Question

Rails has a method form_for which takes a &proc that contains the content present inside the generated form tag. For example, in HAML:

= form_for @my_model do |f|
  = f.label :demo_field
  = f.text_field :demo_field

I’d quite like to prepend something to that &proc block so that the form renders as

= form_for @my_model do |f|
   %h1 Demo Of Breaking Into A Proc
   = f.label :demo_field
   = f.text_Field :demo_field

The question is, how do I go about prepending something to a proc argument? The method I’m calling is:

module ActionView::Helpers::FormHelper
  alias_method :original_form_for, :form_for



   def form_for(record, options = {}, &proc)
     # Prepend to the proc block here
     # ???

     original_form_for(record, options, &proc)
   end

end

If anyone could replace that “# ???” line with a solution (or offer an alternative approach if I’m going about this the wrong way), I’d be really appreciative.

Answer 1

def form_for(record, options = {}, &proc)
    new_proc = proc do |*args, &block|
      "some more html" + proc.call(*args, &block)
    end
  original_form_for(record, options, &new_proc)
end

You can’t change a Proc.