Complex classes like CMB2_REST 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 CMB2_REST, and based on these observations, apply Extract Interface, too.
| 1 | <?php  | 
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| 14 | class CMB2_REST extends CMB2_Hookup_Base { | 
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| 15 | |||
| 16 | /**  | 
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| 17 | * The current CMB2 REST endpoint version  | 
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| 18 | * @var string  | 
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| 19 | * @since 2.2.4  | 
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| 20 | */  | 
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| 21 | const VERSION = '1';  | 
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| 22 | |||
| 23 | /**  | 
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| 24 | * The CMB2 REST base namespace (v should always be followed by $version)  | 
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| 25 | * @var string  | 
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| 26 | * @since 2.2.4  | 
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| 27 | */  | 
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| 28 | const NAME_SPACE = 'cmb2/v1';  | 
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| 29 | |||
| 30 | /**  | 
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| 31 | * @var CMB2 object  | 
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| 32 | * @since 2.2.4  | 
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| 33 | */  | 
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| 34 | public $cmb;  | 
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| 35 | |||
| 36 | /**  | 
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| 37 | * @var CMB2_REST[] objects  | 
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| 38 | * @since 2.2.4  | 
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| 39 | */  | 
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| 40 | public static $boxes;  | 
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| 41 | |||
| 42 | /**  | 
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| 43 | * Array of readable field objects.  | 
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| 44 | * @var CMB2_Field[]  | 
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| 45 | * @since 2.2.4  | 
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| 46 | */  | 
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| 47 | protected $read_fields = array();  | 
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| 48 | |||
| 49 | /**  | 
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| 50 | * Array of editable field objects.  | 
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| 51 | * @var CMB2_Field[]  | 
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| 52 | * @since 2.2.4  | 
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| 53 | */  | 
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| 54 | protected $edit_fields = array();  | 
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| 55 | |||
| 56 | /**  | 
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| 57 | * whether CMB2 object is readable via the rest api.  | 
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| 58 | * @var boolean  | 
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| 59 | */  | 
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| 60 | protected $rest_read = false;  | 
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| 61 | |||
| 62 | /**  | 
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| 63 | * whether CMB2 object is editable via the rest api.  | 
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| 64 | * @var boolean  | 
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| 65 | */  | 
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| 66 | protected $rest_edit = false;  | 
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| 67 | |||
| 68 | /**  | 
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| 69 | * Constructor  | 
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| 70 | *  | 
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| 71 | * @since 2.2.4  | 
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| 72 | *  | 
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| 73 | * @param CMB2 $cmb The CMB2 object to be registered for the API.  | 
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| 74 | */  | 
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| 75 | 	public function __construct( CMB2 $cmb ) { | 
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| 84 | |||
| 85 | 	public function universal_hooks() { | 
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| 97 | |||
| 98 | 	public function init_routes() { | 
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| 107 | |||
| 108 | 	public static function register_appended_fields() { | 
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| 126 | |||
| 127 | 	protected function declare_read_edit_fields() { | 
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| 145 | |||
| 146 | 	protected function can_read( $show_in_rest ) { | 
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| 155 | |||
| 156 | 	protected function can_edit( $show_in_rest ) { | 
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| 165 | |||
| 166 | /**  | 
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| 167 | * Handler for getting custom field data.  | 
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| 168 | *  | 
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| 169 | * @since 2.2.4  | 
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| 170 | *  | 
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| 171 | * @param array $data The data from the response  | 
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| 172 | * @param string $field_name Name of field  | 
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| 173 | * @param WP_REST_Request $request Current request  | 
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| 174 | *  | 
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| 175 | * @return mixed  | 
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| 176 | */  | 
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| 177 | 	public static function get_restable_field_values( $data, $field_name, $request ) { | 
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| 199 | |||
| 200 | /**  | 
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| 201 | * Handler for updating custom field data.  | 
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| 202 | *  | 
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| 203 | * @since 2.2.4  | 
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| 204 | *  | 
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| 205 | * @param mixed $value The value of the field  | 
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| 206 | * @param object $object The object from the response  | 
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| 207 | * @param string $field_name Name of field  | 
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| 208 | *  | 
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| 209 | * @return bool|int  | 
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| 210 | */  | 
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| 211 | 	public static function update_restable_field_values( $values, $object, $field_name ) { | 
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| 237 | |||
| 238 | /**  | 
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| 239 | * Loop through box fields and sanitize the values.  | 
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| 240 | *  | 
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| 241 | * @since 2.2.o  | 
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| 242 | *  | 
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| 243 | * @param array $values Array of values being provided.  | 
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| 244 | * @return array Array of updated/sanitized values.  | 
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| 245 | */  | 
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| 246 | 	public function sanitize_box_values( array $values ) { | 
