Stefan Priebsch
thePHP.cc
ZendCon09
Seven Steps
to Better OOP Code

Stefan Priebsch
Co-Founder and Principal Consultant

Premium PHP Consulting & Training. Worldwide.
Sebastian Arne Stefan
Bergmann Blankerts Priebsch

Disclaimer

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

Is OOP slow?

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

25% slower!

1 µsec

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

I/O is where
the action is.

OOP is
fast enough.

Do not care about
#1 performance *
*Some restrictions may apply.

What
do you
do for a
living?

class Something
{
public function doWork()
{
… 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()
}

#2 Clearly separate
different concerns

One Responsibility

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

Let others
do the work.

class CrystalBall
{
public function predictLottoNumbers($a, $b, $c)
{
…
return new LottoNumbers(...);
}
}

#3 Focus on the API

Interface vs.
Implementation

Keep secrets

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

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

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

Do not talk
to strangers.

Create loosely
#4 coupled classes

Make
dependencies
explicit.

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

class SomeObject
{
protected function loadData()
{
$this->data = $this->db->query(...);
}
public function render(Renderer $renderer)
{
$this->loadData();
return $this->renderer->createTable($this->data);
}
}

class SomeObject
{
protected function loadData(DbGateway $db)
{
$this->data = $db->query(...);
}
public function render(Renderer $renderer)
{
$this->loadData();
return $renderer->createTable($this->data);
}
}

class SomeObject
{
public function __construct(DbGateway $db, Renderer $r)
{
$this->db = $db;
$this->renderer = $r;
}
...
}

Use dependency
#5 injection

class Engine
{
public function start();
public functoin stop();
public function goFaster($amount);
public function goSlower($amount);
}

class Car extends Engine
{
...
}

class SteeringWheel
{
public function turnRight($degrees);
public function turnLeft($degree);
}

class Car extends Engine extends SteeringWheel
{
...
}

Multiple inheritance?

Engine

Engine
+
Steering Wheel

Engine
+
Steering Wheel
+
Seat

Combine
objects.

Seat
Car
Steering
Engine
Wheel

class Car
{
protected $engine;
protected $steeringWheel;
protected $frontSeat;
public function __construct()
{
$this->engine = new Engine();
$this->steeringWheel = new SteeringWheel();
$this->frontSeat = new Seat();
}
}

class Car
{
public function __construct(Engine $engine,
SteeringWheel $steeringWheel,
Seat $seat)
{
$this->engine = $engine;
$this->steeringWheel = $steeringWheel;
$this->frontSeat = $seat;
}
}

$engine = new Engine();
$steeringWheel = new SteeringWheel();
$seat = new Seat();
$car = new Car($engine, $steeringWheel, $seat);

$engine = new SuperStrongEngine();
$steeringWheel = new FancySteeringWheel();
$seat = new MichaelSchuhmacherRacingSeat();
$car = new Car($engine, $steeringWheel, $seat);

Favour composition
#6 over inheritance

Avoid
inheritance.

Constants
Superglobals Session
Class to Test
Webservice Configuration
Database

If it's not tested,
it does not exist

Make it easy
#7 to (unit) test

Fewer
dependencies.

Testable
=
Maintainable

Testable
=
Extensible

Thank you.

Contact
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■ http://www.slideshare.net/spriebsch
■ http://twitter.com/spriebsch
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