Swift Interview Questions and Answers for 7 years experience

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

   • Answer: Structs are value types, meaning copies are created when they are passed around, while classes are reference types, meaning they are passed by reference. Structs have a default memberwise initializer, while classes do not. Structs cannot inherit from other structs or classes, and vice-versa. Classes support inheritance, polymorphism, and deinitializers, while structs do not. Choosing between a struct and a class depends on the specific needs of your data; if mutability is not required and copying is efficient, a struct is generally preferred.

2. Explain the concept of optionals in Swift and how to handle them safely.

   • Answer: Optionals represent values that may or may not be present. They are declared using a `?` after the type. To handle them safely, use optional binding (`if let` or `guard let`), optional chaining (`?.`), the nil-coalescing operator (`??`), or the `??=` operator (nil coalescing assignment). Optional binding checks if an optional has a value before unwrapping it. Optional chaining safely accesses properties or methods of an optional without causing a crash if the optional is nil. The nil-coalescing operator provides a default value if the optional is nil.

3. Describe different ways to achieve concurrency in Swift.

   • Answer: Swift offers several ways to achieve concurrency, including Grand Central Dispatch (GCD) using queues and dispatch functions, Operation Queues providing more control and dependencies between operations, and async/await which makes asynchronous code more readable and maintainable. Each approach has its strengths and weaknesses; GCD is lightweight and efficient for simple tasks, Operation Queues are better for complex tasks with dependencies, and async/await improves readability and simplifies asynchronous programming significantly.

4. What are closures in Swift and how are they used? Provide examples.

   • 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 used for callbacks, event handling, sorting arrays, and more. Examples include using closures as completion handlers, sorting arrays with a custom comparison function, and creating higher-order functions that take other functions as arguments.

5. Explain the importance of memory management in Swift. How does ARC work?

   • Answer: Memory management is crucial to prevent memory leaks and crashes. Automatic Reference Counting (ARC) automatically manages memory by keeping track of references to objects. When an object has no more strong references, ARC deallocates its memory. Understanding strong, weak, and unowned references is crucial for avoiding retain cycles. Weak references don't increase the reference count, and unowned references should only be used when the lifecycle of one object is directly dependent on another, and the other will never outlive it.

6. What is the difference between `let` and `var` in Swift?

   • Answer: `let` declares a constant, whose value cannot be changed after it's initialized. `var` declares a variable, whose value can be modified after initialization. Using `let` promotes immutability and can help prevent unintended modifications, leading to more robust code.

7. How do you handle errors in Swift? Discuss different approaches.

   • Answer: Swift uses `do-catch` blocks to handle errors. Functions can throw errors using the `throws` keyword, and calling functions that throw requires handling potential errors within a `do-catch` block. You can also use `try?` to handle errors optionally, returning nil if an error occurs, or `try!` to forcefully unwrap – but this should be used cautiously.

8. Explain protocols and extensions in Swift. Give practical examples.

   • Answer: Protocols define a blueprint for classes, structs, or enums to conform to. They specify methods, properties, or associated types that conforming types must implement. Extensions add functionality to existing types without subclassing, which is useful for adding methods or computed properties to built-in types or types you don't own.

9. Describe generics in Swift and their benefits.

   • Answer: Generics allow you to write flexible, reusable code that can work with different types without losing type safety. They're defined using angle brackets (`<>`). Benefits include improved code reusability, type safety, and reduced code duplication.

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