Swift: Default value for properties in Protocol - swift

Question

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?

Answer 1

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.

Answer 2

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()