class Tins::StringVersion::Version

def []=(level, value)
  level = level_of(level)
  value = value.to_i
  value >= 0 or raise ArgumentError,
    "version numbers can't contain negative numbers like #{value}"
  a = array
  a[level] = value
  a.map!(&:to_i)
  @version.replace a * ?.
end