Design patterns illustrated 010PHP

Design Patterns
illustrated
010PHP

Törööö
By Laurent Steinmayer

Herman Peeren, February 13, 2014
(Design Patterns illustrations: Nelleke Verhoeff, 2010)

Design Patterns
●●
●●
●●
●●

recipes against common (OO-) programming problems
code reuse: no need to reinvent the wheel
common language
GOF: 23 “classical” patterns

四人帮

classic,
The Book

The one

constant in software development:

The one


CHANGE!

The one


CHANGE!
I knew it ...

Ideal: code as modular black boxes

Single responsibility principle
Open for extension, closed for modification
Liskov subsitution principle
Interface segregation
Dependency inversion

It might get you into trouble...

some code smells:
►►duplicate code
►►long method
►►large class
►►combinatorial explosion
►►conditional complexity
►►switch statements
►►indecent exposure

Classic pattern categories
creational, structural and behavioral patterns:

►►creational: object instantiation
►►structural: larger structures of classes or objects
►►behavioral: interaction and distribution of responsibility

Other categorisations
Loek Bergman (dev. from Rotterdam):
►►transformational
►►transportational
►►translational
Anthony Ferrara:
►►Shim : not necessary (for PHP)
►►decompositional: breaking objects apart
►►compositional: making things simpler by assembling

Creational design patterns
►►Factory Method: Allow subclasses to “decide” which class
to instantiate.
►►Abstract Factory: Encapsulate a set of analo gous factories that produce families of objects.
►►Builder: Encapsulate the construction of com plex objects from their representation; so, the
same building process can create various repre sentations by specifying only type and content.
►►Singleton: Ensure that only a single instance of
a class exists and provide a single method for
gaining access to it.
►►Prototype: Create an initialized instance for
cloning or copying.

Factory Method

Provide an interface for the creation of objects.

©c
yepr

Allow subclasses to “decide” which class to instantiate.

Example: different kinds of customers...

...with different kinds of invoices

Abstract Factory

©c
yepr

Povide an interface for creating families of related
or dependent objects. A factory for factories.

Example: a Gold customer, cart, invoice, etc.

Builder

©c
yepr

Seperate the construction process (how) of a complex object
from the concrete representations (what).

Example: querybuilder:
$qb->select(‘u’)
->from(‘User’, ‘u’)
->where(‘u.id = ?1’)
->orderBy(‘u.name’, ‘ASC’);

Example: documentbuilder (for tree-like structures):
$domtree = new DOMDocument(‘1.0’, ‘UTF-8’);

/

/* create the root element of the xml tree */
$xmlRoot = $domtree->createElement(“xml”);
/* append it to the document created */
$xmlRoot = $domtree->appendChild($xmlRoot);
$currentTrack = $domtree->createElement(“track”);
$currentTrack = $xmlRoot->appendChild($currentTrack);
// etc...

Singleton

Ensure a class only has one instance, and provide a global
point of access to it.

© yepr
c

Oh, I’m so
loooooooonly

Singleton

Ensure a class only has one instance, and provide a global
point of access to it.
Did anybody say GLOBAL???

© yepr
c

Oh, I’m so
loooooooonly

B

N
A

E
N

!
D

“Every
advantage
has its
disadvantages”

(free to Johan Cruyff,
Dutch Football Pattern Designer
and Ajax-fan...)

Prototype

Make variations on copies of a basic-object.

c
© yepr

COPY-SERVICE

Javascript:
var Person = function() { // bladibla };
var Customer = function(name) {
this.name = name;
};
Customer.prototype = new Person();

Prototype in PHP:
►►adding properties is easy
►►adding behaviour is less obvious, but...
►►CLOSURES can help here, with some (dirty) tricks

Structural design patterns
●● Adapter: Adapt an interface to an expected interface.
●● Bridge: Decouple an interface from its implementation.
●● Composite: Create a tree structure for part-whole hierarchies.
●● Decorator: Extend functionality dynamically.
●● Facade: Simplify usage by defining a high-level interface.
●● Flyweight: Support fine-grained objects fficiently by sharing.
e
●● Proxy: Represent an object with another object for access control.

Adapter (= Wrapper)

©c
yepr

Adapt an interface to an expected interface.

Unify interfaces with Adapter:
For instance: different payment gateways
(PayPal, iDEAL, Hipay, Moneybookers, etc.)

Instead of different interfaces

refactor to

one preferred interface
and write adapters for the others

Bridge

Decouple an abstraction from its implementation.

COLA

1 LITER

1 LITER

COLA

1 LITER

1 LITER

COLA

MILK
COLA

MILK

©c
yepr

MILK

COLA

Example: payment and payment providers

Composite

©c
yepr

Create a tree structure for part-whole hierarchies.
A node is also a (part of a) tree. Recursive:

Decorator

©cyepr

Add extra functionallity (at runtime),
while keeping the interface the same.
Matroushka’s...

