melreams.com

Today’s code smell is long parameter lists. If you have lots and lots of parameters, something is likely going wrong.

Odds are good your method is just doing too much, which leads to confusing code that’s hard to understand and change. Another reason lots of parameters causes problems is that when you call that method, it’s very easy to accidentally get two parameters of the same type in the wrong order (not that that’s ever happened to me or anything).

How do you fix it?

Well, if you can break your method into separate methods that each do just one thing, do that. Not only does that solve the problem of a long, confusing, easy to mess up list of parameters, it also fixes the related problem of your method being confusing because it does too many things.

Another option if you can’t break up your method is to make a new object that holds all the parameters. Having named fields in the new object makes it a lot easier to keep track of which value goes where. If you already have an object that most or all of the parameters come from, it’s often simpler just to pass that along instead of pulling values out and passing those into the method you’re calling.

However, the more objects your caller and callee have in common, the more closely coupled they are. If your classes aren’t already closely coupled you’re probably fine to add another object they both use, but if they already have a lot in common then you should think about whether you really need that object. Of course, if your classes are extremely closely related they should maybe just be one class, but that’s a separate code smell.

And if breaking the big method into smaller ones means that the smaller ones absolutely always have to be called together, it’s probably better to leave it as one big method with lots of parameters. If you have to just remember what order to call the smaller methods in you’re asking for trouble, you will definitely mess that up sooner or later. A huge part of being a good programmer is accepting that it’s very very easy to mess it up and trying to avoid the most obvious pitfalls.

Like the other code smells, long parameter lists aren’t an absolute certainty you need to change your code, but I personally think they’re an especially strong sign that your design could be better. It’s just so easy to accidentally switch parameters, and even if you manage to keep them all straight it’s still a serious hassle to call a method with a huge list of parameters.

You know your codebase better than I do, though. Do what makes sense for your particular situation and don’t worry too much about my personal pet peeves :)