promise_type.hpp

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#pragma once
 
#include <yaclib/algo/detail/result_core.hpp>
#include <yaclib/coro/coro.hpp>
#include <yaclib/util/cast.hpp>
#include <yaclib/util/detail/unique_counter.hpp>
#include <yaclib/util/intrusive_ptr.hpp>
 
#include <exception>
 
namespace yaclib::detail {
 
template <typename V, typename E, bool Lazy>
class PromiseType;
 
struct Destroy final {
  constexpr bool await_ready() const noexcept {
    return false;
  }
 
  template <typename Promise>
  YACLIB_INLINE auto await_suspend(yaclib_std::coroutine_handle<Promise> handle) const noexcept {
    auto& promise = handle.promise();
#if YACLIB_FINAL_SUSPEND_TRANSFER != 0
    return promise.template SetResult<true>();
#elif YACLIB_SYMMETRIC_TRANSFER != 0
    return promise.template SetResult<true>().resume();
#else
    return Loop(&promise, promise.template SetResult<false>());
#endif
  }
 
  constexpr void await_resume() const noexcept {
  }
};
 
template <bool Lazy>
struct PromiseTypeDeleter final {
  template <typename V, typename E>
  static void Delete(ResultCore<V, E>& core) noexcept;
};
 
template <typename V, typename E, bool Lazy>
class PromiseType final : public OneCounter<ResultCore<V, E>, PromiseTypeDeleter<Lazy>> {
  using Base = OneCounter<ResultCore<V, E>, PromiseTypeDeleter<Lazy>>;
 
 public:
  PromiseType() noexcept : Base{0} {
  }  // get_return_object is gonna be invoked right after ctor
 
  auto get_return_object() noexcept {
    if constexpr (Lazy) {
      return Task<V, E>{ResultCorePtr<V, E>{NoRefTag{}, this}};
    } else {
      return Future<V, E>{ResultCorePtr<V, E>{NoRefTag{}, this}};
    }
  }
 
  auto initial_suspend() noexcept {
    if constexpr (Lazy) {
      return yaclib_std::suspend_always{};
    } else {
      return yaclib_std::suspend_never{};
    }
  }
 
  Destroy final_suspend() noexcept {
    return {};
  }
 
  void unhandled_exception() noexcept {
    this->Store(std::current_exception());
  }
 
  template <typename Value>
  void return_value(Value&& value) noexcept(std::is_nothrow_constructible_v<Result<V, E>, Value&&>) {
    this->Store(std::forward<Value>(value));
  }
 
  void return_value(Unit) noexcept {
    this->Store(std::in_place);
  }
 
  [[nodiscard]] auto Handle() noexcept {
    auto handle = yaclib_std::coroutine_handle<PromiseType>::from_promise(*this);
    YACLIB_ASSERT(handle);
    return handle;
  }
 
 private:
  void DecRef() noexcept final {
    this->Sub(1);
  }
 
  void Call() noexcept final {
    auto next = Curr();
    next.resume();
  }
 
  void Drop() noexcept final {
    this->Store(StopTag{});
#if YACLIB_SYMMETRIC_TRANSFER != 0
    this->template SetResult<true>().resume();
#else
    Loop(this, this->template SetResult<false>());
#endif
  }
 
  YACLIB_INLINE void Impl(InlineCore& caller) noexcept {
    this->_executor = std::move(DownCast<BaseCore>(caller)._executor);
    YACLIB_ASSERT(this->_executor != nullptr);
  }
  [[nodiscard]] InlineCore* Here(InlineCore& caller) noexcept final {
    Impl(caller);
    Call();
    return nullptr;
  }
#if YACLIB_SYMMETRIC_TRANSFER != 0
  [[nodiscard]] yaclib_std::coroutine_handle<> Next(InlineCore& caller) noexcept final {
    Impl(caller);
    return Curr();
  }
#endif
 
  [[nodiscard]] yaclib_std::coroutine_handle<> Curr() noexcept final {
    auto handle = Handle();
    YACLIB_ASSERT(!handle.done());
    return handle;
  }
};
 
template <bool Lazy>
template <typename V, typename E>
void PromiseTypeDeleter<Lazy>::Delete(ResultCore<V, E>& core) noexcept {
  auto& promise = DownCast<PromiseType<V, E, Lazy>>(core);
  auto handle = promise.Handle();
  handle.destroy();
}
 
}  // namespace yaclib::detail