Standard library header <functional>

namespace std {
  // 调用函数
  template<class F, class... Args>
    constexpr invoke_result_t<F, Args...> invoke(F&& f, Args&&... args)
      noexcept(is_nothrow_invocable_v<F, Args...>);
  template<class R, class F, class... Args>
    constexpr R invoke_r(F&& f, Args&&... args)
      noexcept(is_nothrow_invocable_r_v<R, F, Args...>);
  // 引用包装器
  template<class T> class reference_wrapper;
  template<class T> constexpr reference_wrapper<T> ref(T&) noexcept;
  template<class T> constexpr reference_wrapper<const T> cref(const T&) noexcept;
  template<class T> void ref(const T&&) = delete;
  template<class T> void cref(const T&&) = delete;
  template<class T>
    constexpr reference_wrapper<T> ref(reference_wrapper<T>) noexcept;
  template<class T>
    constexpr reference_wrapper<const T> cref(reference_wrapper<T>) noexcept;
  template<class T> struct unwrap_reference;
  template<class T> using unwrap_reference_t = typename unwrap_reference<T>::type;
  template<class T> struct unwrap_ref_decay;
  template<class T> using unwrap_ref_decay_t = typename unwrap_ref_decay<T>::type;
  // 通用引用相关特化
  template<class R, class T, template<class> class RQual, template<class> class TQual>
    requires /* 详见说明 */
  struct basic_common_reference<R, T, RQual, TQual>;
  template<class T, class R, template<class> class TQual, template<class> class RQual>
    requires /* 详见说明 */
  struct basic_common_reference<T, R, TQual, RQual>;
  // 算术运算
  template<class T = void> struct plus;
  template<class T = void> struct minus;
  template<class T = void> struct multiplies;
  template<class T = void> struct divides;
  template<class T = void> struct modulus;
  template<class T = void> struct negate;
  template<> struct plus<void>;
  template<> struct minus<void>;
  template<> struct multiplies<void>;
  template<> struct divides<void>;
  template<> struct modulus<void>;
  template<> struct negate<void>;
  // 比较运算
  template<class T = void> struct equal_to;
  template<class T = void> struct not_equal_to;
  template<class T = void> struct greater;
  template<class T = void> struct less;
  template<class T = void> struct greater_equal;
  template<class T = void> struct less_equal;
  template<> struct equal_to<void>;
  template<> struct not_equal_to<void>;
  template<> struct greater<void>;</

namespace std {
  template<class T> class reference_wrapper {
  public:
    // 类型定义
    using type = T;
    // 构造/复制/销毁
    template<class U>
      constexpr reference_wrapper(U&&) noexcept(/* 见下文 */);
    constexpr reference_wrapper(const reference_wrapper& x) noexcept;
    // 赋值操作
    constexpr reference_wrapper& operator=(const reference_wrapper& x) noexcept;
    // 访问操作
    constexpr operator T& () const noexcept;
    constexpr T& get() const noexcept;
    // 调用操作
    template<class... ArgTypes>
      constexpr invoke_result_t<T&, ArgTypes...> operator()(ArgTypes&&...) const
        noexcept(is_nothrow_invocable_v<T&, ArgTypes...>);
    // 比较操作
    friend constexpr bool operator==(reference_wrapper, reference_wrapper);
    friend constexpr bool operator==(reference_wrapper, const T&);
    friend constexpr bool operator==(reference_wrapper, reference_wrapper<const T>);
    friend constexpr auto operator<=>(reference_wrapper, reference_wrapper);
    friend constexpr auto operator<=>(reference_wrapper, const T&);
    friend constexpr auto operator<=>(reference_wrapper, reference_wrapper<const T>);
  };
  // 推导指引
  template<class T>
    reference_wrapper(T&) -> reference_wrapper<T>;
}

