[jira] [Created] (MESOS-6439) Try::error returns a std::string instead of an Error

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

Benjamin Bannier created MESOS-6439:
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             Summary: Try::error returns a std::string instead of an Error
                 Key: MESOS-6439
                 URL: https://issues.apache.org/jira/browse/MESOS-6439
             Project: Mesos
          Issue Type: Improvement
          Components: stout
            Reporter: Benjamin Bannier


{{Try}}'s with implicit error types ({{E = Error}}) return a {{std::string}} for {{error}} instead of some error type. This is explained in the code with the following comment:
{code}
// NOTE: This function is intended to return the error of type `E`.
// However, we return a `std::string` if `E` == `Error` since that's what it
// used to return, and it's the only data that `Error` holds anyway.
const typename std::conditional<
    std::is_same<E, Error>::value, std::string, E>::type& error() const
{code}

It seems that always returning an {{E}} here and possibly allowing implicit conversions of {{Error}} to {{std::string}} would be a cleaner solution. It seems this would simpler composition, e.g.,
{code}
Try<Nothing> foo() {
  const Try<int> x = bar();

  if (x.isError()) {
    return x.error(); // ATM: return Error(x.error());
  }

  // work with x's value
  // ...
}
{code}

ATM {{Try::error}} might not actually be an {{Error}}, but instead some implementation detail of it, requiring most users to manually disambiguate with a temporary at the call site.

If we'd implement this change we should probably also make a sweep of the code base.



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