Use pointers to make generic functions work

person.go

@@ -23,12 +23,12 @@ func NewPerson(name string) *Person {
 
 // AddExtension adds the Extension to the Person.
 func (p *Person) AddExtension(e *ExtensionElement) {
-	addToSlice(p.Extensions, e)
+	addToSlice(&p.Extensions, e)
 }
 
 // DeleteExtension deletes the Extension from the Person. It return an error.
 func (p *Person) DeleteExtension(id int) error {
-	if err := deleteFromSlice(p.Extensions, id); err != nil {
+	if err := deleteFromSlice(&p.Extensions, id); err != nil {
 		return fmt.Errorf("error deleting extension %v from person %v: %v", id, p, err)
 	}
 	return nil