code: func (q Quad) Get(d Direction) Value {
  	switch d {
  	case Subject:
  		return q.Subject
  	case Predicate:
  		return q.Predicate
  	case Label:
  		return q.Label
  	case Object:
  		return q.Object
  	default:
  		panic(d.String())
  	}
  }
docs: // Per-field accessor for quads.