Function pipeline

example/cpp11/executors/pipeline.cpp:176–184

// Launch the last stage in a pipeline.
template <class T, class F>
std::future<void> pipeline(queue_back<T> in, F f)
{
  // Get the function's associated executor, defaulting to thread_executor.
  auto ex = get_associated_executor(f, thread_executor());

  // Run the function, and as we're the last stage return a future so that the
  // caller can wait for the pipeline to finish.
  return post(ex, use_future([in, f]() mutable { f(in); }));
}

// Launch an intermediate stage in a pipeline.
template <class T, class F, class... Tail>