Duplicate code is one of the most pungent code smells. A rule that is often used is to re-structure code once it is duplicated in three or more places.
Common duplication problems, and corresponding solutions are:
| 1 | <?php | ||
| 11 | class UserObserver | ||
| 12 | { | ||
| 13 | |||
| 14 | /** | ||
| 15 | * Listen to the User created event. | ||
| 16 | * | ||
| 17 | * @param User $user | ||
| 18 | * @return void | ||
| 19 | */ | ||
| 20 | public function created(User $user) | ||
| 24 | |||
| 25 | /** | ||
| 26 | * Listen to the User deleted event. | ||
| 27 | */ | ||
| 28 | View Code Duplication | public function deleted(User $user) | |
| 43 | } | 
This check looks from parameters that have been defined for a function or method, but which are not used in the method body.