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 WC_Order_Item 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 WC_Order_Item, and based on these observations, apply Extract Interface, too.
| 1 | <?php  | 
            ||
| 17 | class WC_Order_Item extends WC_Data implements ArrayAccess { | 
            ||
| 18 | |||
| 19 | /**  | 
            ||
| 20 | * Data array, with defaults.  | 
            ||
| 21 | * @since 2.7.0  | 
            ||
| 22 | * @var array  | 
            ||
| 23 | */  | 
            ||
| 24 | protected $_data = array(  | 
            ||
| 25 | 'order_id' => 0,  | 
            ||
| 26 | 'order_item_id' => 0,  | 
            ||
| 27 | 'name' => '',  | 
            ||
| 28 | 'type' => '',  | 
            ||
| 29 | );  | 
            ||
| 30 | |||
| 31 | /**  | 
            ||
| 32 | * Stores meta in cache for future reads.  | 
            ||
| 33 | * A group must be set to to enable caching.  | 
            ||
| 34 | * @var string  | 
            ||
| 35 | */  | 
            ||
| 36 | protected $_cache_group = 'order_itemmeta';  | 
            ||
| 37 | |||
| 38 | /**  | 
            ||
| 39 | * Meta type. This should match up with  | 
            ||
| 40 | * the types avaiable at https://codex.wordpress.org/Function_Reference/add_metadata.  | 
            ||
| 41 | * WP defines 'post', 'user', 'comment', and 'term'.  | 
            ||
| 42 | */  | 
            ||
| 43 | protected $_meta_type = 'order_item';  | 
            ||
| 44 | |||
| 45 | /**  | 
            ||
| 46 | * Constructor.  | 
            ||
| 47 | * @param int|object|array $order_item ID to load from the DB (optional) or already queried data.  | 
            ||
| 
                                                                                                    
                        
                         | 
                |||
| 48 | */  | 
            ||
| 49 | 	public function __construct( $item = 0 ) { | 
            ||
| 60 | |||
| 61 | /**  | 
            ||
| 62 | * Set all data based on input array.  | 
            ||
| 63 | * @param array $data  | 
            ||
| 64 | * @access private  | 
            ||
| 65 | */  | 
            ||
| 66 | 	public function set_all( $data ) { | 
            ||
| 75 | |||
| 76 | /**  | 
            ||
| 77 | * Type checking  | 
            ||
| 78 | * @param string|array $Type  | 
            ||
| 79 | * @return boolean  | 
            ||
| 80 | */  | 
            ||
| 81 | 	public function is_type( $type ) { | 
            ||
| 84 | |||
| 85 | /**  | 
            ||
| 86 | * Get qty.  | 
            ||
| 87 | * @return int  | 
            ||
| 88 | */  | 
            ||
| 89 | 	public function get_qty() { | 
            ||
| 92 | |||
| 93 | /*  | 
            ||
| 94 | |--------------------------------------------------------------------------  | 
            ||
| 95 | | Getters  | 
            ||
| 96 | |--------------------------------------------------------------------------  | 
            ||
| 97 | */  | 
            ||
| 98 | |||
| 99 | /**  | 
            ||
| 100 | * Get order item ID.  | 
            ||
| 101 | * @return int  | 
            ||
| 102 | */  | 
            ||
| 103 | 	public function get_id() { | 
            ||
| 106 | |||
| 107 | /**  | 
            ||
| 108 | * Get order ID this meta belongs to.  | 
            ||
| 109 | * @return int  | 
            ||
| 110 | */  | 
            ||
| 111 | 	public function get_order_id() { | 
            ||
| 114 | |||
| 115 | /**  | 
            ||
| 116 | * Get order item ID this meta belongs to.  | 
            ||
| 117 | * @return int  | 
            ||
| 118 | */  | 
            ||
| 119 | 	public function get_order_item_id() { | 
            ||
| 122 | |||
| 123 | /**  | 
            ||
| 124 | * Get order item name.  | 
            ||
| 125 | * @return string  | 
            ||
| 126 | */  | 
            ||
| 127 | 	public function get_name() { | 
            ||
| 130 | |||
| 131 | /**  | 
            ||
| 132 | * Get order item type.  | 
            ||
| 133 | * @return string  | 
            ||
| 134 | */  | 
            ||
| 135 | 	public function get_type() { | 
            ||
| 138 | |||
| 139 | /*  | 
            ||
| 140 | |--------------------------------------------------------------------------  | 
            ||
| 141 | | Setters  | 
            ||
| 142 | |--------------------------------------------------------------------------  | 
            ||
| 143 | */  | 
            ||
| 144 | |||
| 145 | /**  | 
            ||
| 146 | * Set ID  | 
            ||
| 147 | * @param int $value  | 
            ||
| 148 | */  | 
            ||
| 149 | 	public function set_id( $value ) { | 
            ||
| 152 | |||
| 153 | /**  | 
            ||
| 154 | * Set order ID.  | 
            ||
| 155 | * @param int $value  | 
            ||
| 156 | */  | 
            ||
| 157 | 	public function set_order_id( $value ) { | 
            ||
| 160 | |||
| 161 | /**  | 
            ||
| 162 | * Set order item ID.  | 
            ||
