code: func (f *Feed) mapKey() uint64 {
  	serializedData := make([]byte, feedLength)
  	f.binaryPut(serializedData)
  	hasher := hashPool.Get().(hash.Hash)
  	defer hashPool.Put(hasher)
  	hasher.Reset()
  	hasher.Write(serializedData)
  	hash := hasher.Sum(nil)
  	return *(*uint64)(unsafe.Pointer(&hash[0]))
  }
docs: // mapKey calculates a unique id for this feed. Used by the cache map in `Handler`