Advanced OOP and Design Patterns

Copyright © 2009 thePHP.cc, Germany

Advanced OOPand Design Patterns

Stefan PriebschthePHP.cc

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Sebastian Bergmann

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WhyWhy OOP?OOP?

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PHPPHP

HTMLHTML

SQLSQL


PHPPHP

HTMLHTML

SQLSQL


PHPPHP

HTMLHTML

SQLSQL

PHPPHP

HTMLHTML

SQLSQL

PresentationPresentation

LogicLogic

Data AccessData Access

Separation ofSeparation ofConcernsConcerns

Good OOP starts Good OOP starts before classesbefore classescome into playcome into play

Do weDo weneed OOP?need OOP?

IF-GOTO programsIF-GOTO programs

LOOP programsLOOP programs

WHILE programsWHILE programs

IF-GOTO andIF-GOTO andWHILE programsWHILE programsare equally powerful.are equally powerful.

Every WHILE programEvery WHILE programcan be simulated by acan be simulated by aWHILE program withWHILE program withonly one while loop.only one while loop.

OOP isOOP issyntactical sugarsyntactical sugar

Then Why OOP?Then Why OOP?

ReadabilityReadability

class BlogPosting{ public function addComment(Comment $comment)}

class BlogPosting{ public function addComment(Comment $comment) { $this->comments[] = $comment; }}

class BlogPosting{ public function addComment(Comment $comment) { $this->comments[] = $comment;

if ($comment->getAuthor()->isRegistered()) { $comment->setApproved(true); } }}

EncapsulationEncapsulation

Keeping SecretsKeeping Secrets

InterfaceInterfaceand and

ImplementationImplementation

$email->send();$email->send();

$pdf->generate();$pdf->generate();

MaintainabilityMaintainability

Source: Barry Boehm: „EQUITY Keynote Address“, March 19th, 2007Source: Barry Boehm: „EQUITY Keynote Address“, March 19th, 2007

DesignDesign CodeCodeReqReq DevTDevT OpsOps

Rela

tive C

ost

of

a B

ug

fix

Rela

tive C

ost

of

a B

ug

fix

1x1x 5x5x10x10x

20x20x

50x50x

AccTAccT

>150x>150x

ExtensibilityExtensibility

class Customer{ protected $discount = 0;

public function getDiscount() { return $this->discount; }}

class PremiumCustomer extends Customer{ protected $discount = 5;}

class PremiumCustomer extends Customer{ protected $discount = 5;

public function getDiscount() { if ($this->signupYear < 2003) { return 10; }

if ($this->getTotalRevenue() > 100000) { return 10; }

return parent::getDiscount(); }}

class PremiumCustomer extends Customer{ protected $discount = 5;

public function getDiscount() { if ($this->fulfilsYearCriterion() || $this->fulfilsRevenueCriterion()) {

return 10; }

return parent::getDiscount(); }

...}

class PremiumCustomer extends Customer{ ...

protected function fulfilsYearCriterion() { return $this->signupYear < 2003; }

protected function fulfilsRevenueCriterion() { return $this->getTotalRevenue() > 100000; }

...}

class PremiumCustomer extends Customer{ protected $specialDiscount= 10;

public function getDiscount() { if ($this->fulfilsYearCriterion() || $this->fulfilsRevenueCriterion()) {

return $this->specialDiscount; }

return parent::getDiscount(); }}

class MostValuedCustomer extends PremiumCustomer{ protected $discount = 10; protected $specialDiscount= 20;}

ReusabilityReusability

Only isolated andOnly isolated andloosely coupledloosely coupled

classes are reusable.classes are reusable.

MaintainabilityMaintainability

Is OOP slow?Is OOP slow?

Benchmark results are different on every system.Benchmark results are different on every system.

foo() foo() 3.09 µsec3.09 µsec

Test::foo() 3.26 µsec

$test->foo() 3.12 µsec

$test = new Test();$test->foo() 4.03 µsec

25% slower!25% slower!

1 µsec1 µsec

Benchmark results are different on every system.Benchmark results are different on every system.

print ~ 10 µsec

file_get_contents() ~ 30 µsec

mysql_connect() ~ 100 µsec

HTTP GET Request ~ 35,000 µsec

I/O is whereI/O is wherethe action is.the action is.

OOP is fast OOP is fast enough.enough.

