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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:
Complex classes like Walker often do a lot of different things. To break such a class down, we need to identify a cohesive component within that class. A common approach to find such a component is to look for fields/methods that share the same prefixes, or suffixes. You can also have a look at the cohesion graph to spot any un-connected, or weakly-connected components.
Once you have determined the fields that belong together, you can apply the Extract Class refactoring. If the component makes sense as a sub-class, Extract Subclass is also a candidate, and is often faster.
While breaking up the class, it is a good idea to analyze how other classes use Walker, and based on these observations, apply Extract Interface, too.
| 1 | <?php |
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| 14 | class Walker { |
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| 15 | /** |
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| 16 | * What the class handles. |
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| 17 | * |
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| 18 | * @since 2.1.0 |
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| 19 | * @access public |
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| 20 | * @var string |
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| 21 | */ |
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| 22 | public $tree_type; |
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| 23 | |||
| 24 | /** |
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| 25 | * DB fields to use. |
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| 26 | * |
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| 27 | * @since 2.1.0 |
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| 28 | * @var array |
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| 29 | */ |
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| 30 | public $db_fields; |
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| 31 | |||
| 32 | /** |
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| 33 | * Max number of pages walked by the paged walker |
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| 34 | * |
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| 35 | * @since 2.7.0 |
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| 36 | * @var int |
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| 37 | */ |
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| 38 | public $max_pages = 1; |
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| 39 | |||
| 40 | /** |
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| 41 | * Whether the current element has children or not. |
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| 42 | * |
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| 43 | * To be used in start_el(). |
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| 44 | * |
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| 45 | * @since 4.0.0 |
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| 46 | * @var bool |
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| 47 | */ |
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| 48 | public $has_children; |
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| 49 | |||
| 50 | /** |
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| 51 | * Starts the list before the elements are added. |
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| 52 | * |
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| 53 | * The $args parameter holds additional values that may be used with the child |
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| 54 | * class methods. This method is called at the start of the output list. |
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| 55 | * |
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| 56 | * @since 2.1.0 |
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| 57 | * @abstract |
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| 58 | * |
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| 59 | * @param string $output Passed by reference. Used to append additional content. |
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| 60 | * @param int $depth Depth of the item. |
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| 61 | * @param array $args An array of additional arguments. |
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| 62 | */ |
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| 63 | public function start_lvl( &$output, $depth = 0, $args = array() ) {} |
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| 64 | |||
| 65 | /** |
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| 66 | * Ends the list of after the elements are added. |
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| 67 | * |
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| 68 | * The $args parameter holds additional values that may be used with the child |
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| 69 | * class methods. This method finishes the list at the end of output of the elements. |
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| 70 | * |
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| 71 | * @since 2.1.0 |
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| 72 | * @abstract |
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| 73 | * |
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| 74 | * @param string $output Passed by reference. Used to append additional content. |
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| 75 | * @param int $depth Depth of the item. |
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| 76 | * @param array $args An array of additional arguments. |
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| 77 | */ |
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| 78 | public function end_lvl( &$output, $depth = 0, $args = array() ) {} |
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| 79 | |||
| 80 | /** |
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| 81 | * Start the element output. |
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| 82 | * |
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| 83 | * The $args parameter holds additional values that may be used with the child |
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| 84 | * class methods. Includes the element output also. |
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| 85 | * |
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| 86 | * @since 2.1.0 |
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| 87 | * @abstract |
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| 88 | * |
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| 89 | * @param string $output Passed by reference. Used to append additional content. |
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| 90 | * @param object $object The data object. |
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| 91 | * @param int $depth Depth of the item. |
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| 92 | * @param array $args An array of additional arguments. |
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| 93 | * @param int $current_object_id ID of the current item. |
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| 94 | */ |
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| 95 | public function start_el( &$output, $object, $depth = 0, $args = array(), $current_object_id = 0 ) {} |
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| 96 | |||
| 97 | /** |
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| 98 | * Ends the element output, if needed. |
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| 99 | * |
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| 100 | * The $args parameter holds additional values that may be used with the child class methods. |
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| 101 | * |
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| 102 | * @since 2.1.0 |
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| 103 | * @abstract |
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| 104 | * |
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| 105 | * @param string $output Passed by reference. Used to append additional content. |
