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Introduction to Aspect Oriented Programmingby Yan Cui @theburningmonk theburningmonk.com

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Server-side Developer @

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• Overview  Cross-Cutting Concerns  AOP  What’s in it for you• AOP  Terminologies  AOP and OOP  Solutions• Q&A

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the PROBLEM...CROSS-CUTTING CONCERNS

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Cross-Cutting Concerns Image by Mike Rohde

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• Cuts across multiple abstractions• Difficult to decompose• High-coupling• Boilerplate code

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• Code tangling and scattering  Poor traceability  Lower productivity  Less code reuse  Harder refactoring

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the SOLUTION...ASPECT-ORIENTED PROGRAMMING

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“AOP is a programming paradigm whichaims to increase modularity by allowingthe separation of cross-cutting concerns” - wikipedia

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AOP Image by Mike Rohde

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• Centralize concerns implementation• Intercept method calls• Inject new behaviour• More reusable code• Cleaner code

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What’s in it for YOU?

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• Write less code• Read less code• More concise and easy to understand• More maintainable

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• Fewer code = FEWER DEFECTS!• Less boilerplate code• More interesting work• Increased attention• More PRODUCTIVITY!

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dive a little deeper into...AOP

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• Join Point  Place where behaviour can be added  start/end of method  property getter/setter  ...

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• Advice  Code that’s injected at join points  Logging  Validation  ...

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• Point cut  Join points where advice should be applied

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• Aspect  Container holding point cuts and advice  Aspect is to AOP what class is to OOP

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• Weaving  Combines advices with point cuts

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• AOP is complementary to OOP• AOP targets a specific problem• Code modularization  OOP – Real world objects  AOP – Functionalities

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• Help you S.O.L.I.Dify your code  Single responsibility  Open/close

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• You can do AOP via:  Dynamic Proxies  Functional Programming  Code Generation  Dynamic Languages  Static Weaving

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AOP via...DYNAMIC PROXIES

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• IoC framesworks  Castle  Spring.Net• Dynamic interceptors

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Dynamic Proxies Image by Mike Rohde

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• Advantages  Can use existing DI framework  Built-in aspects (logging, etc.)  Aspects can be configured after build

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• Disadvantages  Significant change to base code required to adapt  Limited AOP features  Do not work on static, non-public methods  Do not work on fields, properties, or events  Higher run-time overhead  No build-time verification  Objects must be instantiated using the container

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NOOOO Sir!!Class, is AOP the same as Dependency Injection?

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AOP via...FUNCTIONAL PROGRAMMING

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Functional Programming Image by Mike Rohde

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• Advantages  No external dependencies

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• Disadvantages  Requires modification to every function  No support for matching rules  Manual aspect composition

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AOP via...CODE GENERATION

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• T4, CodeSmith tools

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• Advantages  Easy to generate complex source code

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• Disadvantages  Input is usually XML  Cannot inject new behaviour to existing code

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AOP via...DYNAMIC LANGUAGES

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Dynamic Languages Image by Mike Rohde

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• Advantages  Meta-programming is easy

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• Disadvantages  Switch to a dynamic language can be hard  No (limited) Visual Studio tooling

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AOP via...STATIC WEAVING

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• PostSharp, AspectJ• Uses low-level MSIL transformation• Compile time

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Requirements Aspect DecompositionAspects Core program Aspect Recomposition Final System

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PostSharp Image by Mike Rohde

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• Advantages  Most complete support of AOP features  Aspect usage is verified at build time  Better runtime performance

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• Disadvantages  Increased build time  New to many developers

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PostSharp Examples• Auto-implement INotifyPropertyChanged• Undo/Redo• Thread dispatching• Transaction handling• Performance Monitoring

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• Performance Monitoring  Method execution time  Method execution count  Error count

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Record exec time Publish to Amazon CloudWatch

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• Amazon CloudWatch  Cheap to run  Supports alarms and notifications  Visualization tool

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• http://bit.ly/KRDdgr

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Thank You! @theburningmonktheburningmonk.com