| 163 | * @param int $value  | 
            ||
| 164 | */  | 
            ||
| 165 | 	public function set_order_item_id( $value ) { | 
            ||
| 168 | |||
| 169 | /**  | 
            ||
| 170 | * Set order item name.  | 
            ||
| 171 | * @param string $value  | 
            ||
| 172 | */  | 
            ||
| 173 | 	public function set_name( $value ) { | 
            ||
| 176 | |||
| 177 | /**  | 
            ||
| 178 | * Set order item type.  | 
            ||
| 179 | * @param string $value  | 
            ||
| 180 | */  | 
            ||
| 181 | 	public function set_type( $value ) { | 
            ||
| 185 | |||
| 186 | /*  | 
            ||
| 187 | |--------------------------------------------------------------------------  | 
            ||
| 188 | | CRUD methods  | 
            ||
| 189 | |--------------------------------------------------------------------------  | 
            ||
| 190 | |  | 
            ||
| 191 | | Methods which create, read, update and delete data from the database.  | 
            ||
| 192 | |  | 
            ||
| 193 | */  | 
            ||
| 194 | |||
| 195 | /**  | 
            ||
| 196 | * Insert data into the database.  | 
            ||
| 197 | * @since 2.7.0  | 
            ||
| 198 | */  | 
            ||
| 199 | View Code Duplication | 	public function create() { | 
            |
| 211 | |||
| 212 | /**  | 
            ||
| 213 | * Update data in the database.  | 
            ||
| 214 | * @since 2.7.0  | 
            ||
| 215 | */  | 
            ||
| 216 | View Code Duplication | 	public function update() { | 
            |
| 227 | |||
| 228 | /**  | 
            ||
| 229 | * Read from the database.  | 
            ||
| 230 | * @since 2.7.0  | 
            ||
| 231 | * @param int|object $item ID of object to read, or already queried object.  | 
            ||
| 232 | */  | 
            ||
| 233 | 	public function read( $item ) { | 
            ||
| 252 | |||
| 253 | /**  | 
            ||
| 254 | * Save data to the database.  | 
            ||
| 255 | * @since 2.7.0  | 
            ||
| 256 | * @return int Item ID  | 
            ||
| 257 | */  | 
            ||
| 258 | 	public function save() { | 
            ||
| 268 | |||
| 269 | /**  | 
            ||
| 270 | * Delete data from the database.  | 
            ||
| 271 | * @since 2.7.0  | 
            ||
| 272 | */  | 
            ||
| 273 | 	public function delete() { | 
            ||
| 282 | |||
| 283 | /*  | 
            ||
| 284 | |--------------------------------------------------------------------------  | 
            ||
| 285 | | Meta Data Handling  | 
            ||
| 286 | |--------------------------------------------------------------------------  | 
            ||
| 287 | */  | 
            ||
| 288 | |||
| 289 | /**  | 
            ||
| 290 | * Expands things like term slugs before return.  | 
            ||
| 291 | * @param string $hideprefix (default: _)  | 
            ||
| 292 | * @return array  | 
            ||
| 293 | */  | 
            ||
| 294 | 	public function get_formatted_meta_data( $hideprefix = '_' ) { | 
            ||
| 324 | |||
| 325 | /*  | 
            ||
| 326 | |--------------------------------------------------------------------------  | 
            ||
| 327 | | Array Access Methods  | 
            ||
| 328 | |--------------------------------------------------------------------------  | 
            ||
| 329 | |  | 
            ||
| 330 | | For backwards compat with legacy arrays.  | 
            ||
| 331 | |  | 
            ||
| 332 | */  | 
            ||
| 333 | |||
| 334 | /**  | 
            ||
| 335 | * offsetSet for ArrayAccess  | 
            ||
| 336 | * @param string $offset  | 
            ||
| 337 | * @param mixed $value  | 
            ||
| 338 | */  | 
            ||
| 339 | 	public function offsetSet( $offset, $value ) { | 
            ||
| 353 | |||
| 354 | /**  | 
            ||
| 355 | * offsetUnset for ArrayAccess  | 
            ||
| 356 | * @param string $offset  | 
            ||
| 357 | */  | 
            ||
| 358 | 	public function offsetUnset( $offset ) { | 
            ||
| 370 | |||
| 371 | /**  | 
            ||
| 372 | * offsetExists for ArrayAccess  | 
            ||
| 373 | * @param string $offset  | 
            ||
| 374 | * @return bool  | 
            ||
| 375 | */  | 
            ||
| 376 | 	public function offsetExists( $offset ) { | 
            ||
| 382 | |||
| 383 | /**  | 
            ||
| 384 | * offsetGet for ArrayAccess  | 
            ||
| 385 | * @param string $offset  | 
            ||
| 386 | * @return mixed  | 
            ||
| 387 | */  | 
            ||
| 388 | 	public function offsetGet( $offset ) { | 
            ||
| 412 | }  | 
            ||
| 413 | 
This check looks for PHPDoc comments describing methods or function parameters that do not exist on the corresponding method or function.
Consider the following example. The parameter
$italyis not defined by the methodfinale(...).The most likely cause is that the parameter was removed, but the annotation was not.