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 |
||
16 | trait TagDependencyTrait |
||
17 | { |
||
18 | /** @var array IdentityMap pattern support */ |
||
19 | public static $identityMap = []; |
||
20 | |||
21 | /** |
||
22 | * @return \yii\caching\Cache |
||
23 | */ |
||
24 | 2 | public function getTagDependencyCacheComponent() |
|
28 | |||
29 | /** |
||
30 | * Returns common tag name for model instance |
||
31 | * @return string tag name |
||
32 | */ |
||
33 | 2 | public static function commonTag() |
|
38 | |||
39 | /** |
||
40 | * Returns object tag name including it's id |
||
41 | * @param array Changed fields from Update Event |
||
42 | * @return string tag name |
||
43 | */ |
||
44 | 2 | public function objectTag($oldfields = []) |
|
61 | |||
62 | /** |
||
63 | * Returns composite tags name including fields |
||
64 | * @param array Changed fields from Update Event |
||
65 | * @return array tag names |
||
66 | */ |
||
67 | 1 | public function objectCompositeTag($oldfields = []) |
|
101 | |||
102 | /** |
||
103 | * Specific fields from model for build composite tags for invalidate |
||
104 | * Example: |
||
105 | * return [ |
||
106 | * ['field1', 'field2'], |
||
107 | * ['field1', 'field2', 'field3'], |
||
108 | * ]; |
||
109 | * @return array |
||
110 | */ |
||
111 | 2 | protected function cacheCompositeTagFields() |
|
115 | |||
116 | /** |
||
117 | * Finds or creates new model using or not using cache(objectTag is applied) |
||
118 | * @param string|int $id ID of model to find |
||
119 | * @param bool $createIfEmptyId Create new model instance(record) if id is empty |
||
120 | * @param bool $useCache Use cache |
||
121 | * @param int $cacheLifetime Cache lifetime in seconds |
||
122 | * @param bool|\Exception $throwException False or exception instance to throw if model not found or (empty id AND createIfEmptyId==false) |
||
123 | * @param bool $useIdentityMap True if we want to use identity map |
||
124 | * @return \yii\db\ActiveRecord|null|self|TagDependencyTrait |
||
125 | * @throws \Exception |
||
126 | */ |
||
127 | 1 | public static function loadModel( |
|
184 | |||
185 | /** |
||
186 | * Invalidate model tags. |
||
187 | * @param yii\db\AfterSaveEvent when called as an event handler. |
||
188 | * @return bool |
||
189 | */ |
||
190 | 2 | public function invalidateTags($event = null) |
|
210 | |||
211 | } |
||
212 |
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,
$x
would be read before it is initialized. This was a very basic example, however the principle is the same for the found issue.