Conform to Protocol and Keep Property Private

Question

I need to use a protocol property in the conforming class as a private. But the compiler refuses that. How can I implement that?

protocol ProtocolX: class {
    var x: Int { get set }

    func performAnyActionOnX()
}

extension ProtocolX {
    func performAnyActionOnX() {
        x = 5
        print(x)
    }
}

class A: ProtocolX {
    private var x:Int = 7
}

Thanks.

Answer 1

As @TheAppMentor mentioned, there seems to be no exact solution to this problem as of Swift 4.

There are, however, two approximate solutions:

1.)

Since a protocol in Swift has the access level of internal by default, make the variable also internal. In order for internal to be enforced by the compiler, move the protocol, the class and all of their consumers (users) to a separate module (framework).

/* internal */ protocol ProtocolX: class {
    var x: Any { get set }

    func performAnyActionOnX()
}

extension ProtocolX {
    func performAnyActionOnX() {}
}

/* internal */ class A: ProtocolX {
    internal var x: Any = 0
}

2.)

Give the protocol the access level of private and the variable the access level of fileprivate. In order for the private protocol to be accessible, move the protocol, the class and all of their consumers to the same source file.

private protocol ProtocolX: class {
    var x: Any { get set }

    func performAnyActionOnX()
}

extension ProtocolX {
    func performAnyActionOnX() {}
}

class A: ProtocolX {
    fileprivate var x: Any = 0
}