Set the default FormBuilder without having to restart the server on each change made to the DefaultFormBuilder class

default_form_builder.rb

# in app/helpers
class DefaultFormBuilder < ActionView::Helpers::FormBuilder
  # Example of an added method that wraps custom textfields, where type can be
  # :email_field, :text_field, etc.
  def textfield(type, method, attributes = {})
    @template.content_tag :div, class: 'textfield' do
      @template.send(type, @object_name, method, objectify_options(attributes))
    end
  end
  
  # Example of overriding an existing method that wraps submit buttons and uses
  # the button tag instead of the input tag for the button
  def submit(value = nil, options = {})
    value, options = nil, value if value.is_a?(Hash)
    value ||= submit_default_value
    @template.button_tag(value, options)
  end
end

set_default_form_builder.rb

# in config/initializers
module ActionView
  module Helpers
    module FormHelper
      def form_for_with_defaults(record, options = {}, &proc)
        form_for_without_defaults record, options.reverse_merge(builder: DefaultFormBuilder), &proc
      end
      
      def fields_for_with_defaults(record_name, record_object = nil, options = {}, &block)
        fields_for_without_defaults record_name, record_object, options.reverse_merge(builder: DefaultFormBuilder), &block
      end
      
      alias_method_chain :form_for, :defaults
      alias_method_chain :fields_for, :defaults
    end
  end
end