[MESOS-2716] Add non-const reference version of Option<T>::get.

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.23.0
• Component/s: stout
• Labels: newbie
• Assignee: Mark Wang
• Reporter: Benjamin Mahler
• Created: 12/May/15 01:30
• Updated: 02/Jun/15 08:05
• Resolved: 01/Jun/15 19:55

Description

Currently Option only provides a const reference to the underlying object:

template <typename T>
class Option
{
  ...
  const T& get() const;
  ...
};

Since we use Option as a replacement for NULL, we often have optional variables that we need to perform non-const operations on. However, this requires taking a copy:

    static void cleanup(const Response& response)
    {
      if (response.type == Response::PIPE) {
        CHECK_SOME(response.reader);
        http::Pipe::Reader reader = response.reader.get(); // Remove const.
        reader.close();
      }
    }

Taking a copy is hacky, but works for shared objects and some other copyable objects. Since Option represents a mutable variable, it makes sense to add non-const reference access to the underlying value:

template <typename T>
class Option
{
  ...
  const T& get() const;
  T& get();
  ...
};