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:
| 1 | <?php // phpcs:ignore WordPress.Files.FileName.NotHyphenatedLowercase  | 
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| 19 | class ChangeEntry implements JsonSerializable { | 
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| 20 | |||
| 21 | /**  | 
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| 22 | * Entry significance.  | 
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| 23 | *  | 
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| 24 | * @var string|null  | 
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| 25 | */  | 
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| 26 | protected $significance = null;  | 
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| 27 | |||
| 28 | /**  | 
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| 29 | * Entry timestamp.  | 
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| 30 | *  | 
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| 31 | * @var DateTime  | 
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| 32 | */  | 
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| 33 | protected $timestamp;  | 
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| 34 | |||
| 35 | /**  | 
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| 36 | * Subheading the entry is under.  | 
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| 37 | *  | 
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| 38 | * @var string  | 
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| 39 | */  | 
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| 40 | protected $subheading = '';  | 
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| 41 | |||
| 42 | /**  | 
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| 43 | * Author of the entry.  | 
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| 44 | *  | 
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| 45 | * @var string  | 
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| 46 | */  | 
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| 47 | protected $author = '';  | 
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| 48 | |||
| 49 | /**  | 
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| 50 | * Content of the entry.  | 
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| 51 | *  | 
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| 52 | * @var string  | 
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| 53 | */  | 
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| 54 | protected $content = '';  | 
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| 55 | |||
| 56 | /**  | 
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| 57 | * Constructor.  | 
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| 58 | *  | 
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| 59 | * @param array $data Data for entry fields. Keys correspond to the setters, e.g. key 'content' calls `setContent()`.  | 
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| 60 | * @throws InvalidArgumentException If an argument is invalid.  | 
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| 61 | */  | 
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| 62 | View Code Duplication | 	public function __construct( array $data = array() ) { | 
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| 73 | |||
| 74 | /**  | 
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| 75 | * Compare two ChangeEntry objects.  | 
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| 76 | *  | 
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| 77 | * @param ChangeEntry $a First ChangeEntry.  | 
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| 78 | * @param ChangeEntry $b Second ChangeEntry.  | 
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| 79 | * @param array $config Comparison configuration. Keys are:  | 
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| 80 | * - ordering: (string[]) Order in which to consider the fields. Field  | 
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| 81 | * names correspond to getters, e.g. 'significance' =>  | 
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| 82 | * `getSignificance()`. Default ordering is subheading, content.  | 
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| 83 | * - knownSubheadings: (string[]) Change entries with these headings will  | 
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| 84 | * compare, in this order, after those with no subheading and before any  | 
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| 85 | * other subheadings.  | 
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| 86 | * @return int <0 if $a should come before $b, >0 if $b should come before $a, or 0 otherwise.  | 
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| 87 | * @throws InvalidArgumentException If an argument is invalid.  | 
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| 88 | */  | 
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| 89 | 	public static function compare( ChangeEntry $a, ChangeEntry $b, array $config = array() ) { | 
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| 117 | |||
| 118 | /**  | 
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| 119 | * Get the significance.  | 
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| 120 | *  | 
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| 121 | * @return string|null  | 
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| 122 | */  | 
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| 123 | 	public function getSignificance() { | 
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| 126 | |||
| 127 | /**  | 
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| 128 | * Set the significance.  | 
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| 129 | *  | 
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| 130 | * While entries coming in from users should always have a significance, we allow null here  | 
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| 131 | * because entries created programmatically, particularly when parsing an existing changelog,  | 
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| 132 | * may not include significance information.  | 
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| 133 | *  | 
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| 134 | * @param string|null $significance 'patch', 'minor', or 'major'.  | 
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| 135 | * @returns $this  | 
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| 136 | * @throws InvalidArgumentException If an argument is invalid.  | 
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| 137 | */  | 
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| 138 | 	public function setSignificance( $significance ) { | 
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| 145 | |||
| 146 | /**  | 
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| 147 | * Compare significance values.  | 
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| 148 | *  | 
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| 149 | * @param ChangeEntry $a First entry.  | 
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| 150 | * @param ChangeEntry $b Second entry.  | 
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| 151 | * @param array $config Passed from `compare()`, but unused here.  | 
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| 152 | * @return int  | 
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| 153 | */  | 
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| 154 | 	protected static function compareSignificance( ChangeEntry $a, ChangeEntry $b, array $config ) { // phpcs:ignore VariableAnalysis.CodeAnalysis.VariableAnalysis.UnusedVariable | 
