Object Oriented Apologetics

Vance LucasCodeWorks 2009 Dallas

September 27, 2009

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What?

Not an apologyGreek root- apologia (απολογία)- “speaking in defense”

To defend the use of, andprovide rational reasoning for

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Who is it for?

For People Who:• Are “on the fence” about OOP

vs procedural• Are unconvinced of the

usefulness of OOP• Want to learn WHY they should

learn about OOP

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Purpose: To Get You Hooked on OOP

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NO Academic or Mundane Examples

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No Shapes, Cars, Fruit, or Bicycles

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<?php class myClass { public function myClass(){ } public function echoMe(){ echo 'me'; } } $mine=new myClass(); $mine->echoMe();

?>

No “Hello World” Scripts

SO… WHY OOP?

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Polymorphism

I nheritance

E ncapsulation

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Polymorphism

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• Making things that are not the same look the same

• Relies on a defined interface• Inheritance is probably the most used method

• The ability of type A to be used like type B• Think: Interchangeable types or components

Polymorphism

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Real World: Different Implementations

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Procedural - Inline

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Object-oriented – Polymorphic Interface

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Inheritance

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• Extend from a parent class– “is-a” relationship

• Creates hierarchal relationship• Get functionality for free• Global changes are easier

• Inherits all functions and properties from parent• Think: A is a B, with a few differences

Inheritance

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Controller: Zend Framework

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Model: phpDataMapper

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Warning: Keep Hierarchy Shallow

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Encapsulation

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• Hide specific implementation details• Reveal only methods and properties required to

interact with the object

• Limits interdependencies between components• Think: Separation of responsibilities

Encapsulation

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Payment Interface – Exposed Methods

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Planetoids (by Micah Jones)

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• Asteroids responsible for their own movement• Different: velocities, sizes, shapes, rotations, color,

and fragment pieces• All the code and math calculations for movement are

encapsulated behind ‘move()’• Allows different types of objects and asteroids to be

treated the same in code – “polymorphically”

Planetoids: Code Abstraction

OTHER OOP-ONLY FEATURES?

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Lazy-Loading

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• Uses __get() “magic” method in PHP5 object model

• Also uses SPL interfaces to fire query on:– count()– foreach()

• Used as a hook to retrieve related rows on call• Caches results so only 1 query is fired• Can eliminate N+1 query problem by mapping

Lazy-Loading: OOP Only

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• Classes are actually custom types• Can type-hint for classes or interfaces

• PHP Standard types:– string, int, float, boolean, array, object, null– resource

Custom Type Creation & Type-Hinting

OTHER REASONS TO USE OOP?

• Easily group related properties/data• Avoid using globals or passing/returning arrays• Suppress errors ala ‘undefined index’• More?

Convenience (a.k.a. Laziness)

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• Request object: Why not $_POST?– Data comes from multiple sources• POST/GET, XML, JSON, etc.

– Other functions• isAjax(), isPost(), etc.

– Sanitizing user input

• Session object: Why not $_SESSION?– More options for saving/storing• Database, separate server, memcached, etc.

Request / Session Objects

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Request Object: Convenience, too!

NEED AN EXAMPLE?

E-commerce Cart: Work Scope• Basic categories (1-level)• Simple products, no options, stock, etc.• Simple checkout, no user accounts• Authorize.net integration• UPS rate quotes• Admin backend• Order fulfillment• Invoice/packing slip printing

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Simple Cart

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Simple Checkout

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Simple UPS Integration

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• So far it’s OK• It works• We finished and worked quickly

Status Check

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Client MessageI talked to my next door neighbor’s cousin’s

brother’s niece yesterday, and he says all the serious online stores have regular sales. That’s something I can do too, right?

- Bob

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Product Sales

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New Code for Product Sale

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• We also have to add this code to the admin backend for customer invoices.– And to the email reciepts

• Sin of code duplication– Code smell

Thoughts

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Client MessageHey, I was at the grocery store yesterday and

my daughter got 2 candy bars for $1, when they were originally $0.75 each.

I know that if I am able to do this, I’ll get a lot of sales and it will make me rich. I need to be able to do this.

- Bob

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Multi-Quantity Discounts

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New Code, Again

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• We also have to add this code to the admin backend and other places again.

• Sin of code duplication

• We could use procedural functions for this– Where would we put them?– What responsibilities do they have?

Thoughts

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What about the future?

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Employee Discounts

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Switching to FedEx

Stock Checking

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Clearly, as the project grows, it will become amaintenance nightmare if we continue on thecurrent path.

We don’t want our code to be the running joke ofthe PHP community.

We need something better

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Use the right tool for the right job

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OOP: Right tool for this job

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• Create a Cart class to store items• Encapsulate the pricing logic in an Item class– Single place to change the code– Item is responsible for knowing it’s price (?)• What does this imply?

Thoughts

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Possible Code Changes

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• Still storing cart in session, but now we can change it later when we need to scale

• Cart gets item price so it can check quantities– Cart is responsible for knowing other items in cart

• Better separation of responsibility– It’s not the job of the display logic to calculate the

item’s price or apply discounts• What about changing to FedEx?

Thoughts

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Re-factor it into two classes

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• Package is responsible for knowing it’s own dimensions and weight

• Quote is responsible for fetching a live rate quote from a carrier API service

• Always think in terms of responsibility– What code is responsible for what functions?– Where does it go in my app?– Is this code doing too much?

Thoughts

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Think about how an assembly line works

OOP MYTHS AND MISCONCEPTIONS

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Myth #1:OOP is about code re-use

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Truth:Re-useable code is a by-product of good OO

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Problem:There are lots of ways to make re-useable code

that are not object-oriented nor good.It’s a bad goal.

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<Code with functions and includes – re-useable>Functions are re-useable

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Specific implementations are re-useable

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<UPS-Specific API Code>or<Payment Gateway-specific API Code>

Soft interfaces are re-useable

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• You must set goals that will help direct you to your desired outcome

• Goals narrow attention and direct efforts to goal-relevant activities, and away from perceived undesirable and goal-irrelevant actions

• Re-use as a goal does not help you write good OO code. Re-use is a by-product of good OO.

Point: Set Good Goals

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Myth #2:Objects should always be modeled after real-world

objects when possible

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Truth:Objects should be modeled and built based on

what you need to complete your task

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Problem:Real-world object models are almost never useful

in code

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Real-World Objects Change

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You are modeling things that don’t

exist

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Myth #3:Everything should be objects

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Truth:Make objects for only what you need to. Most of

the time this is data. Don’t over-complicate your code when it’s not necessary.

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Problem:Not everything your code does can be easily

represented with an object

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Application Flow

MVC diagram forXEROX PARC 1978-79

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• Programming PHP for over 10 years• Web: http://www.vancelucas.com• Twitter: @vlucas• Email: vance@vancelucas.com• GitHub: http://github.com/vlucas

• Photo Set: http://www.flickr.com/photos/30728345@N05/galleries/72157622318592067/

Vance Lucas