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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Object Calisthenics</title>
<link rel="stylesheet" href="reveal.js/css/reveal.css">
<link rel="stylesheet" href="reveal.js/css/theme/black.css" id="theme">
<link rel="stylesheet" href="reveal.js/lib/css/zenburn.css">
<link rel="stylesheet" href="css/font-awesome.min.css">
<link rel="stylesheet" href="css/custom.css">
<!-- Printing and PDF exports -->
<script>
var link = document.createElement( 'link' );
link.rel = 'stylesheet';
link.type = 'text/css';
link.href = window.location.search.match( /print-pdf/gi ) ? 'reveal.js/css/print/pdf.css' : 'reveal.js/css/print/paper.css';
document.getElementsByTagName( 'head' )[0].appendChild( link );
</script>
</head>
<body>
<div class="reveal">
<div class="slides">
<section>
<section>
<h3 class="top-2">Make your code great again with the</h3>
<h2>Object Calisthenics</h2>
<p class="me">Maxence POUTORD</p>
<p class="me-link">
<a href="https://twitter.com/_maxpou"><i class="fa fa-twitter"></i> @_maxpou</a> |
<a href="http://www.maxpou.fr/"><i class="fa fa-globe"></i> maxpou.fr</a> |
<a href="mailto:[email protected]"><i class="fa fa-envelope-o"></i> [email protected]</a>
</p>
</section>
</section>
<section>
<section>
<h2 class="top-1">Object Calisthenics?</h2>
<blockquote>
Cal • is • then • ics - /ˌkaləsˈTHeniks/
</blockquote>
<ul>
<li class="fragment" data-fragment-index="0">Object: OOP context</li>
<li class="fragment" data-fragment-index="1">Calisthenics: gymnastics context</li>
</ul>
<br>
<img data-src="img/gym.gif" class="fragment" data-fragment-index="1" style="border:none;width: 25%;">
</section>
<section>
<h2 class="top-1">Object Calisthenics</h2>
<p>In the ThoughtWorks Anthology, Jeff Bay, list 9 rules for writing <b>better Object Oriented code</b>.</p>
<img data-src="img/thoughtWorks-anthology.jpg" style="border:none;width: 25%;">
</section>
<section>
<h2 class="top-1">Motivation</h2>
<p>readability, maintainability, testability, and comprehensibility</p>
<img data-src="img/super_elk.gif" style="border:none;">
<p>...make your OO code great again!</p>
</section>
<aside class="notes">
and velocity
</aside>
</section>
<!-- STEP 1 -->
<section>
<section>
<h2 class="top-3">#1: One level of indentation<br> per method</h2>
</section>
<section>
<img data-src="img/indent-power.jpeg" style="border:none;width: 80%;">
</section>
<section>
<h2>Code (re)organisation:<br> Early return</h2>
<pre class="fragment push" data-fragment-index="0"><code class="php" data-trim>
public someFunction(someParameter)
{
if (firstCondition) {
if (secondCondition) {
// Do Something
// Do Something
// Do Something
}
}
}
</code></pre>
<pre class="fragment push" data-fragment-index="1"><code class="php" data-trim>
public someFunction(someParameter)
{
if (!firstCondition) {
return;
}
if (secondCondition) {
// Do Something
// Do Something
// Do Something
}
}
</code></pre>
<pre class="fragment push" data-fragment-index="2"><code class="php" data-trim>
public someFunction(someParameter)
{
if (!firstCondition) {
return;
}
if (!secondCondition) {
return;
}
// Do Something
// Do Something
// Do Something
}
</code></pre>
<br>
<p class="fragment" data-fragment-index="2">
"Single Entry, Single Exit"...?
</p>
<p class="fragment" data-fragment-index="3">
"Single Entry, Single Exit" <i class="fa fa-arrow-right" aria-hidden="true"></i> was written for assembly languages like Fortran/COBOL
</p>
<aside class="notes">
<a href="http://programmers.stackexchange.com/questions/118703/where-did-the-notion-of-one-return-only-come-from">More reading</a>
</aside>
</section>
<section>
<h2>Too much indentation level with loop?</h2>
<p class="fragment" data-fragment-index="0">
You may need to split your code into multiple functions.<br> This is the <a href="http://refactoring.com/catalog/extractMethod.html">Extract Method</a> (cf. Martin Fowler).
