Using `[weak self]` in the capture list is the standard, idiomatic Swift approach. It explicitly creates a weak reference to `self`, preventing a strong reference cycle. Inside the closure, you must then guard to safely unwrap this optional weak reference (e.g., `guard let self = self else { return }`) before using it, ensuring the code is safe if `self` has been deallocated. Simply marking it weak isn’t enough (option A); you must handle the optionality. While the delegate pattern (C) can solve the issue, it’s a heavier architectural change and not the most direct answer for a closure-based API. `autoclosure` (D) is unrelated to memory management.

This signature correctly uses a default value (`= “Anonymous”`) for the `name` parameter, making it optional for the caller without forcing the use of an Optional type (`String?`) inside the function body. For `age`, it correctly uses an optional `Int?` with a default value of `nil`, which perfectly models the requirement “only provided for users over 18.” Option A makes `age` optional but provides no default, forcing the caller to explicitly pass `nil`. Option B makes `name` an optional `String?`, which is less clean than using a default value. Option C uses an unnamed argument label (`_`) for `name`, which reduces clarity at the call site.

This is a classic UIKit lifecycle issue. Outlets are `nil` until the view controller’s view is loaded. `viewDidLoad()` is called after the view is loaded from the nib/storyboard, so it’s usually safe. However, if the outlet is accessed *before* `viewDidLoad()` (e.g., in an initializer or a property observer set too early), it will be `nil`. While option D is good general advice for safety, it doesn’t diagnose the root cause. Option C is possible but less likely if the developer recently verified the connection. Option B is a more complex issue. The first practical step is to verify the order of operations and ensure outlet-dependent code runs after the view is guaranteed to be loaded.

Swift’s `actor` is the ideal modern tool for this. It provides mutual exclusion (ensuring safe access to shared state like a dictionary of cached images and in-flight requests) and can suspend callers using `async` functions. You can implement logic where the actor checks its cache: if the image is ready, it returns it; if a request is in-flight, it suspends the new caller on a `CheckedContinuation` stored in a dictionary; if no request exists, it starts one. This elegantly prevents duplicate work. Semaphores (A) are lower-level and can lead to deadlock. Operations (B) can manage dependencies but are more cumbersome for this dynamic, key-based deduplication. Promises/Futures (C) are a conceptual model often implemented *using* actors or similar synchronization.

SwiftUI observes an `@ObservedObject` or `@StateObject` as a whole. When any `@Published` property changes, it invalidates the view that holds the reference. The most effective performance optimization is view decomposition: create smaller, focused child views that depend on only a subset of the data. For example, a `UserNameView` that takes a `String` (a `let` property) will only re-render when that specific string changes, not when other `@Published` properties in the view model update. Option A is incorrect because `@StateObject` and `@ObservedObject` have identical observation behavior; they differ in ownership. Option C (`.equatable()`) is for `View` types that conform to `Equatable`, not for solving this observation granularity issue. Option D uses a fictional modifier.

`try?` is appropriate when the success result is desirable, but a failure is a normal, recoverable outcome that doesn’t require diagnostic information. Converting the failure to `nil` allows for concise nil-coalescing (`let data = try? loadData() ?? defaultData`). It should not be used to ignore errors that the caller might need to diagnose (B, C, D are poor justifications). Performance difference (B) is negligible in most cases. Prototyping (C) is acceptable temporarily but not a “defensible” long-term reason. Even a single error type (D) might carry valuable information (e.g., a file-not-found error with a path) that `try?` discards.

A `static private(set) var` provides exactly the required semantics: it’s a static property (satisfying the protocol), its value can be set (presumably in your `AppDelegate` or `@main` struct), but that setter is private to the file or type, preventing accidental modification from elsewhere after configuration. This makes the publicly accessible value effectively constant after initial setup. Option A is a computed property that could change if `Configuration.current` changes, which may be acceptable but doesn’t enforce the “constant thereafter” rule as clearly. Option C is incorrect; static properties can be mutable. Option D introduces an unnecessary singleton and uses a `class var`, which is not the same as `static var` and would not satisfy the protocol requirement.

The key advantage of the generic constraint is abstraction over any `Collection` type, not just `Array`. This makes the function vastly more flexible and reusable—it can work with `Set`, `String` (which is a collection of `Character`), `ArraySlice`, etc., as long as their elements are `Equatable`. While B (specialization) and D (compile-time safety) are true benefits of generics in general, they are not the *most significant* distinction compared to a non-generic `[Equatable]` array (which, notably, cannot exist because `Equatable` can only be used as a generic constraint). Option C is incorrect because `Array` does have `startIndex` and `endIndex`.

The core principle is separation of concerns. The `NetworkService` should be responsible for networking logic and producing errors. The view controller (or a dedicated presenter/view model) is responsible for UI logic, including deciding *if*, *when*, and *how* to present an error to the user. Option D maintains this separation cleanly. Option A tightly couples the service to UIKit and makes it very hard to test. Option B (notifications) introduces global state and indirection, making the data flow harder to trace. Option C partially works but still entangles the service with UI-specific behavior (“a closure for alerting”), reducing its reusability in non-UI contexts (e.g., a background sync).

Using `[weak self]` in the capture list is the standard, idiomatic Swift approach. It explicitly creates a weak reference to `self`, preventing a strong reference cycle. Inside the closure, you must then guard to safely unwrap this optional weak reference (e.g., `guard let self = self else { return }`) before using it, ensuring the code is safe if `self` has been deallocated. Simply marking it weak isn’t enough (option A); you must handle the optionality. While the delegate pattern (C) can solve the issue, it’s a heavier architectural change and not the most direct answer for a closure-based API. `autoclosure` (D) is unrelated to memory management.0