class method self.attr_internal_naming_format=

# File activesupport/lib/active_support/core_ext/module/attr_internal.rb, line 25
    def attr_internal_naming_format=(format)
      if format.start_with?("@")
        raise ArgumentError, <<~MESSAGE.squish
          Setting `attr_internal_naming_format` with a `@` prefix is not supported.

          You can simply replace #{format.inspect} by #{format.delete_prefix("@").inspect}.
        MESSAGE
      end

      @attr_internal_naming_format = format
    end