The other day, I told a developer on my team that I wouldn’t write methods with more than three parameters. I said this in a context where many people would say, “don’t write code with more than three parameters in a method,” in that I am the project architect and coding decisions are mine to make. However, I feel that the way you phrase things has a powerful impact on people, and I believe code reviews that feature orders to change items in the code are creativity-killing and soul-sucking. So, as I’ve explained to people on any number of occasions, my feedback consists neither of statements like “that’s wrong” nor statements like “take that out.” I specifically and always say, “that’s not what I would do.” I’ve found that people listen to this the overwhelming majority of the time and, when they don’t, they often have a good reason I hadn’t considered. No barking of orders necessary.
But back to what I said a few days ago. I basically stated the opinion that methods should never have more than three parameters. And right after I had stated this, I was reminded of the way I’ve seen countless conversations go in person, on help sites like Stack Overflow, and in blog comments. Does this look familiar?
John: You should never have more than three parameters in a method call.
Jane: Blanket statements like that tend to be problematic. Three method parameters is really, technically, more of a “code smell” than necessarily a problem. It’s often a problem, but it might not be.
John: I think it’s necessarily a problem. I can’t think of a situation where that’s desirable.
Jane: How about when someone is holding a gun to your head and telling you to write a method that takes four parameters.
John: (Rolls his eyes)
Jane: Look, there’s probably a better example. All I’m saying is you should never use absolutes, because you never know.
John: “You should never use absolutes” is totally an absolute! You’re a hypocrite!
Both: (Devolves into pointless bickering)
A lot of times during debates, particularly when you have smart and/or exacting participants, the conversation is derailed by a sort of “gotcha” game of one-upsmanship. It’s as though they are at an impasse as to the crux of the matter, so the two begin sniping at one another about tangentially-related or totally non-related minutiae until someone makes a slip, and this somehow settles the debate. Of course, it’s an exercise in futility because both sides think their opponent is the first to slip up. Jane thinks she’s won this argument because John used an absolute qualifier and she pointed out some (incredibly preposterous and contrived) counter-example, and John thinks he won with his ad hominem right before the end about Jane’s hypocrisy.
In this debate, they both lose, in my opinion. I agree with John’s premise but not his justification, and the difference matters. And Jane’s semantic nitpicking doesn’t get us to the right justification (counter or pro), either. Prescriptive matters of canon when it comes to programming are troubling for the same reason that absolutes are often troubling in our day-to-day lives. Even the most clear-cut seeming things, like “it’s morally reprehensible to kill people,” wind up having many loopholes in their application (“it’s morally reprehensible to kill people — unless, of course, it’s war, self-defense, certain kinds of revenge for really bad things, accidental, state-sanctioned execution, etc., etc.”). So for non-important stuff like the number of parameters to a method, aren’t we kind of hosed and thus stuck in a relativistic quagmire?
I’d argue not, and furthermore, I’d argue that the fact of the rules is more important than the rules themselves. It’s more important to have a restriction like “don’t have more than three parameters to a method” than it is to have that specific restriction. If it were “don’t have more than two method parameters” or “don’t have more than four method parameters,” we’d still be sitting pretty. Why, you ask? Well, a man named Barry Schwartz coined this phrase: “the paradox of choice: why more is less.” Restrictions limit choice, which is merciful
Developers are smart, and they want to solve problems — often hard problems. But, really, they want to solve directed problems efficiently. To understand what I mean, ask yourself which of these propositions is more appealing to you: (1) make a website that does anything in any programming language with any framework or (2) use F# to parse a large text file and have the running process use no more than 1 gig of memory. The first proposition makes your head hurt while the second gets your mental juices flowing as you decide whether to try to solve the problem algorithmically or to cheat and write interim results to disk.
Well, the same thing happens with a lot of the “best practice” rules that surround us in software development. Don’t make your classes too big. Don’t make your methods too big. Don’t have too many parameters. Don’t repeat your code. While they can seem like (and be, if you don’t understand the purpose behind them) cargo-cult mandates if you simply focus on the matter of relativism vs absolutes, they’re really about removing (generally bad) options so that you can be creative within the context remaining, as well as productive and happy. Developers who practice DRY and who write small classes with small methods and small method signatures don’t have to spend time thinking “how many parameters should this method have” or “is this class getting too long?” Maybe this sounds restrictive or draconian to you, but think of how many options have been removed from you by others: “does the code have to compile,” or “is the code allowed to wipe out our production data?” If you’re writing code for any sort of business purposes, the number of things you can’t do dwarfs the number of things you can.
Of course, just having rules for the sake of rules is the epitome of dumb cargo cult activity. The restrictions have to be ones that contribute overall to a better code base. And while there may be some debate about this, I doubt that anyone would really argue with statements like “favor small methods over large ones” and “favor simple signatures over complex ones.” Architects (or self-organizing teams) need to identify general goals like these and turn them into liberating restrictions that remove paralysis by analysis while keeping the code base clean. I’ve been of the opinion for a while now that one of the core goals of an architect should be providing a framework that prevents ‘wrong’ decisions so that the developers can focus on being creative and solving problems rather than avoiding pitfalls. I often see this described as “making sure people fall into the pit of success.”
Going back to the “maximum of three parameters rule,” it’s important to realize that the question isn’t “is that right 99% of the time or 100% of the time?” While Jane and John argue over that one percent, developers on their team are establishing patterns and designs predicated upon methods with 20 parameters. Who cares if there’s some API somewhere that really, truly, honestly makes it better to user four parameters in that one specific case? I mean, great — you proved that on a long enough timeline, weird aberrations happen. But you’re missing out on the productivity-harnessing power of imposing good restrictions. The developers in the group might agree, or they might be skeptical. But if they care enough to be skeptical, it probably means that they care about their craft and enjoy a challenge. So when you present it to them as a challenge (in the same way speeding up runtime or reducing memory footprint is a challenge), they’ll probably warm to it.