Standard library header <generator> (C++23)

namespace std {
  // шаблон класса generator
  template<class Ref, class V = void, class Allocator = void>
  class generator;
  namespace pmr {
    template<class Ref, class V = void>
    using generator = std::generator<Ref, V, polymorphic_allocator<>>;
  }
}

namespace std {
  template<class Ref, class V = void, class Allocator = void>
  class generator : public ranges::view_interface<generator<Ref, V, Allocator>>
  {
  private:
    using /*value*/ =
      conditional_t<is_void_v<V>, remove_cvref_t< Ref >, V>;       // только для экспозиции
    using /*reference*/ = conditional_t<is_void_v<V>, Ref&&, Ref>; // только для экспозиции
    // класс generator::iterator
    class /*iterator*/; // только для экспозиции
  public:
    using yielded =
      conditional_t<is_reference_v</*reference*/>, /*reference*/, const /*reference*/&>;
    // класс generator::promise_type
    class promise_type;
    generator(const generator&) = delete;
    generator(generator&& other) noexcept;
    ~generator();
    generator& operator=(generator other) noexcept;
    /*iterator*/ begin();
    default_sentinel_t end() const noexcept;
  private:
    coroutine_handle<promise_type> /*coroutine_*/ = nullptr; // только для экспозиции
    unique_ptr<stack<coroutine_handle<>>> /*active_*/;       // только для экспозиции
  };
}

namespace std {
  template<class Ref, class V, class Allocator>
  class generator<Ref, V, Allocator>::promise_type
  {
  public:
    generator get_return_object() noexcept;
    suspend_always initial_suspend() const noexcept { return {}; }
    auto final_suspend() noexcept;
    suspend_always yield_value(yielded val) noexcept;
    auto yield_value(const remove_reference_t<yielded>& lval)
      requires is_rvalue_reference_v<yielded> &&
               constructible_from<remove_cvref_t<yielded>,
                                  const remove_reference_t<yielded>&>;
    template<class R2, class V2, class Alloc2, class Unused>
      requires same_as<typename generator<R2, V2, Alloc2>::yielded, yielded>
    auto yield_value(ranges::elements_of<generator<R2, V2, Alloc2>&&, Unused> g) noexcept;
    template<class R2, class V2, class Alloc2, class Unused>
      requires same_as<typename generator<R2, V2, Alloc2>::yielded, yielded>
    auto yield_value(ranges::elements_of<generator<R2, V2, Alloc2>&, Unused> g) noexcept;
    template<ranges::input_range R, class Alloc>
      requires convertible_to<ranges::range_reference_t<R>, yielded>
    auto yield_value(ranges::elements_of<R, Alloc> r);
    void await_transform() = delete;
    void return_void() const noexcept {}
    void unhandled_exception();
    void* operator new(size_t size)
      requires same_as<Allocator, void> || default_initializable<Allocator>;
    template<class Alloc, class... Args>
    void* operator new(size_t size, allocator_arg_t, const Alloc& alloc, const Args&...);
    template<class This, class Alloc, class... Args>
    void* operator new(size_t size, const This&, allocator_arg_t, const Alloc& alloc,
                       const Args&...);
    void operator delete(void* pointer, size_t size) noexcept;
  private:
    add_pointer_t<yielded> /*value_*/ = nullptr; // только для демонстрации
    exception_ptr /*except_*/;                   // только для демонстрации
  };
}

namespace std {
  template<class Ref, class V, class Allocator>
  class generator<Ref, V, Allocator>::/*iterator*/
  {
  public:
    using value_type      = /*value*/;
    using difference_type = ptrdiff_t;
    /*iterator*/(/*iterator*/&& other) noexcept;
    /*iterator*/& operator=(/*iterator*/&& other) noexcept;
    /*reference*/ operator*() const
      noexcept(is_nothrow_copy_constructible_v</*reference*/>);
    /*iterator*/& operator++();
    void operator++(int);
    friend bool operator==(const /*iterator*/& i, default_sentinel_t);
  private:
    coroutine_handle<promise_type> /*coroutine_*/; // только для демонстрации
  };
}