</p>
<pre class="fragment push" data-fragment-index="0"><code class="php" data-trim>
//Class Command
public function validateProductList(array $products): array
{
$validProducts[];
foreach ($products as $product)
{
if (!$product->price > 0 && length($product->name)) {
$validProducts[] = $product;
}
}
return $validProducts;
}
</code></pre>
<pre class="fragment push" data-fragment-index="1"><code class="php" data-trim>
//Class Command
public function validateProductList(array $products): array
{
return array_filter($products, 'isValidProduct');
}
public function isValidProduct(Product $product): boolean
{
if (!$product->price > 0 && length($product->name)) {
return true;
}
return false;
}
</code></pre>
</section>
<section>
<h2 class="top-2">Remove useless checks</h2>
<pre class="fragment push" data-fragment-index="0"><code class="php" data-noescape data-trim>
function foo($products)
{
if (isset($products) && count($products)) {
foreach ($products as $product) {
# code
}
}
}
</code></pre>
<pre class="fragment push" data-fragment-index="1"><code class="php" data-noescape data-trim>
function foo($products)
{
<mark>if (isset($products) && count($products)) {</mark>
foreach ($products as $product) {
# code
}
<mark>}</mark>
}
</code></pre>
<pre class="fragment push" data-fragment-index="2"><code class="php" data-noescape data-trim>
function foo($products)
{
foreach ($products as $product) {
# code
}
}
</code></pre>
</section>
<section>
<h2 class="top-2">Benefits</h2>
<ul>
<li>Easier to read</li>
<li>Reduce cyclomatic complexity</li>
<li>Respect KISS principle</li>
<li>Single Responsability Principle ("S" in SOLID)</li>
</ul>
</section>
</section>
<!-- STEP 2 -->
<section>
<section>
<h2 class="top-3">#2: Don’t use the ELSE keyword</h2>
</section>
<section>
<h2 class="top-1">Code (re)organisation</h2>
<pre class="fragment push" data-fragment-index="0"><code class="php" data-trim>
public function login($username, $password)
{
if ($this->isValid($username, $password)) {
redirect("homepage");
} else {
addFlash("error", "Bad credentials");
redirect("login");
}
}
</code></pre>
<pre class="fragment push" data-fragment-index="1"><code class="php" data-trim>
public function login($username, $password)
{
if ($this->isValid($username, $password)) {
return redirect("homepage");
} else {
addFlash("error", "Bad credentials");
return redirect("login");
}
}
</code></pre>
<pre class="fragment push" data-fragment-index="2"><code class="php" data-trim>
public function login($username, $password)
{
// defensive approach
if ($this->isValid($username, $password)) {
return redirect("homepage");
}
addFlash("error", "Bad credentials");
return redirect("login");
}
</code></pre>
<pre class="fragment push" data-fragment-index="3"><code class="php" data-trim>
public function login($username, $password)
{
// optimistic approach
if (!$this->isValid($username, $password)) {
addFlash("error", "Bad credentials");
return redirect("login");
}
return redirect("homepage");
}
</code></pre>
</section>
<section>
<h2 class="top-2">Not enough?</h2>
<ul>
<li>State Pattern</li>
<li>Strategy Pattern</li>
<li>NullObject Pattern</li>
<li>...</li>
</ul>
</section>
<section>
<h2 class="top-2">Benefits</h2>
<ul>
<li>Easier to read</li>
<li>Reduce cyclomatic complexity</li>
</ul>
</section>
</section>
<!-- STEP 3 -->
<section>
<section>
<h2 class="top-3">#3: Wrap all primitives and Strings</h2>
</section>
<section>
<h2>Example</h2>
<pre class="sticky"><code class="php" data-trim>
class User
{
/** @var string */
private $name;
/** @var string */
private $email;
public function __construct(string $name, string $email)
{
$this->name = $name;
$this->email = $email;
}
}
</code><code class="php fragment" data-trim>
//this is ok
$myUser = new User("John", "[email protected]");
</code><code class="php fragment" data-trim>
//this is ok
$anotherUser = new User("Max", "0811223344");
