Signal could be struct

[sashankg]

Wouldn't it be better to have the Signal object be a struct rather than a final class. This is ensures safety when copying and is preferred in Swift (as seen in this talk) over classes. Really, I just wanted to know why it was a final class.

[JensRavens]

Signals have to be classes so they can be referenced (classes are reference types, structs are not).

let a = Signal<String>()

func doSomething(s: Signal<String>) {
  s.next { string in
    // do something important
 }
}

doSomething(a)
a.update("Hello")

If Signal would be a value type, doSomething wouldn't be able to change it (it could declare s as inout mutable, but that just breaks the whole concept of sane dependencies). Therefore the signal couldn't add the func as a subscriber and also it cannot call it back. s would never update and call their subscribers, because it would be a different instance than a.

So no, signal could not be a struct.

[sashankg]

Thanks!