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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| 10 | final class TokenContainer implements Cleanable, ContainsChildren, Removable  | 
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| 11 | { | 
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| 12 | /** @var array[Token] */  | 
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| 13 | private $children;  | 
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| 14 | |||
| 15 | /** @var Configuration */  | 
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| 16 | private $configuration;  | 
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| 17 | |||
| 18 | /**  | 
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| 19 | * Constructor  | 
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| 20 | */  | 
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| 21 | 51 | public function __construct(Configuration $configuration)  | 
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| 26 | |||
| 27 | /**  | 
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| 28 | * Required by ContainsChildren interface.  | 
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| 29 | */  | 
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| 30 | 51 | public function getChildren()  | 
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| 34 | |||
| 35 | /**  | 
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| 36 | * Required by ContainsChildren interface.  | 
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| 37 | */  | 
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| 38 | 1 | public function hasChild(Token $token)  | 
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| 42 | |||
| 43 | /**  | 
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| 44 | * Required by ContainsChildren interface.  | 
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| 45 | */  | 
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| 46 | 50 | public function appendChild(Token $token)  | 
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| 52 | |||
| 53 | /**  | 
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| 54 | * Required by ContainsChildren interface.  | 
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| 55 | */  | 
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| 56 | 1 | public function prependChild(Token $token)  | 
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| 62 | |||
| 63 | /**  | 
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| 64 | * Required by ContainsChildren interface.  | 
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| 65 | */  | 
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| 66 | 5 | View Code Duplication | public function removeChild(Token $token)  | 
            
| 77 | |||
| 78 | /**  | 
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| 79 | * Required by Cleanable interface.  | 
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| 80 | */  | 
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| 81 | 43 | public function clean(LoggerInterface $logger)  | 
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| 89 | |||
| 90 | /**  | 
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| 91 | * Required by the Removable interface.  | 
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| 92 | */  | 
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| 93 | 42 | View Code Duplication | public function remove(LoggerInterface $logger)  | 
            
| 123 | }  | 
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| 124 | 
Let’s assume that you have a directory layout like this:
. |-- OtherDir | |-- Bar.php | `-- Foo.php `-- SomeDir `-- Foo.phpand let’s assume the following content of
Bar.php:If both files
OtherDir/Foo.phpandSomeDir/Foo.phpare loaded in the same runtime, you will see a PHP error such as the following:PHP Fatal error: Cannot use SomeDir\Foo as Foo because the name is already in use in OtherDir/Foo.phpHowever, as
OtherDir/Foo.phpdoes not necessarily have to be loaded and the error is only triggered if it is loaded beforeOtherDir/Bar.php, this problem might go unnoticed for a while. In order to prevent this error from surfacing, you must import the namespace with a different alias: