Combine Framework - Imtiaz211/interviews GitHub Wiki

What is the Combine framework?

The Combine framework is a reactive programming framework introduced by Apple in WWDC 2019. It enables developers to manage and respond to asynchronous events and data streams in a declarative and functional way.

What are the main components of the Combine framework?

The main components of the Combine framework are Publishers, Subscribers, and Operators. Publishers emit values, Subscribers receive and process those values, and Operators transform the values emitted by Publishers.

What is PassthroughSubject

it confirm Subject protocol, it doesn't occupy any state,and drop any value or pass, it will initialized without anyvalue
var subject = PassThroughSubject<String, Error>()

What is CurrentValueSubject

It confirm Subject protocol, wraps a single value and publishes a new element whenever the value changes.
let subject = CurrentValueSubject<State, Error>(.pending)

How does Combine differ from ReactiveCocoa or RxSwift?

Combine is a native framework for iOS, whereas ReactiveCocoa and RxSwift are third-party libraries. Combine also has a simpler API and a more Swift-like syntax, making it easier for developers to learn and use.

How do you create a publisher in Combine?

To create a publisher in Combine, you can use the Publishers factory class or create your own custom publisher by conforming to the Publisher protocol.
class TimerPublisher: Publisher {
typealias Output = Date
typealias Failure = Never

func receive(S)(Subscriber : S) where S : Subscriber, TimerPublisher.Failure = S.Failure, TimerPublisher.Output = S.Ouput {
let subscription = TimerSubscription(subscriber: subscriber)
subscriber.receive(subscription: subscription)
}
}

How do you create a subscriber in Combine?

To create a subscriber in Combine, you can use the Subscribers factory class or create your own custom subscriber by conforming to the Subscriber protocol.

What are the two ways to cancel a subscription in Combine?

The two ways to cancel a subscription in Combine are to call the cancel() method on the subscriber or to call the subscription.cancel() method on the returned Subscription object.

What is a subject in Combine?

A subject in Combine is a special kind of publisher that can also receive values and pass them on to its subscribers.

How can you merge two publishers in Combine?

To merge two publishers in Combine, you can use the merge() operator.

How can you filter the values emitted by a publisher in Combine?

To filter the values emitted by a publisher in Combine, you can use the filter() operator.

How can you handle errors in Combine?

To handle errors in Combine, you can use the catch() operator, which allows you to specify a closure that will be called when an error occurs. You can also use tryCatch operator to handle errors in a more elegant way.

How can you use the reduce operator in Combine?

The reduce operator allows you to accumulate the values emitted by a publisher and return the final result.
let numbers = [1, 2, 3, 4, 5]
@State private var cancellables = Set()
let publisher = numbers.publisher

publisher
.reduce(0, +)
.sink(receiveValue: { sum in
print("The sum is: (sum)")
})
.store(in: &cancellables)

How can you use the scan operator in Combine?

The scan operator is similar to reduce, but it emits the intermediate results as well as the final result.
let numbers = [1, 2, 3, 4, 5]
@State private var cancellables = Set()
let publisher = numbers.publisher

publisher
.scan(0, +)
.sink(receiveValue: { total in
print("The running total is: (total)")
})
.store(in: &cancellables)

How can you use the debounce operator in Combine?

The debounce operator allows you to delay the emission of values by a certain amount of time.

How can you use the zip operator in Combine?

The zip operator allows you to combine the values emitted by two or more publishers.

How can you use the throttle operator in Combine?

The throttle operator allows you to limit the frequency of the values emitted by a publisher.

How can you chain multiple operators together in Combine?

To chain multiple operators together in Combine, you can use the . operator to chain the operators together, like this: publisher.operator1().operator2().operator3(). This way, the output of the previous operator is passed as the input to the next operator.

What is the difference between sink and assign?

sink is used to subscribe to a publisher and receive its emitted values, while assign is used to bind the value emitted by a publisher to a property on an object. sink also allows you to handle completion and error events while assign does not.

What is a Cancellable in Combine?

A Cancellable is an object that represents an active subscription to a publisher. It allows you to cancel the subscription by calling its cancel() method.