object calisthenics

Object Calisthenics9 steps to better software design today, by Jeff Bay

By: DarwinApril 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 myCODE 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 method2. Don’t use the ELSE keyword3. Wrap all primitives and Strings4. First class collections5. One -> per line6. Don’t abbreviate7. Keep all entities small8. 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

Education

better software design

method object calisthenics

thing object calisthenics

keyword object calisthenics

behavior object calisthenics

object calisthenics

reuse object calisthenics

return arrayform