CODEWITHSUNDEEP
swiftprotocols
user1107173
user1107173

Reputation: 10744

Swift: Default value for properties in Protocol

I am trying to provide a default value for a variable in a Protocol. I am getting an error:

Type ViewController does not conform to protocol Test

Code:

protocol Test {
    var aValue: CGFloat { get set }
}

extension Test {
    var aValue: CGFloat {
        return 0.3
    }
}


class ViewController: UIViewController, Test {

    override func viewDidLoad() {
       super.viewDidLoad()
       print("value \(aValue)")
    }
}

How can I provide a default value so the ViewController can use the default value (in the protocol extension) without to declaring it?

Upvotes: 4

Views: 8737

Answers (2)

CrazyPro007
CrazyPro007

Reputation: 1062

protocol Test {
    var aValue: CGFloat {get set}
}

extension Test {
//    var aValue: CGFloat {
//        return 0.3
//    }
    var aValue: CGFloat {
        get {
            return 0.3
        }
        set {
            debugPrint("new value is \(aValue)")
        }
    }
}

struct TestClass: Test {
        
    func printData() {
        debugPrint(aValue)
    }
}

let aTestClass = TestClass()
aTestClass.printData()

Upvotes: 0

Huy-Anh Hoang
Huy-Anh Hoang

Reputation: 797

protocol Test {
    var aValue: CGFloat { get set }
}

extension Test {
    var aValue: CGFloat {
        get {
            return 0.3
        }
        set {
            print("the new value is \(newValue)")
        }
    }
}

class Default: Test {
    init() {
        print("value \(aValue)")
    }
}


class ViewController: Test {

    var aValue: CGFloat {
        get {
            return 0.4
        }
        set {
            print("i am overriding the setter")
        }
    }

    init() {
        print("value \(aValue)")
    }
}

var d = Default() // value 0.3
d.aValue = 1 // the new value is 1.0

var vc = ViewController() // value 0.4
vc.aValue = 1 // i am overriding the setter

Since you have a protocol extension, you don't have to implement neither the getter nor the setter if you don't want to.

https://docs.swift.org/swift-book/LanguageGuide/Properties.html#//apple_ref/doc/uid/TP40014097-CH14-ID259

In addition to stored properties, classes, structures, and enumerations can define computed properties, which do not actually store a value. Instead, they provide a getter and an optional setter to retrieve and set other properties and values indirectly.

You can't set the value of the same variable in the setter itself.

Upvotes: 11

Related Questions