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| 106 | * @param object $object The data object. |
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| 107 | * @param int $depth Depth of the item. |
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| 108 | * @param array $args An array of additional arguments. |
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| 109 | */ |
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| 110 | public function end_el( &$output, $object, $depth = 0, $args = array() ) {} |
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| 111 | |||
| 112 | /** |
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| 113 | * Traverse elements to create list from elements. |
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| 114 | * |
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| 115 | * Display one element if the element doesn't have any children otherwise, |
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| 116 | * display the element and its children. Will only traverse up to the max |
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| 117 | * depth and no ignore elements under that depth. It is possible to set the |
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| 118 | * max depth to include all depths, see walk() method. |
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| 119 | * |
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| 120 | * This method should not be called directly, use the walk() method instead. |
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| 121 | * |
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| 122 | * @since 2.5.0 |
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| 123 | * |
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| 124 | * @param object $element Data object. |
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| 125 | * @param array $children_elements List of elements to continue traversing. |
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| 126 | * @param int $max_depth Max depth to traverse. |
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| 127 | * @param int $depth Depth of current element. |
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| 128 | * @param array $args An array of arguments. |
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| 129 | * @param string $output Passed by reference. Used to append additional content. |
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| 130 | */ |
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| 131 | public function display_element( $element, &$children_elements, $max_depth, $depth, $args, &$output ) { |
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| 174 | |||
| 175 | /** |
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| 176 | * Display array of elements hierarchically. |
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| 177 | * |
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| 178 | * Does not assume any existing order of elements. |
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| 179 | * |
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| 180 | * $max_depth = -1 means flatly display every element. |
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| 181 | * $max_depth = 0 means display all levels. |
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| 182 | * $max_depth > 0 specifies the number of display levels. |
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| 183 | * |
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| 184 | * @since 2.1.0 |
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| 185 | * |
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| 186 | * @param array $elements An array of elements. |
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| 187 | * @param int $max_depth The maximum hierarchical depth. |
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| 188 | * @return string The hierarchical item output. |
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| 189 | */ |
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| 190 | public function walk( $elements, $max_depth ) { |
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| 259 | |||
| 260 | /** |
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| 261 | * paged_walk() - produce a page of nested elements |
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| 262 | * |
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| 263 | * Given an array of hierarchical elements, the maximum depth, a specific page number, |
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| 264 | * and number of elements per page, this function first determines all top level root elements |
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| 265 | * belonging to that page, then lists them and all of their children in hierarchical order. |
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| 266 | * |
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| 267 | * $max_depth = 0 means display all levels. |
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| 268 | * $max_depth > 0 specifies the number of display levels. |
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| 269 | * |
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| 270 | * @since 2.7.0 |
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| 271 | * |
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| 272 | * @param array $elements |
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| 273 | * @param int $max_depth The maximum hierarchical depth. |
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| 274 | * @param int $page_num The specific page number, beginning with 1. |
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| 275 | * @param int $per_page |
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| 276 | * @return string XHTML of the specified page of elements |
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| 277 | */ |
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| 278 | public function paged_walk( $elements, $max_depth, $page_num, $per_page ) { |
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| 383 | |||
| 384 | /** |
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| 385 | * Calculates the total number of root elements. |
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| 386 | * |
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| 387 | * @since 2.7.0 |
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| 388 | * @access public |
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| 389 | * |
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| 390 | * @param array $elements Elements to list. |
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| 391 | * @return int Number of root elements. |
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| 392 | */ |
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| 393 | public function get_number_of_root_elements( $elements ){ |
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| 403 | |||
| 404 | /** |
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| 405 | * Unset all the children for a given top level element. |
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| 406 | * |
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| 407 | * @param object $e |
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| 408 | * @param array $children_elements |
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| 409 | */ |
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| 410 | public function unset_children( $e, &$children_elements ){ |
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| 424 | |||
| 425 | } // Walker |
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| 426 |
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If you define a variable conditionally, it can happen that it is not defined for all execution paths.
Let’s take a look at an example:
In the above example, the variable $x is defined if you pass “foo” or “bar” as argument for $a. However, since the switch statement has no default case statement, if you pass any other value, the variable $x would be undefined.
Available Fixes
Check for existence of the variable explicitly:
Define a default value for the variable:
Add a value for the missing path: