Common PHP Design Patterns

David Stockton Front Range PHP User Group - Feb 18, 2015

What are design patterns?

Common Language

Gang of FourCartman, Kyle, Stan, Kenny

Gang of FourGamma, Helm, Johnson, Vlissides

What aren’t design patterns?

Silver Bullets

Legos for Coding

Scratch is Legos for Coding

This talk is not about scratch

Design Patterns Help You Talk to

Other Coders

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…

LOL WUT?

I’m building a factory.

What does a factory do?

• Builds objects

• Encapsulates building of objects so there’s only one place to find how to build it

Singleton

SingletonThere can be only one

Singleton

• For classes where we want only one instance

Downsides of Singleton

• It is a global

• Hard to test

• Better ways to do this

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

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

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

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.

Command Pattern

• Uses:

• Recording Macros

• Multi-level Undo

• Progress Bars

• Transactional Behavior

• Wizards

Chain of Responsibility

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

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

Observer Pattern

• Notify interested objects of state changes in subject

• Interested objects subscribe to subject

• When subject changes, it calls update on all observers

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

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

Adapter Pattern

• Allow interface for an existing class to be used from another interface

Facade Pattern

• Provide simplified access to a complex system

Other Patterns• Bridge

• Composite

• Decorator

• Front Controller

• Blackboard

• Iterator

• Mediator

• Memento

• Null Object

• Specification

• State

• Template Method

• Visitor

• Abstract Factory

• Prototype