A problem I'm having setting a contract on a class-level method. The problem may be related to that or to something else.

gistfile1.txt

I know class-method contracts have been discussed (and fixed -- #7 ) before, but I have occasional problems with contracts on class methods. Here is the latest one, for example.

    #<ParamContractError: Contract violation for argument 3 of 3:
          Expected: nil,
          Actual: #<Proc:0x80354744@.../lib/scm_roster/report/roster.rb:19>
          Value guarded in: SCMRoster::Report::Util::process_data_and_notify_change
          With Contract: Module, Func => None
          At: .../lib/scm_roster/report/util.rb:22 >

[I have snipped the paths for readability.]

Here is the calling code:

          Report::Util.process_data_and_notify_change(
                         roster_report_infos,
                         -> x { x.task.date.month} ) do |rri, change|
            out.puts() if change
            out.puts csv_line(rri)
          end

And here is the implementing code:

      Contract Enumerable, Func[Any => Any] => None
      def Util.process_data_and_notify_change(data, fn)
        ...
          yield [item, changed]
        ...
      end

Now here is what I don't get: why is there a contract violation on argument 3 of 3 when there are only two arguments to the method???