标准库头文件 <coroutine>

#include <compare>
 
namespace std {
  // 协程表征
  template<class R, class... ArgTypes>
    struct coroutine_traits;
 
  // 协程柄
  template<class Promise = void>
    struct coroutine_handle;
 
  // 比较运算符
  constexpr bool operator==(coroutine_handle<> x, coroutine_handle<> y) noexcept;
  constexpr strong_ordering operator<=>(coroutine_handle<> x, coroutine_handle<> y) noexcept;
 
  // 散列支持
  template<class T> struct hash;
  template<class P> struct hash<coroutine_handle<P>>;
 
  // 无操作协程
  struct noop_coroutine_promise;
 
  template<> struct coroutine_handle<noop_coroutine_promise>;
  using noop_coroutine_handle = coroutine_handle<noop_coroutine_promise>;
 
  noop_coroutine_handle noop_coroutine() noexcept;
 
  // 平凡可等待体
  struct suspend_never;
  struct suspend_always;
}

namespace std {
  template<>
  struct coroutine_handle<void>
  {
    // 构造/重置
    constexpr coroutine_handle() noexcept;
    constexpr coroutine_handle(nullptr_t) noexcept;
    coroutine_handle& operator=(nullptr_t) noexcept;
 
    // 导入/导出
    constexpr void* address() const noexcept;
    static constexpr coroutine_handle from_address(void* addr);
 
    // 观察器
    constexpr explicit operator bool() const noexcept;
    bool done() const;
 
    // 恢复
    void operator()() const;
    void resume() const;
    void destroy() const;
 
  private:
    void* ptr;  // 仅用于阐释
  };
 
  template<class Promise>
  struct coroutine_handle : coroutine_handle<>
  {
    // 构造/重置
    using coroutine_handle<>::coroutine_handle;
    static coroutine_handle from_promise(Promise&);
    coroutine_handle& operator=(nullptr_t) noexcept;
 
    // 导出/导入
    static constexpr coroutine_handle from_address(void* addr);
 
    // 承诺访问
    Promise& promise() const;
  };
}

namespace std {
  struct noop_coroutine_promise {};
}

namespace std {
  template<>
  struct coroutine_handle<noop_coroutine_promise> : coroutine_handle<>
  {
    // 观察器
    constexpr explicit operator bool() const noexcept;
    constexpr bool done() const noexcept;
 
    // 恢复
    constexpr void operator()() const noexcept;
    constexpr void resume() const noexcept;
    constexpr void destroy() const noexcept;
 
    // 承诺访问
    noop_coroutine_promise& promise() const noexcept;
 
    // 地址
    constexpr void* address() const noexcept;
  private:
    coroutine_handle(/* 未指明 */);
  };
}

namespace std {
  struct suspend_never {
    constexpr bool await_ready() const noexcept { return true; }
    constexpr void await_suspend(coroutine_handle<>) const noexcept {}
    constexpr void await_resume() const noexcept {}
  };
}

namespace std {
  struct suspend_always {
    constexpr bool await_ready() const noexcept { return false; }
    constexpr void await_suspend(coroutine_handle<>) const noexcept {}
    constexpr void await_resume() const noexcept {}
  };
}