instance method define_attribute_method

# File activemodel/lib/active_model/attribute_methods.rb, line 285
      def define_attribute_method(attr_name)
        attribute_method_matchers.each do |matcher|
          unless instance_method_already_implemented?(matcher.method_name(attr_name))
            generate_method = "define_method_#{matcher.prefix}attribute#{matcher.suffix}"

            if respond_to?(generate_method, true)
              send(generate_method, attr_name)
            else
              method_name = matcher.method_name(attr_name)

              generated_attribute_methods.module_eval <<-RUBY, __FILE__, __LINE__ + 1
                if method_defined?('#{method_name}')
                  undef :'#{method_name}'
                end
              RUBY

              if method_name.to_s =~ COMPILABLE_REGEXP
                generated_attribute_methods.module_eval <<-RUBY, __FILE__, __LINE__ + 1
                  def #{method_name}(*args)
                    send(:#{matcher.method_missing_target}, '#{attr_name}', *args)
                  end
                RUBY
              else
                generated_attribute_methods.module_eval <<-RUBY, __FILE__, __LINE__ + 1
                  define_method('#{method_name}') do |*args|
                    send('#{matcher.method_missing_target}', '#{attr_name}', *args)
                  end
                RUBY
              end
            end
          end
        end
      end