Implement sort.Interface to required struct slice

domain.go

@@ -8,6 +8,13 @@ type Domain struct {
 	CatchAllUser *CatchAllUser
 }
 
+// DomainSlice attaches the methods of sort.Interface to []*Domain.
+type DomainSlice []*Domain
+
+func (p DomainSlice) Len() int           { return len(p) }
+func (p DomainSlice) Less(i, j int) bool { return p[i].Name() < p[j].Name() }
+func (p DomainSlice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+
 // NewDomain creates a new Domain instance.
 func NewDomain(name string) (*Domain, error) {
 	if !validDomainName(name) {