module Colors
  module Helper
    private def check_type(obj, type, name)
      return obj if obj.instance_of?(type)
      check_fail TypeError, "#{name} must be a #{type}, but #{obj.class} is given"
    end

    private def check_range(value, range, name)
      return value if range.cover?(value)
      check_fail ArgumentError,
                 "#{name} must be in #{range}, but %p is given" % value
    end

    private def check_fail(exc_class, message)
      raise exc_class, message, caller(2)
    end
  end
end