This document discusses the principles of "Object Calisthenics", which are nine rules of thumb for writing better object-oriented code. The rules focus on ideas like reducing indentation levels, avoiding else keywords, wrapping primitive types, keeping collections as first-class objects, limiting dots/arrows per line, avoiding abbreviations, keeping entities small, limiting instance variables per class, and avoiding getters/setters. Following these rules aims to improve code qualities like cohesion, loose coupling, readability and testability. The document provides examples of refactoring code according to these principles.

1. Writing better
code with
Object Calisthenics
Lucas Arruda
lucas@ciandt.com
github.com/larruda
Adapted from Jeff Bay’s paper from
“The ThoughtWorks Anthology”
and Guilherme Blanco’s presentation.

2. Calis...what?!

4. 7 code qualities
cohesion
loose coupling
no redundancy
encapsulation
testability
readability
focus

5. 9
rules of thumb

6. 1. One level of indentation per method
class Board {
...
String board() {
StringBuffer buf = new StringBuffer();
for (int i = 0; i < 10; i++) {
for (int j = 0; j < 10; j++)
buf.append(data[i][j]);
buf.append(“n”);
}
return buf.toString();
}
}

7. 1. One level of indentation per method
class Board {
...
String Board() {
StringBuffer buf = new StringBuffer();
collectRows(buf);
return buf.toString();
}
void collectRows(StringBuffer buf) {
for (int i = 0; i < 10; i++)
collectRow(buf, i);
}
void collectRow(StringBuffer buf, int row) {
for (int i = 0; i < 10; i++)
Buf.append(data[row][i]);
buf.append(“n”);
}
}

8. 1. One level of indentation per method
public function validateForm($filters='', $validators='', $options='')
{
$data = $_POST;
$input = new Zend_Filter_Input($filters, $validators, $data);
$input->setDefaultEscapeFilter(new Zend_Filter_StringTrim());
if ($input->hasInvalid() || $input->hasMissing()) {
foreach ($input->getMessages() as $field => $messageList) {
foreach ($messageList as $message) {
if (strpos($message, "empty")) {
throw new Tss_FormException(
"The field {$field} cannot be empty!",
3, 'javascript:history.back();'
);
} else {
throw new Tss_FormException(
"{$message}", 3, 'javascript:history.back();'
);
}
}
}
}
return $input;
}

9. 1. One level of indentation per method
public function validateForm($filters='', $validators='', $options='')
{
$data = $_POST;
$input = new Zend_Filter_Input($filters, $validators, $data);
$input->setDefaultEscapeFilter(new Zend_Filter_StringTrim());
if ( ! ($input->hasInvalid() || $input->hasMissing())) {
return $input;
}
foreach ($input->getMessages() as $field => $messageList) {
foreach ($messageList as $message) {
if (strpos($message, "empty")) {
throw new Tss_FormException(
"The field {$field} cannot be empty!",
3, 'javascript:history.back();'
);
} else {
throw new Tss_FormException(
"{$message}", 3, 'javascript:history.back();'
);
}
}
}
}

10. 1. One level of indentation per method
public function validateForm($filters='', $validators='', ...
{
$data = $_POST;
$input = new Zend_Filter_Input ($filters, $validators, $data);
$input->setDefaultEscapeFilter( new Zend_Filter_StringTrim ());
if ( ! ($input->hasInvalid() || $input->hasMissing())) {
return $input;
}
foreach ($input->getMessages() as $field => $messageList) {
foreach ($messageList as $message) {
$errorMessage = (strpos($message, "empty") === false)
? "The field {$field} cannot be empty!"
: "{$message}";
throw new Tss_FormException (
$errorMessage, 3, 'javascript:history.back();'
);
}
}
}

11. 1. One level of indentation per method
public function validateForm($filters='', $validators='', ...
{
$data = $_POST;
$input = new Zend_Filter_Input ($filters, $validators, $data);
$input->setDefaultEscapeFilter( new Zend_Filter_StringTrim ());
if ( ! ($input->hasInvalid() || $input->hasMissing())) {
return $input;
}
foreach ($input->getMessages() as $field => $messageList) {
$messageKey = key($message);
$message = $message[$messageKey];
$errorMessage = (strpos($message, "empty") === false)
? "The field {$field} cannot be empty!"
: "{$message}";
throw new Tss_FormException (
$errorMessage, 3, 'javascript:history.back();'
);
}
}

