class ActionController::MimeResponds::Collector

def response
  response = @responses.fetch(format, @responses[Mime::ALL])
  if response.is_a?(VariantCollector) # `format.html.phone` - variant inline syntax
    response.variant
  elsif response.nil? || response.arity == 0 # `format.html` - just a format, call its block
    response
  else # `format.html{ |variant| variant.phone }` - variant block syntax
    variant_collector = VariantCollector.new(@variant)
    response.call(variant_collector) # call format block with variants collector
    variant_collector.variant
  end
end