A quick overview of some common design patterns in PHP

1. Common PHP Design
Patterns
David Stockton
Front Range PHP User Group - Feb 18, 2015

2. What are design patterns?

3. Common Language

4. Gang of Four
Cartman, Kyle, Stan, Kenny

5. Gang of Four
Gamma, Helm, Johnson, Vlissides

6. What aren’t design patterns?

7. Silver Bullets

8. Legos for Coding

9. Scratch is Legos
for Coding
This talk is not about scratch

10. Design Patterns
Help You Talk to
Other Coders

11. Hey, I’m building a chunk
of code that is used to
build an object which has
a lot of dependencies and
setup and each of those
has a few of their own so
this piece of code will take
care of putting together all
those pieces so that when
I need the object I just
have to ask this one object
to give me the other one
and then I can use it where
ever I need instead of
having to build a huge
dependency tree before
using this code…

12. LOL
WUT?

13. I’m building a factory.

14. What does a factory do?
• Builds objects
• Encapsulates building of objects so there’s only one
place to find how to build it

16. Singleton

17. Singleton
There can be only one

18. Singleton
• For classes where we want only one instance

20. Downsides of Singleton
• It is a global
• Hard to test
• Better ways to do this

21. Another pattern description
• I’m going to create a shopping cart where I can
choose how the discounts or promo codes will be
applied by injecting various objects, each of which can
include how to apply these discounts; for example
apply discounts only to items that don’t have other
discounts, apply discount percentage on the base
price not counting already applied discounts, apply
discount percentage after other applied discounts,
apply a flat amount of a discount for each item, apply
a discount on an item based on what type of item it is,
etc

22. Strategy pattern
• I’m going to create a shopping cart where I can
choose how the discounts or promo codes will be
applied by injecting various objects, each of which can
include how to apply these discounts; for example
apply discounts only to items that don’t have other
discounts, apply discount percentage on the base
price not counting already applied discounts, apply
discount percentage after other applied discounts,
apply a flat amount of a discount for each item, apply
a discount on an item based on what type of item it is,
etc

23. Strategy pattern
• Allow injection of object that provides some aspect of
the functionality
• Algorithm’s functionality can be decided at run-time
• Examples:
• usort - Provide comparison part of sort
• Car - brakingStrategy

24. Command Pattern
• I’m doing a bunch of stuff that I want to be able to
keep track of and potentially save and replay later,
possibly be able to undo. In order for this to work my
object will have to capture everything it needs to know
about as far as parameters and what-not in order to be
able to run later as well as potentially capturing state
so I can get back to where I was before.

25. Command Pattern
• Uses:
• Recording Macros
• Multi-level Undo
• Progress Bars
• Transactional Behavior
• Wizards

26. Chain of Responsibility
• Each object can take care of something (or not), then it
passes to the next object

27. Chain of Responsibility
Examples
• Loggers - set next logger in chain, each calls the next
when it is done
• Managers with purchasing power - if amount is above
manager’s level, pass to the next object in the chain

28. Observer Pattern
• Notify interested objects of state changes in subject
• Interested objects subscribe to subject
• When subject changes, it calls update on all observers

29. MVC - Model View Controller
• Organizational pattern for web dev
• View code contains output
• Model code is for data/business logic
• Controller links model and view code

30. Front Controller
• Central entry point for handling requests for web
application
• Route all calls through index.php, then figure out what
to do with it

31. Adapter Pattern
• Allow interface for an existing class to be used from
another interface

32. Facade Pattern
• Provide simplified access to a complex system

33. Other Patterns
• Bridge
• Composite
• Decorator
• Front Controller
• Blackboard
• Iterator
• Mediator
• Memento
• Null Object
• Specification
• State
• Template Method
• Visitor
• Abstract Factory
• Prototype