Return the index of the added element

person.go

@@ -21,9 +21,9 @@ func NewPerson(name string) *Person {
 	}
 }
 
-// AddExtension adds the Extension to the Person.
-func (p *Person) AddExtension(e *ExtensionElement) {
-	addToSlice(&p.Extensions, e)
+// AddExtension adds the Extension to the Person. It returns an int.
+func (p *Person) AddExtension(e *ExtensionElement) int {
+	return addToSlice(&p.Extensions, e)
 }
 
 // DeleteExtension deletes the Extension at index from the Person. It return an