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| 160 | |||
| 161 | /**  | 
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| 162 | * Get the timestamp.  | 
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| 163 | *  | 
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| 164 | * @return DateTime  | 
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| 165 | */  | 
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| 166 | 	public function getTimestamp() { | 
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| 169 | |||
| 170 | /**  | 
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| 171 | * Set the timestamp.  | 
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| 172 | *  | 
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| 173 | * @param DateTime|string $timestamp Timestamp to set.  | 
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| 174 | * @returns $this  | 
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| 175 | * @throws InvalidArgumentException If an argument is invalid.  | 
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| 176 | */  | 
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| 177 | View Code Duplication | 	public function setTimestamp( $timestamp ) { | 
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| 188 | |||
| 189 | /**  | 
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| 190 | * Compare timestamps.  | 
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| 191 | *  | 
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| 192 | * @param ChangeEntry $a First entry.  | 
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| 193 | * @param ChangeEntry $b Second entry.  | 
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| 194 | * @param array $config Passed from `compare()`, but unused here.  | 
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| 195 | * @return int  | 
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| 196 | */  | 
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| 197 | 	protected static function compareTimestamp( ChangeEntry $a, ChangeEntry $b, array $config ) { // phpcs:ignore VariableAnalysis.CodeAnalysis.VariableAnalysis.UnusedVariable | 
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| 202 | |||
| 203 | /**  | 
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| 204 | * Get the subheading.  | 
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| 205 | *  | 
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| 206 | * @return string  | 
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| 207 | */  | 
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| 208 | 	public function getSubheading() { | 
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| 211 | |||
| 212 | /**  | 
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| 213 | * Set the subheading.  | 
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| 214 | *  | 
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| 215 | * @param string $subheading Subheading to set.  | 
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| 216 | * @returns $this  | 
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| 217 | */  | 
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| 218 | 	public function setSubheading( $subheading ) { | 
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| 222 | |||
| 223 | /**  | 
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| 224 | * Compare subheadings.  | 
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| 225 | *  | 
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| 226 | * @param ChangeEntry $a First entry.  | 
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| 227 | * @param ChangeEntry $b Second entry.  | 
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| 228 | * @param array $config Passed from `compare()`, used for 'knownSubheadings'.  | 
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| 229 | * @return int  | 
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| 230 | */  | 
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| 231 | 	protected static function compareSubheading( ChangeEntry $a, ChangeEntry $b, array $config ) { | 
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| 262 | |||
| 263 | /**  | 
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| 264 | * Get the author.  | 
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| 265 | *  | 
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| 266 | * @return string  | 
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| 267 | */  | 
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| 268 | 	public function getAuthor() { | 
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| 271 | |||
| 272 | /**  | 
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| 273 | * Set the author.  | 
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| 274 | *  | 
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| 275 | * @param string $author Author to set.  | 
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| 276 | * @returns $this  | 
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| 277 | */  | 
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| 278 | 	public function setAuthor( $author ) { | 
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| 282 | |||
| 283 | /**  | 
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| 284 | * Get the content.  | 
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| 285 | *  | 
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| 286 | * @return string  | 
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| 287 | */  | 
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| 288 | 	public function getContent() { | 
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| 291 | |||
| 292 | /**  | 
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| 293 | * Set the content.  | 
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| 294 | *  | 
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| 295 | * @param string $content Content to set.  | 
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| 296 | * @returns $this  | 
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| 297 | */  | 
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| 298 | 	public function setContent( $content ) { | 
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| 302 | |||
| 303 | /**  | 
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| 304 | * Return data for serializing to JSON.  | 
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| 305 | *  | 
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| 306 | * @return array  | 
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| 307 | */  | 
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| 308 | 	public function jsonSerialize() { | 
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| 318 | |||
| 319 | /**  | 
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| 320 | * Unserialize from JSON.  | 
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| 321 | *  | 
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| 322 | * @param array $data JSON data as returned by self::jsonSerialize().  | 
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| 323 | * @return static  | 
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| 324 | * @throws InvalidArgumentException If the data is invalid.  | 
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| 325 | */  | 
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| 326 | 	public static function jsonUnserialize( $data ) { | 
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| 338 | |||
| 339 | }  | 
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| 340 |