Saturday, 1 December 2012

Object Discovery

Recently we had @kevinrutherford in to talk about object discovery. While TDD is a great tool, it is no excuse for some sort of design process. If you don't, you'll most likely end up with a mess. This session was based around this principle.

One point that was discussed what that the first few seconds of a test for a new class is the most important part of the TDD process. It is here where you will decide whether to take a state or interaction based approach to testing. This first test will dictate the structure of the new class. Once you start with tests, it becomes difficult to evolve or change the design of a class without friction.

There is generally two types of code at Codeweavers.

The trick comes from the fact that just because you use C#/Java/etc.. most of the time you aren't actually writing OO code. You often end up writing procedural code in a rather obtuse manner. A takeaway from this afternoon was to try and perform more CRC (class-responsibility-collaborator) sessions.

CRC (Object Cube)

During this session we performed a modified version of a CRC. One thing I always find with CRC sessions is how useful they are. The problem I and others find is when it comes to day to day development, I'm too eager to start coding without performing some sort of up front design.


In order to write flexible OO code, you need to hide as much state as possible. While this is great in practice it turns out to be very difficult to achieve in the real world. One method of getting around this is to make use of events aka the observer pattern.

Kevin used a wiki as an example. Consider a page that is updated. If this page was to fire a changed event, then anything that is listening for these events would be notified. The observers could then react once the event was received. The nice thing about this approach is that the code obeys the open/closed principle. New features can be added without the need for the change to have a large, rippling effect.

Nouns and Namespaces

When I was first exposed to object oriented programming, apart from believing that inheritance was the coolest aspect of OO, I was also led to believe that using nouns when designing classes can be useful. It turned out that this was a fallacy. If you follow this advice you'll end up with a small collection of classes that do everything. The biggest revelation I had during the session came from the importance of namespaces. Using nouns for up front design can be extremely useful if you remember that the noun can potentially be a namespace. This means you'll end up with a handful of namespaces that are relevant to the domain in question. Inside these namespaces you will have one or more classes that do one thing, and one thing well.


At the end of the session I was left with many questions and new ideas to test and try out. Using events to hide state, yet allow other objects to interact when required was a real eye opener. However it turns out that when actually trying to implement these ideas in code, it is actually quite difficult due to my current thinking. The plan for the next month will be to explore these ideas in more detail and see what affect it has on my day to day development.

No comments:

Post a Comment