namespace std {
  template<class T>
    struct unwrap_reference;
}

namespace std {
  template<class T>
    struct unwrap_ref_decay;
}

namespace std {
  template<class T = void> struct plus {
    constexpr T operator()(const T& x, const T& y) const;
  };
  template<> struct plus<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) + std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct minus {
    constexpr T operator()(const T& x, const T& y) const;
  };
  template<> struct minus<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) - std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct multiplies {
    constexpr T operator()(const T& x, const T& y) const;
  };
  template<> struct multiplies<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) * std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct divides {
    constexpr T operator()(const T& x, const T& y) const;
  };
  template<> struct divides<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) / std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct modulus {
    constexpr T operator()(const T& x, const T& y) const;
  };
  template<> struct modulus<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) % std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct negate {
    constexpr T operator()(const T& x) const;
  };
  template<> struct negate<void> {
    template<class T> constexpr auto operator()(T&& t) const
      -> decltype(-std::forward<T>(t));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct equal_to {
    constexpr bool operator()(const T& x, const T& y) const;
  };
  template<> struct equal_to<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) == std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct not_equal_to {
    constexpr bool operator()(const T& x, const T& y) const;
  };
  template<> struct not_equal_to<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) != std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct greater {
    constexpr bool operator()(const T& x, const T& y) const;
  };
  template<> struct greater<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) > std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct less {
    constexpr bool operator()(const T& x, const T& y) const;
  };
  template<> struct less<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) < std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct greater_equal {
    constexpr bool operator()(const T& x, const T& y) const;
  };
  template<> struct greater_equal<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) >= std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct less_equal {
    constexpr bool operator()(const T& x, const T& y) const;
  };
  template<> struct less_equal<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) <= std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  struct compare_three_way {
    template<class T, class U>
    constexpr auto operator()(T&& t, U&& u) const;
    using is_transparent = /* 未指定 */;
  };
}

namespace std::ranges {
  struct equal_to {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
    using is_transparent = /* 未指定 */;
  };
}

namespace std::ranges {
  struct not_equal_to {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
    using is_transparent = /* 未指定 */;
  };
}

namespace std::ranges {
  struct greater {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
    using is_transparent = /* 未指定 */;
  };
}

namespace std::ranges {
  struct less {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
    using is_transparent = /* 未指定 */;
  };
}

namespace std::ranges {
  struct greater_equal {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
    using is_transparent = /* 未指定 */;
  };
}

namespace std::ranges {
  struct less_equal {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct logical_and {
    constexpr bool operator()(const T& x, const T& y) const;
  };
  template<> struct logical_and<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) && std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct logical_or {
    constexpr bool operator()(const T& x, const T& y) const;
  };
  template<> struct logical_or<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) || std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct logical_not {
    constexpr bool operator()(const T& x) const;
  };
  template<> struct logical_not<void> {
    template<class T> constexpr auto operator()(T&& t) const
      -> decltype(!std::forward<T>(t));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct bit_and {
    constexpr T operator()(const T& x, const T& y) const;
  };
  template<> struct bit_and<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) & std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct bit_or {
    constexpr T operator()(const T& x, const T& y) const;
  };
  template<> struct bit_or<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) | std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct bit_xor {
    constexpr T operator()(const T& x, const T& y) const;
  };
  template<> struct bit_xor<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) ^ std::forward<U>(u));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T = void> struct bit_not {
    constexpr T operator()(const T& x) const;
  };
  template<> struct bit_not<void> {
    template<class T> constexpr auto operator()(T&& t) const
      -> decltype(~std::forward<T>(t));
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  struct identity {
    template<class T>
      constexpr T&& operator()(T&& t) const noexcept;
    using is_transparent = /* 未指定 */;
  };
}

namespace std {
  template<class T> struct is_bind_expression;
}

namespace std {
  template<class T> struct is_placeholder;
}

namespace std {
  class bad_function_call : public exception {
  public:
    // 有关特殊成员函数的规范说明请参阅 [exception]
    const char* what() const noexcept override;
  };
}

