真正干事的是__builtin_coro_done, __builtin_coro_resume和__builtin_coro_destroy, coroutine_handle只是在void*外面包了一层。它没有析构函数，得去调destroy(). 它重载了(), h()等于h.resume()等于__builtin_coro_resume(ptr);

示意:

template<> struct coroutine_handle<void> {
    void*    m_ptr;
    bool done() { return __builtin_coro_done(m_ptr); }
    void resume() { __builtin_coro_resume(m_ptr); }
    void operator()() { resume(); }
    void destroy() { __builtin_coro_destroy(m_ptr); }
    operator bool() { return bool(m_ptr); }
    void* address() { return m_ptr; }
    static coroutine_handle from_address(void*);
    coroutine_handle();
    // https://en.cppreference.com/w/cpp/types/nullptr_t
    // coroutine_handle h(0); coroutine_handle h(NULL); h = 0; h = NULL;
    // oneptr_t, twoptr_t ... _10000ptr_t?
    coroutine_handle(std::nullptr_t);
    coroutine_handle& operator=(std::nullptr_t);
};

D:\gcc\lib\gcc\mingw32\10.3.0\include\c++\coroutine: tab size不为8时更乱:

  template <> struct
    coroutine_handle<void>
    {
    public:
      // 17.12.3.1, construct/reset
      constexpr coroutine_handle() noexcept : _M_fr_ptr(0) {}

      constexpr coroutine_handle(std::nullptr_t __h) noexcept
    : _M_fr_ptr(__h)
      {}

      coroutine_handle& operator=(std::nullptr_t) noexcept
      {
    _M_fr_ptr = nullptr;
    return *this;
      }

    public:
      // 17.12.3.2, export/import
      constexpr void* address() const noexcept { return _M_fr_ptr; }

      constexpr static coroutine_handle from_address(void* __a) noexcept
      {
    coroutine_handle __self;
    __self._M_fr_ptr = __a;
    return __self;
      }

    public:
      // 17.12.3.3, observers
      constexpr explicit operator bool() const noexcept
      {
    return bool(_M_fr_ptr);
      }

      bool done() const noexcept { return __builtin_coro_done(_M_fr_ptr); }

      // 17.12.3.4, resumption
      void operator()() const { resume(); }

      void resume() const { __builtin_coro_resume(_M_fr_ptr); }

      void destroy() const { __builtin_coro_destroy(_M_fr_ptr); }

    protected:
      void* _M_fr_ptr;
  };

  // 17.12.3.6 Comparison operators
  /// [coroutine.handle.compare]
  constexpr bool operator==(coroutine_handle<> __a,
                coroutine_handle<> __b) noexcept
  {
    return __a.address() == __b.address();
  }

View Code

_M_fr_ptr咋就比m_ptr高档了？我倒是也觉得reinterpret_cast没鸟用。VC的coroutine也未必好看到哪里去，STL好像是SGI的相对最好看。封装是OOP的头一条，protected的成员变量用_打头有必要吗？struct默认public, class默认private，struct后紧跟public没必要。