</code><code class="php fragment" data-trim>
//this is ok
$whoeverUser = new User("Louise", "Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.");
</code><code class="php fragment" data-trim>
//this is ok
$whoeverUserBis = new User("Lucie", "打才我醫集老電了快洋，西足並良步細主！");
</code></pre>
</section>
<section>
<h2>Proposition - Value Object</h2>
<pre class="sticky"><code class="php" data-trim>
class Email
{
/** @var string */
private $email;
public function __construct(string $email)
{
if (!filter_var($email, FILTER_VALIDATE_EMAIL) {
throw new InvalidArgumentException("Invalid format!");
}
$this->email = $email;
}
}
</code><code class="php fragment" data-trim>
// This is ok
$myUser = new User("John", new Email("[email protected]"));
</code><code class="php fragment" data-trim>
// This is NOT ok
$anotherUser = new User("Max", new Email("0811223344"));
</code><code class="php fragment" data-trim>
// This is NOT ok
$whoeverUser = new User("Louise", new Email("Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."));
</code><code class="php fragment" data-trim>
// This is NOT ok
$whoeverUserBis = new User("Lucie", new Email("打才我醫集老電了快洋，西足並良步細主！"));
</code></pre>
</section>
<section>
<h2 class="top-2">Should I wrap all primitives and strings?</h2>
<br>
<h2 class="fragment" style="color: red">NO!</h3>
</section>
<section>
<h2 class="top-1">Be pragmatic!</h2>
<h4>only wrap primitive with behaviour:</h4>
<ul>
<li>UUID</li>
<li>BIC, IBAN</li>
<li>email, URL</li>
<li>IP address</li>
<li>...</li>
</ul>
</section>
<section>
<h2>Stop abusing arrays!</h2>
<pre class="sticky fragment push" data-fragment-index="0"><code class="php" data-trim>
$command = array(
array(
"user" => array(
"id" => 42,
"name" => "Maxence",
"address" => "Dublin"
),
"date" => "1989-04-11 07:28:47",
"beers" => array(
array(
"ID" => "76b44e1a-a8d6-11e6-80f5-76304dec7eb7",
"name" => "Tripel Karmeliet",
"quantity" => 4,
),
array(
"ID" => "76b45220-a8d6-11e6-80f5-76304dec7eb7",
"name" => "Journeyman's Pale Ale",
"quantity" => 8,
),
array(
"ID" => "76b45356-a8d6-11e6-80f5-76304dec7eb7",
"name" => "Duvel tripel hop",
"quantity" => 15,
)
)
)
);
</code></pre>
<div class="fragment push" data-fragment-index="1">
<ul>
<li><a href="https://en.wikipedia.org/wiki/Big_ball_of_mud">Big ball of mud anti-pattern</a></li>
<li>No defined structure</li>
<li>Comprehension is time consuming</li>
<li>Needless complexity</li>
<li>Procedural programming is hard to scale</li>
</ul>
<pre><code class="php" data-trim>
foreach ($command["beers"] as $beer) {
if (isset($beer["quantity"])) {
$itemsCounter += $beer["quantity"];
}
}
// ...or
$itemsCounter = $command->countItems();
</code></pre>
</div>
<aside class="notes">
<a href="http://nomad.so/2014/06/stop-abusing-arrays-in-php/">stop abusing arrays in php</a>
</aside>
</section>
<section>
<h2 class="top-2">Benefits</h2>
<ul>
<li>Type hinting</li>
<li>Easier to reuse</li>
<li>Prevent code duplication</li>
</ul>
</section>
</section>
<!-- STEP 4 -->
<section>
<section>
<h2 class="top-3">#4: First class collections</h2>
</section>
<section>
<h2>Why?</h2>
<pre><code class="php" data-trim>
class Company
{
private $name;
private $employes;
# code
}
</code></pre>
<p class="fragment">Where can I put filters/contains/... methods?</p>
<pre class="fragment"><code class="php" data-trim>
class Team
{
private $name;
private $employes;
# code
}
</code></pre>
<p class="fragment"><i class="fa fa-arrow-right" aria-hidden="true"></i> 'employes' collection need to be wrapped in its own class</p>
</section>
<section>
<h2 class="top-1">Example</h2>
<pre><code class="php" data-trim>
class EmployeesCollection
{
private $employes;
public function add(Employe $employe) {/** ... **/};
public function remove(Employe $employe) {/** ... **/};
public function count() {/** ... **/};
public function filter(Closure $p): {/** ... **/};
//...
