Basic PHP Design Patterns

Stefan Priebsch, e-novative GmbH

„ Every pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over,without ever doing it the same way twice.“ (Christopher Alexander)

Software Design Patterns Are

Blueprints for proven solutions

A common language for developers

Useful to understand frameworks

They Are Not

The solution to all design problems

Ready-made implementations

Magic bullets

Map

An object that maps keys to values. A map cannot contain duplicate keys.

Map

class Map { }

Map

class Map { protected $values = array(); }

Map

class Map { protected $values = array(); public function set($aKey, $aValue) { return $this->values[$aKey] = $aValue; } }

Map

class Map { protected $values = array(); public function set($aKey, $aValue) { return $this->values[$aKey] = $aValue; } public function get($aKey) { return $this->values[$aKey]; } }

Map

class Map { protected $values = array(); public function __construct() { $this->values = array('ip' => '192.168.1.1'); } public function set($aKey, $aValue) { return $this->values[$aKey] = $aValue; } public function get($aKey) { return $this->values[$aKey]; } }

Using the Map

$map = new Map(); var_dump($map->get('ip')); $map->set('ip', '192.168.1.2'); var_dump($map->get('ip'));

Using the Map

$map = new Map(); var_dump($map->get('ip')); $map->set('ip', '192.168.1.2'); var_dump($map->get('ip')); > php Map.php string(11) "192.168.1.1" string(11) "192.168.1.2"

Using the Map

$map = new Map(); var_dump($map->get('nonexisting key'));

Using the Map

$map = new Map(); var_dump($map->get('nonexisting key')); > php Map.php Notice: Undefined index: nonexisting key in Map.php on line 21 NULL

Map

class Map { protected $values = array(); public function __construct() ... public function set($aKey, $aValue) ... public function get($aKey) { if (!isset($this->values[$aKey])) { throw new RuntimeException('No key "' . $aKey . '"'); } return $this->values[$aKey]; } }

Map

class Map { protected $values = array(); public function __construct() ... public function set($aKey, $aValue) ... public function has($aKey) { return isset($this->values[$aKey]); } public function get($aKey) ... }

Extending the Map

class MyMap extends Map { public function __construct() { // load values from ini or XML file, database, or PHP data } }

Map Data Loader

class MapDataLoader { protected $source; public function __construct($aSource) { $this->source = $aSource; } }

Map Data Loader

class MapDataLoader { protected $source; public function __construct($aSource) { $this->source = $aSource; } public function load() { // load data from $this->source return $result; // e.g. array('key' => 'value', ...) } }

Map using Data Loader

class MyMap { public function __construct( MapDataLoader $aLoader) { $this->values = $aLoader->load(); } }

Registry

A well-known object that other objects can use to find common objects and services.

Registry

class Registry { protected $dsn; public function setDsn($aDsn) { $this->dsn = $aDsn; } public function getDsn() { return $this->dsn; } }

Registry

class Registry { protected $dsn; protected $username; protected $password; public function setDsn($aDsn) ... public function getDsn() ... public function setUsername() {} public function getUsername() {} public function setPassword() {} public function getPassword() {} }

Registry

$registry = new Registry(); $registry->setDsn('sqlite::memory:'); var_dump($registry->getDsn());

Registry

$registry = new Registry(); $registry->setDsn('sqlite::memory:'); var_dump($registry->getDsn()); > php Registry.php string(15) "sqlite::memory:"

Singleton

Singleton is used to restrict instantiation of a class to one object.

Singleton

class Singleton { }

Singleton

class Singleton { protected static $instance; }

Singleton

class Singleton { protected static $instance; public static function getInstance() { return self::$instance; } }

Singleton

class Singleton { protected static $instance; public static function getInstance() { return self::$instance; } } $singleton = Singleton::getInstance();

Singleton

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

Singleton

class Singleton { protected static $instance; private function __construct() {} public static function getInstance() { if (is_null(self::$instance)) { self::$instance = new Singleton(); } return self::$instance; } } $singleton = Singleton::getInstance();

Singleton

class Singleton { protected static $instance; private function __construct() {} private function __clone() {} public static function getInstance() { if (is_null(self::$instance)) { self::$instance = new Singleton(); } return self::$instance; } } $singleton = Singleton::getInstance();

Singleton

class Singleton { protected static $instance; private function __construct() {} private function __clone() {} public static function getInstance() { if (is_null(self::$instance)) { self::$instance = new Singleton(); } return self::$instance; } } $singleton = Singleton::getInstance();

Subject/Observer

The observer maintains a list of its dependents and notifies them automatically of any state changes, usually by calling one of their methods.

Subject/Observer Interfaces (available through SPL)

interface SplSubject { public function attach (SplObserver $aObserver); public function detach (SplObserver $aObserver); public function notify (); }

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

Subject

class Subject implements SplSubject { protected $observers = array(); }

Subject

class Subject implements SplSubject { protected $observers = array(); public function attach(SplObserver $aObserver) { $this->observers[] = $aObserver; } }

Subject

class Subject implements SplSubject { protected $observers = array(); public function attach(SplObserver $aObserver) { $this->observers[] = $aObserver; } public function detach(SplObserver $aObserver) { $this->observers[] = array_diff($this->observers, array($aObserver)); } }

Subject

class Subject implements SplSubject { protected $observers = array(); public function attach(SplObserver $aObserver) ... public function detach(SplObserver $aObserver) ... public function notify() { foreach ($this->observers as $observer) { $observer->update($this); } } }

Subject

class Subject implements SplSubject { protected $observers = array(); public function attach(SplObserver $aObserver) ... public function detach(SplObserver $aObserver) ... public function notify() ... public function doSomething() { // Do some work $this->notify(); } }

Observer

class Observer implements SplObserver { public function update(SplSubject $aSubject) { var_dump($this, 'updated'); } }

Using Subject/Observer

$subject = new Subject(); $observer = new Observer(); $observer2 = new Observer(); $subject->attach($observer); $subject->attach($observer2); $subject->doSomething();

Using Subject/Observer

$subject = new Subject(); $observer = new Observer(); $observer2 = new Observer(); $subject->attach($observer); $subject->attach($observer2); $subject->doSomething(); > php Subject_Observer.php object(Observer)#2 (0) { } string(7) "updated" object(Observer)#3 (0) { } string(7) "updated"

Iterator

An iterator allows traversing through all elements of a collection. Iterators encapsulate the internal structure of how the iteration occurs.

Iterator Interface

interface Iterator { // Returns the current value function current(); // Returns the current key function key(); // Moves the internal pointer to the next element function next(); // Moves the internal pointer to the first element function rewind(); // If the current element is valid (boolean) function valid(); }

SPL Iterators in PHP