Combine Basics

import Combine
var subscriptions = Set<AnyCancellable>()
let publisher = Just("Hello from Combine")
publisher.sink { value in
    print(value)
}.store(in: &subscriptions)

import Combine
var subscriptions = Set<AnyCancellable>()
let publisher = Just(5)
publisher.map { $0 * $0 }.sink { value in
    print("Squared: \(value)")
}.store(in: &subscriptions)

1. Assuming Combine values from a Just publisher arrive asynchronously across multiple run-loop turns; a Just publisher actually emits its single value synchronously to the subscriber.
2. Forgetting to keep a strong reference (e.g. in a Set<AnyCancellable>) to a subscription; letting it deallocate immediately can stop the pipeline from delivering values.
3. Using Combine for a one-off synchronous computation where a plain function would be simpler; Combine shines for ongoing streams of values over time.

• Combine models asynchronous event streams using Publishers and Subscribers.
• .sink { } is a simple way to subscribe to a publisher's values directly with a closure.
• A Just publisher emits exactly one value and then finishes immediately.
• Real Combine pipelines commonly involve network calls or timers, which need a running event loop to observe -- this example intentionally uses the simplest possible synchronous publisher so its output is deterministic.