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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| 23 | final class RobotMover  | 
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| 24 | { | 
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| 25 | private $repository;  | 
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| 26 | |||
| 27 | private $logger;  | 
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| 28 | |||
| 29 | /**  | 
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| 30 | * @param RobotRepositoryInterface $repository  | 
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| 31 | * @param LoggerInterface $logger  | 
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| 32 | */  | 
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| 33 | 7 | public function __construct(  | 
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| 40 | |||
| 41 | /**  | 
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| 42 | * @Subscribe  | 
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| 43 | *  | 
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| 44 | * @param TurnLeft $command  | 
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| 45 | */  | 
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| 46 | 1 | View Code Duplication | public function handleTurningLeft(TurnLeft $command): void  | 
            
| 56 | |||
| 57 | /**  | 
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| 58 | * @Subscribe  | 
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| 59 | *  | 
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| 60 | * @param TurnRight $command  | 
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| 61 | */  | 
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| 62 | 1 | public function handleTurningRight(TurnRight $command): void  | 
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| 72 | |||
| 73 | /**  | 
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| 74 | * @Subscribe  | 
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| 75 | *  | 
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| 76 | * @param MoveForward $command  | 
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| 77 | */  | 
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| 78 | 1 | View Code Duplication | public function handleMoveForward(MoveForward $command): void  | 
            
| 88 | |||
| 89 | /**  | 
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| 90 | * @return Robot  | 
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| 91 | */  | 
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| 92 | 3 | private function getRobot(): Robot  | 
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| 104 | }  | 
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| 105 | 
This check looks from parameters that have been defined for a function or method, but which are not used in the method body.