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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| 16 | trait TagDependencyTrait |
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| 17 | { |
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| 18 | /** @var array IdentityMap pattern support */ |
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| 19 | public static $identityMap = []; |
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| 20 | |||
| 21 | /** |
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| 22 | * @return \yii\caching\Cache |
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| 23 | */ |
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| 24 | 1 | public function getTagDependencyCacheComponent() |
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| 28 | |||
| 29 | /** |
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| 30 | * Returns common tag name for model instance |
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| 31 | * @return string tag name |
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| 32 | */ |
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| 33 | 1 | public static function commonTag() |
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| 38 | |||
| 39 | /** |
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| 40 | * Returns object tag name including it's id |
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| 41 | * @param array Changed fields from Update Event |
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| 42 | * @return string tag name |
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| 43 | */ |
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| 44 | 1 | public function objectTag($oldfields = []) |
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| 61 | |||
| 62 | /** |
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| 63 | * Returns composite tags name including fields |
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| 64 | * @param array Changed fields from Update Event |
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| 65 | * @return array tag names |
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| 66 | */ |
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| 67 | 1 | public function objectCompositeTag($oldfields = []) |
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| 100 | |||
| 101 | /** |
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| 102 | * Specific fields from model for build composite tags for invalidate |
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| 103 | * Example: |
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| 104 | * return [ |
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| 105 | * ['field1', 'field2'], |
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| 106 | * ['field1', 'field2', 'field3'], |
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| 107 | * ]; |
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| 108 | * @return array |
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| 109 | */ |
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| 110 | 2 | protected function cacheCompositeTagFields() |
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| 114 | |||
| 115 | /** |
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| 116 | * Finds or creates new model using or not using cache(objectTag is applied) |
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| 117 | * @param string|int $id ID of model to find |
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| 118 | * @param bool $createIfEmptyId Create new model instance(record) if id is empty |
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| 119 | * @param bool $useCache Use cache |
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| 120 | * @param int $cacheLifetime Cache lifetime in seconds |
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| 121 | * @param bool|\Exception $throwException False or exception instance to throw if model not found or (empty id AND createIfEmptyId==false) |
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| 122 | * @param bool $useIdentityMap True if we want to use identity map |
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| 123 | * @return \yii\db\ActiveRecord|null|self|TagDependencyTrait |
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| 124 | * @throws \Exception |
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| 125 | */ |
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| 126 | 1 | public static function loadModel( |
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| 183 | |||
| 184 | /** |
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| 185 | * Invalidate model tags. |
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| 186 | * @param yii\db\AfterSaveEvent when called as an event handler. |
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| 187 | * @return bool |
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| 188 | */ |
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| 189 | 1 | public function invalidateTags($event = null) |
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| 209 | |||
| 210 | } |
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| 211 |
This error can happen if you refactor code and forget to move the variable initialization.
Let’s take a look at a simple example:
The above code is perfectly fine. Now imagine that we re-order the statements:
In that case,
$xwould be read before it is initialized. This was a very basic example, however the principle is the same for the found issue.