namespace std {
  template<class> class function; // 未定义
  template<class R, class... ArgTypes>
  class function<R(ArgTypes...)> {
  public:
    using result_type = R;
    // 构造/复制/销毁
    function() noexcept;
    function(nullptr_t) noexcept;
    function(const function&);
    function(function&&) noexcept;
    template<class F> function(F);
    function& operator=(const function&);
    function& operator=(function&&);
    function& operator=(nullptr_t) noexcept;
    template<class F> function& operator=(F&&);
    template<class F> function& operator=(reference_wrapper<F>) noexcept;
    ~function();
    // 函数修饰符
    void swap(function&) noexcept;
    // 函数容量
    explicit operator bool() const noexcept;
    // 函数调用
    R operator()(ArgTypes...) const;
    // 函数目标访问
    const type_info& target_type() const noexcept;
    template<class T>       T* target() noexcept;
    template<class T> const T* target() const noexcept;
  };
  template<class R, class... ArgTypes>
    function(R(*)(ArgTypes...)) -> function<R(ArgTypes...)>;
  template<class F> function(F) -> function</* 详见描述 */>;
  // 空指针比较函数
  template<class R, class... ArgTypes>
    bool operator==(const function<R(ArgTypes...)>&, nullptr_t) noexcept;
  // 特化算法
  template<class R, class... ArgTypes>
    void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&) noexcept;
}

namespace std {
  template<class... S> class move_only_function; // 未定义
  template<class R, class... ArgTypes>
  class move_only_function<R(ArgTypes...) /*cv-ref*/ noexcept(/*noex*/)> {
  public:
    using result_type = R;
    // 构造/移动/析构
    move_only_function() noexcept;
    move_only_function(nullptr_t) noexcept;
    move_only_function(move_only_function&&) noexcept;
    template<class F> move_only_function(F&&);
    template<class T, class... Args>
      explicit move_only_function(in_place_type_t<T>, Args&&...);
    template<class T, class U, class... Args>
      explicit move_only_function(in_place_type_t<T>, initializer_list<U>, Args&&...);
    move_only_function& operator=(move_only_function&&);
    move_only_function& operator=(nullptr_t) noexcept;
    template<class F> move_only_function& operator=(F&&);
    ~move_only_function();
    // 调用操作
    explicit operator bool() const noexcept;
    R operator()(ArgTypes...) /*cv-ref*/ noexcept(/*noex*/);
    // 工具函数
    void swap(move_only_function&) noexcept;
    friend void swap(move_only_function&, move_only_function&) noexcept;
    friend bool operator==(const move_only_function&, nullptr_t) noexcept;
  private:
    // 仅用于说明
    template<class VT>
      static constexpr bool /*is-callable-from*/ = /* 参见描述 */; 
  };
}

namespace std {
  template<class... S> class copyable_function; // 未定义
  template<class R, class... ArgTypes>
  class copyable_function<R(ArgTypes...) /*cv-ref*/ noexcept(/*noex*/)> {
  public:
    using result_type = R;
    // 构造/移动/销毁
    copyable_function() noexcept;
    copyable_function(nullptr_t) noexcept;
    copyable_function(const copyable_function&);
    copyable_function(copyable_function&&) noexcept;
    template<class F> copyable_function(F&&);
    template<class T, class... Args>
      explicit copyable_function(in_place_type_t<T>, Args&&...);
    template<class T, class U, class... Args>
      explicit copyable_function(in_place_type_t<T>, initializer_list<U>, Args&&...);
    copyable_function& operator=(const copyable_function&);
    copyable_function& operator=(copyable_function&&);
    copyable_function& operator=(nullptr_t) noexcept;
    template<class F> copyable_function& operator=(F&&);
    ~copyable_function();
    // 调用操作
    explicit operator bool() const noexcept;
    R operator()(ArgTypes...) /*cv-ref*/ noexcept(/*noex*/);
    // 工具函数
    void swap(copyable_function&) noexcept;
    friend void swap(copyable_function&, copyable_function&) noexcept;
    friend bool operator==(const copyable_function&, nullptr_t) noexcept;
  private:
    // 仅用于说明
    template<class VT>
      static constexpr bool /*is-callable-from*/ = /* 参见描述 */; 
  };
}

