Rails routing - how to add scope param to url_for helper?
= link_to "Add new bio", [:new, :admin, :bio]

namespace :admin do
  scope "/:bio_type", :defaults => {:bio_type => "company"} do
    resources :bios
  end
end

= link_to "Add new bio", [:new, :admin, :bio, { bio_type: params[:bio_type] }]

def url_for(options = {})
    options ||= {}
    case options
    when String
      options
    when Hash
      options = options.symbolize_keys.reverse_merge!(:only_path => options[:host].nil?)
      super
    when :back
      controller.request.env["HTTP_REFERER"] || 'javascript:history.back()'
    else
      polymorphic_path(options)
    end
  end


  def polymorphic_path(record_or_hash_or_array, options = {})
    polymorphic_url(record_or_hash_or_array, options.merge(:routing_type => :path))
  end

  def polymorphic_url(record_or_hash_or_array, options = {})
    if record_or_hash_or_array.kind_of?(Array)
      record_or_hash_or_array = record_or_hash_or_array.compact
      if record_or_hash_or_array.first.is_a?(ActionDispatch::Routing::RoutesProxy)
        proxy = record_or_hash_or_array.shift
      end
      record_or_hash_or_array = record_or_hash_or_array[0] if record_or_hash_or_array.size == 1
    end

    record = extract_record(record_or_hash_or_array)
    record = convert_to_model(record)

    args = Array === record_or_hash_or_array ?
      record_or_hash_or_array.dup :
      [ record_or_hash_or_array ]

    inflection = if options[:action] && options[:action].to_s == "new"
      args.pop
      :singular
    elsif (record.respond_to?(:persisted?) && !record.persisted?)
      args.pop
      :plural
    elsif record.is_a?(Class)
      args.pop
      :plural
    else
      :singular
    end

    args.delete_if {|arg| arg.is_a?(Symbol) || arg.is_a?(String)}
    named_route = build_named_route_call(record_or_hash_or_array, inflection, options)

    url_options = options.except(:action, :routing_type)
    unless url_options.empty?
      args.last.kind_of?(Hash) ? args.last.merge!(url_options) : args << url_options
    end

    args.collect! { |a| convert_to_model(a) }

    (proxy || self).send(named_route, *args)
  end

polymorphic_path([:new, :admin, :bio], bio_type: params[:bio_type])