Do Extension Methods Hide Dependencies?

Question

All,

Wanted to get a few thoughts on this. Lately I am becoming more and more of a subscriber of \"purist\" DI/IOC principles when designing/developing. Part of thi

Answer 1

Extension methods, partial classes and dynamic objects. I really like them, however you must tread carefully , there be monsters here.

I would take a look at dynamic languages and see how they cope with these sort of problems on a day to day basis, its really enlightening. Especially when they have nothing to stop them from doing stupid things apart from good design and discipline. Everything is dynamic at run time, the only thing to stop them is the computer throwing a major run time error. "Duck Typing" is the maddest thing I have ever seen, good code is down to good program design, respect for others in your team, and the trust that every member, although have the ability to do some wacky things choose not to because good design leads to better results.

As for your test scenario with mock objects/ICO/DI, would you really put some heavy duty work in an extension method or just some simple static stuff that operate in a functional type way? I tend to use them like you would in a functional programming style, input goes in, results come out with no magic in the middle, just straight up framework classes that you know the guys at MS have designed and tested :P that you can rely on.

If your are doing some heavy lifting stuff using extension methods I would look at your program design again, check out your CRC designs, Class models, Use Cases, DFD's, action diagrams or whatever you like to use and figure out where in this design you planned to put this stuff in an extension method instead of a proper class.

At the end of the day, you can only test against your system design and not code outside of your scope. If you going to use extension classes, my advice would be to look at Object Composition models instead and use inheritance only when there is a very good reason.

Object Composition always wins out with me as they produce solid code. You can plug them in, take them out and do what you like with them. Mind you this all depends on whether you use Interfaces or not as part of your design. Also if you use Composition classes, the class hierarchy tree gets flattened into discrete classes and there are fewer places where your extension method will be picked up through inherited classes.

If you must use a class that acts upon another class as is the case with extension methods, look at the visitor pattern first and decide if its a better route.