Swift Case Studies & Practical Application 5

Question 1

You're building a feature flag system. Flags are checked thousands of times per second. A dictionary-backed solution with `String` keys works but a colleague proposes using an enum. What is the runtime advantage?

Accepted Answer

Enum cases are compared as integers, making switch exhaustive and O(1) with no hashing

Answer

Switching on an enum compiles to an integer comparison or jump table, which is faster and exhaustively checked by the compiler, unlike string-keyed dictionary lookups.

Question 2

A `RecipeParser` must support JSON, XML, and CSV formats. You want to add new formats without modifying the parser. Which design embodies the Open/Closed Principle in Swift?

Accepted Answer

Define a `FormatParser` protocol; create `JSONParser`, `XMLParser`, `CSVParser` conformances injected at runtime

Answer

Protocol-based strategy injection lets you add `YAMLParser` later by writing a new conformance, leaving `RecipeParser` itself unchanged — open for extension, closed for modification.

Question 3

Your app's test suite uses real `URLSession` calls and intermittently fails due to network conditions. What is the most effective fix without rewriting the production API layer?

Accepted Answer

Introduce a `URLProtocol` subclass that intercepts requests and returns canned responses

Answer

A custom `URLProtocol` subclass registered with the test session intercepts all URLSession requests at the protocol level, returning deterministic mock responses without changing production code.

Question 4

You profile an app with Instruments and find a hot path allocates a new `TransformMatrix` struct on every animation frame. What optimization should you investigate first?

Accepted Answer

Cache or reuse the struct across frames rather than reallocating each time

Answer

Avoiding per-frame allocation by caching the struct (or using a pre-allocated buffer) reduces memory pressure and eliminates the initialization cost on the hot path.

Question 5

A Swift property wrapper `@Clamped(range: 0...100)` should constrain any `Int` to the given range on set. Which stored property inside the wrapper holds the backing value?

Accepted Answer

`wrappedValue` with a setter that clamps before storing to a private variable

Answer

Property wrappers use `wrappedValue` as the primary interface; a custom setter there can clamp the incoming value before assigning it to a private backing store.

Swift Practice Test

Swift Practice Test

Swift Case Studies & Practical Application 5