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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| 5 | class ConnectedDifferences |
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| 6 | { |
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| 7 | /** |
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| 8 | * @var array |
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| 9 | */ |
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| 10 | private $bitmap; |
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| 11 | |||
| 12 | /** |
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| 13 | * @var int |
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| 14 | */ |
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| 15 | private $width; |
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| 16 | |||
| 17 | /** |
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| 18 | * @var int |
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| 19 | */ |
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| 20 | private $height; |
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| 21 | |||
| 22 | /** |
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| 23 | * @var array |
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| 24 | */ |
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| 25 | private $boundaries = []; |
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| 26 | |||
| 27 | /** |
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| 28 | * @param Difference $difference |
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| 29 | */ |
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| 30 | public function __construct(Difference $difference) |
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| 38 | |||
| 39 | /** |
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| 40 | * Find separate boundaries. |
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| 41 | * |
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| 42 | * @return array |
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| 43 | */ |
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| 44 | private function findBoundaries() |
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| 130 | |||
| 131 | /** |
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| 132 | * @return ConnectedDifferences |
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| 133 | */ |
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| 134 | public function withJoinedBoundaries() |
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| 166 | |||
| 167 | /** |
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| 168 | * @param string $property |
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| 169 | * @param mixed $value |
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| 170 | * |
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| 171 | * @return ConnectedDifferences |
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| 172 | */ |
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| 173 | private function cloneWith($property, $value) |
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| 180 | |||
| 181 | /** |
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| 182 | * Labels for adjacent pixels. |
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| 183 | * |
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| 184 | * @param array $pixel |
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| 185 | * |
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| 186 | * @return array |
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| 187 | */ |
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| 188 | private function adjacent($pixel) |
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| 202 | |||
| 203 | /** |
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| 204 | * Tell if two boundaries overlap. |
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| 205 | * |
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| 206 | * @param array $p |
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| 207 | * @param array $q |
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| 208 | * |
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| 209 | * @return bool |
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| 210 | */ |
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| 211 | private function intersect(array $p, array $q) |
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| 215 | |||
| 216 | /** |
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| 217 | * @return array |
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| 218 | */ |
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| 219 | public function boundaries() |
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| 223 | } |
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| 224 |
PHP has two types of connecting operators (logical operators, and boolean operators):
and&&or||The difference between these is the order in which they are executed. In most cases, you would want to use a boolean operator like
&&, or||.Let’s take a look at a few examples:
Logical Operators are used for Control-Flow
One case where you explicitly want to use logical operators is for control-flow such as this:
Since
dieintroduces problems of its own, f.e. it makes our code hardly testable, and prevents any kind of more sophisticated error handling; you probably do not want to use this in real-world code. Unfortunately, logical operators cannot be combined withthrowat this point:These limitations lead to logical operators rarely being of use in current PHP code.