cf.OBJECTIVE (ANZ) Design Patterns and Form Processing Jaime Metcher Software Architect, Centre for Innovation in Professional Learning, University of Queensland

About me B.Sc (maths) Aerial survey software (in the 80's!) Kids LAN wrangler at UQ Coldfusioneer at Med-E-Serv Archi-thingie back at UQ B.Sc (maths) Aerial survey software (in the 80's!) Kids LAN wrangler at UQ Coldfusioneer at Med-E-Serv Archi-thingie back at UQ OUTPUT 2500AD ORG 2000H MOV DX,0FFE6H MOV AX,82H OUT DX,AL NEXT:MOV AX,3000H MOV BX,0000H CALL DISP NOT AL MOV 3001H,AL MOV BX,0100H CALL DISP JMP SHORT NEXT DISP:PUSH AX MOV CX,1 CALL FAR 0FF00:0B12H POP AX RET END

About you Your team lead is bugging you You are the team lead and you want to bug your juniors: What do you do that's so great? How do you teach that? You want to pad your CV You know all about patterns and you're here to heckle You thought this was the Railo talk

Outline Design Patterns by Example Template method Composite Design Patterns World Tour Architecture Software engineering Education Conclusion Motherhood statements Resources Questions

Example – form processing Simple See code sample - simple

Example – form processing Let's componentize a bit... See code sample - simple.cfc

Example – form processing Add some functionality: Support multiple forms on a page Detect incomplete form transmission See code sample - bettercfc

Example – form processing Now refactor out some common functionality: See code sample - bettercfcrefactored

Example – form processing A little less procedural, just for fun: See code sample - templatemethod

Template method if (isSubmitted() and validated()) { commit(); } Other ways to do this? Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure. - Design Patterns: Gamma et al. (aka GoF)

Example – form processing OK, let's separate some concerns: See code sample - templatemethodrefactored

Example – form processing More guts, more glory See code sample – composite

Composite Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly - Design Patterns: Gamma et al. (aka GoF) myCompositeFormGuts = CreateObject("component", "compositeFormGuts").init("puttin_it_togetha"); myCompositeFormGuts.addChild(myFormGuts1); myCompositeFormGuts.addChild(myFormGuts2);

What's a pattern? Name Intent Context How it works Trade-offs

And why should I care? Prevent 'defactoring' “Hey, I noticed there was this totally unnecessary inheritance lying around so I refactored it out” Communication “Why do we have this one crazy class that has the same interface as all the others but is completely different under the hood?” Education

World tour - architecture Alexander's “A Pattern Language” - read it! Light on two sides: When they have a choice, people will always gravitate to those rooms which have light on two sides, and leave the rooms which are lit only from one side unused and empty. Therefore: Locate each room so that it has outdoor space outside it on at least two sides, and then place windows in these outdoor walls so that natural light falls into every room from more than one direction.

World Tour – Software Engineering GoF – Design Patterns Singleton Iterator Decorator Martin Fowler – PoEAA Front Controller Gateway Single Table Inheritance Gregor Hohpe – Enterprise Integration Patterns Message Endpoint Publish-Subscribe Channel Guaranteed Delivery

World tour - education CIPL (my lot) Chunking & toggling Peer leader Hypothetical professionals E-LEN project Coherence principle Provide personal identity information

Motherhood statements Patterns are primarily about communication Patterns are not templates or rules Pattern use is all about professional judgement A pattern by definition is not new

Resources Books A Pattern Language: Towns, Buildings, Construction Christopher Alexander, Sara Ishikawa, Murry Silverstein ISBN Design Patterns: Elements of Reusable Object-Oriented Software Erich Gamma, Richard Helm, Ralph Johnson, John M. Vlissides ISBN Enterprise Integration Patterns: Designing, Building, and Deploying Messaging Solutions Gregor Hohpe & Bobby Woolf ISBN Patterns of Enterprise Application Architecture Martin Fowler ISBN Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and Iterative Development Craig Larman ISBN Websites E-LEN Some patterns in the education field CIPL No patterns here yet :( Article by Aino Corry on patterns vs language constructs. See also her talk on patterns in functional languages on InfoQ.

Argue!