Swift is the language for iOS and Apple-platform development, and its interviews test optionals (its signature safety feature), value vs reference semantics, ARC memory management, and protocol-oriented programming. Here are the Swift interview questions that actually get asked, with answers. (See also our iOS developer guide.)
Optionals & types
- What is an optional, and how do you safely unwrap it?
- Optional binding (if let, guard let) vs force unwrapping.
- Optional chaining and nil coalescing.
- Struct vs class — value vs reference types.
- let vs var.
Memory (ARC)
- How does ARC (Automatic Reference Counting) work?
- Strong, weak, and unowned references.
- What is a retain cycle and how do you break one?
- Capture lists in closures.
Protocols & closures
- Protocols and protocol-oriented programming.
- Protocol extensions; what makes Swift protocol-oriented?
- Closures and escaping vs non-escaping closures.
- Error handling — do, try, catch.
How to prepare
Swift rounds probe optionals, ARC, and protocols verbally. Practise explaining retain cycles and optional handling out loud. Greenroom runs spoken technical interviews that follow up on your reasoning. Pair it with our iOS guide.
Frequently asked questions
What are the most common Swift interview questions?
Common Swift questions cover optionals (safe unwrapping with if let and guard let, optional chaining, nil coalescing, force unwrapping), struct vs class and value vs reference types, ARC memory management (strong/weak/unowned references, retain cycles, capture lists), protocols and protocol-oriented programming, closures (escaping vs non-escaping), and error handling with do/try/catch.
What is an optional in Swift?
An optional is a type that either holds a value or is nil, declared with a ? (like String?). It forces you to handle the absence of a value explicitly, preventing many null-related crashes. You safely access the value with optional binding (if let, guard let), optional chaining (?.), or the nil-coalescing operator (??), and force unwrap with ! only when you're certain it's non-nil.
How does ARC work in Swift?
Automatic Reference Counting tracks how many strong references point to each class instance and deallocates the instance when that count reaches zero. Retain cycles happen when two objects hold strong references to each other, so neither is freed; you break them using weak references (which become nil) or unowned references (assumed to always exist), often via capture lists in closures.
How should I prepare for a Swift interview?
Focus on optionals and safe unwrapping, value vs reference semantics, ARC and retain cycles, and protocol-oriented programming, since these are Swift's signature topics. Practise explaining how you'd avoid a retain cycle and handle nil out loud with a voice-based mock interview that follows up, because Swift rounds probe understanding over syntax.