guard :depend,
  # The path to the output generated by cmd.
  output_paths: -> () { Dir['build/bin/*.dll'] },
  # The command to run if the output is outdated or does not exist.
  cmd: %w(bundle exec rake compile),
  # Whether to run at startup.
  run_on_start: false do
    watch(%r{^source/.*\.cs$}i)
end