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 2.2.0  | 
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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 2.2.0  | 
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| 27 | */  | 
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| 28 | const BASE = 'cmb2/v1';  | 
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| 29 | |||
| 30 | /**  | 
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| 31 | * @var CMB2 object  | 
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| 32 | * @since 2.2.0  | 
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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 2.2.0  | 
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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 2.2.0  | 
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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 writeable field objects.  | 
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| 51 | * @var CMB2_Field[]  | 
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| 52 | * @since 2.2.0  | 
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| 53 | */  | 
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| 54 | protected $write_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 readable via the rest api  | 
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| 64 | * @var boolean  | 
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| 65 | */  | 
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| 66 | protected $rest_write = false;  | 
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| 67 | |||
| 68 | /**  | 
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| 69 | * Constructor  | 
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| 70 | * @since 2.2.0  | 
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| 71 | * @param CMB2 $cmb The CMB2 object to be registered for the API.  | 
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| 72 | */  | 
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| 73 | 	public function __construct( CMB2 $cmb ) { | 
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| 81 | |||
| 82 | 	public function universal_hooks() { | 
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| 91 | |||
| 92 | 	public function init_routes() { | 
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| 101 | |||
| 102 | 	public static function register_appended_fields() { | 
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| 120 | |||
| 121 | 	protected function declare_read_write_fields() { | 
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| 139 | |||
| 140 | 	protected function can_read( $show_in_rest ) { | 
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| 145 | |||
| 146 | 	protected function can_write( $show_in_rest ) { | 
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| 151 | |||
| 152 | /**  | 
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| 153 | * Handler for getting custom field data.  | 
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| 154 | * @since 2.2.0  | 
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| 155 | * @param array $object The object from the response  | 
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| 156 | * @param string $field_id Name of field  | 
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| 157 | * @param WP_REST_Request $request Current request  | 
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| 158 | * @return mixed  | 
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| 159 | */  | 
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| 160 | 	public static function get_restable_field_values( $object, $field_id, $request ) { | 
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| 182 | |||
| 183 | /**  | 
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| 184 | * Handler for updating custom field data.  | 
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| 185 | * @since 2.2.0  | 
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| 186 | * @param mixed $value The value of the field  | 
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| 187 | * @param object $object The object from the response  | 
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| 188 | * @param string $field_id Name of field  | 
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| 189 | * @return bool|int  | 
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| 190 | */  | 
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| 191 | 	public static function update_restable_field_values( $values, $object, $field_id ) { | 
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| 217 | |||
| 218 | /**  | 
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| 219 | * Loop through box fields and sanitize the values.  | 
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| 220 | * @since 2.2.o  | 
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| 221 | * @param array $values Array of values being provided.  | 
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| 222 | * @return array Array of updated/sanitized values.  | 
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| 223 | */  | 
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| 224 | 	public function sanitize_box_values( array $values ) { | 
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| 237 | |||
| 238 | /**  | 
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| 239 | * Handles returning a sanitized field value.  | 
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| 240 | * @since 2.2.0  | 
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| 241 | * @param array $values Array of values being provided.  | 
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| 242 | * @param string $field_id The id of the field to update.  | 
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| 243 | * @return mixed The results of saving/sanitizing a field value.  | 
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| 244 | */  | 
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| 245 | 	protected function sanitize_field_value( array $values, $field_id ) { | 
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| 265 | |||
| 266 | /**  | 
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| 267 | * Handles returning a sanitized group field value.  | 
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| 268 | * @since 2.2.0  | 
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| 269 | * @param array $values Array of values being provided.  | 
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| 270 | * @param CMB2_Field $field CMB2_Field object.  | 
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| 271 | * @return mixed The results of saving/sanitizing the group field value.  | 
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| 272 | */  | 
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| 273 | 	protected function sanitize_group_value( array $values, CMB2_Field $field ) { | 
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| 283 | |||
| 284 | /**  | 
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| 285 | * Filter whether a meta key is protected.  | 
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| 286 | * @since 2.2.0  | 
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| 287 | * @param bool $protected Whether the key is protected. Default false.  | 
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| 288 | * @param string $meta_key Meta key.  | 
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| 289 | * @param string $meta_type Meta type.  | 
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| 290 | */  | 
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| 291 | 	public function is_protected_meta( $protected, $meta_key, $meta_type ) { | 
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| 298 | |||
| 299 | 	protected static function get_object_data( $object ) { | 
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| 321 | |||
| 322 | 	public function field_can_read( $field_id, $return_object = false ) { | 
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| 325 | |||
| 326 | 	public function field_can_write( $field_id, $return_object = false ) { | 
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| 329 | |||
| 330 | 	protected function field_can( $type = 'read_fields', $field_id, $return_object = false ) { | 
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| 337 | |||
| 338 | /**  | 
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| 339 | * Get an instance of this class by a CMB2 id  | 
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| 340 | *  | 
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| 341 | * @since 2.2.0  | 
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| 342 | *  | 
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| 343 | * @param string $cmb_id CMB2 config id  | 
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| 344 | *  | 
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| 345 | * @return CMB2_REST|false The CMB2_REST object or false.  | 
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| 346 | */  | 
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| 347 | 	public static function get_rest_box( $cmb_id ) { | 
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| 350 | |||
| 351 | /**  | 
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| 352 | * Magic getter for our object.  | 
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| 353 | * @param string $field  | 
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| 354 | * @throws Exception Throws an exception if the field is invalid.  | 
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| 355 | * @return mixed  | 
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| 356 | */  | 
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| 357 | 	public function __get( $field ) { | 
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| 368 | |||
| 369 | }  | 
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| 370 | 
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.