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How many parameters should a function accept?

Paul Hudson    @twostraws   

Updated for Xcode 12.0

At first glance, this question seems like “how long is a piece of a string?” That is, it’s something where there is no real, hard answer – a function could take no parameters or take 20 of them.

That’s certainly true, but when a function takes many parameters – perhaps six or more, but this is extremely subjective – you need to start asking whether that function is perhaps doing a bit too much work.

  • Does it need all six of those parameters?
  • Could that function be split up into smaller functions that take fewer parameters?
  • Should those parameters be grouped somehow?

We’ll look at some techniques for solving this later on, but there’s an important lesson to be learned here: this is called a “code smell” – something about our code that suggests an underlying problem in the way we’ve structured our program.

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