An example of how to create CurrentValueSubject behavior without needing to set an initial value.

LazyCurrentValueSubject.swift

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()