Dealing with Dealing with DependenciesDependencies

DecouplingDecoupling

DependenciesDependencieson Constantson Constants

define('BASEPATH', '/some/absolute/path');...

class Something{ public function loadData() { $this->data = file_get_contents(BASEPATH . '/file.ext'); }}

...$something = new Something();$something->loadData();

class Something{ protected $basePath = BASEPATH; public function loadData() { $this->data = file_get_contents($this->basePath . '/file.ext'); }}

class Something{ protected $basePath = BASEPATH; public function setBasePath($basePath) { $this->basePath = $basePath; }

public function loadData() { $this->data = file_get_contents($this->basePath . '/file.ext'); }}

$something = new Something();$something->setBasePath(BASEPATH);$something->loadData();

class Something{ protected $basePath; public function setBasePath($basePath) { $this->basePath = $basePath; }

public function loadData() { $this->data = file_get_contents($this->basePath . '/file.ext'); }}

class Something{ protected $basePath; public function setBasePath($basePath) { $this->basePath = $basePath; }

public function loadData() { if (is_null($this->basePath)) { throw new RuntimeException('No basepath set'); }

$this->data = file_get_contents($this->basePath . '/file.ext'); }}

class Something{ protected $basePath; public function __construct($basePath) { $this->basePath = $basePath; }

public function loadData() { if (is_null($this->basePath)) { throw new RuntimeException('No basepath set'); }

$this->data = file_get_contents($this->basePath . '/file.ext'); }}

Files are also a Files are also a dependencydependency

class Something{ public function __construct($data) { $this->data = $data; }}

Dependencies on Dependencies on Global VariablesGlobal Variables

class Something{ public function loadData() { global $dsn;

… load data from database ... }}

class Something{ public function loadData($dsn) { … load data from database ... }}

class Something{ protected $dsn;

public function __construct($dsn) { $this->dsn = $dsn; }

public function loadData() { … load data from database ... }}

class Something{ protected $dbAdapter;

public function __construct(DatabaseAdapter $dbAdapter) { $this->dbAdapter = $dbAdapter; }}

Dependency Dependency InjectionInjection


public function __construct(DatabaseAdapter $dbAdapter) { $this->dbAdapter = $dbAdapter; }

public function loadData() { … ask somebody else to load data from database ... }}

DelegationDelegation

Let othersLet othersdo the work.do the work.

class DatabaseAdapter{ protected $dsn;

public function __construct($dsn) { $this->dsn = $dsn; }}

$dbAdapter = new DatabaseAdapter();

$something = new Something($dbAdapter);$something->doWork();

class DummyDatabaseAdapter extends DatabaseAdapter{}

$dbAdapter = new DummyDatabaseAdapter();

$something = new Something($dbAdapter);$something->doWork();


public function __construct(DatabaseAdapter $dbAdapter = null) { if (is_null($dbAdapter)) { $dbAdapter = new DefaultDatabaseAdapter(); }

$this->dbAdapter = $dbAdapter; }

public function loadData() { … load data from database ... }}

DependenciesDependencieson Functionson Functions

class Something{ public function doWork() { ... global_function(...); ... }}

require_once 'global_function.php';

$something = new Something();$something->doWork();

require_once 'mock_global_function.php';

$something = new Something();$something->doWork();

DependenciesDependencieson Static Callson Static Calls

class Something{ public function loadData() { $dsn = Configuration::getDsn();


class Something{ protected $configurationClass = 'Configuration';

public function setConfigurationClass($classname) { $this->configurationClass = $classname }

public function loadData() { $classname = $this->configurationClass; $db = $classname::getDsn();


??





Will $classnameWill $classnameactually be a class?actually be a class?





Will the class haveWill the class havea getDsn() method?a getDsn() method?

Better let PHP Better let PHP enforce this.enforce this.

DependenciesDependencieson Objectson Objects

class Something{ public function doWork() { ... $this->log('…'); ... }}

class Something{ protected function log($message) { file_put_contents(LOGFILE, $message, FILE_APPEND); }

public function doWork() { ... $this->log('…'); ... }}

class Logger{ public function log($message) { file_put_contents(LOGFILE, $message, FILE_APPEND); }}

class Something{ protected $logger;

public function __construct() { $this->logger = new Logger(); }

...}


public function __construct() { $this->logger = new Logger(); }

public function doWork() { … $this->logger->log(...); ... }}


public function __construct(Logger $logger) { $this->logger = $logger; }

public function doWork() { … $this->logger->log(...); ... }}

class Logger{ public function log($message) { file_put_contents(LOGFILE, $message, FILE_APPEND); }}

class Logger{ protected $file;

public function __construct($file) { $this->file = $file; }

public function log($message) { ... file_put_contents($this->file, $message, FILE_APPEND); ... }}

class DatabaseLogger extends Logger{ protected $dsn;


public function log($message) { … log $message to database $dsn ... }}

class DbGateway{ protected $dsn;


