Uploaded bySam Hennessy
Implementing The Open/Closed Principle
The document discusses the open/closed principle (OCP) of software design, which states that software entities should be open for extension but closed for modification. It provides examples of how OCP can be applied at the class, application, and enterprise levels through techniques like inheritance, polymorphism, interfaces, small methods, encapsulation, and dependency injection. The document also addresses when it may be acceptable to break from OCP, such as when separation of concerns is violated or a feature does not fit the overall design.
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Implementing The Open/Closed Principle
- 1. Implementing The Open/ClosedPrinciple
- 2. Sam Hennessy • Originally from the UK • Now live in Denver, CO • Software Architect at i3logix • Ex-Pro Services Consultant For Zend • Regular at Front Range PHP Users Group 2
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- 4. What is it? Part of SOLID Protect your system from change Do you already do it? 4
- 5. SOLID S Single responsibility principle O Open/closed principle L Liskov substitution principle I Interface segregation principle 5 D Dependency inversion principle
- 6. Open/Closed Principle "Be open for extension, but closed for modification." 6
- 7. And I CareWhy? Maintenance Let your Customer users bridge a customization feature gap Competitive Preventing edge the "FORK"! A-la-cart feature offerings 7
- 8. What about YAGNIand KISS? 8
- 9. Where Can ItBe Applied? Class Application Enterprise 9
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- 11. Classes Inheritance Polymorphism Interfaces 11
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- 13. No Public Properties Always be private? Encapsulation Information hiding It's cheap to do 13
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- 16. class Calculator{ public function __invoke($calc, $left, $right) { if ($calc == 'add') { return $left + $right; } else if ($calc == 'sub') { return $left - $right; } } }
- 17. class Calculator{ public function __invoke(Calc $calc, $left, $right){ return $calc($left, $right); } } $calculator = new Calculator(); echo $calculator(new AddCalc(), 2, 1), "n"; echo $calculator(new SubCalc(), 2, 1), "n";
- 18. interface Calc { public function __invoke($left, $right); } class AddCalc implements Calc { public function __invoke($left, $right) { return $left + $right; } } class SubCalc implements Calc { public function __invoke($left, $right) { return $left - $right; } }
- 19. if ($logType =='echo') { echo $message; } else if ($logType == 'file') { $logger->writeToFile($message); }
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- 32. Service Oriented Architecture(SOA) 32
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- 34. When to breakOCP!?
- 35. When to breakOCP!? Separation of concerns Excessive Single duplication responsibility 35
- 36. Everyday vs. theRevolutionary Facts don't Feature fit the doesn't fit theory the design 36
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Editor's Notes
- #2 A note
- #5 I hope to enable you to add some consistency by formalizing your thinking around OCP
- #8 Risk of making changeLessened by good automated testing coveragePlatforms Amazon vs. GoogleTwitter
- #9 You can apply the principle reactively
- #10 Let’s take a look at techniques for each layer
- #12 Traditional ideas of OCP what you be able to write the class code once and never have to come back to edit itThese techniques focus on this level changeSome of my application level techniques kind of blur the linePrevent changes to a classDoesn’t prevent change to the app, unless you are using DI or something like it
- #13 Small is fast when it comes to changing direction10 executable lines is a good target, 20 the max (obviously there are always exceptions)
- #14 Just one client can mess it up for everyone
- #15 Traditional ideas of OCP say that globals break OCPThese are points of view that are just thinking about riskYou are introducing risk that other parts of the system will break this code
- #16 Making your code ignorantAbstracting – to
- #20 Imagine this all over your application.Then we want to add FireBug/FirePHP logging support for our Ajax calls
- #21 Also called Composite Reuse Principle
- #22 What’s your goal
- #23 Can anyone think of any more class level techniques
- #24 Lots of examples from ZFThink how this has helped word press
- #27 Signal & SlotsPub/Sub
- #28 Cross cutting concernsFlow 3
- #31 Can anyone think of any more APPLICATION level techniques
- #33 Message bus
- #34 PubsubQueueTrue broadcast
- #37 Martin FowlerIsolate the assumptions scattered around the code to a single element (by assumptions, you assumed they wouldn't need to change) E.g. You are echoing all over the code, but you need to support encoding to jsonThis will reduce the risk for the big change Or start from scratch
- #38 Why are you doing this?