Do you use AOP (Aspect Oriented Programming) in production software?

Question

AOP is an interesting programming paradigm in my opinion. However, there haven't been discussions about it yet here on stackoverflow (at least I couldn't find them). What do you think about it in general? Do you use AOP in your projects? Or do you think it's rather a niche technology that won't be around for a long time or won't make it into the mainstream (like OOP did, at least in theory ;))?

If you do use AOP then please let us know which tools you use as well. Thanks!

Answer 1

Python supports AOP by letting you dynamically modify its classes at runtime (which in Python is typically called monkeypatching rather than AOP). Here are some of my AOP use cases:

1. I have a website in which every page is generated by a Python function. I'd like to take a class and make all of the webpages generated by that class password-protected. AOP comes to the rescue; before each function is called, I do the appropriate session checking and redirect if necessary.

2. I'd like to do some logging and profiling on a bunch of functions in my program during its actual usage. AOP lets me calculate timing and print data to log files without actually modifying any of these functions.

3. I have a module or class full of non-thread-safe functions and I find myself using it in some multi-threaded code. Some AOP adds locking around these function calls without having to go into the library and change anything.

This kind of thing doesn't come up very often, but whenever it does, monkeypatching is VERY useful. Python also has decorators which implement the Decorator design pattern (http://en.wikipedia.org/wiki/Decorator_pattern) to accomplish similar things.

Note that dynamically modifying classes can also let you work around bugs or add features to a third-party library without actually having to modify that library. I almost never need to do this, but the few times it's come up it's been incredibly useful.

Answer 2

Yes.

Orthogonal concerns, like security, are best done with AOP-style interception. Whether that is done automatically (through something like a dependency injection container) or manually is unimportant to the end goal.

One example: the "before/after" attributes in xUnit.net (an open source project I run) are a form of AOP-style method interception. You decorate your test methods with these attributes, and just before and after that test method runs, your code is called. It can be used for things like setting up a database and rolling back the results, changing the security context in which the test runs, etc.

Another example: the filter attributes in ASP.NET MVC also act like specialized AOP-style method interceptors. One, for instance, allows you to say how unhandled errors should be treated, if they happen in your action method.

Many dependency injection containers, including Castle Windsor and Unity, support this behavior either "in the box" or through the use of extensions.