Buzzword Buster – AOP

Definition:

Aspect Oriented Programming (AOP) is a programming paradigm where each application can focus on its primary functions and core concerns by encouraging greater modularity and increasing separation of cross-cutting concerns (such as logging and authentication).

Purpose:

In any real-world applications, when you’re writing code to address the problem domain (say, booking an order) you might need to address other concerns such as:

  • persistence – writing to the database for example
  • transaction handling – defining transaction scope and setting rollback strategy, etc.
  • security – user authentication for example
  • logging – for auditing and debugging

So effectively you’re mixing multiple domains with fine-grained intersections and likely to end up with:

  • tangled code – making it more difficult to work out what the code is doing to address the core concern
  • boilerplate code at every intersection point – introducing duplicated code and increasing the size of the code base and the blast radius of any change that are not related to the problem domain, e.g. changing the persistence media..

AOP aims to address these problems by separating cross-cutting concerns into single units called aspects, each aspect encapsulates behaviours that affect multiple classes into reusable modules.

Parting thoughts..

As far as I can think of, the only drawback of AOP is that you no longer see all the behaviours of your class when you open it and it requires knowledge of the whole system to know what else are happening under the cover. Which interestingly, is the flip side of the same coin because you employ AOP when you don’t want to deal with cross-cutting concerns all the time!

One of the ways to mitigate this problem is to build up a culture in your team and standardise how AOP is implemented so that everyone is on the same page and there are few surprises.

Frameworks:

PostSharp provides a lightweight AOP framework for the .Net platform and is establishing itself as the de facto standard much like the way AspectJ has done for Java.