Swift For-In Loops

In Swift, if you want to iterate over a sequence, such as an array or ranges of numbers, you can take advantage of the for-in loop. Not only performant but super readable too.

Arrays

Take a look at this example:

let sports = ["🏉", "⚽️", "🏀", "🎾", "⛳️"]

for icon in sports {
    print(icon)
}

In your code above, you have an array of sports icons, and you’re looping through the array using a for-in loop and print each icon.

Your console will print:

🏉
⚽️
🏀
🎾
⛳️

Dictionaries

You can also imply the same logic for dictionaries.

let sports = ["🏉": "Rugby", "⚽️": "Football", "🏀": "Basketball", "🎾": "Tennis", "⛳️": "Golf"]

for (icon, name) in sports {
    print("\(icon) is called \(name)")
}

You have a dictionary that contains both the icon and the name of the sport. You’re accessing both key and value within the for-in loop.

Your console will print the following:

🏉 is called Rugby
⚽️ is called Football
🎾 is called Tennis
⛳️ is called Golf
🏀 is called Basketball

If you run this many times, you’ll notice that the order is always different. This is because Dictionaries are unordered by default.

Numeric Ranges

A for-in loop is super powerful because you can also utilise these for numeric ranges.

Take this example:

for index in 1...10 {
    print("\(index) times by 2 is \(index * 2)")
}

In this example, we are iterating between 1 and 10, and each time is running a multiplication of 2.

Your console will look like this:

1 times by 2 is 2
2 times by 2 is 4
3 times by 2 is 6
4 times by 2 is 8
5 times by 2 is 10
6 times by 2 is 12
7 times by 2 is 14
8 times by 2 is 16
9 times by 2 is 18
10 times by 2 is 20

The range will begin at 1 and end at 10 inclusively, and this is denoted with the use of the ...