[jira] [Created] (MESOS-3188) Add tuple-awareness to Future callbacks.

["Benjamin Mahler (JIRA)" <ji...@apache.org>]

Benjamin Mahler created MESOS-3188:
--------------------------------------

             Summary: Add tuple-awareness to Future callbacks.
                 Key: MESOS-3188
                 URL: https://issues.apache.org/jira/browse/MESOS-3188
             Project: Mesos
          Issue Type: Improvement
          Components: libprocess
            Reporter: Benjamin Mahler


Future is currently single-valued and so the only way to create a multi-value Future is to use a custom struct or a tuple. Since Future is not currently "tuple-aware", continuations have to take a tuple as well, and manually unpack:

{code}
  {
    // Subprocess example.
    await(s.get().status(),
          io::read(s.get().out().get()),
          io::read(s.get().err().get()))
      .then(defer(self(), &Self::continue, lambda::_1));
  }

  void continue(std::tuple<
      Future<Option<int>>,
      Future<string>,
      Future<string>> results)
  {
    Future<Option<int>> status = std::get<0>(results);
    Future<string> output = std::get<1>(results);
    Future<string> error = std::get<2>(results);
  }
{code}

Since multi-value Future (i.e. Future<T1, T2, ...>) seems to be a bad design choice, being tuple aware can improve the code cleanliness by unpacking the tuple automatically for the continuation:

{code}
  {
    // Subprocess example.
    await(s.get().status(),
          io::read(s.get().out().get()),
          io::read(s.get().err().get()))
      .then(defer(self(), &Self::continue, lambda::_1));
  }

  void continue(
      Future<Option<int>> status,
      Future<string> output,
      Future<string> error)
  {
    ...
  }
{code}



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