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  | 
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| 21 | class User extends AggregateRoot implements EventSourcedAggregateRoot  | 
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| 22 | { | 
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| 23 | private $id;  | 
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| 24 | |||
| 25 | private function __construct(UserId $id)  | 
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| 29 | |||
| 30 | public static function signUp(UserId $id) : self  | 
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| 37 | |||
| 38 | protected function applyUserSignedUp(UserSignedUp $event) : void  | 
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| 41 | |||
| 42 | View Code Duplication | public static function reconstitute(Stream $stream) : self  | 
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| 52 | |||
| 53 | public function id() : UserId  | 
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| 57 | |||
| 58 | public function __toString() : string  | 
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| 62 | }  | 
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| 63 | 
This check looks from parameters that have been defined for a function or method, but which are not used in the method body.