RETHINKING OBJECT ORIENTATIONKathleen Dollard

kathleen@mvps.orgmsmvps.com/blogs/kathleen

Without passion, nobody is interested. Without responsibility, nothing will get done…If passion isn’t aroused, not much is going to happen, and responsibility will never have a chance.

From Open Space Technology website

AUCTIONING A DOLLAR

Auction of One US Dollar

Real auction - real money Whoever bids highest buys the dollar

Gives me what they bid Gets the dollar

Whoever bids next highest Gives me what they bid Gets nothing

The Point of the Auction

Individual decisions that are correct in context can lead to negative outcomes

This is especially true of incremental decisions extending past decisions You have working software with ugly difficult to

maintain code to accomplish a task. Today you need to make a very small change that will slightly increase the code’s complexity. Do you refactor it?

A core decision is whether to learn a technique

FAST TRACK HISTORY AND BASICS

Where did we start?

Four Pillars of Object Oriented Design

Abstraction Logical boundaries in a fluffy space Discrete, well defined entities

Encapsulation Secretive internals to objects “Black Box”

Inheritance Objects are specializations of other concepts/objects Objects share across specialization

Polymorphism Interchangeability Common features recognized

Where did we start?

Types of Relationships

“Is a” My Subaru is a car My pet is a cat

“Has a” My Subaru has an engine My cat has fur

“Uses a” My Subaru uses a roadway My cat uses my couch to nap and shed fur on

Where did we start?

A Few Basics

Public Billboard, sky writing

Protected No real world analogy

Friend (Internal) Notes on my refrigerator

Protected Friend Union Protected and Friend

Private My private journal

Quality of code matters Metaphors essential Good routines and

classes Self-documenting Short Strong cohesion Sin better than

SinAndTan Sine even better

Few order dependencies

Loose coupling

Scope Code Complete

Logical Biz Object

BizBase

BizBase(Of Tentity)

ProjectBizBase(Of Tentity)

Customer

IPersistenceProvider

IValidationProvider

IAuthorizationProvider

IFieldProvider

ExtensionMethod

ExtensionMethod

ExtensionMethod

ExtensionMethod

Construct

or

Timeline

1980’s

2009

SOLID (Bob Martin)

SRP: Single Responsibility One reason to exist, one reason to change

OCP: Open Closed Principle Open for extension, closed for modification

LSP: Liskov Substitution Principle An object should be semantically replaceable for it's base

class/interface – it should do the same thing ISP: Interface Segregation Principle

Don't force a client to depend on an interface it doesn't need to know about

DIP: Dependency Inversion Principle Depend on abstractions, not concrete detail or

implementations

OO Extended By…

1. Parallel entities

2. N-Tier

3. Sheer magnitude

4. Application code generation

5. SOA (Service Oriented Architecture)

6. Semantics and canonical messages

7. Workflow

8. Rules engines

9. Aspect oriented programming

10. Assembly organization

11. Designers (Property & UI)

12. Design Patterns

13. Unit testing

14. Refactoring

15. Overloads

16. Interfaces and contracts

17. Multiple assemblies

18. InternalsVisibleTo attribute

19. DependencyProperties

20. Perf and virtual table issues

21. Generics

22. Reflection

23. Intellisense

24. Partial classes

25. Partial methods

26. Extension methods

27. Lambda expressions

28. Anonymous types

29. Declarative - XAML

30. WPF

31. Declarative – LINQ

32. Dynamic languages

33. Functional languages

34. SilverlightAnnotation:See more at msmvps.com/blogs/kathleen December, 2007 (see notes in a few slides)

In a Service/Workflow World,Do Objects Matter?

