Subjects

General information on Subjects can be found in the Core Concepts section.

• Subjects

  • CurrentValueSubject

  • PassthroughSubject

CurrentValueSubject

A subject that wraps a single value and publishes a new element whenever the value changes.

Declaration:

final class CurrentValueSubject<Output, Failure> where Failure : Error

Overview:

Unlike PassthroughSubject, CurrentValueSubject maintains a buffer of the most recently published element.

Calling send(_:) on a CurrentValueSubject also updates the current value, making it equivalent to updating the value directly.

PassthroughSubject

A subject that broadcasts elements to downstream subscribers.

Declaration:

final class PassthroughSubject<Output, Failure> where Failure : Error

Discussion:

As a concrete implementation of Subject, the PassthroughSubject provides a convenient way to adapt existing imperative code to the Combine model.

Unlike CurrentValueSubject, a PassthroughSubject doesn’t have an initial value or a buffer of the most recently-published element. A PassthroughSubject drops values if there are no subscribers, or its current demand is zero.