Interview Prep: Common Swift Coding Questions and Solutions


Swift, Apple's powerful and intuitive programming language, is widely used for developing iOS, macOS, watchOS, and tvOS applications. As such, Swift coding questions are a staple in technical interviews for positions related to Apple's ecosystem. This article will explore common Swift coding questions and provide insights into their solutions.

Understanding Swift's Core Concepts

Before diving into specific questions, it's crucial to grasp Swift's core concepts, which include optionals, closures, memory management (ARC), protocol-oriented programming, and error handling. Mastery of these concepts is often tested in interviews.

Common Swift Coding Questions

  1. Explain Optionals in Swift. How Do You Safely Unwrap an Optional?

    Concept: Optionals represent variables that can hold either a value or nil. Safe unwrapping ensures that the program doesn't crash if an optional is nil.

    Solution: Use optional binding (if let) or guard statements to safely unwrap optionals.

  2. Implement a Singleton Pattern in Swift.

    Concept: Singleton is a design pattern that ensures a class has only one instance and provides a global access point to it.

    Solution: Use a static instance and a private initializer.

    class MySingleton {
        static let shared = MySingleton()
        private init() {}
  3. Write a Function to Check if a String is a Palindrome.

    Concept: A palindrome is a string that reads the same backward as forward.

    Solution: Compare the string with its reversed version.

    func isPalindrome(_ str: String) -> Bool {
        return str == String(str.reversed())
  4. Explain ARC in Swift. How Does It Work?

    Concept: Automatic Reference Counting (ARC) manages the memory usage of objects by deallocating objects no longer needed.

    Solution: Discuss how ARC uses reference counting to track and manage an app's memory usage.

  5. Demonstrate the Use of Closures in Swift.

    Concept: Closures are self-contained blocks of functionality that can be passed around in code.

    Solution: Write a simple closure, perhaps for sorting an array.

    let numbers = [1, 3, 5, 2, 4]
    let sortedNumbers = numbers.sorted { $0 < $1 }
  6. How Do You Handle Errors in Swift?

    Concept: Swift provides error handling using throwing functions, do-catch blocks, and the try keyword.

    Solution: Demonstrate with a custom error type and a throwing function.

    enum MyError: Error {
        case runtimeError(String)
    func canThrowError() throws {
        throw MyError.runtimeError("Something went wrong")
  7. What is Protocol-Oriented Programming in Swift?

    Concept: Protocol-oriented programming is a paradigm that emphasizes defining protocols and implementing them.

    Solution: Discuss the advantages and create a simple protocol with extensions.

Tips for Tackling Swift Interview Questions

  • Understand the Question: Clarify any ambiguities before attempting to solve the problem.
  • Think Aloud: Explain your thought process as you write the code.
  • Optimize Your Solution: Discuss and implement potential optimizations.
  • Practice Common Algorithms: Be familiar with sorting algorithms, recursion, and data structures like arrays, dictionaries, and linked lists.


Preparing for Swift coding interviews requires a deep understanding of the language’s nuances and practical experience with its constructs. By mastering these common questions and their solutions, candidates can approach Swift interviews with confidence. Regular practice and keeping abreast of the latest Swift developments will further enhance one's proficiency and readiness for technical interviews.

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