def diff(other)
raise ArgumentError, "Can only diff with a RubyVersion, not a #{other.class}" 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