code: func NewUserSource(seed int64, max uint64) *UserSource {
  	if max == 0 {
  		max = math.MaxUint64
  	}
  	var n uint64
  	s := &UserSource{
  		n:   &n,
  		max: max,
  		ug:  NewUserGenerator(seed),
  	}
  
  	return s
  }
docs: // NewUserSource creates a new Source with the given random seed. Using the same
  // seed should give the same series of events on a given version of Go.