publisher
A Combine publisher that publishes this instance’s value to each subscriber exactly once, if it has any value at all.
Declaration
var publisher: Optional<Wrapped>.Publisher { get }Discussion
In the following example, the publisher for an Int? optional publishes its value once, then finishes normally:
let optional1: Int? = 1
optional1.publisher
.sink(receiveCompletion: { print("optional1 completed.") },
receiveValue: { print("optional1 = \($0)") }
)
// Prints:
// optional1 = 1.
// optional1 completed.In contrast with the Just publisher, which always publishes a single value, this publisher might not send any values and instead finish normally if the optional’s output is nil. In the next example, an Int? optional that’s nil immediately sends the Subscribers.Completion.finished completion, without producing any values.
let optional2: Int? = nil
optional2.publisher
.sink(receiveCompletion: { print("optional2 completed.") },
receiveValue: { print("optional2 = \($0)") }
)
// Prints:
// optional2 completed.