gistfile1.txt

# This doesn't work – it calls nil.join (the map seems to return nil?)
puts things.to_a.sort_by(&:id).map do |thing|
  "#{thing.id} #{thing.url}"
end.join("\n")

# This DOES work (the only difference is that the map uses curlies instead of do/end).
puts things.to_a.sort_by(&:id).map { |thing|
  "#{thing.id} #{thing.url}"
}.join("\n")