freestanding-deleted
    constexpr reference       at(size_type n); // freestanding-deleted
    constexpr reference       front();
    constexpr const_reference front() const;
    constexpr reference       back();
    constexpr const_reference back() const;
 
    // 数据访问
    constexpr       T* data()       noexcept;
    constexpr const T* data() const noexcept;
 
    // 修改器
    template <class... Args> constexpr reference emplace_back(Args&&... args); 
      // freestanding-deleted
    constexpr reference push_back(const T& x); // freestanding-deleted
    constexpr reference push_back(T&& x); // freestanding-deleted
    template<container-compatible-range<T> R>
      constexpr void append_range(R&& rg); // freestanding-deleted
    constexpr void pop_back();
 
    template<class... Args>
      constexpr pointer try_emplace_back(Args&&... args);
    constexpr pointer try_push_back(const T& x);
    constexpr pointer try_push_back(T&& x);
    template<container-compatible-range<T> R>
      constexpr ranges::borrowed_iterator_t<R> try_append_range(R&& rg);
 
    template<class... Args>
      constexpr reference unchecked_emplace_back(Args&&... args);
    constexpr reference unchecked_push_back(const T& x);
    constexpr reference unchecked_push_back(T&& x);
 
    // freestanding-deleted
    template <class... Args>
      constexpr iterator emplace(const_iterator position, Args&&... args); 
    // freestanding-deleted
    constexpr iterator insert(const_iterator position, const T& x); 
    // freestanding-deleted
    constexpr iterator insert(const_iterator position, T&& x); 
    // freestanding-deleted
    constexpr iterator insert(const_iterator position, size_type n, const T& x); 
    // freestanding-deleted
    template <class InputIterator>
      constexpr iterator insert(const_iterator position,
                                InputIterator first, InputIterator last);
    // freestanding-deleted
    template<container-compatible-range<T> R>
      constexpr iterator insert_range(const_iterator position, R&& rg); 
    // freestanding-deleted
    constexpr iterator insert(const_iterator position, std::initializer_list<T> il); 
    constexpr iterator erase(const_iterator position);
    constexpr iterator erase(const_iterator first, const_iterator last);
    constexpr void swap(inplace_vector& x)
      noexcept(N == 0 || 
              (std::is_nothrow_swappable_v<T> &&
               std::is_nothrow_move_constructible_v<T>));
    constexpr void clear() noexcept;
 
    constexpr friend bool operator==(const inplace_vector& x, const inplace_vector& y);
    constexpr friend synth-three-way-result<T>
      operator<=>(const inplace_vector& x, const inplace_vector& y);
    constexpr friend void swap(inplace_vector& x, inplace_vector& y)
      noexcept(N == 0 || 
              (std::is_nothrow_swappable_v<T> &&
               std::is_nothrow_move_constructible_v<T>))
      { x.swap(y); }
  };
}