...}

class DbGateway{ protected $isConnected = false;

...

protected function connect() { … connect to $dsn ... }

public function query($query) { if (!$this->isConnected) { $this->connect(); }

… run $query ... }

...}

class DatabaseLogger extends Logger extends DbGateway{ ...}

Multiple Inheritance

??

class Something{ public function __construct(Logger $logger) { $this->logger = $logger; }

public function doWork() { ... $this->logger->log(...); ... }}

Do we really need to Do we really need to extend Logger?extend Logger?

class FileLogger{ protected $file;



class DatabaseLogger extends DbGateway{ public function log($message) { ... … write $message to database using $this->query() … ... }}

class Something{ public function __construct(Logger $logger) { $this->logger = $logger; }

public function doWork() { ... $this->logger->log(...); ... }}

How do we makeHow do we makethe type hint work?the type hint work?

InterfacesInterfaces

interface Loggable{ public function log($message);}

class FileLogger implements Loggable{ protected $file;



class DatabaseLogger extends DbGateway implements Loggable{ public function log($message) { ... … write $message to database using $this->query() … ... }}

class Something{ public function __construct(Loggable $logger) { $this->logger = $logger; }

protected function doWork() { ... $this->logger->log(...); ... }}

$logger = new FileLogger('/path/to/logfile');

$something = new Something($logger);$something->doWork();

$logger = new DatabaseLogger($dsn);


$logger = new DummyLogger();


class DummyLogger implements Loggable{ public function log($message) { }}

Interfaces makeInterfaces makegood type hints.good type hints.

Abstract Classes Abstract Classes and Methodsand Methods

class Something{ public function run() { // initialize …

// perform calculations …

// write log entry …

// sort output ... }}

class Something{ public function run() { $this->initialize(); $this->calculateStuff(); $this->doLogging(); $this->sortOutput(); }}

Template MethodTemplate Method

class Something{ abstract protected function initialize(); abstract protected function calculateStuff(); abstract protected function doLogging(); abstract protected function sortOutput();

public function run() { $this->initialize(); $this->calculateStuff(); $this->doLogging(); $this->sortOutput(); }}

abstract class Something{ abstract protected function initialize(); abstract protected function calculateStuff(); abstract protected function doLogging(); abstract protected function sortOutput();

public function run() { $this->initialize(); $this->calculateStuff(); $this->doLogging(); $this->sortOutput(); }}

abstract class Something{ abstract protected function initialize(); abstract protected function calculateStuff(); abstract protected function doLogging(); abstract protected function sortOutput();

final public function run() { $this->initialize(); $this->calculateStuff(); $this->doLogging(); $this->sortOutput(); }}

class ConcreteSomething extends Something{ protected function initialize() { }

protected function calculateStuff() { }

protected function doLogging() { }

protected function sortOutput() { }}

Abstract classes Abstract classes cannot be instantiated.cannot be instantiated.

„„Every pattern describes a problemEvery pattern describes a problemwhich occurs over and over again inwhich occurs over and over again in

our environment, and then describes our environment, and then describesthe core of the solution to that problem,the core of the solution to that problem,

in such a way that you can use thisin such a way that you can use thissolution a million times over, withoutsolution a million times over, withoutever doing it the same way twice.“ever doing it the same way twice.“

-- Christopher Alexander -- Christopher Alexander

A design patternA design patternis a general reusableis a general reusable

solution to a commonly solution to a commonly occurring problem.occurring problem.

A design pattern is not a A design pattern is not a finished design that can be finished design that can be

transformed directly into code.transformed directly into code.

