Write a post
Published Aug 19, 2015Last updated Feb 10, 2017

Swift Tips & Tricks: Using Functions as Parameters in Swift

Suppose you have a function that returns the double of any integer that it takes.

func doubleOfNumber(number: Int) -> Int {
    return number * 2
}

And you want to double every Int in an array. You might want to do this:

[3, 1, 2, 4].map {
    return doubleOfNumber($0)
}
// Returns [6, 2, 4, 8]

Now the map function in this case takes a closure that takes an Int and returns an Int. Just like our function doubleOfNumber.

We can actually use this function as a parameter instead of providing the closure ourselves. Like this:

[3, 1, 2, 4].map(doubleOfNumber)
// Returns [6, 2, 4, 8]

It gets better. Now suppose you want to convert these Ints to Strings:

[3, 1, 2, 4].map {
    return String($0)
}
// Returns ["3", "1", "2", "4"]

Since String.init is itself a function, you can do this:

[3, 1, 2, 4].map(String.init)

You can even do this:

[3, 1, 2, 4].sort(<)

You can do very cool and actually practical things with Swift if you know where to look.

Discover and read more posts from Seyithan Teymur
get started
Enjoy this post?

Leave a like and comment for Seyithan