Interview Questions
ARC automatically manages memory by: 1) Tracking strong references to class instances, 2) Deallocating memory when reference count reaches zero, 3) Managing reference cycles through weak and unowned references, 4) Handling retain/release operations at compile time, 5) Working only with reference types (classes), not value types (structs, enums). ARC eliminates manual memory management while ensuring deterministic cleanup.
Key differences include: 1) weak references are optional and can become nil, 2) unowned references are non-optional and assume always valid, 3) weak is used when reference might become nil during lifetime, 4) unowned is used when reference never becomes nil while instance exists, 5) weak requires explicit unwrapping, 6) unowned assumes permanent valid reference. Choose weak for optional references and unowned for guaranteed valid references.
Retain cycle identification and fixing involves: 1) Using Memory Graph Debugger in Xcode, 2) Implementing weak or unowned references appropriately, 3) Using capture lists in closures [weak self], 4) Proper delegate pattern implementation, 5) Breaking parent-child cyclic references, 6) Memory leak instruments usage. Regular testing and monitoring help prevent memory leaks.
Closure capture lists: 1) Define how values are captured by closures, 2) Use [weak self] or [unowned self] to prevent retain cycles, 3) Allow multiple captured variables, 4) Support value type capturing, 5) Enable explicit capture rules, 6) Help manage reference cycles in asynchronous operations. Proper use prevents memory leaks in closure-heavy code.
Strong vs weak references: 1) Strong references increment reference count, weak don't, 2) Strong references keep objects alive, weak allow deallocation, 3) Strong is the default reference type, 4) Weak must be optional variables, 5) Strong creates ownership relationship, 6) Weak used for delegate patterns and breaking retain cycles. Understanding this difference is crucial for proper memory management.
ARC and deinitializers: 1) Deinit called automatically when reference count reaches zero, 2) Only available in class types, 3) Can't be called directly, 4) Used for cleanup operations, 5) Called in reverse order of inheritance chain, 6) Helps verify proper memory management. Deinitializers are crucial for resource cleanup and debugging memory issues.
Memory management best practices: 1) Use value types when possible, 2) Implement proper weak/unowned references, 3) Break retain cycles in closures, 4) Use proper delegate patterns, 5) Monitor memory usage with instruments, 6) Implement deinitializers for cleanup. Regular testing and monitoring ensure optimal memory usage.
Async operation memory management: 1) Use capture lists in closures, 2) Implement proper cancellation handling, 3) Break retain cycles in completion handlers, 4) Handle self references carefully, 5) Clean up resources on cancellation, 6) Monitor async operation lifecycle. Careful management prevents leaks in async code.
Autoreleasepool usage: 1) Manages temporary objects memory, 2) Useful in loops processing many objects, 3) Helps reduce peak memory usage, 4) Important for command-line tools, 5) Handles bridged Objective-C objects, 6) Provides explicit memory release points. Used less in Swift than Objective-C but still important for specific scenarios.
Collection memory management: 1) Value type collections copy on write, 2) Reference type elements managed by ARC, 3) Proper cleanup of collection elements, 4) Memory efficient array slicing, 5) Capacity management for arrays, 6) Collection lifecycle management. Understanding collection behavior ensures efficient memory usage.
Reference counting: 1) Tracks number of references to objects, 2) Increments count for new references, 3) Decrements count when references removed, 4) Deallocates when count reaches zero, 5) Handles in compile time by ARC, 6) Only applies to class instances. Forms the basis of Swift's memory management system.
Memory leak debugging: 1) Use Xcode Memory Graph Debugger, 2) Implement Instruments for leak detection, 3) Monitor object deallocation, 4) Check retain cycles, 5) Analyze memory usage patterns, 6) Use runtime memory debugging tools. Regular debugging prevents memory issues in production.
Delegate memory management: 1) Use weak references for delegates, 2) Prevent retain cycles, 3) Handle delegate lifecycle properly, 4) Clean up delegate references, 5) Consider multiple delegate patterns, 6) Implement proper delegate cleanup. Proper delegate management prevents common memory leaks.
Closure memory management: 1) Captures referenced variables strongly by default, 2) Uses capture lists for custom capturing, 3) Manages closure lifecycle, 4) Handles async closure memory, 5) Prevents retain cycles with weak self, 6) Cleans up captured references. Understanding closure capture rules is crucial.
Copy-on-write impact: 1) Optimizes value type performance, 2) Shares memory until modification, 3) Creates copies only when needed, 4) Reduces memory usage, 5) Applies to standard library collections, 6) Balances safety and efficiency. Important optimization technique for value types.