}
</code></pre>
</section>
<section>
<h2 class="top-2">Benefits</h2>
<ul>
<li>Readability</li>
<li>Easier to merge collection and not worry about member behaviour in them</li>
</ul>
</section>
</section>
<!-- STEP 5 -->
<section>
<section>
<h2 class="top-3">#5: One dot per line</h2>
<i>...or an arrow (->) if you use PHP!</i>
</section>
<section>
<h2 class="top-2">A.K.A. Law of Demeter (LoD)</h2>
<blockquote>
"Don't talk to strangers. Only talk to your immediate friends"
</blockquote>
</section>
<section>
<h2>What are strangers?</h2>
<pre><code class="php" data-trim>
$objectA->getObjectB()->getObjectC();
</code></pre>
<img src="img/lod.png" style="background-color:white;">
</section>
<section>
<h2 class="top-2">Example</h2>
<pre><code class="php" data-trim>
$objectA->getThis()->getThat()->getSomethingElse()->doSomething();
</code></pre>
<p><i class="fa fa-question-circle" aria-hidden="true"></i> What happen if getThat() return NULL?</p>
</section>
<!-- <section>
<blockquote style="margin-top: 20%;">
"you can play with your toys, with toys that you make, and with toys that someone gives you. You don’t ever, ever play with your toy’s toys."
<br> — Jeff BAY
</blockquote>
</section> -->
<section>
<h2 class="top-2">Benefits</h2>
<ul>
<li>Law of Demeter</li>
<li>Readability</li>
<li>Easier to debug</li>
</ul>
</section>
</section>
<!-- STEP 6 -->
<section>
<section>
<h2 class="top-3">#6: Don’t abbreviate</h2>
</section>
<section>
<h2 class="top-2">Why do you abbreviate?</h2>
<ul>
<li class="fragment">
It's repeated many times<br>
<i class="fa fa-exclamation-triangle" aria-hidden="true"></i> Code duplication
</li>
<li class="fragment">
The method name is too long <br>
<i class="fa fa-exclamation-triangle" aria-hidden="true"></i> Violates the Single Responsibility Principle
</li>
</ul>
</section>
<section>
<h2>1st SOLID Principle</h2>
<p><b>S</b> mean Single Responsibility Principle (SRP)</p>
<video src="img/fancy-beer.webm" id="main-video" autoplay="" loop=""></video>
</section>
<section>
<h2>Tips</h2>
<ul>
<li>Class and method names with 1-2 words</li>
<li>Be explicit! <br>
<i><i class="fa fa-exclamation-triangle" aria-hidden="true"></i> Wrong/non explicit names often leads to errors.</i>
</li>
<li>Naming is too hard? Ask yourself if this class/method/... make sense!</li>
</ul>
<blockquote>
There are only two hard things in Computer Science:<br> cache invalidation and naming things.
<br> — Phil Karlton
</blockquote>
</section>
<section>
<h2 class="top-2">It's all about reading!</h2>
<pre><code class="php" data-trim>
foreach ($users as $u) {
// code
// code
// code
// code
// code
$u->sendMail($aMail); // "$u": what does it stand for?
