All 'classic' 23 GOF Design Patterns, illustrated by Nelleke Verhoeff (Red Cheeks Factory). Trying to show the essence of each Design Pattern, with some examples from PHP. Second version of my Design Patterns presentation. This presentation was held February 13, 2014 at the 010PHP meeting in Rotterdam. Presentation was in Dutch.

1. Design Patterns
illustrated
010PHP
Törööö
By Laurent Steinmayer
Herman Peeren, February 13, 2014
(Design Patterns illustrations: Nelleke Verhoeff, 2010)

2. 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

3. The one
constant in software development:

4. The one
constant in software development:
CHANGE!

5. The one
constant in software development:
CHANGE!
I knew it ...

6. Ideal: code as modular black boxes

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

8. Avoid: tight coupling!

9. It might get you into trouble...

10. Beware of:
Code
smells!

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

12. Classic pattern categories
creational, structural and behavioral patterns:
►►creational: object instantiation
►►structural: larger structures of classes or objects
►►behavioral: interaction and distribution of responsibility

13. 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

14. 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.

15. Factory Method
Provide an interface for the creation of objects.
©c
yepr
Allow subclasses to “decide” which class to instantiate.

16. Example: different kinds of customers...

17. ...with different kinds of invoices

18. Abstract Factory
©c
yepr
Povide an interface for creating families of related
or dependent objects. A factory for factories.

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

20. Builder
©c
yepr
Seperate the construction process (how) of a complex object
from the concrete representations (what).

21. 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...

22. Singleton
Ensure a class only has one instance, and provide a global
point of access to it.
© yepr
c
Oh, I’m so
loooooooonly

23. 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

24. “Every
advantage
has its
disadvantages”
(free to Johan Cruyff,
Dutch Football Pattern Designer
and Ajax-fan...)

25. Prototype
Make variations on copies of a basic-object.
c
© yepr
COPY-SERVICE

26. 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

27. 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.

28. Adapter (= Wrapper)
©c
yepr
Adapt an interface to an expected interface.

29. 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

30. 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

31. Example: payment and payment providers

32. Composite
©c
yepr
Create a tree structure for part-whole hierarchies.
A node is also a (part of a) tree. Recursive:

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

34. Decorator

35. 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!

36. Facade
Provide a general (simpler) interface for a set of interfaces.
©c
yepr
looks
simple

37. Flyweight
©c
yepr
Use one instance of a class
to provide many “virtual” instances.

38. Proxy
©c
yepr
Provide a surrogate or placeholder for another object
to control access to it.

39. 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.

40. Command
Encapsulate a command request in an object.
©c
yepr
YOU,DO YOUR
TASK!
TASK
LIGHT
ON
TASK
LIGHT
OFF

41. 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.

42. Chain of Responsibility
© yepr
c
Define a method of passing a request among a chain of objects.

43. Interpreter
Domain -> (little) language -> grammar -> objects (DSL)
©c
yepr
HÉ!
he means:
do this, do that,
and after finishing it,
go there!

44. 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)

45. Iterator
Enable sequential access to collection elements, without showing
the underlying data-structures (array, list, records, etc)
next
©c
yepr
next

46. 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

47. Mediator
©c
yepr
Layer in between: communication via one object.

48. Memento
Save and restore the internal state of an object.
©cyepr
ME

49. Observer
Notify “subscribers” of changes.
ME
ME
©c
yepr
WHO?
NO
ME

50. 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

51. Strategy
When something can be done in several ways, make those
ways interchangeable.
©c
yepr
POSSIBILITIES

52. Strategy
For instance: different payment possibilities at checkout

53. 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

54. Template Method
©c
yepr
The skeleton of an algorithm is fixed,
but parts can be filled in differently.

55. Visitor
Make a kind of plugin-possibility for methods:
in that way methods can be added in runtime.
©c
yepr
printservice!

56. Move Accumulation to Visitor

57. Some books
GOF: 23 “classical” patterns:
fun!
classic,
The Book
good start

58. PHP and Design Patterns
PHPexamples
Dec. 2013
Simple
Febr.
2013
Selection

59. PEAA & Refactoring
Fowler:
architectural patterns
for
enterprise applications
Fowler: also
known from
refactoring
Kerievsky:
refactoring
to patterns

60. Resign Patterns:
Ailments of Unsuitable Project-Disoriented Software

61. 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