def url(style_name = default_style, use_timestamp = @use_timestamp)
      url = original_filename.nil? ? interpolate(@default_url, style_name) : interpolate(@url, style_name)
      use_timestamp && updated_at ? [url, updated_at].compact.join(url.include?("?") ? "&" : "?") : url
    end
def url(style_name = default_style, use_timestamp = @use_timestamp)
      url = original_filename.nil? ? interpolate(@default_url, style_name) : interpolate(@url, style_name)
      use_timestamp && updated_at ? [url, updated_at].compact.join(url.include?("?") ? "&" : "?") : url
    end
Returns the public URL of the attachment, with a given style. Note that
 this does not necessarily need to point to a file that your web server
 can access and can point to an action in your app, if you need fine
 grained security.  This is not recommended if you don't need the
 security, however, for performance reasons. Set use_timestamp to false
 if you want to stop the attachment update time appended to the url