12. 2. Don’t use the ELSE keyword
if (status == DONE) {
doSomething();
} else {
…
}

13. YOU
MUST BE
JOKING!!!

14. 2. Don’t use the ELSE keyword
class Board {
...
String board(StringBuffer buf) {
if (buf.length()) {
return buf.toString();
}
else {
collectRows(buf);
return buf.toString();
}
}
...
}

15. 2. Don’t use the ELSE keyword
class Board {
...
String board(StringBuffer buf) {
if (!buf.length()) {
collectRows(buf);
}
return buf.toString();
}
...
}

16. 2. Don’t use the ELSE keyword
function login() {
$login = $this->input->post('email', true);
$password = $this->input->post('password', true);
$reference = $this->input->post('reference', true);
if ($this->clients_model->login($login, $password)) {
redirect( $reference);
} else {
$this->session->set_flashdata(
'error' , 'User or password invalid.'
);
$this->session->set_flashdata( 'reference', $reference);
redirect( 'clients');
}
}

17. 2. Don’t use the ELSE keyword
function login() {
$login = $this->input->post('email', true);
$password = $this->input->post('password', true);
$reference = $this->input->post('reference', true);
if (!$this->clients_model->login($login, $password)) {
$this->session->set_flashdata(
'error' , 'User or password invalid.'
);
$this->session->set_flashdata( 'reference', $reference);
$reference = 'clients';
}
redirect($reference);
}

18. 3. Wrap all primitives and Strings

19. If the primitive type has a behavior it
should be encapsulated

20. 3. Wrap all primitives and Strings
class UIComponent
{
// ...
public function repaint($animate = true)
{
// …
}
// ...
$component->repaint(false);
}

21. 3. Wrap all primitives and Strings
class UIComponent
{
// ...
public function repaint(Animate $animate)
{
// ...
}
}
class Animate
{
public $animate;
public function __construct($animate = true)
{
$this->animate = $animate;
}
}
// ...
$component->repaint(new Animate(false));

22. 4. First class collections
Any class that contains a collection/array
should not contain any other member
variables
Java Collections follow this rule

23. 4. First class collections
Transversable
Countable
Iterator
Filtering
Mapping
Combining

24. 5. One dot/arrow per line
Sign of misplaced responsibilities
The Law of Demeter
“Only talk to your friends”

25. 5. One dot/arrow per line
class Board {
...
class Piece {
...
String representation;
}
class Location {
...
Piece current;
}
String boardRepresentation () {
StringBuffer buf = new StringBuffer();
for (Location l: squares())
buf .append(l.current.representation .substring(0,
1));
return buf.toString();
}
}

26. 5. One dot/arrow per line
class Board {
...
class Piece {
...
private String representation;
String character() {
return representation.substring(0, 1);
}
void addTo(StringBuffer buf) {
buf.append(character());
}
}
class Location {
...
private Piece current;
void addTo(StringBuffer buf) {
current.addTo(buf);
}
}
String boardRepresentation() {
StringBuffer buf = new StringBuffer();
for (Location l: squares())
l.addTo(buf);
return buf.toString();
}
}

27. 6. Don’t abbreviate
Are you writing the same name repeatedly?
method being used multiple times
sign of code duplication
Is the method name too long?
class with multiple responsibilities
missing additional class
redundancy

28. 7. Keep all entities small
Java
No class over 50 lines
No packages over 10 files
PHP
No class over 100 lines
No packages over 15 files
Packages, like classes, should be
cohesive and have a purpose

29. 8. No classes with more than two/five instance variables
Improve cohesion
Split on more entities

30. 9. No getters/setters/properties
Improve encapsulation
“Tell, don’t ask”

31. Q&A
ciandt.com
http://www.cs.helsinki.fi/u/luontola/tdd-2009/ext/ObjectCalisthenics.pdf
http://www.slideshare.net/guilhermeblanco/object-calisthenics-applied-to-php
https://www.youtube.com/watch?v=ftBUHrxfOcc

32. THANKS
FOR
BEING
HERE!

33. ciandt.com
lunascar@gmail.com
@lunascarruda
google.com/+LucasArruda
fb.com/lucasnarruda
linkedin.com/in/larruda
github.com/larruda
coderbits.com/larruda
drupal.org/user/1009514