gistfile1.txt

json.array! @ranking.results_with_change.each_with_index.to_a do |args|
  # We can't unpack the args in the block param because Jbuilder does
  # something magic.
  (user, player, diff), index = *args

  json.rank index+1
  json.user user, :id, :facebook_id, :name, :square_avatar
  json.score player.r.to_i
  json.change_today diff.to_i

  json.r player.r
  json.rd player.rd
  json.vol player.vol
end

Nice hack 😄