I saw so many examples with below format
extension Protocolname where Self: UIViewController
What is where Self
in protocol extension. I couldn't find the documentation on this.
I saw so many examples with below format
extension Protocolname where Self: UIViewController
What is where Self
in protocol extension. I couldn't find the documentation on this.
Here is an example which explains that what is the use of where self: UIViewController
protocol SBIdentifiable {
static var sbIdentifier: String { get }
}
extension SBIdentifiable where Self: UIViewController {
static var sbIdentifier: String {
return String(describing: self)
}
}
extension UIVieWcontroller: SBIdentifiable { }
class ViewController: UIViewController {
func loadView() {
/*Below line we are using the sbIdentifier which will return the
ViewController class name.
and same name we would mentioned inside ViewController
storyboard ID. So that we do not need to write the identifier everytime.
So here where Self: UIViewController means it will only conform the protocol of type UIViewController*/
let viewController = self.instantiateViewController(withIdentifier:
self.sbIdentifier) as? SomeBiewController
}
}
You can find the same example here: WWDC2015-408, (Highly recommend to watch it,it illustrates the reason)
And also, another similar example is Extensions with a Generic Where Clause
struct Stack<Element> {
var items = [Element]()
mutating func push(_ item: Element) {
items.append(item)
}
mutating func pop() -> Element {
return items.removeLast()
}
}
The where clause add a requirement to the extension, so that the extension adds the isTop(_:) method only when the items in the stack are equatable.
extension Stack where Element: Equatable {
func isTop(_ item: Element) -> Bool {
guard let topItem = items.last else {
return false
}
return topItem == item
}
}
That syntax is: https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Protocols.html#//apple_ref/doc/uid/TP40014097-CH25-ID521
Consider:
The below will give a compiler error because Obj doesn't have access to Meh extension functions.
But the below will work.
In other words,
Meh.blah()
is only available to classes that are of typeUIViewController
.