advanced php: design patterns - dennis-jan broerse

Advanced PHP

Advanced PHPA touch of Design Patterns

Dennis-Jan Broerse - 13 juni 2008

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Sources

• Download the sources:http://www.ibuildings.nl/downloads/trainingusername: dpc_2008password: dpc_2008

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Introduction

• First conference where I’m a speaker

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Topics

• Introduction to Design Patterns

• Duck simulator

• Weather application

• Coffee bar

• Traveller

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Introduction to Design Patterns

• Best-practise ‘design’ solution

• Lessons learned by other developers

• Based on the OO principles

• Language in-depended

• Puzzles for the creative mind of developer

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OO Basics

* Abstraction* Encapsulation* Polymorphism* Inheritance

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OO Basics


OO Principles

* Encapsulate what varies* Favour composition over inheritance* Program to interfaces, not implementations

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• It’s all about creating flexible designs that are maintainable and are able to deal with changes!

• Don’t re-invent the wheel!

• Load the design patterns into your brain and then design/build your application

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Duck simulator

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Duck simulator

What we want

• Creating as many ducks as needed

• Ducks quack and swim

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Duck simulator

What we want

• That’s easy!!

• We can use INHERITANCE

• Yes, we know our OO basics

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Duck simulator

What we want

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Duck simulator

First change

• Our ducks have to fly!

• No problem

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Duck simulator

First problem

• Rubber ducks don’t fly!(and I don’t mean throwing)

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Duck simulator

First change

• This can't be the solution(imagine what you have to do if you want to create a decoy duck)

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Duck simulator

Cleaner solution

• How about an interface?

• Only implementing the interface if the duck is flyable

• Hmm that’s it, that’s the solution

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Duck simulator

Cleaner solution

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Duck simulator

Think again

• What happens if we have to change the fly behaviour?

• Exactly, we have to change all instances!

• And we duplicate code

• Wouldn’t it be dreamy if we can change its behaviour at runtime?

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Duck simulator

Think again

• Do you remember the OO basics and principles?

• ‘Identify the aspects of your application that vary and separate them from what stays the same’

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Duck simulator

Last change

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Duck simulator

Benefits• Flexible

• Maintainable

• Extendable

• No code duplication

• Encapsulated

• Change behaviour at runtime

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Duck simulator

Code sample

• Code sample

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Duck simulator

Strategy Design Pattern

• ‘The strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.’


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Duck simulator

Guru

• Now you’ll understand why you should know about design patterns!

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Weather application

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Weather application

What we want

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Weather application

What we want

WheatherData object

Pulls dataDisplays

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Weather application

Requirements

• There are 3 get methods for temperature, humidity and pressure

• measurementsChanged method will be automatically called if the measurements are changed

• We have to implement the 3 display elements and they must be updated when measurements change

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Weather application

First implementation

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Weather application

What’s wrong

• What if we want to add a new display?

• Exactly: we have to change the code

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Weather application

What’s wrong

• Remember the OO basics and principles!

• Not flexible

• Not extendable

• No encapsulation

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Weather application

Let’s look

• Investigate what’s going on

• What is the relationship between the weather object and the display elements?

• Maybe we can apply a design pattern?

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Weather application

Let’s look

• The relationship looks like a newspaper subscription

• If you want to receive the newspaper, you have to subscribe yourself at the publisher

• The publisher will send you your newspaper every time until you unsubscribe

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Weather application

So....

• The weather object is the publisher

• The display elements are the people who are willing to receive the newspaper

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Weather application

And that is...

• Yes, that is a design pattern!

• Called ‘The Observer Pattern’

• Publisher == Weather object == Subject

• People == Display elements == Observers

• Subject notifies every observer to update

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Weather application

Formal description

• ‘The Observer Pattern defines a one-to-many dependency between objects so that when one object changes state, all of its dependents are notified and updated automatically.’