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| 259 | |||
| 260 | /**  | 
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| 261 | * Handles returning a sanitized field value.  | 
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| 262 | *  | 
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| 263 | * @since 2.2.4  | 
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| 264 | *  | 
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| 265 | * @param array $values Array of values being provided.  | 
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| 266 | * @param string $field_id The id of the field to update.  | 
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| 267 | *  | 
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| 268 | * @return mixed The results of saving/sanitizing a field value.  | 
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| 269 | */  | 
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| 270 | 	protected function sanitize_field_value( array $values, $field_id ) { | 
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| 290 | |||
| 291 | /**  | 
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| 292 | * Handles returning a sanitized group field value.  | 
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| 293 | *  | 
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| 294 | * @since 2.2.4  | 
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| 295 | *  | 
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| 296 | * @param array $values Array of values being provided.  | 
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| 297 | * @param CMB2_Field $field CMB2_Field object.  | 
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| 298 | *  | 
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| 299 | * @return mixed The results of saving/sanitizing the group field value.  | 
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| 300 | */  | 
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| 301 | 	protected function sanitize_group_value( array $values, CMB2_Field $field ) { | 
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| 311 | |||
| 312 | /**  | 
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| 313 | * Filter whether a meta key is protected.  | 
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| 314 | *  | 
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| 315 | * @since 2.2.4  | 
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| 316 | *  | 
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| 317 | * @param bool $protected Whether the key is protected. Default false.  | 
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| 318 | * @param string $meta_key Meta key.  | 
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| 319 | * @param string $meta_type Meta type.  | 
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| 320 | */  | 
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| 321 | 	public function is_protected_meta( $protected, $meta_key, $meta_type ) { | 
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| 328 | |||
| 329 | 	protected static function get_object_data( $object ) { | 
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| 351 | |||
| 352 | 	public function field_can_read( $field_id, $return_object = false ) { | 
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| 355 | |||
| 356 | 	public function field_can_edit( $field_id, $return_object = false ) { | 
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| 359 | |||
| 360 | 	protected function field_can( $type = 'read_fields', $field_id, $return_object = false ) { | 
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| 361 | 		if ( ! in_array( $field_id instanceof CMB2_Field ? $field_id->id() : $field_id, $this->{$type}, true ) ) { | 
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| 362 | return false;  | 
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| 363 | }  | 
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| 364 | |||
| 365 | return $return_object ? $this->cmb->get_field( $field_id ) : true;  | 
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| 366 | }  | 
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| 367 | |||
| 368 | /**  | 
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| 369 | * Get an instance of this class by a CMB2 id  | 
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| 370 | *  | 
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| 371 | * @since 2.2.4  | 
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| 372 | *  | 
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| 373 | * @param string $cmb_id CMB2 config id  | 
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| 374 | *  | 
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| 375 | * @return CMB2_REST|false The CMB2_REST object or false.  | 
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| 376 | */  | 
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| 377 | 	public static function get_rest_box( $cmb_id ) { | 
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| 380 | |||
| 381 | /**  | 
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| 382 | * Checks if given value is readable.  | 
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| 383 | *  | 
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| 384 | * Value is considered readable if it is not empty and if it does not match the editable blacklist.  | 
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| 385 | *  | 
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| 386 | * @since 2.2.4  | 
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| 387 | *  | 
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| 388 | * @param mixed $value Value to check.  | 
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| 389 | *  | 
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| 390 | * @return boolean Whether value is considered readable.  | 
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| 391 | */  | 
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| 392 | 	public static function is_readable( $value ) { | 
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| 399 | |||
| 400 | /**  | 
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| 401 | * Checks if given value is editable.  | 
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| 402 | *  | 
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| 403 | * Value is considered editable if matches the editable whitelist.  | 
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| 404 | *  | 
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| 405 | * @since 2.2.4  | 
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| 406 | *  | 
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| 407 | * @param mixed $value Value to check.  | 
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| 408 | *  | 
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| 409 | * @return boolean Whether value is considered editable.  | 
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| 410 | */  | 
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| 411 | 	public static function is_editable( $value ) { | 
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| 417 | |||
| 418 | /**  | 
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| 419 | * Magic getter for our object.  | 
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| 420 | *  | 
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| 421 | * @param string $field  | 
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| 422 | * @throws Exception Throws an exception if the field is invalid.  | 
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| 423 | *  | 
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| 424 | * @return mixed  | 
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| 425 | */  | 
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| 426 | 	public function __get( $field ) { | 
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| 437 | |||
| 438 | }  | 
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| 439 | 
You can fix this by adding a namespace to your class:
When choosing a vendor namespace, try to pick something that is not too generic to avoid conflicts with other libraries.