Rethinking Object Orientation
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Rethinking Object Orientation - By Kathleen Dollard Decades after object orientation design altered programming, it¡¯s still evolving, and we¡¯re still learning to use it better. Many changes in the tools we use and how we write applications affect the approach we take to OOD. Some of these changes relate to architecture where approaches like SOA and the layering revolution behind Silverlight alter the place of traditional OOD within the bigger picture of architecture. Other changes are language improvements that alter the very meaning of the phrase ¡°object¡± from a design point of view. Language features that alter our implementation of logical objects include generics, extension methods, delegates/lambda expressions, partial classes/methods, reflection, anonymous types, and declarative programming. We¡¯ll also explore the growing role of interfaces as a contractual base in composable applications and explore differences between traditional applications and ecosystem empowering applications. I¡¯m really excited to give this talk to a group with diverse skillsets! Come ready for multi-way conversations because I want to learn from you.
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Rethinking Object Orientation
- 1. Rethinking Object OrientationKathleen Dollardkathleen@mvps.orgmsmvps.com/blogs/kathleen
- 2. 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
- 4. Auction of One US DollarReal auction - real moneyWhoever bids highest buys the dollarGives me what they bidGets the dollarWhoever bids next highestGives me what they bidGets nothing
- 5. The Point of the AuctionIndividual decisions that are correct in context can lead to negative outcomesThis is especially true of incremental decisions extending past decisionsYou 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
- 6. Fast Track History and Basics
- 7. Where did we start?Four Pillars of Object Oriented DesignAbstractionLogical boundaries in a fluffy spaceDiscrete, well defined entitiesEncapsulationSecretive internals to objects¡°Black Box¡±InheritanceObjects are specializations of other concepts/objectsObjects share across specializationPolymorphismInterchangeabilityCommon features recognized
- 8. Where did we start?Types of Relationships¡°Is a¡±My Subaru is a carMy pet is a cat¡°Has a¡±My Subaru has an engineMy cat has fur¡°Uses a¡±My Subaru uses a roadwayMy cat uses my couch to nap and shed fur on
- 9. Where did we start?A Few BasicsPublicBillboard, sky writingProtectedNo real world analogyFriend (Internal)Notes on my refrigeratorProtected FriendUnion Protected and FriendPrivateMy private journalQuality of code mattersMetaphors essentialGood routines and classesSelf-documentingShortStrong cohesionSin better than SinAndTanSine even betterFew order dependenciesLoose couplingScopeCode Complete
- 10. Logical Biz ObjectBizBaseIPersistenceProviderExtensionMethod1980¡¯s2009BizBase(Of Tentity)IValidationProviderExtensionMethodIAuthorizationProviderExtensionMethodProjectBizBase(Of Tentity)IFieldProviderExtensionMethodCustomerConstructorTimeline
- 11. 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 ¨C it should do the same thingISP: 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
- 12. OO Extended By¡Interfaces and contractsMultiple assemblies InternalsVisibleTo attributeDependencyPropertiesPerf and virtual table issuesGenerics ReflectionIntellisensePartial classesPartial methodsExtension methodsLambda expressionsAnonymous typesDeclarative - XAMLWPFDeclarative ¨C LINQDynamic languagesFunctional languagesSilverlightParallel entitiesN-TierSheer magnitudeApplication code generationSOA (Service Oriented Architecture)Semantics and canonical messagesWorkflowRules enginesAspect oriented programmingAssembly organizationDesigners (Property & UI)Design PatternsUnit testingRefactoringOverloadsAnnotation:See more at msmvps.com/blogs/kathleen December, 2007 (see notes in a few slides)
- 13. In a Service/Workflow World,Do Objects Matter?¡°Objects¡± are distinct from servicesWrapping objects is fragile ¨Cobjects != servicesObject thinking remains important orthogonal to processGranularity is essentialFlexibility is essentialEvolution is essentialConceptualization is essentialReuse is essentialYes, they matter because they help get the job doneIf their getting the job done, they must be written well to allow reasonable maintenance
- 14. MEF = Managed Extensibility FrameworkOpen set of extensionsCustom additions to applicationDon¡¯t have to know finite set ahead of discoveryEncourages ecosystemUm, so what is it?Plug-in enablerCompositional engineDependency injection / inversion of control ¨C sort ofCar object not responsible for wheels they just show up MEF is not registration basedManages unknown things while IOC manages known thingsWhat¡¯s it made of?Consists or parts that has exports and importsExtensions can be extendedCan provide extensions what they need
- 15. Word HighlighterBack colorDSL SyntaxMEF: Managed Extensibility FrameworkIntellisense extensionsText ColorationStart pageComposition Container
- 16. MEF RequestsPartPart I have an ¡°x¡±I need an ¡°x¡±Part Part BPart A
- 17. 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 meRefuse 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 uptakeThis is bad for the industry. In general, new tools/techniques allow us to do our job betterToday we are writing a vast amount of code that is of legacy quality on the day it is writtenWork 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 ¨C 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 ¨C hire experts. Not people who claim to be experts, but the best people in the world in areas of concernBuild in a full 50% resources for technology spiking in a combination of dedicated experts and committed percentage of every person in the chain¡¯s timeTraining almost completely fails for many reasons here.
- 18. Notes added morning after talk (2 of 2)Build process, reduce friction, minimize inefficiencies, but know that¡¯s a temporary stop gap measureFind heroes to followYou 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 commuteQuitI know it sounds depressing to say, but there are careers that are less insane than ours will be in the next five yearsI 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 #171I 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.
- 22. April 2008 for System.AddIn discussion
- 23. April 2009 for MEF discussion
- 24. Also Bill McCarthy and Bill Wagner¡¯s columns
- 25. Hanselminutes: #152 March 5, 2009
- 26. Also, good Bob Martin interview
- 27. DotNetRocks: #436 April 9, 2009 (also, #304, 171, 121, 63)
- 28. About MEF ¨C www.Hanselminutes.com Show #148 (3 times)
- 29. MEF download - www.codeplex.com/MEF
- 30. TL49 (MEF-ifyBabySmash), TL33 (Glenn Block) at PDC
- 31. Pipeline Builder download: www.codeplex.com/clrAddin
- 32. Video on MAF: http://channel9.msdn.com/posts/DanielMoth/Managed-AddIn-Framework/Thank You!www.appventure.com