Implement sort.Interface to required struct slice

user.go

@@ -7,6 +7,13 @@ type User struct {
 	forwards       []string
 }
 
+// UserSlice attaches the methods of sort.Interface to []*User.
+type UserSlice []*User
+
+func (p UserSlice) Len() int           { return len(p) }
+func (p UserSlice) Less(i, j int) bool { return p[i].Name() < p[j].Name() }
+func (p UserSlice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+
 // NewUser creates a new User instance.
 func NewUser(name, hashedPassword string, forwards []string) (*User, error) {
 	if !validUserName(name) {