📱 iOS Developer Interview Prep: Mastering Swift Fundamentals

If you’re an iOS developer preparing for interviews, there’s one thing you can’t afford to overlook: Swift fundamentals. While companies often ask you about architecture patterns, system design, or even algorithms, your understanding of Swift basics will be put to the test too.

This post will help you review and refresh the key Swift topics that interviewers expect you to know cold.

🎯 Why Focus on Swift Fundamentals?

Even senior iOS interviews include Swift questions. Why? Because your code quality depends on how well you know the language:
✅ Writing idiomatic Swift
✅ Avoiding bugs related to optionals or reference cycles
✅ Making your code readable and maintainable

Most importantly, if you fumble basic Swift questions in an interview, it raises red flags about your experience level.

🧭 What to Review? The Essential Swift Topics

Below is a checklist with explanations. Use it to self-test or plan your study sessions.

1️⃣ Optionals

1. What is an optional?
2. How do you safely unwrap it? (if let, guard let, nil coalescing)
3. Force-unwrapping — when is it safe (or not)?
4. Optional chaining
5. Implicitly unwrapped optionals

✅ Example Question: What’s the difference between ? and ! in Swift?

2️⃣ Value Types vs. Reference Types

1. Struct vs. Class
2. Copy-on-write behaviour
3. When to choose struct over class
4. Mutating methods in structs

✅ Example Question: Why might you choose a struct instead of a class for a model?

3️⃣ Protocols & Protocol-Oriented Programming

1. Defining protocols
2. Protocol conformance
3. Protocol extensions
4. Associated types

✅ Example Question: How do you use protocols to design for testability?

4️⃣ Closures

1. Closure syntax
2. Capturing values
3. Escaping vs. non-escaping
4. Trailing closure syntax
5. @escaping keyword

✅ Example Question: What happens if you forget [weak self] in a closure?

5️⃣ Memory Management

1. ARC basics
2. Strong, weak, unowned references
3. Retain cycles and how to break them
4. Common pitfalls in closures

✅ Example Question: Explain how ARC works in Swift.

6️⃣ Enumerations

1. Raw values vs. associated values
2. Switch statements with enums
3. Enum cases with associated values
4. Codable conformance

✅ Example Question: How would you use an enum to model network request results?

7️⃣ Generics

1. Why use generics
2. Writing a generic function or type
3. Type constraints

✅ Example Question: Can you write a function that swaps two values of any type?

8️⃣ Error Handling

1. do-try-catch
2. Throwing functions
3. Propagating errors
4. Custom error types

✅ Example Question: How do you design a function that can throw an error?

9️⃣ Property Observers

1. willSet and didSet
2. Use cases
3. Interaction with computed properties

✅ Example Question: What is the difference between a stored property and a computed property?

🔟 Concurrency (Swift 5.5+)

1. async/await
2. Tasks
3. Structured concurrency
4. Actors for avoiding data races

✅ Example Question: How would you perform a network call using async/await?

💡 Pro Tip: Practice With Code
It’s not enough to read about these. Open Xcode Playgrounds or your favourite Swift REPL and:

• Write out the syntax from scratch
• Build small examples
• Try breaking things and fixing them
• Interviews favor candidates who can write code on the spot.

📚 Additional Resources
Apple’s Swift Programming Language Guide

• Swift by Sundell
• Hacking with Swift

✅ Final Thoughts
Swift fundamentals are the bedrock of iOS development interviews. Whether you’re applying for junior or senior roles, mastering these basics is essential.

Start by reviewing each topic, practicing code, and answering mock questions. Once you’re confident, you’ll be in great shape for your next interview.

Happy coding — and good luck in your interviews! 🚀