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README.md

Day 4: Loops

Follow along at https://www.hackingwithswift.com/100/4

📒 Field Notes

For Loops

Swift for loops are either range-based or collection-based, but they involve the same "for-in" syntactic approach:

for i in 1 ... 10 {
  // do something
}

for item in items {
  // do something
}

Some languages, C++, also use a three-expression for loop:

for (i = 1; i <= 10; i++)

But I like how Swift seems to have made a deliberate decision to keeping for-loops streamlined and consistent. If we absolutely need an index and an item at the same time, we can always use enumerated on the collection being iterated over:

for (index, score) in scores.enumerated() {
  print("Score \(index): \(score)")
}

While & Repeat-While Loops

I find that I use these much less frequently, but there's also no reason not to support them!

I like how Swift uses repeat in place of where many languages use do. It's more informative to what's actually happening while we're here — and it allows do to be used for "try blocks", where do and catch are the outer constructs:

Exiting loops

Using break or continue within a single loop is pretty straightforward. Things get tricky when it comes to nested loops, though, because breaking only applies to a single layer (or "block"/"level"/etc).

Enter labeled statements.

Swift isn't the only language to use these, but to be picky briefly, this is where not having to wrap the conditional statement itself in parentheses gives Swift an edge in cleanliness.

deepNesting: for planet in planets {
    print("Passing through \(planet)")

    numbers: for i in 1...10 {
        if i == 3 { break numbers }
        print("Inside of `numbers` loop")
    }

    spaceDust: for i in 1...3 {
        print("Moving through space dust")
        asteroids: for j in 1...3 {
            print("Saw an asteroid")

            if i == 2 { break spaceDust }
        }

        if i == 2 { break }
        if i == 333 { break deepNesting }
    }
}

Anyway, while rare, this is a handy way to write cleaner code in situations where, given the nature of deep nesting, we're likely to need all the help we can get. (Whether or not it's a code smell to be there in the first place... that's another matter 🙂.)

Infinite Loops

print("Infinite loops can be powerful")

while true {
  print("and dangerous!")
}

🔗 Related Links