code: func (o OutPoint) String() string {
  	// Allocate enough for hash string, colon, and 10 digits.  Although
  	// at the time of writing, the number of digits can be no greater than
  	// the length of the decimal representation of maxTxOutPerMessage, the
  	// maximum message payload may increase in the future and this
  	// optimization may go unnoticed, so allocate space for 10 decimal
  	// digits, which will fit any uint32.
  	buf := make([]byte, 2*chainhash.HashSize+1, 2*chainhash.HashSize+1+10)
  	copy(buf, o.Hash.String())
  	buf[2*chainhash.HashSize] = ':'
  	buf = strconv.AppendUint(buf, uint64(o.Index), 10)
  	return string(buf)
  }
docs: // String returns the OutPoint in the human-readable form "hash:index".