Introduction to Aspect Oriented Programming

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Introduction to Yan Cui Aspect Oriented Programming by theburningmonk.com @theburningmonk

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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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CROSS-CUTTING CONCERNS the PROBLEM...

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Image by Mike Rohde Cross-Cutting Concerns

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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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ASPECT-ORIENTED PROGRAMMING the SOLUTION...

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“AOP is a programming paradigm which aims to increase modularity by allowing the separation of cross-cutting concerns” - wikipedia

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Image by Mike Rohde AOP

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

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AOP dive a little deeper into...

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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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DYNAMIC PROXIES AOP via...

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

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Image by Mike Rohde Dynamic Proxies

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

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FUNCTIONAL PROGRAMMING AOP via...

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Image by Mike Rohde Functional Programming

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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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CODE GENERATION AOP via...

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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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DYNAMIC LANGUAGES AOP via...

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Image by Mike Rohde Dynamic Languages

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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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STATIC WEAVING AOP via...

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

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Aspect Decomposition Aspects Core program Aspect Recomposition Requirements Final System

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Image by Mike Rohde PostSharp

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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