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 namespace Fenos\Notifynder\Builder;  | 
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| 16 | trait BuilderRules  | 
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| 17 | { | 
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| 18 | |||
| 19 | /**  | 
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| 20 | * @var array  | 
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| 21 | */  | 
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| 22 | private $requiredFields = ['from_id','to_id','url','category_id'];  | 
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| 23 | |||
| 24 | /**  | 
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| 25 | * Value has to be a string  | 
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| 26 | *  | 
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| 27 | * @param $value  | 
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| 28 | * @return bool  | 
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| 29 | */  | 
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| 30 | protected function isString($value)  | 
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| 38 | |||
| 39 | /**  | 
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| 40 | * Value has to be a valid Carbon Instance  | 
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| 41 | *  | 
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| 42 | * @param $value  | 
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| 43 | * @return bool | InvalidArgumentException  | 
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| 44 | */  | 
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| 45 | protected function isCarbon($value)  | 
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| 51 | |||
| 52 | /**  | 
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| 53 | * Value has to be numeric  | 
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| 54 | *  | 
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| 55 | * @param $value  | 
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| 56 | * @return bool  | 
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| 57 | */  | 
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| 58 | protected function isNumeric($value)  | 
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| 66 | |||
| 67 | /**  | 
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| 68 | * Returns all required fields including the config ones  | 
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| 69 | *  | 
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| 70 | * @return array  | 
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| 71 | */  | 
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| 72 | public function getRequiredFields()  | 
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| 82 | |||
| 83 | /**  | 
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| 84 | * Check that the builder has  | 
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| 85 | * the required field to send the  | 
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| 86 | * notifications correctly  | 
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| 87 | *  | 
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| 88 | * @param $array  | 
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| 89 | * @return bool  | 
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| 90 | */  | 
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| 91 | public function hasRequiredFields($array)  | 
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| 101 | |||
| 102 | /**  | 
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| 103 | * Check if is a required field  | 
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| 104 | *  | 
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| 105 | * @param $offset  | 
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| 106 | * @return bool  | 
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| 107 | */  | 
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| 108 | public function isRequiredField($offset)  | 
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| 112 | |||
| 113 | /**  | 
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| 114 | * Check if the array passed is  | 
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| 115 | * multidimensional  | 
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| 116 | *  | 
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| 117 | * @param $arr  | 
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| 118 | * @return bool  | 
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| 119 | */  | 
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| 120 | protected function isReadyArrToFormatInJson(array $arr)  | 
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| 133 | |||
| 134 | /**  | 
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| 135 | * @param array $arr  | 
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| 136 | * @return bool  | 
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| 137 | */  | 
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| 138 | protected function isAssociativeArr(array $arr)  | 
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| 142 | |||
| 143 | /**  | 
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| 144 | * Check if the array is  | 
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| 145 | * multidimensional  | 
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| 146 | *  | 
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| 147 | * @param $arr  | 
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| 148 | * @return bool  | 
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| 149 | */  | 
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| 150 | View Code Duplication | public function isMultidimensionalArray($arr)  | 
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| 159 | }  | 
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| 160 | 
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: