Concept

The core idea of Combine is the Publisher → Subscriber relationship.

A publisher produces values over time, while a subscriber receives and processes those values.

Data flows through a pipeline like this:

Publisher → Operators → Subscriber

In the simplest case (without operators), the flow becomes:

Publisher → Subscriber

The publisher emits values, and the subscriber receives them.

Example

let numbers = [1, 2, 3, 4, 5]

let publisher = numbers.publisher

publisher
    .sink(
        receiveCompletion: { completion in
            print("Completion:", completion)
        },
        receiveValue: { value in
            print("Received:", value)
        }
    )
    .store(in: &cancellables)

Publisher

A publisher is a source of data that emits values to subscribers.

In this example:

let publisher = numbers.publisher

The array is converted into a publisher.

This publisher emits values sequentially:

1
2
3
4
5

After emitting all values, the publisher sends a completion event.