fill_in_form_helper.rb

def fill_in_form(form_name, &block)
  previous_self = eval "self", block.binding

  # Break scope barrier to be able to call on previous self context fill_in method
  form_filler = Class.new do
    define_method(:initialize) do |form_name|
      @form_name = form_name
    end

    define_method(:method_missing) do |method_name, *args|
      previous_self.send(:fill_in, "#{@form_name}[#{method_name}]", with: args[0])
    end
  end

  yield form_filler.new(form_name)
end