ArchitecturalArchitecturalPatternsPatterns

DesignDesignPatternsPatterns

IdiomsIdioms

Problem: displayProblem: displaya progress bara progress bar

class Something{ protected function performCalculation() { ... foreach ($items as $item) { … process the item … print '.'; } ... }}

Subject/ObserverSubject/Observer

The subject maintains a list of The subject maintains a list of observers and notifies them on observers and notifies them on

status changes.status changes.

interface SplSubject{ public function attach(SplObserver $observer); public function detach(SplObserver $observer);

public function notify();}

interface SplObserver{ public function update(SplSubject $subject);}

class Subject implements SplSubject{ protected $observers;

public function __construct() { $this->observers = new SplObjectStorage(); }

...}

class Subject implements SplSubject{ …

public function attach(SplObserver $observer) { $observers->attach($observer); } public function detach(SplObserver $observer) { $observers->detach($observer); }

...}

class Subject implements SplSubject{ ...

public function notify() { foreach ($this->observers as $observer) { $observer->update($this); } }}

class Something extends Subject implements SplSubject{ public function doWork() { … foreach ($items as $item) { … $this->notify(); } ... }}

class ProgressBar implements SplObserver{ public function update(SplSubject $subject) { print '. '; }}

class Something extends Subject implements SplSubject{ public function doWork() { … foreach ($items as $item) { $this->currentItem = $item; … $this->notify(); } ... }

public function getCurrentItem() { return $this->currentItem() }}

class ProgressBar implements SplObserver{ public function update(SplSubject $subject) { $item = $subject->getCurrentItem(); … }}

class ProgressBar implements SplObserver{ public function update(SplSubject $subject) { $item = $subject->getCurrentItem();

if ($item->isDir()) { print '[' . $item->getPathname() . '] '; }

if ($item->isFile()) { print '.'; } }}

$progressBar = new ProgressBar();

$something = new Something();$something->attach($progressBar);

$something->doWork();

FactoryFactory

Defines an interface for creatingDefines an interface for creatinga family of objects. The concretea family of objects. The concrete

classes that are to be instantiated classes that are to be instantiated are not clearly defined.are not clearly defined.

Creates objects for you.Creates objects for you.

abstract class Plane{ static public function getInstance($type) { return new $type; }}

class Boeing extends Plane{}

class Airbus extends Plane{}

class Boeing777 extends Boeing{}

class AirbusA340 extends Airbus{}

$a = Plane::getInstance('Boeing777');

$b = Plane::getInstance('AirbusA340');

abstract class Plane{ static public function getInstance($type) { switch ($type) { case 'Boeing777': return new Boeing777(); … default:

throw new RuntimeException('...'); } }}

abstract class Plane{ static public function getInstance($type) { if (!in_array($type, array('Boeing777', 'AirbusA340', …))) { throw new RuntimeException('...'); }

return new $type; }}

abstract class Plane{ static public function getInstance($type) { if (!class_exists($type)) { throw new RuntimeException('...'); }

return new $type; }}

abstract class Plane{ protected $classMap = array( '777' => 'Boeing777', ... );

static public function getInstance($type) { if (!isset($this->classMap[$type])) { throw new RuntimeException('...'); }

$classname = $this->classMap[$type]; return new $classname; }}

SingletonSingleton

Limits number of instancesLimits number of instancesof a class to one object.of a class to one object.

Limits number of instancesLimits number of instancesof a class to one object.of a class to one object.

class Singleton{ static protected $instance;

static public function getInstance() { if (is_null(self::$instance)) { self::$instance = new Singleton(); }

return self::$instance; }}

class Singleton{ static protected $instance;

private function __construct() {} private function __clone() {}

static public function getInstance() { if (is_null(self::$instance)) { self::$instance = new Singleton(); }

return self::$instance; }}

class Something{ public function doWork() { $singleton = Singleton::getInstance(); $singleton->... ... }}

class Something{ public function doWork($reference) { $reference->... ... }}

RegistryRegistry

A well-known object usedA well-known object usedby others to find sharedby others to find shared

objects and services.objects and services.

…$db = StaticRegistry::getDbAdapter();...

class StaticRegistry{ static protected $dbAdapter;

static public function getDbAdapter() { if (is_null(self::$dbAdapter)) { self::$dbAdapter = new DbAdapter(); }

return self::$dbAdapter; }}

…$db = Registry::getInstance()->getDbAdapter();...

