experimental coroutines for kernel mode

#pragma once

#include <type_traits>

namespace std::experimental {
  template<typename R, typename... ArgTypes>
  struct coroutine_traits {
    using promise_type = typename R::promise_type;
  };

  template<class Promise = void>
    struct coroutine_handle;

  template<>
  struct coroutine_handle<void>
  {
    constexpr coroutine_handle() noexcept 
    : ptr(nullptr)
    {
    }

    constexpr coroutine_handle(nullptr_t) noexcept 
    : ptr(nullptr)
    {
    }

    coroutine_handle& operator=(nullptr_t) noexcept {
      ptr = nullptr;
      return *this;
    }

    constexpr void* address() const noexcept {
      return ptr;
    }
    static constexpr coroutine_handle from_address(void* addr) {
      return coroutine_handle{addr};
    }

    constexpr explicit operator bool() const noexcept {
      return ptr != nullptr;
    }
    bool done() const;

    void operator()() const;
    void resume() const {
      __builtin_coro_resume(ptr);

    }
    void destroy() const;

  public:
    constexpr coroutine_handle(void* p) noexcept
    : ptr(p)
    {}
    void* ptr;
  };

  template<class Promise>
  struct coroutine_handle : coroutine_handle<>
  {
    using coroutine_handle<>::coroutine_handle;
    static coroutine_handle from_promise(Promise&p) {
        using RawPromise = typename s2::remove_cv_t<Promise>;
        coroutine_handle __tmp;
        __tmp.ptr = __builtin_coro_promise(&const_cast<RawPromise&>(p), alignof(Promise), true);
        return __tmp;
    }
    coroutine_handle& operator=(nullptr_t) noexcept {
      ptr = nullptr;
      return *this;
    }

    static constexpr coroutine_handle from_address(void* addr) noexcept {
      return coroutine_handle{addr};
    }

    Promise& promise() const {

    }
  };

  constexpr bool operator==(coroutine_handle<> x, coroutine_handle<> y) noexcept;
//  constexpr strong_ordering operator<=>(coroutine_handle<> x, coroutine_handle<> y) noexcept;

  template<class T> struct hash;
  template<class P> struct hash<coroutine_handle<P>>;

  struct noop_coroutine_promise;

  using noop_coroutine_handle = coroutine_handle<noop_coroutine_promise>;

  noop_coroutine_handle noop_coroutine() noexcept;

  struct suspend_never {
    bool await_ready() noexcept {
        return true;
    }
    void await_suspend(std::experimental::coroutine_handle<> awaiting) noexcept {}
    void await_resume() noexcept {}
  };
  struct suspend_always {
    bool await_ready() noexcept {
        return false;
    }
    void await_suspend(std::experimental::coroutine_handle<> awaiting) noexcept {}
    void await_resume() noexcept {}
  };
}