This is a technique suggested to me by Jordan Gustafson (@minnesota_gus) on how to make a CurrentValueSubject that doesn’t require an initial value. This should probably be developed into an actual type which conforms to Subject, but I haven’t figured that out yet.
| import Foundation | |
| import Combine | |
| class Example { | |
| private var index = 1 | |
| private let valuePublisher = CurrentValueSubject<Int?, Never>(nil) | |
| var value: AnyPublisher<Int, Never> { | |
| valuePublisher.compactMap({ $0 }).eraseToAnyPublisher() | |
| } | |
| func doSomething() { | |
| print("[Example] sending value: \(index)") | |
| valuePublisher.send(index) | |
| index += 1 | |
| } | |
| } | |
| let example = Example() | |
| print("First subscription.") | |
| let subscription1 = example.value.sink { print("sub1: \($0)") } | |
| example.doSomething() | |
| print("Second subscription.") | |
| let subscription2 = example.value.sink { print("sub2: \($0)") } | |
| example.doSomething() |
This will produce the following output:
First subscription.
[Example] sending value: 1
sub1: 1
Second subscription.
sub2: 1
[Example] sending value: 2
sub2: 2
sub1: 2
As you can see, the first subscription did not receive a value until the first time doSomething() was called. Conversely, the second subscription—which was added after the first value had been sent—received a value immediately. Both subscriptions receive all values thereafter.