The document discusses "Object Calisthenics", which are guidelines for writing object-oriented code that results in code that is more robust, maintainable and extensible. The guidelines include things like having only one level of indentation per method, wrapping primitives in objects, using first class collections, following the Law of Demeter, avoiding abbreviations, keeping classes small with only a few properties, and avoiding getters/setters in favor of methods. The overall goal is to create simple and well-structured object-oriented code through applying these types of guidelines.

1. PHP - Object Calisthenics

2. I am Giorgio Cefaro
I work as Lead Software Engineer in Hootsuite
You can find me at @giorrrgio
Hello!

3. “
Our code sucks!
let’s fix it!

4. Calisthenics
/ˌkalɪsˈθɛnɪks/
kalòs (καλός) good
sthénos (σθένος) strength

5. Calisthenics are
not rules

6. Code
class SpreadSheet
{
private $headers;
private $rows;
public function printCSV(string $endLine, string $separator): string {
$sheet = $this->headers . $endLine;
foreach ($this->rows as $row) {
foreach ($row as $cell) {
$sheet .= $cell->print() . $separator;
}
$sheet .= $endLine;
}
return $sheet;
}
}

7. Only one level of
indentation per line
1

8. Code
class SpreadSheet {
private $headers;
private $rows;
public function printCSV(string $endLine, string $separator): string {
return $this->headers . $endLine . $this->printRows();
}
private function printRows(string $endLine, string $separator): string {
$printed = '';
foreach ($this->rows as $row) {
$printed .= $this->printRow($row, $separator) . $endLine;
}
return $printed;
}
private function printRow(array $row, string $separator): string {
$printed = '';
foreach ($row as $cell) {
$printed .= $cell->print() . $separator;
}
return $printed;
}
}

9. Code
class SpreadSheet
{
public function isMultitab(): bool {
if (count($this->tabs) > 1) {
return true;
} else {
return false;
}
}
}

10. Don’t use the ELSE
keyword
2

11. Code
class SpreadSheet
{
public function isMultitab(): bool {
if (count($this->tabs) > 1) {
return true;
}
return false;
}
}

12. Code
class Task
{
/** @var int Task priority. */
private $priority;
public function isHighPriority(): bool {
return $this->priority > 9;
}
}

13. Wrap all primitives
and strings
3

14. Code
class Task
{
/** @var Priority Task priority. */
private $priority;
public function isHighPriority(): bool {
return $this->priority->isHigh();
}
}
class Priority
{
const PRIORITY_HIGH = 9;
/** @var int priority value. */
private $value;
public function isHigh(): bool {
return $this->value > self::PRIORITY_HIGH;
}
}

15. Code
class SpreadSheet
{
private $headers;
private $title;
private $rows;
public function __construct(
string $headers,
string $title,
array $rows) {
//[...]
}
public function addRow(Row $row) {
$this->rows[] = $row;
}
}

16. First class
collections
4

17. Code
class SpreadSheet
{
private $headers;
private $title;
private $rows;
public function __construct(string $headers, string $title, RowCollection $rows) {
//[...]
}
public function addRow(Row $row) {
$this->rows->add($row);
}
}
class RowCollection implements ArrayAccess
{
private $rows;
public function __construct(array $rows) {
$this->rows = $rows;
}
//[...]
}

18. Code
class SpreadSheet
{
private $user;
public function userCanUseSpreadsheet() {
return $this->user->getSettings()->canUseSpreadsheet();
}
}

19. One arrow per line5

20. ● Each unit should have only limited knowledge
about other units: only units "closely" related
to the current unit.
● Each unit should only talk to its friends; don't
talk to strangers.
● Only talk to your immediate friends.
Law of Demeter

21. Code
class SpreadSheet
{
private $user;
public function userCanUseSpreadsheet() {
return $this->user->canUseSpreadsheet();
}
}
class User
{
private $settings;
public function canUseSpreadsheet() {
return $this->settings->canUseSpreadsheet();
}
}

22. Don’t abbreviate6

23. Keep all entities
small
7

24. No classes with more than
two instance variables
8

25. “
Decomposing objects from a set of
attributes into a hierarchy of
collaborating objects, leads much
more directly to an effective object
model
https://github.com/TheLadders/object-calisthenics#rule-8-no-classes-with-more-than-two-instance-variables

26. Code
class User
{
private $firstname;
private $lastname;
public function getFirstname() {
return $this->firstname;
}
public function setFirstname($firstname) {
return $this->firstname = $firstname;
}
public function getLastname() {
return $this->lastname;
}
public function setLastname($lastname) {
return $this->lastname = $lastname;
}
}

27. No Getters
No Setters
No Properties
9

28. Code
class User
{
private $firstname;
private $lastname;
private function __constructor(string $firstname, string $lastname) {
$this->firstname = $firstname;
$this->lastname = $lastname;
}
public static function create(string $firstname, string $lastname): self {
return new self($firstname, $lastname);
}
public function toArray(): array {
return [
'firstname' => $firstname,
'lastname' => $lastname
];
}
}

29. Any questions ?
You can find me at
◉ @giorrrgio
Thanks!