In PHP you can use __call to copy parent methods:
public function __call($method, $args) {
return call_user_func_array(
array($this->decoratedInstance, $method),
$args
);
}

N.B.: Magic functions are magic...
but come at a cost!

Facade

Provide a general (simpler) interface for a set of interfaces.

©c
yepr

looks
simple

Flyweight

©c
yepr

Use one instance of a class
to provide many “virtual” instances.

Proxy

©c
yepr

Provide a surrogate or placeholder for another object
to control access to it.

Behavioral design patterns
●● Chain of Responsibility: Define a method of passing a

request among a chain of objects.
●● Command: Encapsulate a command request in an object.
●● Interpreter: Allow inclusion of language elements in an application.
●● Iterator: Enable sequential access to collection elements.
●● Mediator: Define simplified communication between classes.
●● Memento: Save and restore the internal state of an object.
●● Observer: Define a scheme for notifying objects of changes to
another object.
●● State: Alter the behavior of an object when its state changes.
●● Strategy: Encapsulate an algorithm inside a class.
●● Template Method: Allow subclasses to redefine the steps of
an algorithm.
●● Visitor: Define a new operation on a class without changing it.

Command

Encapsulate a command request in an object.

©c
yepr

YOU,DO YOUR
TASK!

TASK
LIGHT
ON

TASK
LIGHT
OFF

A command is an object to execute 1 method
Decoupling (Symfony2) Forms from Entities:

http://verraes.net/2013/04/decoupling-symfony2-forms-from-entities/

Chain of Command: Chain of Responsability with Commands

Replace Conditional Dispatcher with Command
if ($actionName == NEW_WORKSHOP) {
//do a lot
} else if ($actionName == ALL_WORKSHOPS) {
// do a lot of other things
} // and many more elseif-statements

NewWorkshopHandler, AllWorkshopsHandler, etc.

Chain of Responsibility
© yepr
c

Define a method of passing a request among a chain of objects.

Interpreter

Domain -> (little) language -> grammar -> objects (DSL)

©c
yepr

HÉ!

he means:
do this, do that,
and after finishing it,
go there!

Replace implicit language with Interpreter:
search-methods including combinations:
►►belowPriceAvoidingAColor( )
►►byColorAndBelowPrice( )
►►byColorSizeAndBelowPrice( )
interpretable expression:
$productSpec =
new AndSpec(
new BelowPriceSpec(9.00),
new NotSpec(newColorSpec(WHITE))
);
“You don’t need an Interpreter for complex languages
or for really simple ones.” (Joshua Kerievsky)

Iterator

Enable sequential access to collection elements, without showing

the underlying data-structures (array, list, records, etc)

next

©c
yepr

next

PHP: SPL iterators
►►http://www.php.net/manual/en/class.iterator.php
►►http://www.php.net/manual/en/spl.iterators.php
Stefan Froelich:
►►http://www.sitepoint.com/using-spl-iterators-1/
►►http://www.sitepoint.com/using-spl-iterators-2/
Anthony Ferrara video:
►►http://blog.ircmaxell.com/2013/01/todays-programming-with-anthony-video.html

State

Let an object show other methods
after a change of internal state (as if it changes it’s class).

in a.....hick......different state,
....hick....I behave differently....hick.....

©c
yepr

Strategy

For instance: different payment possibilities at checkout

Replace Conditional Logic with Strategy
if ($income >= 10000) {
return $income*0.365;
} else if ($income <= 30000) {
return ($income-10000)*0.2+35600;
} else //etc (...)
return ($income-60000)*0.02+105600;
} // note: mutual exclusive grouping
if ($income <= 100000) {
$strategy = new InsuranceStrategyLow($income);
} else if ($income <= 300000) {
$strategy = new InsuranceStrategyMedium($income);
} else //etc (...)
$strategy = new InsuranceStrategyVeryHigh($income);
}
return $strategy->calculateInsurance();
http://wiki.jetbrains.net/intellij/Replace_conditional_logic_with_strategy_pattern

Visitor

Make a kind of plugin-possibility for methods:
in that way methods can be added in runtime.

©c
yepr

printservice!

Some books
GOF: 23 “classical” patterns:

fun!
classic,
The Book

good start

PHP and Design Patterns
PHPexamples

Dec. 2013
Simple

Febr.
2013
Selection

PEAA & Refactoring

Fowler:
architectural patterns
for
enterprise applications

Fowler: also
known from
refactoring

Kerievsky:
refactoring
to patterns

Resign Patterns:

Ailments of Unsuitable Project-Disoriented Software

Questions?

Contact info:
Herman Peeren
herman@yepr.nl
© Yepr
Design Pattern Illustrations: Nelleke Verhoeff, Red Cheeks Factory, 2010
Creative Commons Public License for noncommercial use
http://creativecommons.org/licenses/by-nc/3.0/legalcode

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