instance method define_method_attribute=

# File activemodel/lib/active_model/attributes.rb, line 31
        def define_method_attribute=(name)
          safe_name = name.unpack("h*".freeze).first
          ActiveModel::AttributeMethods::AttrNames.set_name_cache safe_name, name

          generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
            def __temp__#{safe_name}=(value)
              name = ::ActiveModel::AttributeMethods::AttrNames::ATTR_#{safe_name}
              write_attribute(name, value)
            end
            alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
            undef_method :__temp__#{safe_name}=
          STR
        end