code: func (k *CacheKey) ToMapKey() string {
  	b, _ := bufPool.Get().(*bytes.Buffer)
  	if b == nil {
  		b = &bytes.Buffer{}
  	} else {
  		b.Reset()
  	}
  	defer bufPool.Put(b)
  	b.WriteString(k.Key)
  	b.WriteByte(0)
  	for _, s := range k.Scopes {
  		b.WriteString(s)
  		b.WriteByte(0)
  	}
  	return b.String()
  }
docs: // ToMapKey returns a string that can be used as map[string] key.
  //
  // This string IS NOT PRINTABLE. It's a merely a string-looking []byte.