Lesson 04 of 20

8 mins read

Operators, Range Types & Nil-Coalescing

In Plain English

Swift provides standard arithmetic and logical operators alongside expressive Range types. Learn closed ranges (1...5), half-open ranges (0..<count), one-sided ranges (...5), and the nil-coalescing operator (??) for fallback handling.

The Mental Model

"A closed range (1...5) is inclusive like an RSVP list inviting guests 1 through 5. A half-open range (0..<5) is like an index ruler stopping just before 5, matching zero-indexed collection bounds perfectly."

Deep Dive: How It Works

Closed Range (a...b): Includes both a and b (e.g. 1...5 contains 1, 2, 3, 4, 5).

Half-Open Range (a..<b): Includes a up to but excluding b (e.g. 0..<5 contains 0, 1, 2, 3, 4).

Nil-Coalescing (a ?? b): Unwraps optional a if it contains a value, or returns default fallback b if a is nil.

Overflow Operators: Standard arithmetic halts on overflow; use &+, &-, &* if wrapping behavior is explicitly desired.

Syntax Blueprint

let closed = 1...5
let halfOpen = 0..<3
let fallback = optionalVal ?? "default"

Use ... for inclusive ranges, ..< for upper-bound exclusive ranges, and ?? for fallback unwrapping.

Core Rules to Remember

Overflow Protection: Swift prevents silent integer overflow crashes by trapping at runtime unless overflow operators (&+) are used.

Range Pattern Matching: Ranges integrate directly into switch cases: case 90...100: print("A").

Nil Coalescing: Short-circuits evaluation: if the left operand is not nil, the right fallback operand is never executed.

Common Beginner Traps & How to Fix Them

Mistake:Using 0...array.count for loop iterations.

Why it happens: array.count is out-of-bounds for zero-indexed arrays, causing a fatal IndexOutOfBounds runtime crash.

How to fix: Use half-open range 0..<array.count or simply for item in array.

Pro Tip: Use one-sided ranges like numbers[2...] to slice an array from index 2 to the end.

Live Interactive Example

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Range Iteration and Nil-Coalescing Fallback

Swift 5.10 / LLVM

Output Console

Click "Run Code" to view the rendered output.

How it works: Nil-coalescing ?? resolved to default port 8080, and range 1...3 summed 1 + 2 + 3 = 6.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Calculate Factorial with Closed Range

Declare var factorial = 1.
Use a for-in loop over closed range 1...5 to multiply factorial *= n.
Print "Factorial of 5: \(factorial)".

Sandbox Output

Click "Run & Check" to test your solution.

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