Object Calisthenics

Object Calisthenics
9 steps to better software design today, by Jeff Bay
By: Darwin
April 30, 2014

Before we start...
As developers we all are aware of the core concepts that make up good OO code…
cohesion, loose coupling, no redundancy, encapsulation,
testability, readability, maintainability, etc.
But the question is, are we really implementing these concepts properly in code?

Why does my
CODE suck?
Is it MAINTAINABLE? Is it READABLE?
Is it TESTABLE?Is it REUSABLE?
Let’s ask ourselves of the following...

And what does it have to do with good OO coding?
What is Object Calisthenics?
Object Calisthenics: 9 steps to better software design today, by Jeff Bay

Calisthenics ( cal·is·then·ics )
Definition :
Calisthenics are a form of dynamic exercise consisting of a variety of
simple, often rhythmical, movements, generally using minimal equipment or
apparatus.
Object Calisthenics
Definition :
A variety of simple, often rhythmical, exercises to achieve better OO
(Object Oriented) design and code quality.

1. One level of indentation per method
2. Don’t use the ELSE keyword
3. Wrap all primitives and Strings
4. First class collections
5. One -> per line
6. Don’t abbreviate
7. Keep all entities small
8. Limit the number of instance variables
in a class (max: 2~5)
9. Do use accessors (getters/setters)

OC #1
“Only one level of indentation per
method”

function validateProducts ($products) {
foreach ($products as $rawProduct) {
$fields = array_keys($rawProduct);
foreach ($requiredFields as $requiredField) {
if (!in_array($requiredField, $fields)) {
$valid = false;
}
}
}
}

OC #1: Only one level of indentation per method
• A giant method lacks cohesiveness.
• Try to ensure that each method does exactly one thing – one
control structure, or one block of statements, per method.
• Nested control structures in a method, works at multiple levels of
abstraction which means it does more than one thing.

Basically…
• Do one thing per method
• one control structure
• one block of statements
• Avoid nested control structures
• it means you are doing more than one thing

function validateProductList ( $products) {
$invalidProducts = array_filter($products, ‘isInvalidProduct’ );
return (count($invalidProducts ) === 0);
}
function isInvalidProduct ( $rawProduct) {
$requiredFields = array(‘price’, ‘name’, ‘description’, ‘type’);
$fields = array_keys($rawProduct);
$missingFields = array_diff($requiredFields , $fields);
return (count($missingFields ) > 0);
}
reusable method

Benefits…
• Cohesiveness
• Methods do only one thing
• Increases re-use

OC #2
“Do not use the ‘else‘ keyword”

if ($form->isValid) {
$repository = $this->getRepository( ‘MyBundle:Post’ );
if (!$repository->exists($entity)) {
$repository->save($entity);
return $this->redirect(‘create_ok’);
} else {
$error = “Post Title already exists” ;
return array(‘form’ => $form, ‘error’ => $error);
}
} else {
$error = “Invalid fields” ;
return array(‘form’ => $form, ‘error’ => $error);
}
ELSE

OC #2: Do not use the ‘else’ keyword
• Conditionals are also a frequent source of duplication.
if (status == ‘DONE’) {
doSomething();
} else {
…
}

Basically…
• Nested conditionals & long case statements
• hard to follow
• Frequent source of code duplication

$repository = $this->getRepository( ‘MyBundle:Post’ );
if (!$form->isValid) {
return array(‘form’ => $form, ‘error’ => ‘Invalid fields’ );
}
if ($repository->exists($entity)) {
return array(‘form’ => $form, ‘error’ => ‘Post Title already exists’ );
}
$repository->save($entity);
return $this->redirect(‘create_ok’);
early return

Benefits…
• Helps avoid code duplication
• Makes code clearer, easier to read

OC #3
“Wrap all primitive types and strings, if
it has behavior”

class UIComponent
{
//...
public function repaint($animate = true) {
//...
}
}
//...
$component->repaint(false);
unclear operation

OC #3: Wrap all primitive types and strings, if it has behavior
• To give the programmer additional information about what the
value is and why it is being used
• This rule tries to encapsulate all the primitives within objects for
these to work in all our code in an OO-way.

class UIComponent
{
//...
public function repaint(Animate $animate) {
//...
}
}
class Animate
{
public $animate
public function __construct( $animate = true) {
$this->animate = $animate;
}
}
//...
$component->repaint(new Animate(false));
This can now
encapsulate all
animation related
operations

<?php
class IntegerNumber
{
private $number;
public function __construct($number)
{
$this->number = $number;
}
//...
}
An example of how we
can wrap the int
primitive.

<?php
class Item
{
final public static function find(Id $id)
{
// do find...
}
final public static function create(Id $id, array $data)
{
// do create...
}
}
$id is now
guaranteed
to be valid.
$id is now
guaranteed
to be valid.

