My relationship with SOLID - The big O

Open closed is dead, long live Open closed

I'm blogging about SOLID for some reason, and now we're onto the beast that set me off:

OCP

Yikes

 They are “Open For Extension”. This means that the behavior of the module can be extended. That we can make the module behave in new and different ways as the requirements of the application change, or to meet the needs of new applications.

and

 They are “Closed for Modification”. The source code of such a module is inviolate. No one is allowed to make source code changes to it.

Thanks Uncle Bob, you're right, this is over-stated, and because it's so over stated, I believe it to be the cause of so many of the over-designed pieces of crap I've had to deal with in my career :-)

This is the conversation I imagine developers having with themselves when writing this stuff, I don't have to imagine too hard because I've been there too:

 What if somebody at some point wants to change this so they can have another behaviour for this value, I'd better use the strategy pattern here instead of this switch statement, but oh my word now I've done that what if somebody wants to use this code from some other system than this one, I'd better stick a command system in front of this and use double dispatch for handling them - but wait, what if other code needs to react from this and do something else, I'd better raise a pile of events, but what if those aren't enough I'd better make sure I split all this behaviours out into their own interfaces so they can be overridden and...

And on it goes until suddenly what was a couple of classes behind a controller or presenter blow up into a mess of a hundred classes that all do the square root of diddly squat, but together manage to cause a lot of headaches for anybody coming across the code in the future.

Now, I'm sure this wasn't the intent behind these statements, and it sure isn't now - but you know what?

Read more: Rob Ashton

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