Combine: Asynchronous Programming with Swift by By Marin Todorov & By Shai Mishali & By Florent Pillet

Author:By Marin Todorov & By Shai Mishali & By Florent Pillet
Language: eng
Format: epub
Publisher: Ray Wenderlich

To put this concept into practice, imagine you’re performing a network request, like you learned how to do in Chapter 9, “Networking.” You want multiple subscribers to receive the result without requesting multiple times. Your code would look something like this:

let shared = URLSession.shared .dataTaskPublisher(for: URL(string: "https://www.raywenderlich.com")!) .map(\.data) .print("shared") .share() print("subscribing first") let subscription1 = shared.sink( receiveCompletion: { _ in }, receiveValue: { print("subscription1 received: '\($0)'") } ) print("subscribing second") let subscription2 = shared.sink( receiveCompletion: { _ in }, receiveValue: { print("subscription2 received: '\($0)'") } )

The first subscriber triggers the “work” (in this case, performing the network request) of share()’s upstream publisher. The second subscriber will simply “connect” to it and receive values at the same time as the first.

Running this code in a playground, you’d see an output similar to:

subscribing first shared: receive subscription: (DataTaskPublisher) shared: request unlimited subscribing second shared: receive value: (303425 bytes) subscription1 received: '303425 bytes' subscription2 received: '303425 bytes' shared: receive finished

Using the print(_:to:) operator‘s output, you can see that:

The first subscription triggers a subscription to the DataTaskPublisher.

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