Manual retry with double subscribe.

manual_retry.swift

enum SomeError: Error {
	case anError
}

let subject = PassthroughSubject<Int, SomeError>()

let sink = Subscribers.Sink<Int, SomeError>(
	receiveCompletion: { print($0) },
	receiveValue: { print("Sink: \($0)") }
)

subject
	.subscribe(sink) /// (1) Note, `Publisher.subscribe(_:)` (the `Subscriber` variant)
	/// is `Void`-returning, so we don’t need to store away an `AnyCancellable`.

subject.send(1)
subject.send(2)
subject.send(3)

subject.send(completion: .failure(.anError))

subject
	.subscribe(sink) /// (2) Mimicking `retry(1)` attempt to recreate the subscription.

subject.send(4)

/// (3) Output:
/// ```none
/// Sink: 1
/// Sink: 2
/// Sink: 3
/// failure(__lldb_expr_146.SomeError.anError)
/// failure(__lldb_expr_146.SomeError.anError)
/// ```