Swift Ranges Cheatsheet

Ranges are fantastic for when we want to work with a range of sorted values that contain no duplicates.

Core Concepts:

• Ranges in Swift define a sequence of values between two bounds (lower and upper) and are widely used in loops, slicing collections, and pattern matching.
• There are different types of ranges that control whether the bounds are included or excluded.
• Pattern Matching: Ranges can be used in switch statements or if conditions to check if a value falls within a specific range.
• Comparable: Ranges must hold a Comparable type.
• Prefer ranges when you want to work with a sequence of values without storing the elements in memory, unlike an array that holds all its values.

Range Types Side by Side:

Common Use Cases:

Iteration:

for i in 0..<5 {
    print(i) // Outputs 0 to 4
}

Pattern Matching:

Ranges are great to use in switch or if-case conditions to check if a value lies in a range.¹

let number = 7
switch number {
    case 0..<5: print("0 to 4")
    case 5...10: print("5 to 10")
    default: print("Out of range")
}

Slicing

By slicing a collection we can create a smaller “view” of that collection without actually needing to copy it.

let numbers = [10, 20, 30, 40, 50, 60]

// Slice the array to get elements from index 1 to 3 (i.e., 20, 30, 40)
let slice = numbers[1..<4] // ArraySlice<Int>

print(slice) // Output: [20, 30, 40]

Make sure you read Sundell’s article on slicing!

Benefits Over Arrays:

• Memory Efficient: Ranges don’t store the values they represent, they just define the bounds.
• Performance: Faster when iterating over numbers or intervals since there’s no need to allocate memory for an entire sequence.
• Use a range when you need to express a numeric interval without storing values in memory.
  • Arrays should be used when the actual values need to be accessed or manipulated.

Conclusion

Ranges are a core part of Swift, used for efficient iteration, pattern matching, and controlling bounds in a concise and readable way.