Seven Steps to Better OOP Code

Seven Steps to Better OOP Code Stefan Priebsch, thePHP.cc php|tek 09, Chicago, IL, U.S.A.

Stefan Priebsch Co-Founder and Principal Consultant

Disclaimer

„ Hang the rules. They're more like guidelines anyway.“ --Elizabeth Swann, Pirates of the Caribbean

Is OOP slow?

The usual disclaimer for benchmarks applies! foo() 3.09 µsec Test::foo() 3.26 µsec $test->foo() 3.12 µsec $test = new Test(); $test->foo() 4.03 µsec

Wow, 25% slower!

Let us put 1 µsec into perspective

The usual disclaimer for benchmarks applies! print ~ 10 µsec file_get_contents() ~ 30 µsec mysql_connect() ~ 100 µsec HTTP GET Request ~ 35,000 µsec

Do not care about performance *

*Some restrictions may apply. #1

Use objects

Use more objects

class Something { protected $status = array(); public function run(...) { if (...) { … $this->status['fail'] = $e->getMessage(); } else { $this->status['skip'] = 'File is unavailable'; } return $this->status; } }

class Something { protected $status = array(); public function run(...) { if (...) { … return new FailResult($e->getMessage()); } else { return new SkipResult('File is unavailable'); } } }

class Result { protected $message; public function __construct($message) { $this->message = $message; } } class FailResult extends Result {} class SkipResult extends Result {}

What do you do for a living?

class Something { public function doManyThings() { … load data … … perform calculations … … render HTML output … … store calculation result ... } }

class Something { public function doManyThings() { $this->loadData(); $this->performCalculations(); $this->renderHtml(); $this->storeResult(); } protected function loadData() protected function performCalulations() protected function renderHtml() protected function storeResult() }

class DataLoader { public function loadData() } class Calculator { public function calculateResult() } class HtmlRenderer { public function render() } class StorageManager { public function storeResult() }

One class One responsibility

class DomainObject { protected function loadData() { $this->data = $this->db->query(...); } public function render() { $this->loadData(); return HtmlRenderer::createTable($this->data); } }

Let others do the work

class DomainObject { protected function loadData() { $this->data = $this->dataManager->query(...); } public function render() { $this->loadData(); $this->dataRenderer->renderTable($this->data); } }

Keep your secrets

class SomeDomainObject { public function doSomething($a, $b, $c) { … return new SomeResult($x, $y, $z); } }

Keep objects dumb

class SomeDataProcessor { public function process($filename) { … $data = file_get_contents($filename); … } }

class SomeDataProcessor { public function process($data) { … } }

Do not talk to strangers

class MeMySelfAndI { protected function talk() { Stranger::askForACigarette(); } }

class MeMySelfAndI { protected function talk() { Stranger::getInstance()->askForACigarette(); } }

class MeMySelfAndI { protected function talkTo($friend) { $friend->askForACigarette(); } } class Friend { public function askForACigarette() { return new Cigarette(); } }

Create loosely coupled classes #3

Which tools do you need to do your job?

class DomainObject { protected function loadData() { $this->data = $this->dataManager->query(...); } public function render() { $this->loadData(); $this->dataRenderer->renderTable($this->data); } }

class DomainObject { protected $dataManager; protected $dataRenderer; public function __construct($dataManager, $dataRenderer) { $this->dataManager = $dataManager; $this->dataRenderer = $dataRenderer; } protected function loadData() public function render() }

Use dependency injection #4

fuel injection a means of metering fuel into an internal combustion engine

class Car { protected $engine; protected $wheels = array(); public function __construct() { $this->engine = new Engine(); $this->wheels = array( new Wheel(), new Wheel(), new Wheel(), new Wheel(), ); } }

class Car { protected $engine; protected $wheels = array(); public function __construct($engine, array $wheels) { $this->engine = $engine; $this->wheels = $wheels; } }

class Car { protected $engine; protected $wheels = array(); public function __construct(Engine $engine, array $wheels) { $this->engine = $engine; $this->wheels = $wheels; } }

class Car { protected $engine; protected $wheels = array(); public function __construct(Engine $engine) { $this->engine = $engine; } public function addWheel(Wheel $wheel) { $this->wheels[] = $wheel; } }

Composition over inheritance #5

You can always extend good OOP code

Solve the problem, do not generalize #6

Try test-driven development #7

If it's not tested, it does not exist

Test-Driven Development

Write a (unit) test first
Make sure it fails
Write code to make the test pass
Start over again

require 'PHPUnit/Framework.php'; class TryingTddTest extends PHPUnit_Framework_TestCase { }

require 'PHPUnit/Framework.php'; class TryingTddTest extends PHPUnit_Framework_TestCase { public function test() { } }

require 'PHPUnit/Framework.php'; class TryingTddTest extends PHPUnit_Framework_TestCase { public function test...() { } }

require 'PHPUnit/Framework.php'; class TryingTddTest extends PHPUnit_Framework_TestCase { public function testSomething() { } }

Focus on the API

require 'PHPUnit/Framework.php'; class TryingTddTest extends PHPUnit_Framework_TestCase { public function testAnElePHPantIsBlue() { $e = new ElePHPant(); } }

require 'PHPUnit/Framework.php'; class TryingTddTest extends PHPUnit_Framework_TestCase { public function testAnElePHPantIsBlue() { $e = new ElePHPant(); $this->assertEquals('#009', $e->getColor()); } }

I don't know what an ElePHPant is, idiot!

class ElePHPant { protected $color = '#009'; public function getColor() { return $this->color; } }

Congratulations, you've just created a blue ElePHPant!

class ElePHPant { protected $color = '#008'; public function getColor() { return $this->color; } }

No, this ElePHPant is not blue any more!

require 'PHPUnit/Framework.php'; class TryingTddTest extends PHPUnit_Framework_TestCase { public function testAnElePHPantIsBlue() { $e = new ElePHPant(); $this->assertEquals('#009', $e->getColor()); } public function testAnElePHPantHasPhpLogo() { $e = new ElePHPant(); $this->assertTrue($e->getLogo() instanceOf Logo); } }

class ElePHPant { protected $color = '#009'; public function getColor() { return $this->color; } public function getLogo() { return $this->logo; } }

No, there is no logo on that ElePHPant!

class ElePHPant { protected $color = '#009'; protected $logo; public function __construct(Logo $logo) { $this->logo = $logo; } public function getColor() { return $this->color; } public function getLogo() { return $this->logo; } }

require 'PHPUnit/Framework.php'; class TryingTddTest extends PHPUnit_Framework_TestCase { public function testAnElePHPantIsBlue() { $e = new ElePHPant(); $this->assertEquals('#009', $e->getColor()); } public function testAnElePHPantHasPhpLogo() { $e = new ElePHPant(new Logo()); $this->assertTrue($e->getLogo() instanceOf Logo); } }

require 'PHPUnit/Framework.php'; class TryingTddTest extends PHPUnit_Framework_TestCase { public function testAnElePHPantIsBlue() { $e = new ElePHPant(); $this->assertEquals('#009', $e->getColor()); } public function testAnElePHPantHasPhpLogo() { $e = new ElePHPant(new Logo()); $this->assertTrue($e->getLogo() instanceOf Logo); $this->assertEquals('PHP', $e->getLogo()->getText()); } }

class Logo { protected $text; public function __construct($text) { $this->text = $text; } }

… and they kept coding happily ever after ...

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