![]() ![]() Note that I erased the Deferred publisher to AnyPublisher. So the Future still runs only once and executes immediately when it's created, but we defer the creation of the Future to a later time. This means that a new Future is created every time we subscribe to the Deferred publisher. The Deferred publisher runs its closure every time it receives a subscriber. We're expected to return a publisher from this closure. The Deferred publisher's initializer takes a closure. So how does a Future work? And how do we use it in code? Let's look at a simple example: func createFuture() -> Future ) // the Future executes again because it received another subscriber ![]() This means that you can map over Futures and apply other transformations just like you can with any other publisher. If you examine Combine's documentation for Future, you'll find that Future conforms to Publisher. In Combine, a Future is implemented as a Publisher that only emits a single value, or an error. A function can return an object that will eventually resolve with a value or an error. The implementation of Combine's Futures and Promises is quite similar to the one that you'd find in Javascript on a surface level. Instead, we got an API that is based on Futures, which is also a common concept in this kind of working area. In Combine, we didn't get a Promises API that's identical to Javascript and PromiseKit's implementations. I even wrote a post about improving async code with PromiseKit in 2015. We've had implementations of Promises in iOS for a while too. The Javascript community has been working with Promises for a while now. The concept of Promises and Futures isn't unique to Combine or even iOS. Understanding what Promises and Futures are SWIFT PUBLISHER 4 TUTORIAL HOW TOWrapping an existing asynchronous operation in a Futureīy the end of this post, you will be able to take virtually any async operation in your codebase and you will know how to expose it to combine using a Future.Understanding what Promises and Futures are.In this post I will cover the following topics: ![]()
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