Use generics for Add and Delete Methods

person.go

@@ -23,22 +23,14 @@ func NewPerson(name string) *Person {
 
 // AddExtension adds the Extension to the Person.
 func (p *Person) AddExtension(e *ExtensionElement) {
-	if p.Extensions == nil {
-		p.Extensions = make([]*ExtensionElement, 1)
-		p.Extensions[0] = e
-	} else {
-		p.Extensions = append(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 {
-	length := len(p.Extensions)
-	if id > length {
-		return fmt.Errorf("error deleting extension from person %v: id %v out of range %v", p, id, length)
+	if err := deleteFromSlice(p.Extensions, id); err != nil {
+		return fmt.Errorf("error deleting extension %v from person %v: %v", id, p, err)
 	}
-
-	p.Extensions = append(p.Extensions[:id], p.Extensions[id+1:]...)
 	return nil
 }