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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| 14 | class EventStream  | 
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| 15 | { | 
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| 16 | /**  | 
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| 17 | * @var Connection  | 
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| 18 | */  | 
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| 19 | protected $connection;  | 
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| 20 | |||
| 21 | /**  | 
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| 22 | * @var SerializerInterface  | 
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| 23 | */  | 
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| 24 | protected $payloadSerializer;  | 
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| 25 | |||
| 26 | /**  | 
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| 27 | * @var SerializerInterface  | 
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| 28 | */  | 
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| 29 | protected $metadataSerializer;  | 
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| 30 | |||
| 31 | /**  | 
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| 32 | * @var string  | 
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| 33 | */  | 
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| 34 | protected $tableName;  | 
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| 35 | |||
| 36 | /**  | 
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| 37 | * @var QueryBuilder  | 
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| 38 | */  | 
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| 39 | protected $queryBuilder;  | 
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| 40 | |||
| 41 | /**  | 
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| 42 | * @var int  | 
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| 43 | */  | 
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| 44 | protected $previousId;  | 
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| 45 | |||
| 46 | /**  | 
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| 47 | * @var string  | 
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| 48 | */  | 
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| 49 | protected $aggregateType;  | 
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| 50 | |||
| 51 | /**  | 
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| 52 | * @var EventStreamDecoratorInterface  | 
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| 53 | */  | 
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| 54 | private $domainEventStreamDecorator;  | 
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| 55 | |||
| 56 | /**  | 
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| 57 | * @param Connection $connection  | 
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| 58 | * @param SerializerInterface $payloadSerializer  | 
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| 59 | * @param SerializerInterface $metadataSerializer  | 
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| 60 | * @param string $tableName  | 
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| 61 | */  | 
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| 62 | public function __construct(  | 
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| 77 | |||
| 78 | /**  | 
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| 79 | * @param int $startId  | 
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| 80 | * @return EventStream  | 
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| 81 | */  | 
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| 82 | public function withStartId($startId)  | 
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| 88 | |||
| 89 | /**  | 
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| 90 | * @param string $aggregateType  | 
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| 91 | * @return EventStream  | 
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| 92 | */  | 
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| 93 | public function withAggregateType($aggregateType)  | 
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| 99 | |||
| 100 | /**  | 
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| 101 | * @param EventStreamDecoratorInterface $domainEventStreamDecorator  | 
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| 102 | * @return EventStream  | 
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| 103 | */  | 
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| 104 | public function withDomainEventStreamDecorator(EventStreamDecoratorInterface $domainEventStreamDecorator)  | 
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| 110 | |||
| 111 | public function __invoke()  | 
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| 147 | |||
| 148 | /**  | 
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| 149 | * @return int  | 
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| 150 | */  | 
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| 151 | public function getPreviousId()  | 
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| 155 | |||
| 156 | /**  | 
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| 157 | * @return QueryBuilder  | 
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| 158 | * @throws DBALException  | 
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| 159 | */  | 
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| 160 | protected function prepareLoadQuery()  | 
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| 189 | |||
| 190 | /**  | 
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| 191 | * @param $row  | 
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| 192 | * @return DomainMessage  | 
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| 193 | */  | 
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| 194 | View Code Duplication | private function deserializeEvent($row)  | 
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| 204 | }  | 
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| 205 | 
In PHP it is possible to write to properties without declaring them. For example, the following is perfectly valid PHP code:
Generally, it is a good practice to explictly declare properties to avoid accidental typos and provide IDE auto-completion: