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 Give_DB_Meta 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 Give_DB_Meta, and based on these observations, apply Extract Interface, too.
| 1 | <?php  | 
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| 17 | class Give_DB_Meta extends Give_DB { | 
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| 18 | /**  | 
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| 19 | * Post type  | 
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| 20 | *  | 
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| 21 | * @since 2.0  | 
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| 22 | * @access protected  | 
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| 23 | * @var bool  | 
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| 24 | */  | 
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| 25 | protected $post_type = '';  | 
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| 26 | |||
| 27 | /**  | 
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| 28 | * Meta type  | 
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| 29 | *  | 
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| 30 | * @since 2.0  | 
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| 31 | * @access protected  | 
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| 32 | * @var bool  | 
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| 33 | */  | 
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| 34 | protected $meta_type = '';  | 
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| 35 | |||
| 36 | /**  | 
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| 37 | * Flag to handle result type  | 
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| 38 | *  | 
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| 39 | * @since 2.0  | 
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| 40 | * @access protected  | 
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| 41 | */  | 
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| 42 | protected $raw_result = false;  | 
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| 43 | |||
| 44 | /**  | 
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| 45 | * Flag for short circuit of meta function  | 
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| 46 | *  | 
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| 47 | * @since 2.0  | 
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| 48 | * @access protected  | 
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| 49 | */  | 
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| 50 | protected $check = false;  | 
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| 51 | |||
| 52 | |||
| 53 | /**  | 
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| 54 | * Meta supports.  | 
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| 55 | *  | 
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| 56 | * @since 2.0  | 
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| 57 | * @access protected  | 
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| 58 | * @var array  | 
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| 59 | */  | 
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| 60 | protected $supports = array(  | 
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| 61 | 'add_post_metadata',  | 
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| 62 | 'get_post_metadata',  | 
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| 63 | 'update_post_metadata',  | 
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| 64 | 'delete_post_metadata',  | 
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| 65 | 'posts_where',  | 
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| 66 | 'posts_join',  | 
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| 67 | 'posts_groupby',  | 
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| 68 | 'posts_orderby'  | 
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| 69 | );  | 
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| 70 | |||
| 71 | /**  | 
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| 72 | * Give_DB_Meta constructor.  | 
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| 73 | *  | 
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| 74 | * @since 2.0  | 
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| 75 | */  | 
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| 76 | 	function __construct() { | 
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| 114 | |||
| 115 | |||
| 116 | /**  | 
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| 117 | * Retrieve payment meta field for a payment.  | 
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| 118 | *  | 
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| 119 | * @access public  | 
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| 120 | * @since 2.0  | 
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| 121 | *  | 
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| 122 | * @param int $id Pst Type ID.  | 
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| 123 | * @param string $meta_key The meta key to retrieve.  | 
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| 124 | * @param bool $single Whether to return a single value.  | 
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| 125 | *  | 
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| 126 | * @return mixed Will be an array if $single is false. Will be value of meta data field if $single  | 
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| 127 | * is true.  | 
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| 128 | */  | 
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| 129 | 	public function get_meta( $id = 0, $meta_key = '', $single = false ) { | 
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| 151 | |||
| 152 | |||
| 153 | /**  | 
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| 154 | * Add meta data field to a payment.  | 
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| 155 | *  | 
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| 156 | * For internal use only. Use Give_Payment->add_meta() for public usage.  | 
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| 157 | *  | 
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| 158 | * @access private  | 
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| 159 | * @since 2.0  | 
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| 160 | *  | 
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| 161 | * @param int $id Post Type ID.  | 
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| 162 | * @param string $meta_key Metadata name.  | 
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| 163 | * @param mixed $meta_value Metadata value.  | 
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| 164 | * @param bool $unique Optional, default is false. Whether the same key should not be added.  | 
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| 165 | *  | 
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| 166 | * @return int|bool False for failure. True for success.  | 
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| 167 | */  | 
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| 168 | View Code Duplication | 	public function add_meta( $id = 0, $meta_key = '', $meta_value, $unique = false ) { | 
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| 184 | |||
| 185 | /**  | 
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| 186 | * Update payment meta field based on Post Type ID.  | 
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| 187 | *  | 
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| 188 | * For internal use only. Use Give_Payment->update_meta() for public usage.  | 
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| 189 | *  | 
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| 190 | * Use the $prev_value parameter to differentiate between meta fields with the  | 
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| 191 | * same key and Post Type ID.  | 
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| 192 | *  | 
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| 193 | * If the meta field for the payment does not exist, it will be added.  | 
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| 194 | *  | 
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| 195 | * @access public  | 
