class Bundler::RubyVersion

def diff(other)

3. engine_version
2. ruby_version
1. engine
The priority of attributes are
[diff, this, other]
Returns a tuple of these things: 
def diff(other)
  raise ArgumentError, "Can only diff with a RubyVersion" unless other.is_a?(RubyVersion)
  if engine != other.engine && @input_engine
    [:engine, engine, other.engine]
  elsif versions.empty? || !matches?(versions, other.gem_version)
    [:version, versions_string(versions), versions_string(other.versions)]
  elsif @input_engine && !matches?(engine_versions, other.engine_gem_version)
    [:engine_version, versions_string(engine_versions), versions_string(other.engine_versions)]
  elsif patchlevel && (!patchlevel.is_a?(String) || !other.patchlevel.is_a?(String) || !matches?(patchlevel, other.patchlevel))
    [:patchlevel, patchlevel, other.patchlevel]
  end
end