“Objects” are distinct from services Wrapping objects is fragile –objects != services

Object thinking remains important orthogonal to process Granularity is essential Flexibility is essential Evolution is essential Conceptualization is essential Reuse is essential

Yes, they matter because they help get the job done If their getting the job done, they must be written well to

allow reasonable maintenance

MEF = Managed Extensibility Framework

Open set of extensions Custom additions to application Don’t have to know finite set ahead of discovery Encourages ecosystem

Um, so what is it? Plug-in enabler Compositional engine Dependency injection / inversion of control – sort of

Car object not responsible for wheels they just show up

MEF is not registration based Manages unknown things while IOC manages known things

What’s it made of? Consists or parts that has exports and imports Extensions can be extended Can provide extensions what they need

MEF: Managed Extensibility Framework

Com

posit

ion

C

on

tain

er

Intellisense

extensions Word

Highlighter

Text Coloratio

n

Back color

Start page

DSL Syntax

MEF Requests

Part A

I need

an “x”

Part BPart

Part Part

I have an “x”

Notes added morning after talk (1 of 2)

Thank you for coming. I enjoyed it. I learned a lot from Dave’s talk and I think it’s important to understand and express that range. We are all part of creating IT business value. That takes perspective (Dave) and code (me). I liked that we covered that range.

One approach to managing complexity is “Kathleen’s Happy Place” where we have actual tools for sharing and expressing architecture based on well-known metadata patterns. But, I neglected to discuss other approaches, if you see/imagine/vision more, please email me Refuse to uptake. This is the pattern emerging in the industry. I am still asked to give my

generics talk. It’s four years old and I’ve given it about 30 times. WPF uptake is slow and it’s a good technology. WCF generally has uptake only when there is a real service need. Sometimes this is because of technology issues (WF and EF), but more often it’s simply the inability to get our jobs done and uptake This is bad for the industry. In general, new tools/techniques allow us to do our job better Today we are writing a vast amount of code that is of legacy quality on the day it is written

Work in teams/network. .NET killed the hobbyist programmer. I drew the curve where the amount of time to learn meets available time with productivity approaching zero. The hobbyist programmer was “canary in a coal mine”. Hobbyists programmed and had unrelated jobs – the grip, pet store owner, radio sales manager, advisor to Canadian politicians. They were (in industry, not humanitarian terms) expendable. Today we are fast losing one person shops. No one can be competent, but today teams can still be competent. This will not last forever if the curve continues to increase because communications limits team efficacy

A corollary of the previous – hire experts. Not people who claim to be experts, but the best people in the world in areas of concern

Build in a full 50% resources for technology spiking in a combination of dedicated experts and committed percentage of every person in the chain’s time Training almost completely fails for many reasons here.

Notes added morning after talk (2 of 2)

Build process, reduce friction, minimize inefficiencies, but know that’s a temporary stop gap measure

Find heroes to follow You must be selective in what you bother with. One way to do that is to select, respect, and

turnover the people you listen to. If Glenn Block is doing it, I want to know about it (although that’s leaning way past the bleeding edge). Listen to DNR and especially Hanselminutes on you commute

Quit I know it sounds depressing to say, but there are careers that are less insane than ours will be in

the next five years

I felt that composability (MEF) is an important enough architectural change to call out in an architecture group. It’s new thinking for solution architects. Perhaps I can speak on this topic in a future meeting.

I don’t think I put my full list of change items on my blog, or perhaps I exaggerated. But a lot has been added in the last 18 months. I talked about this list on DNR #171 I stopped creating this list when I realized it was fractal. What I mean by that is as

you look at it under increasing zoom, it becomes more complicated, it became non-interesting as it seemed I would add things forever. However, I have considered returning to update it with announcements in the last 18 months.

Thank You!

•www.msmvps.com/blogs/kathleen •kathleen@mvps.org •Ask Kathleen, www.VisualStudioMagazine.com

•April 2008 for System.AddIn discussion•April 2009 for MEF discussion•Also Bill McCarthy and Bill Wagner’s columns

•Hanselminutes: #152 March 5, 2009•Also, good Bob Martin interview

•DotNetRocks: #436 April 9, 2009 (also, #304, 171, 121, 63)•About MEF – www.Hanselminutes.com Show #148 (3 times)

•MEF download - www.codeplex.com/MEF •TL49 (MEF-ify BabySmash), TL33 (Glenn Block) at PDC•Pipeline Builder download: www.codeplex.com/clrAddin •Video on MAF: http://channel9.msdn.com/posts/DanielMoth/Managed-AddIn-Framework/

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