20 Swift Combine Interview Questions and Answers

Swift Combine is a new framework that allows developers to declaratively compose asynchronous code. It provides a declarative Swift API for processing values over time. Combine is a powerful tool that can help you build reactive and responsive applications. When interviewing for a position that uses Swift Combine, you can expect to be asked questions about your experience and understanding of the framework. In this article, we review some of the most common Swift Combine interview questions and provide example answers to help you prepare for your next interview.

Swift Combine Interview Questions and Answers

Here are 20 commonly asked Swift Combine interview questions and answers to prepare you for your interview:

1. What is the Swift language?

Swift is a powerful and intuitive programming language for macOS, iOS, watchOS, tvOS, and Linux. Swift combines the best in modern language thinking with wisdom from the wider Apple engineering culture and the contributions of the open source community. The compiler is optimized for performance and the language is optimized for development, without compromising on either.

2. Can you explain what Combine is in the context of Apple’s development ecosystem?

Combine is a new framework from Apple that makes it easier to work with asynchronous events in Swift. It provides a declarative Swift API for processing values over time. Combine also introduces a new operator, called “publish”, which allows you to multicast values to multiple subscribers.

3. What are some key features of Swift and how does it compare to other languages like C, C++ or Java?

Swift is a powerful and fast programming language for iOS, macOS, tvOS, and watchOS. Swift is easy to learn and use and it’s open source, so anyone with an idea can create something incredible. Swift is a compiled programming language that is faster than Objective-C and doesn’t require a separate library.

4. What do you understand about a publisher in the context of Combine?

A publisher is a Combine entity that emits values over time, and can be used to perform various transformations on those values. Publishers can be used to create custom operators, to transform values, and to perform other operations.

5. How can publishers be created using the Swift programming language?

Publishers can be created using the Swift programming language by using the Publisher class. This class provides a number of methods for creating publishers, such as the create method, which takes a closure that returns a publisher.

6. What are the different types of subscription options available with Combine?

There are three different types of subscription options available with Combine:

1. sink – This option allows you to receive updates from the publisher as they happen, and also allows you to cancel the subscription at any time.

2. receiveValue – This option allows you to receive updates from the publisher as they happen, but you cannot cancel the subscription.

3. assign – This option allows you to receive updates from the publisher as they happen, and also allows you to update the value of a property with the latest value from the publisher.

7. What happens if two subscriptions attempt to modify the same value simultaneously?

If two subscriptions attempt to modify the same value simultaneously, then a CombineError.Conflict error will be thrown.

8. What is the difference between an asynchronous and synchronous stream of values in Combine?

An asynchronous stream of values is one where each value is emitted on a separate thread, and the order in which values are emitted is not guaranteed. A synchronous stream of values is one where each value is emitted on the same thread, and the order in which values are emitted is guaranteed.

9. What kind of operations can be performed on a publisher?

There are a variety of operations that can be performed on a publisher, depending on the type of publisher. Some common operations include filtering, mapping, and reducing. These operations can be used to transform the data emitted by a publisher, or to perform some kind of calculation on that data.

10. Can you give me some examples of publishers that are already used by developers in the wild?

There are a few popular publishers that are used by developers in the wild. For example, the URLSession publisher can be used to fetch data from a remote API. Another popular publisher is the Timer publisher, which can be used to emit events at regular intervals.

11. Can you explain what an operator is in the context of Combine?

In Combine, an operator is a method that transforms or combines publisher streams. For example, the map operator transforms each value emitted by a publisher by applying a closure you provide. The filter operator allows you to specify which values you are interested in, and discards the rest.

12. Are there any limits to the number of operators that can be combined together?

There are no limits to the number of operators that can be combined together.

13. What is a subscriber in the context of Swift?

A subscriber is an object that conforms to the Subscriber protocol and can receive values from a Publisher.

14. What are the advantages of using Combine instead of traditional event-handling architectures like delegates and callbacks?

There are several advantages to using Combine instead of traditional event-handling architectures like delegates and callbacks. First, Combine allows you to declaratively express your event-handling logic, which can make your code more readable and easier to understand. Second, Combine can help you avoid common pitfalls associated with traditional event-handling architectures, such as race conditions and memory leaks. Finally, Combine provides a number of built-in operators and publishers that can make it easier to work with asynchronous data sources.

15. Why was Combine introduced as part of Swift 5.1?

Combine was introduced as a way to provide a declarative Swift API for processing values over time. This is similar to the way that RxSwift and ReactiveCocoa work, but with a more Swift-like syntax. Combine is also designed to work well with the SwiftUI framework, and so it is possible that it will see more use in the future as SwiftUI becomes more popular.

16. What is the importance of a cancellable?

A cancellable is important in Combine because it allows you to cancel an upstream subscription. This is important because it means that you can avoid processing data that you no longer need, which can help improve performance.

17. What is the purpose of the ConnectablePublisher class in Swift?

The ConnectablePublisher class is used to manage the execution of a publisher that emits elements to its subscribers. This class is used to ensure that elements are only emitted when there is an active subscription, and that elements are only emitted once per subscription. This class is also used to manage the backpressure of a publisher so that it does not overwhelm its subscribers.

18. Is it possible for a publisher to fail? If yes, then what happens?

Yes, it is possible for a publisher to fail. In this case, the publisher will send a failure event to the subscriber.

19. Which data type should be used to represent errors when building a publisher?

The Error type should be used to represent errors when building a publisher.

20. What happens if a Combine pipeline has multiple subscribers?

If a Combine pipeline has multiple subscribers, each subscriber will receive its own independent stream of events. This means that if one subscriber cancels its subscription, the other subscribers will continue to receive events.