gistfile1.rb

def self.guid_from_entry(entry)
  [:guid, :url, :content, :summary].each do |sym|
    next unless available_for_guid? entry
    return Digest::MD5.hexdigest(entry.send(sym))
  end
end
    
def self.available_for_guid?(entry)        
  entry.respond_to?(sym) and entry.send(sym).present?
end