Swift Interview Questions and Answers for 10 years experience

1. What are the key differences between structs and classes in Swift?

   • Answer: Structs are value types, meaning they are copied when passed around, while classes are reference types, meaning they are passed as references. Structs have a default memberwise initializer, while classes do not. Structs do not support inheritance, while classes do. Value types offer better performance and thread safety in many cases due to the copy-on-write mechanism. Classes support deinitializers, while structs do not.

2. Explain the concept of memory management in Swift.

   • Answer: Swift uses Automatic Reference Counting (ARC) to manage memory. ARC automatically keeps track of how many references exist to an object. When the reference count drops to zero, the object is deallocated, freeing up memory. This avoids manual memory management and reduces the risk of memory leaks. Strong, weak, unowned, and strong references are used to manage object lifecycles appropriately.

3. What are closures in Swift, and how are they used? Provide an example.

   • Answer: Closures are self-contained blocks of code that can be passed around and executed later. They can capture values from their surrounding context. They're useful for callbacks, asynchronous operations, and higher-order functions. Example: `let numbers = [1, 2, 3, 4, 5] let doubledNumbers = numbers.map { $0 * 2 }`

4. Describe different ways to handle errors in Swift.

   • Answer: Swift uses error handling with `do-catch` statements and the `throws` keyword. Functions can declare that they throw errors using `throws`. The `try` keyword attempts to execute code that might throw an error. A `catch` block handles any thrown errors. Optional chaining and optional binding can also be used to gracefully handle potential nil values.

5. Explain the difference between `let` and `var` in Swift.

   • Answer: `let` declares a constant, whose value cannot be changed after initialization. `var` declares a variable, whose value can be modified after initialization.

6. What is Generics in Swift and why are they useful? Provide an example.

   • Answer: Generics allow you to write flexible, reusable code that can work with different types without losing type safety. They improve code reusability and reduce code duplication. Example: `func printArray(array: [T]) { for item in array { print(item) } }`

7. How does Swift handle optionals? Explain optional binding and optional chaining.

   • Answer: Optionals represent values that may or may not exist. Optional binding safely unwraps an optional value using `if let` or `guard let`. Optional chaining allows you to access properties or methods of an optional value without explicitly unwrapping it, returning `nil` if the optional is `nil`.

8. Explain the use of protocols in Swift and provide a practical example.

   • Answer: Protocols define a blueprint of methods, properties, and other requirements that conforming types must implement. They promote code reusability and polymorphism. Example: A protocol defining a `fly()` method could be adopted by different types of birds or aircraft.

9. What are extensions in Swift, and how are they used?

   • Answer: Extensions add new functionality to existing types (structs, enums, classes, and protocols) without modifying their original implementation. They're useful for adding convenience methods or properties to types you don't control.

10. Discuss different concurrency models in Swift (e.g., Grand Central Dispatch (GCD), Operation Queues).

    • Answer: GCD provides a low-level, efficient way to perform concurrent operations using queues and blocks. Operation queues provide a higher-level abstraction, offering more control over dependencies and cancellation.

11. Explain the difference between `==` and `===` in Swift.

    • Answer: `==` performs value equality checks, while `===` checks for reference equality (whether two references point to the same object in memory).

12. What are computed properties in Swift? Give an example.

    • Answer: Computed properties don't store values; instead, they calculate a value on demand. Example: A `diameter` computed property for a `circle` struct based on its radius.

13. Describe the role of `@escaping` and `@noescape` in closures.

    • Answer: `@escaping` indicates that a closure can be executed after the function it's passed to returns. `@noescape` (the default) implies the closure will be executed within the function's scope.

14. How do you use `guard` statements in Swift, and what are their benefits?

    • Answer: `guard` statements allow you to write more concise error-handling code. They're used to check for conditions; if the condition is false, the `else` block is executed, exiting the current scope.

15. What are the different access control levels in Swift?

    • Answer: `open`, `public`, `internal`, `fileprivate`, `private` control the accessibility of code elements within and outside modules.

16. Explain the concept of polymorphism in Swift.

    • Answer: Polymorphism allows objects of different classes to be treated as objects of a common type, typically through inheritance and protocols.

17. How to handle asynchronous operations in Swift using `async`/`await`?

    • Answer: `async`/`await` simplifies asynchronous programming by making it look and feel like synchronous code. `async` functions can suspend execution until an asynchronous operation completes.

18. What are Result types and how do they improve error handling?

    • Answer: Result types explicitly represent either success (with a value) or failure (with an error), enhancing error handling clarity and safety.

19. Explain the benefits and drawbacks of using singletons in Swift.

    • Answer: Singletons provide a global access point to a single instance of a class, but overuse can lead to tightly coupled code and difficulties in testing.

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