Function then

3rdparty/libprocess/include/process/future.hpp:1487–1502

template <typename T, typename X>
void then(lambda::CallableOnce<X(const T&)>&& f,
          std::unique_ptr<Promise<X>> promise,
          const Future<T>& future)
{
  if (future.isReady()) {
    if (future.hasDiscard()) {
      promise->discard();
    } else {
      promise->set(std::move(f)(future.get()));
    }
  } else if (future.isFailed()) {
    promise->fail(future.failure());
  } else if (future.isDiscarded()) {
    promise->discard();
  }
}


template <typename T>