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Weather application

The class diagram

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Weather application

New design principle

• Creating new observers won’t require a change in the subject

• Changes to either the subject or an observer will not affect the other

• Reusing a subject or an observer can independently of each other

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Weather application


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Weather application


OO Principles

* Encapsulate what varies* Favour composition over inheritance* Program to interfaces, not implementations* Strive for loosely coupled designs between objects that interact

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Weather application

New design

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Weather application

New design

• Code sample

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Coffee bar

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Coffee bar

What we want

• An application that calculates the price of different beverages

• The flexibility to add new beverages

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Coffee bar

Simple solution

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Coffee bar

Condiments??

• No problem!

• We have an OO application; just inherit

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Coffee bar

First attempt

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Coffee bar

First attempt

• Euhm, this isn’t maintainable, this is a class explosion!!

• Try again!!

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Coffee bar

OK, sorry

• Well that’s better, wouldn’t you agree?

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Coffee bar

Really?

• Did you really learn something?


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Coffee bar


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Coffee bar


OO Principles

* Encapsulate what varies* Favour composition over inheritance* Program to interfaces, not implementations* Strive for loosely coupled designs between objects that interact* Classes should be open for extension, but closed for modification

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Coffee bar

What we really want

• We’d like to extend a beverage with condiments

• We wouldn’t like to change the beverage

• We’d like to add new beverages and condiments without changing the existing code

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Coffee bar

New design pattern

• The ‘Decorator Design Pattern’ saves our day

• ‘The decorator pattern attaches additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.’

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Coffee bar

Our new design

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Coffee bar

Our new design

• This is really great!

• Now we can say:One HouseBlend coffee with milk and mocha.What is the price?€ 1,95

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Coffee bar

How does it work?

• Wrap the houseBlend object with Milk object and wrap that with a mocha object

• Ok, this is hard.Show me the code man.

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Coffee bar

How does it work?

• Code sample

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Traveller

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Traveller

What we want

• An application which tells us if the conditions are suitable enough to make the trip

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Traveller

Wait a minute

• The traveller doesn’t want to make the trip if the average temperature of the destination is lower than his minimum required temperature

For example:

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Traveller


• What do you think?

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Traveller


• Indeed, not very smart!

• Not possible to add requirements

• Requirements changes, so trip class has to be changed

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Traveller

Take that out

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Traveller

That’s nice

• We are able to create multiple specifications without changing other objects

• Readable, maintainable, simple and effective

• And it is a design pattern too!!‘Hard-coded Specification Pattern’

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Traveller

But...

• The specification knows too much

• Not able to make logical specifications

• Does violate some OO principlesYou know them by now, right?

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Traveller

What we really want

• A design which is flexible enough to validate almost every object

• Validating against several conditions

• Making logical expressions

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Traveller

Let’s redesign

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Traveller

Wow, that’s heavy

• Code sample

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Traveller

This is ...

• ‘The Specification Pattern’ by Martin Fowler (www.martinfowler.com)

• Flexible, maintainable

• Ready for complex validation

• Loosely coupled

• Most unknown design pattern

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Summary

• Best-practise ‘design’ solution

• Lessons learned by other developers

• Based on the OO principles

• Language in-depended

• Puzzles for the creative mind of developer

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Summary

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Summary

OO Basics


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Summary

OO Basics


OO Principles

* Encapsulate what varies* Favour composition over inheritance* Program to interfaces, not implementations* Strive for loosely coupled designs between objects that interact* Classes should be open for extension, but closed for modification

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Summary

• Strategy Design Pattern

• Observer Design Pattern

• Decorator Design Pattern

• Specification Design Pattern

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Questions

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References

• [email protected]

• www.ibuildings.nl / www.ibuildings.com

• php|architect’s Guide to PHP Design Patterns

• O’Reilly Head First Design Patterns

• www.ibuildings.com/training/

advanced php: design patterns - dennis-jan broerse

Technology

inheritance advanced

implementation advanced

newspaper advanced php

duck simulator advanced

runtime advanced php

speaker advanced php

swim advanced php

implementations advanced