Software design

The benefits of OO aren’t obvious: Part I of V, data hiding

Sometimes you work with something for so long that you forget that other people aren’t familiar with it. This happened recently talking to a friend of mine — “I’ve got no need for object orientation”, he said, and I was shocked. Yet I couldn’t easily explain why I thought OO was far superior to procedural languages. And thinking about it afterwards I realised that its advantages for me weren’t obvious — almost none of them are clear from OO’s fundamentals (inheritance, abstraction, etc), and almost all of the advantanges are things that have been learnt by most of us recently, years after OO first appeared.

My friend spends most of his time writing embedded software, but occasionally is called upon to write a front-end interface. His front-ends are Windows-based and for his last GUI project he chose to try out VB.NET rather than his usual VB6. He was baffled by the verbosity and he felt it didn’t add anything. It all seemed rather unnecessary. And yet to me it’s long been the only way.

What, I wondered to myself, were the benefits of OO that he was missing? How could I persuade him that it does have a point? So here is my attempt to trawl my memory and see how I’ve changed in response to OO, and why I think it serves me (and my projects) better. In the end I’ve found that the benefits are real, but nothing I would have guessed at when I first started in this field.

Not the point of OO

DNJ Online has an article on migrating from VB6 to VB.NET, and it says that from this point of view the OO language is “unlike anything you’ve used before”. This is helpful in its honesty, but that particular article explains the low level differences rather than the high level aims. Try/catch blocks and namespaces are definite steps forward, but they hardly justify learning an entirely new paradigm, let alone phasing out a well-established one.

Similarly, common justifications of OO is that objects promote code re-use and allow better modelling of user requirements, but it’s hard to see how this is obvious. Regards the former, procedural languages allow code reuse via libraries. Regards the latter, it’s just as easy to see user requirements as procedural things as object-based things — easier, arguably.

For me, the advantages of OO are not obvious. But they are tangible once experienced, given the right environment. For me, those advantages are…

Data hiding

Even I’m horrified by how little fits into my tiny brain, and the more I have to keep in my head at any one time the more likely I am to make mistakes. In terms of development, the more attention I have to pay to the intricacies of my software the less attention I can pay to solving whatever the immediate problem happens to be.

Fortunately OO’s concept of data hiding (or encapsulation, if you like long words) is for people like me. By making explicit what I need to know (public methods/functions) and hiding what I don’t (private methods/functions and fields/variables) I am freed to focus on the task in hand. Private fields and methods allow my classes to manage themselves without having to burden the user with the details. You can look at the class (or its auto-generated documentation [1, 2, 3, 4]) and focus on what you need to know, without getting distracted by the details.

Anything which makes me think less is huge benefit.

Of course, data hiding by itself isn’t enough to switch programming paradigm, and if you’re writing in VB6 you’ll already have the “private” keyword. But this is only the start…

All installments, which I’ll post over the next few days:

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