Is it possible to point class instance variables to `inout` parameters in Swift?

muZero Published at Dev

muZero

Is it possible for multiple class methods to access and modify a single inout parameter that is set in the class constructor? For example something like this:

class X {
    var mySwitch: Bool
    
    init(mySwitch: inout Bool) {
        self.mySwitch = mySwitch
    }
    
    func updateSwitch() {
        self.mySwitch.toggle() // this should toggle the external Boolean value that was originally passed into the init
  }
}

// usage
var myBool: Bool = false
let x = X(mySwitch: &myBool)
x.updateSwitch()
print(myBool) // this should read 'true'

Jake

Short Answer

No.

Long Answer

There are other approaches that can satisfy this.

Binding Variables

In SwiftUI we use Binding Variables to do stuff like this. When the Binding variable updates, it also updates the bound variable. I'm not sure if it will work in Sprite Kit.

class X {
    var mySwitch: Binding<Bool>

    init(_ someSwitch: Binding<Bool>) {
        self.mySwitch = someSwitch 
    }

   func toggle() { mySwitch.wrappedValue.toggle() }
}

struct Y {
    @State var mySwitch: Bool = false
    lazy var switchHandler = X($mySwitch)
}

Callbacks

We can add a callback to X and call it on didSet of the boolean.

class X {
    var mySwitch: Bool {
        didSet { self.callback(mySwitch) } // hands the new value back to the call site in Y
    }

    let callback: (Bool) -> Void

    init(_ someSwitch: Bool, _ callback: @escaping (Bool) -> Void) {
        self.mySwitch = someSwitch
        self.callback = callback
    }

    func toggle() { mySwitch = !mySwitch } // explicitly set to trigger didSet
}

class Y {
    var mySwitch: Bool = false
    lazy var switchHandler = X(mySwitch) {
        self.mySwitch = $0 // this is where we update the local value
    }
}

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