Swift Technology & Digital Applications 4

Question 1

Which Swift property wrapper automatically publishes changes so SwiftUI views re-render?

Accepted Answer

@Published

Answer

`@Published` is a Combine property wrapper inside `ObservableObject` classes that emits through `objectWillChange` before each value change.

Question 2

What is the output of `[1, 2, 3].reduce(0, +)` in Swift?

Accepted Answer

6

Answer

`reduce(0, +)` starts with an initial value of 0 and adds each element, producing 0+1+2+3 = 6.

Question 3

In Swift, what distinguishes a `struct` from a `class` regarding memory management?

Accepted Answer

Structs are value types copied on assignment; classes are reference types

Answer

Structs are value types, so assignment and function argument passing produce independent copies, while classes share a single reference.

Question 4

Which Swift error-handling mechanism is used to propagate errors without using `throw`?

Accepted Answer

Result<Success, Failure>

Answer

`Result` lets functions return either a success value or an error without throwing, useful in callbacks and Combine pipelines.

Question 5

What does the `@objc` attribute enable in Swift?

Accepted Answer

It allows a Swift declaration to be visible and used from Objective-C code

Answer

`@objc` exposes Swift declarations to the Objective-C runtime, enabling interoperability with Objective-C frameworks and dynamic dispatch features.

Swift Practice Test