Introduction to Aspect Oriented Programming (DDD South West 4.0)

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

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

the PROBLEM...CROSS-CUTTING CONCERNS

Cross-Cutting Concerns Image by Mike Rohde

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

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

the SOLUTION...ASPECT-ORIENTED PROGRAMMING

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

AOP Image by Mike Rohde

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

What’s in it for YOU?

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

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

dive a little deeper into...AOP

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

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

• Point cut  Join points where advice should be applied

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

• Weaving  Combines advices with point cuts

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

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

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

AOP via...DYNAMIC PROXIES

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

Dynamic Proxies Image by Mike Rohde

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

• 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

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

AOP via...FUNCTIONAL PROGRAMMING

Functional Programming Image by Mike Rohde

• Advantages  No external dependencies

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

AOP via...CODE GENERATION

• T4, CodeSmith tools

• Advantages  Easy to generate complex source code

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

AOP via...DYNAMIC LANGUAGES

Dynamic Languages Image by Mike Rohde

• Advantages  Meta-programming is easy

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

AOP via...STATIC WEAVING

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

Requirements Aspect DecompositionAspects Core program Aspect Recomposition Final System

PostSharp Image by Mike Rohde

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

• Disadvantages  Increased build time  New to many developers

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

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

Record exec time Publish to Amazon CloudWatch

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

• http://bit.ly/KRDdgr

Thank You! @theburningmonktheburningmonk.com

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Introduction to Aspect Oriented Programming (DDD South West 4.0)

by Yan Cui on May 27, 2012

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