namespace std {
  template<class... S> class function_ref; // 未定义
  template<class R, class... ArgTypes>
  class function_ref<R(ArgTypes...) /*cv*/ noexcept(/*noex*/)> {
  public:
    // 构造函数与赋值运算符
    template<class F> function_ref(F*) noexcept;
    template<class F> constexpr function_ref(F&&) noexcept;
    template<auto f> constexpr function_ref(nontype_t<f>) noexcept;
    template<auto f, class U>
      constexpr function_ref(nontype_t<f>, U&&) noexcept;
    template<auto f, class T>
      constexpr function_ref(nontype_t<f>, /*cv*/ T*) noexcept;
    constexpr function_ref(const function_ref&) noexcept = default;
    constexpr function_ref& operator=(const function_ref&) noexcept = default;
    template<class T> function_ref& operator=(T) = delete;
    // 调用操作
    R operator()(ArgTypes...) /*cv*/ noexcept(/*noex*/);
  private:
    // 仅用于说明
    template<class... T>
      static constexpr bool /*is-invocable-using*/ = /* 见描述 */;
    R (*thunk-ptr)(BoundEntityType, ArgTypes&&...) noexcept(/*noex*/); // 仅用于说明
    BoundEntityType bound-entity; // 仅用于说明
  };
  // 推导指引
  template<class F>
    function_ref(F*) -> function_ref<F>;
  template<auto f>
    function_ref(nontype_t<f>) -> function_ref</* 见描述 */>;
  template<auto f, class T>
    function_ref(nontype_t<f>, T&&) -> function_ref</* 见描述 */>;
}

namespace std {
  template<class ForwardIter1, class BinaryPredicate = equal_to<>>
    class default_searcher {
    public:
      constexpr default_searcher(ForwardIter1 pat_first, ForwardIter1 pat_last,
                                 BinaryPredicate pred = BinaryPredicate());
      template<class ForwardIter2>
        constexpr pair<ForwardIter2, ForwardIter2>
          operator()(ForwardIter2 first, ForwardIter2 last) const;
    private:
      ForwardIter1 pat_first_;            // 仅用于说明
      ForwardIter1 pat_last_;             // 仅用于说明
      BinaryPredicate pred_;              // 仅用于说明
  };
}

namespace std {
  template<class RandomAccessIter1,
           class Hash = hash<typename iterator_traits<RandomAccessIter1>::value_type>,
           class BinaryPredicate = equal_to<>>
    class boyer_moore_searcher {
    public:
      boyer_moore_searcher(RandomAccessIter1 pat_first,
                           RandomAccessIter1 pat_last,
                           Hash hf = Hash(),
                           BinaryPredicate pred = BinaryPredicate());
      template<class RandomAccessIter2>
        pair<RandomAccessIter2, RandomAccessIter2>
          operator()(RandomAccessIter2 first, RandomAccessIter2 last) const;
    private:
      RandomAccessIter1 pat_first_;       // 仅用于说明
      RandomAccessIter1 pat_last_;        // 仅用于说明
      Hash hash_;                         // 仅用于说明
      BinaryPredicate pred_;              // 仅用于说明
    };
}

namespace std {
  template<class RandomAccessIter1,
           class Hash = hash<typename iterator_traits<RandomAccessIter1>::value_type>,
           class BinaryPredicate = equal_to<>>
    class boyer_moore_horspool_searcher {
    public:
      boyer_moore_horspool_searcher(RandomAccessIter1 pat_first,
                                    RandomAccessIter1 pat_last,
                                    Hash hf = Hash(),
                                    BinaryPredicate pred = BinaryPredicate());
      template<class RandomAccessIter2>
        pair<RandomAccessIter2, RandomAccessIter2>
          operator()(RandomAccessIter2 first, RandomAccessIter2 last) const;
    private:
      RandomAccessIter1 pat_first_;       // 仅用于说明
      RandomAccessIter1 pat_last_;        // 仅用于说明
      Hash hash_;                         // 仅用于说明
      BinaryPredicate pred_;              // 仅用于说明
  };
}