}
</code></pre>
</section>
<section>
<h2 class="top-2">Avoid tautologies</h2>
<pre><code class="php" data-trim>
class Manager
{
function perform()
{
// ...
}
}
</code></pre>
<p>You can also replace perform by <code>process()</code>...</p>
</section>
<section>
<h2>Ubiquitous Language<br>to the rescue!</h2>
<img data-src="img/stairs.gif" style="border:none;width: 80%;background-color: #FFF">
</section>
<section>
<h2 class="top-2">Benefits</h2>
<ul>
<li>Readability</li>
<li>Communication</li>
<li>Help to reveal underlying problems</li>
</ul>
</section>
</section>
<!-- STEP 7 -->
<section>
<section>
<h2 class="top-3">#7: Keep all entities small</h2>
</section>
<section>
<h2 class="top-2">Avoid God Object</h2>
<p><i> An object that knows too much or does too much</i></p>
</section>
<section>
<h2 class="top-3">Rule #7: Keep <u>everything</u> small</h2>
<br>
<blockquote cite="http://">
"Simplicity Comes from Reduction"
<br> — Paul W. Homer
</blockquote>
<aside class="notes">
simplicity is the ultimate sophistication
</aside>
</section>
<section>
<h2 class="top-1">Why?</h2>
<p>Long files are hard to:</p>
<ul>
<li>read</li>
<li>understand</li>
<li>maintain</li>
<li>reuse</li>
</ul>
</section>
<section>
<h2 class="top-2"><i class="fa fa-exclamation-triangle" aria-hidden="true"></i> Code Gravity <i class="fa fa-exclamation-triangle" aria-hidden="true"></i></h2>
<p><i>"big stuff attracts even more stuff and gets bigger"</i></p>
<p><i>≈ theory of the broken window</i></p>
</section>
<section>
<h2 class="top-2">Benefits</h2>
<ul>
<li>Easier to reuse</li>
<li>Better code segregation</li>
<li>Clear methods and their objectives</li>
<li>Single Responsability Principle ("S" in SOLID)</li>
</ul>
</section>
</section>
<!-- STEP 8 -->
<section>
<section>
<h2 class="top-3">#8: No classes with several instance variables</h2>
</section>
<section>
<h2 class="top-1">High cohesion, and better encapsulation</h2>
<p>Try to keep <s style="color:#FF5733">2</s> 5 instance variables (max)</p>
<pre><code class="php" data-trim>
class MyWonderfulService
{
private $anotherService;
private $logger;
private $translator;
private $entityService;
// code
}
</code></pre>
</section>
<section>
<h2 class="top-2">Benefits</h2>
<ul>
<li>Loose coupling / Easier to reuse</li>
<li>Better encapsulation</li>
<li>Short dependency list</li>
<li>Single Responsability Principle ("S" in SOLID)</li>
</ul>
</section>
</section>
<!-- STEP 9 -->
<section>
<section>
<h2 class="top-3">#9: No getters/setters/properties</h2>
<aside class="notes">
<ul>
<li>http://whitewashing.de/2012/08/22/building_an_object_model__no_setters_allowed.html</li>
</ul>
</aside>
</section>
<section>
<h2 class="top-2">Why do we use GETTER/SETTER so much?</h2>
<ul>
<li>Frameworks <i>(i.e. Symfony's entities)</i></li>
<li>IDE generate them automatically</li>
<li>We can change every properties we need<br> and also... we are lazy!</li>
</ul>
</section>
<section>
<h2 class="top-2">Tell, don’t ask principle</h2>
<blockquote cite="http://">
"Don't ask for the information you need to do the work; ask the object that has the information to do the work for you"
<br> — Allen Holub
</blockquote>
</section>
<section>
<h2>What is better?</h2>
<pre><code class="php" data-trim>
// Game
private $score;
public function setScore(int $score): void {
$this->score = $score;
}
public function getScore(): int {
