Complex classes like AbstractCollection 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 AbstractCollection, and based on these observations, apply Extract Interface, too.
| 1 | <?php  | 
            ||
| 11 | abstract class AbstractCollection implements Collection { | 
            ||
| 12 | |||
| 13 | protected $collection = [];  | 
            ||
| 14 | |||
| 15 | 5 | 	public function contains($element) { | 
            |
| 18 | |||
| 19 | 40 | 	public function size() { | 
            |
| 22 | |||
| 23 | 1 | 	public function isEmpty() { | 
            |
| 26 | |||
| 27 | 4 | 	public function clear() { | 
            |
| 30 | |||
| 31 | 25 | 	public function toArray() { | 
            |
| 34 | |||
| 35 | /**  | 
            ||
| 36 | * Applies the callback to the elements  | 
            ||
| 37 | *  | 
            ||
| 38 | * @param callable $callback the applied callback function  | 
            ||
| 39 | * @return static  | 
            ||
| 40 | */  | 
            ||
| 41 | 9 | 	public function map(callable $callback) { | 
            |
| 44 | |||
| 45 | /**  | 
            ||
| 46 | * Filters elements using a callback function  | 
            ||
| 47 | *  | 
            ||
| 48 | * @param callable $callback the filter function  | 
            ||
| 49 | * @return static  | 
            ||
| 50 | */  | 
            ||
| 51 | 3 | 	public function filter(callable $callback) { | 
            |
| 54 | |||
| 55 | /**  | 
            ||
| 56 | * Tests whether all elements in the collection pass the test implemented by the provided function.  | 
            ||
| 57 | *  | 
            ||
| 58 | * Returns <code>true</code> for an empty collection.  | 
            ||
| 59 | *  | 
            ||
| 60 | * @param callable $callback  | 
            ||
| 61 | * @return boolean  | 
            ||
| 62 | */  | 
            ||
| 63 | 1 | 	public function every(callable $callback) { | 
            |
| 71 | |||
| 72 | /**  | 
            ||
| 73 | * Tests whether at least one element in the collection passes the test implemented by the provided function.  | 
            ||
| 74 | *  | 
            ||
| 75 | * Returns <code>false</code> for an empty collection.  | 
            ||
| 76 | *  | 
            ||
| 77 | * @param callable $callback  | 
            ||
| 78 | * @return boolean  | 
            ||
| 79 | */  | 
            ||
| 80 | 1 | 	public function some(callable $callback) { | 
            |
| 88 | |||
| 89 | /**  | 
            ||
| 90 | * Searches the collection for query using the callback function on each element  | 
            ||
| 91 | *  | 
            ||
| 92 | * The callback function takes one or two parameters:  | 
            ||
| 93 | *  | 
            ||
| 94 | 	 *     function ($element [, $query]) {} | 
            ||
| 95 | *  | 
            ||
| 96 | * The callback must return a boolean  | 
            ||
| 97 | *  | 
            ||
| 98 | * @param mixed $query (optional)  | 
            ||
| 99 | * @param callable $callback  | 
            ||
| 100 | * @return boolean  | 
            ||
| 101 | */  | 
            ||
| 102 | 1 | 	public function search() { | 
            |
| 119 | |||
| 120 | /**  | 
            ||
| 121 | * Searches the collection with a given callback and returns the first element if found.  | 
            ||
| 122 | *  | 
            ||
| 123 | * The callback function takes one or two parameters:  | 
            ||
| 124 | *  | 
            ||
| 125 | 	 *     function ($element [, $query]) {} | 
            ||
| 126 | *  | 
            ||
| 127 | * The callback must return a boolean  | 
            ||
| 128 | *  | 
            ||
| 129 | * @param mixed $query OPTIONAL the provided query  | 
            ||
| 130 | * @param callable $callback the callback function  | 
            ||
| 131 | * @return mixed|null the found element or null if it hasn't been found  | 
            ||
| 132 | */  | 
            ||
| 133 | 2 | 	public function find() { | 
            |
| 151 | |||
| 152 | /**  | 
            ||
| 153 | * Searches the collection with a given callback and returns the last element if found.  | 
            ||
| 154 | *  | 
            ||
| 155 | * The callback function takes one or two parameters:  | 
            ||
| 156 | *  | 
            ||
| 157 | 	 *     function ($element [, $query]) {} | 
            ||
| 158 | *  | 
            ||
| 159 | * The callback must return a boolean  | 
            ||
| 160 | *  | 
            ||
| 161 | * @param mixed $query OPTIONAL the provided query  | 
            ||
| 162 | * @param callable $callback the callback function  | 
            ||
| 163 | * @return mixed|null the found element or null if it hasn't been found  | 
            ||
| 164 | */  | 
            ||
| 165 | 2 | 	public function findLast() { | 
            |
| 184 | |||
| 185 | /**  | 
            ||
| 186 | * Searches the collection with a given callback and returns all matching elements.  | 
            ||
| 187 | *  | 
            ||
| 188 | * The callback function takes one or two parameters:  | 
            ||
| 189 | *  | 
            ||
| 190 | 	 *     function ($element [, $query]) {} | 
            ||
| 191 | *  | 
            ||
| 192 | * The callback must return a boolean  | 
            ||
| 193 | *  | 
            ||
| 194 | * @param mixed $query OPTIONAL the provided query  | 
            ||
| 195 | * @param callable $callback the callback function  | 
            ||
| 196 | * @return mixed|null the found element or null if it hasn't been found  | 
            ||
| 197 | */  | 
            ||
| 198 | 1 | 	public function findAll() { | 
            |
| 217 | |||
| 218 | /**  | 
            ||
| 219 | * Internal sort function  | 
            ||
| 220 | *  | 
            ||
| 221 | * @param array $collection the collection on which is operated on  | 
            ||
| 222 | * @param Comparator|callable|null $cmp the compare function  | 
            ||
| 223 | * @param callable $usort the sort function for user passed $cmd  | 
            ||
| 224 | * @param callable $sort the default sort function  | 
            ||
| 225 | */  | 
            ||
| 226 | 3 | 	protected function doSort(&$collection, $cmp, callable $usort, callable $sort) { | 
            |
| 237 | |||
| 238 | /**  | 
            ||
| 239 | * @internal  | 
            ||
| 240 | */  | 
            ||
| 241 | 4 | 	public function rewind() { | 
            |
| 244 | |||
| 245 | /**  | 
            ||
| 246 | * @internal  | 
            ||
| 247 | */  | 
            ||
| 248 | 4 | 	public function current() { | 
            |
| 251 | |||
| 252 | /**  | 
            ||
| 253 | * @internal  | 
            ||
| 254 | */  | 
            ||
| 255 | 1 | 	public function key() { | 
            |
| 258 | |||
| 259 | /**  | 
            ||
| 260 | * @internal  | 
            ||
| 261 | */  | 
            ||
| 262 | 4 | 	public function next() { | 
            |
| 265 | |||
| 266 | /**  | 
            ||
| 267 | * @internal  | 
            ||
| 268 | */  | 
            ||
| 269 | 4 | 	public function valid() { | 
            |
| 272 | |||
| 273 | /**  | 
            ||
| 274 | * @internal  | 
            ||
| 275 | */  | 
            ||
| 276 | 5 | 	public function __clone() { | 
            |
| 279 | |||
| 280 | }  |