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| 196 | * @since 2.0  | 
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| 197 | *  | 
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| 198 | * @param int $id Post Type ID.  | 
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| 199 | * @param string $meta_key Metadata key.  | 
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| 200 | * @param mixed $meta_value Metadata value.  | 
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| 201 | * @param mixed $prev_value Optional. Previous value to check before removing.  | 
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| 202 | *  | 
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| 203 | * @return int|bool False on failure, true if success.  | 
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| 204 | */  | 
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| 205 | View Code Duplication | 	public function update_meta( $id = 0, $meta_key = '', $meta_value, $prev_value = '' ) { | 
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| 221 | |||
| 222 | /**  | 
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| 223 | * Remove metadata matching criteria from a payment.  | 
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| 224 | *  | 
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| 225 | * You can match based on the key, or key and value. Removing based on key and  | 
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| 226 | * value, will keep from removing duplicate metadata with the same key. It also  | 
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| 227 | * allows removing all metadata matching key, if needed.  | 
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| 228 | *  | 
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| 229 | * @access public  | 
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| 230 | * @since 2.0  | 
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| 231 | *  | 
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| 232 | * @param int $id Post Type ID.  | 
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| 233 | * @param string $meta_key Metadata name.  | 
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| 234 | * @param mixed $meta_value Optional. Metadata value.  | 
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| 235 | * @param mixed $delete_all Optional.  | 
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| 236 | *  | 
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| 237 | * @return bool False for failure. True for success.  | 
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| 238 | */  | 
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| 239 | View Code Duplication | 	public function delete_meta( $id = 0, $meta_key = '', $meta_value = '', $delete_all = '' ) { | 
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| 255 | |||
| 256 | /**  | 
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| 257 | * Rename query clauses of every query for new meta table  | 
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| 258 | *  | 
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| 259 | * @since 2.0  | 
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| 260 | * @access public  | 
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| 261 | *  | 
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| 262 | * @param string $clause  | 
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| 263 | * @param WP_Query $wp_query  | 
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| 264 | *  | 
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| 265 | * @return string  | 
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| 266 | */  | 
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| 267 | 	public function __rename_meta_table_name_in_query( $clause, $wp_query ) { | 
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| 308 | |||
| 309 | |||
| 310 | /**  | 
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| 311 | * Check if current query for post type or not.  | 
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| 312 | *  | 
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| 313 | * @since 2.0  | 
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| 314 | * @access protected  | 
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| 315 | *  | 
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| 316 | * @param WP_Query $wp_query  | 
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| 317 | *  | 
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| 318 | * @return bool  | 
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| 319 | */  | 
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| 320 | 	protected function is_post_type_query( $wp_query ) { | 
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| 340 | |||
| 341 | /**  | 
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| 342 | * Check if current id of post type or not  | 
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| 343 | *  | 
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| 344 | * @since 2.0  | 
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| 345 | * @access protected  | 
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| 346 | *  | 
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| 347 | * @param $ID  | 
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| 348 | *  | 
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| 349 | * @return bool  | 
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| 350 | */  | 
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| 351 | 	protected function is_valid_post_type( $ID ) { | 
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| 354 | |||
| 355 | /**  | 
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| 356 | * check if custom meta table enabled or not.  | 
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| 357 | *  | 
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| 358 | * @since 2.0  | 
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| 359 | * @access protected  | 
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| 360 | * @return bool  | 
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| 361 | */  | 
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| 362 | 	protected function is_custom_meta_table_active() { | 
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| 365 | |||
| 366 | |||
| 367 | /**  | 
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| 368 | * Update last_changed key  | 
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| 369 | *  | 
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| 370 | * @since 2.0  | 
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| 371 | * @access private  | 
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| 372 | *  | 
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| 373 | * @param int $id  | 
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| 374 | * @param string $meta_type  | 
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| 375 | *  | 
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| 376 | * @return void  | 
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| 377 | */  | 
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| 378 | 	private function delete_cache( $id, $meta_type = '' ) { | 
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| 393 | |||
| 394 | /**  | 
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| 395 | * Add support for hidden functions.  | 
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| 396 | *  | 
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| 397 | * @since 2.0  | 
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| 398 | * @access public  | 
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| 399 | *  | 
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| 400 | * @param $name  | 
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| 401 | * @param $arguments  | 
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| 402 | *  | 
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| 403 | * @return mixed  | 
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| 404 | */  | 
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| 405 | 	public function __call( $name, $arguments ) { | 
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| 464 | }  |