gistfile1.rb

class User < ActiveRecord::Base
  # ...
  def self.sync_users
    users_to_sync = where synced: false
    SyncUsers.new(users_to_sync).tap &:sync
  end
  # ...
end

class UsersSyncer
  attr_reader :users_to_sync

  def initialize(users_to_sync)
    @users_to_sync = users_to_sync
  end

  def sync
    users_to_sync.each(&:sync!)
    @has_synced_users = true
  end
  
  def synced_users
    has_synced_users? ? users_to_sync : []
  end
  
  def has_synced_users?
    !!@has_synced_users
  end
end

sync_users = User.sync_users
synced_users = sync_users.synced_users