func (set TargetIDSet) Difference(sset TargetIDSet) TargetIDSet {
	nset := NewTargetIDSet()
	for k := range set {
		if _, ok := sset[k]; !ok {
			nset.add(k)
		}
	}

	return nset
}

// NewTargetIDSet - creates new TargetID set with given TargetIDs.
func NewTargetIDSet(targetIDs ...TargetID) TargetIDSet {
	set := make(TargetIDSet)
	for _, targetID := range targetIDs {

func (set TargetIDSet) Difference(sset TargetIDSet) TargetIDSet {
	nset := NewTargetIDSet()
	for k := range set {
		if _, ok := sset[k]; !ok {
			nset.add(k)
		}
	}

	return nset
}

// NewTargetIDSet - creates new TargetID set with given TargetIDs.
func NewTargetIDSet(targetIDs ...TargetID) TargetIDSet {
	set := make(TargetIDSet)
	for _, targetID := range targetIDs {