Define_method with a block

gistfile1.rb

def self.define_user_field(field_name, &block)
  block ||= lambda{|x| x}
  define_method("user_#{field_name}"} do |f|
    if user_signed_in?
      block.call(current_user.send(field_name))
    else
      f.text_field field_name
    end
  end
end