Aspect oriented programming
Nov 17, 2014
AOP is a way of making code easier to write and work with by extracting cross cutting concerns into small easily reusable code that is applied with attribututes. This session looks at that and the various options available to us, from free items to commercial offerings like PostSharp.
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Transcript
Agenda
• What, when, why of AOP?• How is it implemented in PostSharp
and how does it work?• Alternatives to PostSharp• Looking to the future• Discussion
Every project has “boring” code
source: Microsoft Application Architecture Guide, 2nd Edition
AOP Details
• Goal to make cross cutting concerns easy to implement and focus on business code
• Xerox PARC in 2001• AspectJ• Many implementations now days• AKA: AOSD
Scenario code – simple prime calculator
Customer says it’s wrong. We need logging to diagnose…
Let’s add logging – trace input & output
5 extra lines of code
Easy to miss some places
Lots of repetition of code
Need to teach this
Not portable
What about some procedural help?
15 extra lines of code
Not junior friendly
Need 1 per signature
So how does aspects solve that?
1 extra line of code
Feel like you are missing something?
Demo time…
Under the hood
Source: .NET Reflector 6.8
IL modified
Many ways to implement AOP in .NET currently
• Popular: – IL Weaving @ compile or JIT– PostSharp & Mono.Cecil
• Less:– Hooking into .NET profiler API– Proxies
Hooking the profiler
CLR
Application
Profiler
Environmental
COM API
Disadvantages• Poor performance• Exceptionally
complex• Not designed for this
Advantages• Nothing is safe from
it’s power• Solves some fringe
cases (i.e. mocking static methods)
Proxies
Object
Method Call
Proxy
Method Call
Object
Normal Proxied
Disadvantages• Complex with ContextBoundObject• Perf is worse than IL weavingAdvantages• Using DI it can be easier• Perf is better than .NET profiler
Future: Post Roslyn Theory
• Roslyn– Next version of C#/VB “compiler”– Written in managed code– Available as a service
• Post Roslyn– Insert new language semantics – Approach the AspectJ style
Summary
• AOP–Way to untangle cross cutting concerns
out of business code– Great re-use– Can be easy to use (depending on
implementation)–Many options to do this!
Questions & Discussions
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