Swift tuple declaration in a protocol

Question

I have a tuple variable in my code, that comes from ReactiveSwift:

class MyClass {
   var (signal, signalSender) = Signal<Bool, Error>.pipe()
}

How can I declare that variable tuple in a protocol?

Similar like this (doesn't work):

protocol MyProtocol {
   var (signal, signalSender): Signal<Bool, Error> { get set }
}

There appears a syntax error: "Getter/setter can only be defined for a single variable"

Thank you!

score 3 · Accepted Answer · answered Mar 07 '19 at 14:42

Type of your property should be tuple, not just declaration of some class/struct. So, look what your pipe() returns. It should return tuple with two types

func pipe() -> (Type1, Type2) { ... }

To protocol declaration use these two types

protocol MyProtocol {
    var tuple: (signal: Type1, signalSender: Type2) { get set }
}

then implement this protocol to your class and assign it with return value of pipe()

class MyClass: MyProtocol {
    var tuple: (signal: Type1, signalSender: Type2) = Signal<Bool, Error>.pipe() 
}

then when you need get element of tuple, just use

tuple.signal
tuple.signalSender

score 0 · Answer 2 · answered Mar 07 '19 at 14:29

Your class definition is defining two properties, and then happens to be assigning them from a tuple, but they're still two independent properties. You can see this if you use init syntax instead (the syntax you're using is just a convenience for this):

class MyClass {
    var signal: ...
    var signalSender: ...

    init() {
        let (signal, signalSender) = Signal<Bool, Error>.pipe()
        self.signal = signal
        self.signalSender = signalSender
   }
}

What you want here is:

protocol MyProtocol {
    var signal: ... { get set }
    var signalSender: ... { get set }
}

The type of signal and signalSender are not Signal<Bool, Error>. They're whatever pipe() returns.

You can still conform to that protocol with the syntax that MyClass is using.

score 0 · Answer 3 · answered Mar 07 '19 at 14:31

0

You can declare the variable like this as long the single accepts only one variable, so this variable will be tuple.

protocol MyProtocol {

   var varName: Signal<(signal: Bool, signalSender: Error)> { get set }
}

answered Mar 07 '19 at 14:31

Bassem Qoulta

341
1
7
17

score 0 · Answer 4 · answered Mar 14 '19 at 10:50

You can simply define your protocol like this:

protocol MyProtocol {
    associatedtype E: Error
    var signal: Signal<Bool, E> {get}
    var signalObserver: Signal<Bool, E>.Observer {get}
}

and then in your conformed class:

class TestClass: MyProtocol {
    var (signal, signalObserver) = Signal<Bool, NSError>.pipe() //you can replace NSError with your custom error type
}

Swift tuple declaration in a protocol

4 Answers4