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When to use variadic functions

Paul Hudson    @twostraws   

Swift’s variadic functions let us accept any number of parameters of the same type, separated by a comma. Inside the function they are handed to us as an array, which we can index into, loop over, and so on.

The power of variadic parameters is that we can treat them as if they weren’t variadic most of the time. For example, if you had an open() function that opened a file for editing in Preview, TextEdit, or whatever was the correct program, you might call it like this:

open("photo.jpg")

But that same function could take a variadic parameter – lots of filenames to open, so several could be opened at once:

open("photo.jpg", "recipes.txt", "myCode.swift")

So, by making that parameter variadic, we can open up a whole range of additional functionality without having to change the way the function is called – it’s really useful!

As for when you should use them, chances are you won’t use them that much while you’re learning because you’re going to be focused on very specific problems that are usually fairly small. But as your skills increase, you’ll find that you can change your existing functions to make them variadic without breaking any of your code – you can add functionality without changing what you already have.

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