code: func (q Quantity) DeepCopy() Quantity {
  	if q.d.Dec != nil {
  		tmp := &inf.Dec{}
  		q.d.Dec = tmp.Set(q.d.Dec)
  	}
  	return q
  }
docs: // DeepCopy returns a deep-copy of the Quantity value.  Note that the method
  // receiver is a value, so we can mutate it in-place and return it.