Every time I here a podcast or read a blog entry about it, even here, they make it sound like string theory or something. Is the best way to describe it OOP with Dependency Injection on steroids?
Every time someone tries to explain it, it’s like, Aspects, [Adults from Peanuts Cartoon sound], Orthogonal, [more noise], cross cutting concerns, etc. Seriously, can anyone describe it in layman’s terms.
Laymans terms so let me give you an example. Let's say you have a web application, and you need to add error logging / auditing. One implementation would be to go into every public method and add your try catch blocks etc...
Well Aspect oriented says hogwash with that, let me inject my method around your method so for example instead of calling YourClass.UpdateModel(), the system might call,
LoggingHandler.CallMethod() this method might then redirect the call to UpdateModel but wraps it in a try catch block to handle logging errors.
Now the trick is that this redirection happens automagically, through configuration or by applying attributes to methods.
This works for as you said cross cutting things which are very common programing elements that exist in every domain, such as: Logging, Auditing, Transaction Mgmt, Authorization.
The idea behind it is to remove all this common plumbing code out of your business / app tier so you can focus on solving the problem not worrying about logging this method call or that method call.
I currently use Post Sharp, i would read the info from their website. I use it to provide a security around method calls.
"PostSharp is an open platform for the analysis and transformation of .NET assemblies. It comes with PostSharp Laos, a powerful yet simple plug-in that let you develop custom attributes that actually adds behavior of your code. PostSharp Laos is the leading aspect-oriented programming (AOP) solution for the .NET Framework."
Class and method attributes in .NET are a form of aspect-oriented programming. You decorate your classes/methods with attributes. Behind the scenes this adds code to your class/method that performs the particular functions of the attribute. For example, marking a class serializable allows it to be serialized automatically for storage or transmission to another system. Other attributes might mark certain properties as non-serializable and these would be automatically omitted from the serialized object. Serialization is an aspect, implemented by other code in the system, and applied to your class by the application of a "configuration" attribute (decoration) .
The classic examples are security and logging. Instead of writing code within your application to log occurance of x or check object z for security access control there is a language contraption "out of band" of normal code which can systematically inject security or logging into routines that don't nativly have them in such a way that even though your code doesn't supply it -- its taken care of.
A more concrete example is the operating system providing access controls to a file. A software program does not need to check for access restrictions because the underlying system does that work for it.
If you think you need AOP in my experience you actually really need to be investing more time and effort into appropriate meta-data management within your system with a focus on well thought structural / systems design.
AOP is all about managing the common functionality (which span across the application, hence cross cutting) within the application such that it is not embedded within the business logic.
Examples to such cross cutting concerns are logging, managing security, transaction management etc.
Frameworks allows this to managed automatically with the help of some configuration files.