return score;
}
// Usage
$game->setScore($game->getScore() + ENEMY_DESTROYED_SCORE);
</code></pre>
<pre class="fragment"><code class="php" data-trim>
// Game
public function addScore(int $delta): void {
this->score += $delta;
}
// Usage
$game->addScore(ENEMY_DESTROYED_SCORE);
</code></pre>
</section>
<section>
<h2>What is the difference between...</h2>
<div class="row">
<div class="col-md-6">
<pre><code class="php" data-trim>
class Employe
{
private $name;
public function getName() {
return $this->name;
}
public function setName($name) {
$this->name = $name;
return $this;
}
}
</code></pre>
</div>
<div class="col-md-6 fragment">
<pre><code class="php" data-trim>
class Employe
{
public $name;
}
</code></pre>
</div>
</div>
</section>
<section>
<h2 class="top-2">Benefits</h2>
<ul>
<li>Avoid to violate the <abbr title="open for extension, but closed for modification">Open/Closed principle</abbr> (the <b>O</b> in SOLID)</li>
<li>Easier to read</li>
</ul>
</section>
</section>
<section>
<img data-src="img/object-calisthenics.png" style="border:none;width: 80%;">
</section>
<section>
<section>
<h2 class="top-1">Reading</h2>
<ul>
<li><a href="http://code.joejag.com/2016/anti-if-the-missing-patterns.html">Anti-If: The missing patterns</a> by Joe Wright</li>
<li><a href="http://www.maxpou.fr/else-unnecessary-expression/">"Else": the unnecessary expression</a> by me :)</li>
<li><a href="http://www.yegor256.com/2014/09/16/getters-and-setters-are-evil.html">Getters/Setters. Evil. Period.</a> by Yegor Bugayenko</li>
<li><a href="http://williamdurand.fr/2013/06/03/object-calisthenics/">Object Calisthenics</a> by William Durand</li>
</ul>
</section>
<section>
<h2>Thank you</h2>
<h3>Questions?</h3>
<img data-src="img/question.gif" style="border:none;width: 40%;">
<br>
<a href="https://twitter.com/_maxpou"><i class="fa fa-twitter"></i> @_maxpou</a>
</section>
</section>
<section>
<section>
<h2 class="top-3">Backup slides</h2>
</section>
<section>
<h2 class="top-1">No classes with more than two instance variable</h2>
<img src="img/instance-variables.png" alt="">
</section>
<section>
<h2>Using / Personal POV</h2>
<table>
<tr>
<td>#1: One level of indentation</td><td><i class="fa fa-thumbs-o-up"></i><i class="fa fa-thumbs-o-up"></i><i class="fa fa-thumbs-o-up"></i></td>
</tr>
<tr>
<td>#2: Don’t use the ELSE keyword</td><td><i class="fa fa-thumbs-o-up"></i><i class="fa fa-thumbs-o-up"></i><i class="fa fa-thumbs-o-up"></i></td>
</tr>
<tr>
<td>#3: Wrap all primitives and Strings</td><td><i class="fa fa-thumbs-o-up"></i><i class="fa fa-thumbs-o-up"></i></td>
</tr>
<tr>
<td>#4: First class collections</td><td><i class="fa fa-thumbs-o-up"></i></td>
</tr>
<tr>
<td>#5: One dot per line</td><td><i class="fa fa-thumbs-o-up"></i></td>
</tr>
<tr>
<td>#6: Don’t abbreviate</td><td><i class="fa fa-thumbs-o-up"></i><i class="fa fa-thumbs-o-up"></i><i class="fa fa-thumbs-o-up"></i></td>
</tr>
<tr>
<td>#7: Keep all entities small</td><td><i class="fa fa-thumbs-o-up"></i><i class="fa fa-thumbs-o-up"></i></td>
</tr>
<tr>
<td>#8: No classes with several instance variables</td><td><i class="fa fa-thumbs-o-up"></i><i class="fa fa-thumbs-o-up"></i></td>
</tr>
<tr>
<td>#9: No getters/setters/properties</td><td><i class="fa fa-thumbs-o-up"></i></td>
</tr>
</table>
</section>
</section>
</div>
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