You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: op_msg.rb
    path of file: ./repos/mongo-ruby-driver/lib/mongo/operation/parallel_scan
    
    the code of the file until where you have to start completion: # frozen_string_literal: true
# rubocop:todo all

# Copyright (C) 2018-2020 MongoDB Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use
    
        def selector(connection)
          sel = { :parallelCollectionScan => coll_name, :numCursors => cursor_count }
          sel[:maxTimeMS] = max_time_ms if max_time_ms
          if read_concern
            sel[:readConcern] = Options::Mapper.transform_values_to_strings(
              read_concern)
          end