Combine and Functional reactive programming
Combine has just like RxSwift observables and observers noted as publishers and subscribers and an extra concept feature known as back-pressure that gives the idea of cancelling the data flow when it wants(cancellable publishers).
Combine takes this further, enabling watching of properties, binding to objects, sending and receiving higher level events from UI controls, and supporting integration with almost all of Apple’s existing API ecosystem.
Subjects are a special case of publisher that also adhere to the
Subject protocol. This protocol requires subjects to have a
.send(_:) method to allow the developer to send specific values to a subscriber (or pipeline).