Benefits…
• More maintainable code
• Helps identify what should be an Object
• Type hinting
• Encapsulation of operations
• Context of value is more obvious

OC #4
“Use first class collections”

$collection->getIterator();
$collection->filter(...);
$collection->append(...);
$collection->map(...);

OC #4: Use first class collections
• Any class that contains a collection should contain no other
member variables.
• Each collection gets wrapped in its own class. So now, behaviors
related to the collection have a home.
• Class will contain related behaviors.

class Items
{
private $item = [];
public function add(Item $item, array $data)
{
// do add...
}
public function filter(array $filters)
{
// do filter...
}
}

Benefits…
• Implements collection operations
• Uses SPL interfaces

OC #5
“Only one -> per line”

$this->base_url = $this->CI->config->site_url().’/’.$this->CI->uri->segment(1).$this->CI->uri-
>slash_segment(2, ‘both’);
$this->base_uri = $this->CI->uri->segment(1).$this->CI->uri->slash_segment(2, ‘leading’);
$this->base_uri = $this->getCI()->getUriBuilder()->getBaseUri(‘leading’);
Move everything to uri object
no whitespace
properties are harder to mock

$this->manager->getConfig()->getSegment()->setName(‘foo’);
properties are harder to mock
previous call could return NULL

OC #5: Only one -> per line
• An object should not deal with two other objects at once

Basically…
• Multiple ->
• indicate misplaced responsibilities
• violate encapsulation
• Law of Demeter
• “Talk only to your friends”

Benefits…
• Readability
• Easier Mocking
• Easier to Debug

OC #6
“Do NOT abbreviate”

if ($sx >= $sy) {
if ($sx > $strSysMatImgW ) {
//…
}
if ($ny > $strSysMatImgH ) {
//…
}
} else {
if ($sy > $strSysMatImgH ) {
//…
}
if ($nx > $strSysMatImgW ) {
//…
}
}
?
?
?
?

OC #6: Do NOT abbreviate
• Abbreviations can be confusing, and they tend to hide larger
problems.
• Keep class and method names to 1-2 words, and avoid names that
duplicate the context.

Basically…
• Keep names to one-two words
• class names
• method names
• entities

function getPage($data) { ... }
function startProcess() { ... }
$tr->process(“site.login”);
Use a thesaurus: fork,
create, begin, open
Easy understanding,
complete scope:
$translatorService
Use clearer names:
fetchPage()
downloadPage()
get from where?
table row?

Benefits…
• Clearer communication
• Indicates underlying problems

OC #7
“Keep all entities small”

OC #7: Keep classes small
• 200 lines per class (including docblocks)
• 15 - 20 lines per method
• 10 methods per class
• 15 classes per namespace (package or folder)

Benefits…
• Easier to grasp quickly
• Single responsibility
• Objective method
• Slimmer namespaces
• Less clunky folders

OC #8
“Limit the number of instance variables
in a class (max: 2 5)”

class Client
{
private $_adapter;
private $_cache;
private $_logger;
//...
}
Limit: 2 - 5

Benefits…
• Shorter dependency list
• Better understanding of commonality

OC #9
“Do not use accessors (getter/setter)”

class Tally
{
public $total = 0;
public function add($amount)
{
$this->total += $amount;
}
}
$tally = new Tally();
$tally->add(1);
// some other code...
$tally->total = -1;
// some other code...
$tally->add(1);
echo $tally->total . PHP_EOL
$total can be changed without
this instance knowing
causes unexpected results

class Tally
{
private $total = 0;
public function add($amount)
{
$this->total += $amount;
}
public function getTotal()
{
return $this->total;
}
}
$tally = new Tally();
$tally->add(1);
$tally->add(1);
echo $tally->getTotal() . PHP_EOL
total cannot be “reset”
no unexpected results

Benefits…
• Injector operations
• Encapsulation of transformations

1. “Only one level of indentation per method”
2. “Do not use the ‘else‘ keyword”
3. “Wrap all primitive types and strings, if it has behavior”
4. “Use first class collections”
5. “Only one -> per line”
6. “Do NOT abbreviate”
7. “Keep all entities small”
8. “Limit the number of instance variables in a class (max: 2 5)”
9. “Do not use accessors (getter/setter)”
The Recap...

• To visualize and implement the holy grail of object oriented
programming – encapsulation of data
• To use polymorphism appropriately
• To encourage concise and straightforward naming standards
• To craft code that has no duplication in code or idea
The Aim...

• http://www.bennadel.com/resources/uploads/2012/ObjectCalisthenics.pdf
• http://www.slideshare.net/rdohms/your-code-sucks-lets-fix-it
• http://www.slideshare.net/chadwick0678/getting-your-code-into-shape-with-object
References

Object Calisthenics

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