#Swift publisher 3 tutorials update#

The body of the function is trivial: we combine the publisher with another one passed as a parameter and then call two other basic operators: removeDuplicates and map. We want to make it generic otherwise, the operator loses its versatility to work with any kind of Publisher. Next, because the output from both publishers has to be compared, the Output has to adopt the Equatable protocol. Tip: Using AnyPublisher as a return type is a good choice because when chaining operators, it becomes really easy to make the signature complicated. First of all, it returns an AnyPublisher with the same output and Failure type of the current publisher you’re working on. The most complex thing is the method signature, but don’t worry, it’s easier than you may think. What the operator does is: take two publishers, combines them, removes the duplicates, and emit the outputs. To give a more concrete example, imagine you want to recreate an operator from RxSwift, another declarative framework for Swift that you may know. Imagine you want to create a new operator because the standard ones do not implement the functionality you need. In case you need a custom publisher because it fits your needs, the easiest way is to create an extension to the Publisher namespace. Use the annotation on a property so that the property gains a publisher that emits an event whenever the property’s value changes.

The CurrentValueSubject, in fact, is a subject that wraps a single value and publishes a new element whenever the value changes.

#Swift publisher 3 tutorials update#

Use a CurrentValueSubject to publish whenever you update the subject’s value.

You can use a PassthroughSubject, for example, a subclass of Subject, to publish values by calling its send(_:) method.

Sometimes, implementing the Publisher protocol itself is not necessary and the same goal can be achieved in other ways: Steps 4, 5, and 6 are repeated indefinitely.Īs you may have noticed, the entire communication is pretty easy, and once understood, implementing custom publishers is a doable task.

Once the Demand is received by the Subscription, it starts the whole processing again and emits values until the Demand is satisfied.

Note that the Demand that is sent adds the number of values it wants to receive upon the previous demand already sent as the number of values requested can increase or stay the same but never decrease.

The subscriber receives values from the subscription, and, as a response, it sends a new Demand.

Those values are sent one by one using the subscriber’s receive(_:) method until the maximum demand is reached.

The subscription receives the demand and starts to process information and emit values.

This is done by sending the number of values it wants, by calling request(_:).

Now that the subscriber has the subscription and a contract between it and the publisher has been made, it can request for values to the publisher.

The subscriber receives the subscription via the receive(subscription:) method.

The publisher creates a subscription and delivers it to the subscriber.This is usually done via the sink() method, which allows the programmer to manage both the completion and the values received by the publisher. A subscriber subscribes to the publisher.