class SingletonRegistry{ static protected $instance;

protected $dbAdapter;

static public function getInstance() { … }

public function getDbAdapter() { if (is_null($this->dbAdapter)) { $this->dbAdapter = new DbAdapter(); }

return $this->dbAdapter; }}

class Registry{ …

protected $dbAdapterClass = 'DbAdapter'; protected $dbAdapter;

public function setDbAdapterClass($class) { $this->dbAdapterClass = $class; }

public function getDbAdapter() { if (is_null($this->dbAdapter)) { $classname = $this->dbAdapterClass; $this->dbAdapter = new $classname; }

return $this->dbAdapter; }}

MVCMVC

ClassicalClassical

MVCMVC

ModelModel

RepresentsRepresentsdomain-specific datadomain-specific data

View View

RendersRendersmodel datamodel data

ControllerController

Handles eventsHandles eventsand modifies modeland modifies model

PresentationPresentation

LogicLogic

Data AccessData Access MM

VV

CC

Model != Data AccessModel != Data Access

Model != Data AccessModel != Data Access


ModelModelViewView


ModelModelViewView

Controller observes ViewController observes View


ModelModelViewView

Controller fetches data from ViewController fetches data from View


ModelModelViewView

Controller modifies ModelController modifies Model


ModelModelViewView

View observes ModelView observes Model


ModelModelViewView

View fetches data from ModelView fetches data from Model

MVCMVCon the Webon the Web

ServerServer

ClientClient

HTTP RequestHTTP Request HTTP ResponseHTTP Response

VV

CC MM

View is View is remoteremote


ModelModelViewView


ModelModelViewView

Controller can't observe ViewController can't observe View


ModelModelViewView

View can't observe ModelView can't observe Model


ModelModelViewView

FrontFrontControllerController

View doesn't talk to ControllerView doesn't talk to Controller


ModelModelViewView


HTTPHTTPRequestRequest


ModelModelViewView



execute()execute()


ModelModelViewView



execute()execute()

getData()getData()


ModelModelViewView



execute()execute()

getData()getData()

setData()

setData()

ControllerControllerselects Viewselects View

View generatesView generatesfull HTML pagefull HTML page

Workflows by Workflows by Controller chainingController chaining

Lean Controller, Lean Controller, Fat ModelFat Model

No data accessNo data accessin Controller or Modelin Controller or Model

No presentationNo presentationin Controller or Modelin Controller or Model

Separation ofSeparation ofConcernsConcerns

Golden Golden RulesRules

„„Hang the rules. Hang the rules. They're more like They're more like guidelines anyway.“guidelines anyway.“

--Elizabeth Swann,--Elizabeth Swann,Pirates of the CaribbeanPirates of the Caribbean

Make Make dependencies dependencies

explicit.explicit.

„„Life can only beLife can only beunderstoodunderstood backwardsbackwards,,but it must be but it must be livedlivedforwardsforwards.“.“

-- Soren Kierkegaard-- Soren Kierkegaard

Solve your Solve your problem.problem.

Do one thingDo one thingat a time.at a time.

Let othersLet othersdo the work.do the work.

Do not care Do not care about others.about others.

Keep itKeep itsimple.simple.

„„Debugging is twice as hardDebugging is twice as hardas writing the code in theas writing the code in thefirst place. Therefore, if youfirst place. Therefore, if youwrite the code as cleverly as write the code as cleverly as possible, you are, by definition, possible, you are, by definition, not smart enoughnot smart enoughto debug it.“to debug it.“

-- Brian W. Kernighan-- Brian W. Kernighan

Do notDo notcomment.comment.

Do notDo notcomment.comment.**

** Some restrictions apply. Some restrictions apply.

””The most important The most important single aspect of software single aspect of software development ...development ...

… is to be … is to be clearclear about about what you are trying to what you are trying to build.”build.”

-- Bjarne Stroustrup-- Bjarne Stroustrup

Name the thing.Name the thing.

„„There's no sense beingThere's no sense beingexact about somethingexact about somethingif you don't even knowif you don't even know

what you're talking about.“what you're talking about.“-- John von Neumann-- John von Neumann

It has to fitIt has to fiton one page.on one page.

””Measuring programming Measuring programming progress by lines of codeprogress by lines of codeis like measuring aircraft is like measuring aircraft building progress by building progress by weightweight.”.”

-- Bill Gates-- Bill Gates

Accept Change.Accept Change.

””I may not have gone I may not have gone where I intended to go, where I intended to go, but I think I have ended but I think I have ended up where I needed to be.“up where I needed to be.“

-- Douglas Adams-- Douglas Adams

Thank you.Thank you.

Please rate me:Please rate me:http://joind.inhttp://joind.in

Copyright © 2009 thePHP.cc, Germany

Contact■ http://thePHP.cc■ http://www.priebsch.de■ http://www.slideshare.net/spriebsch■ http://twitter.com/spriebsch■ [email protected], IRC: spriebsch

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Advanced OOP and Design Patterns