Swift Typealias for Class and Protocol

Question

I have a variable that must be a UIView that also implements the protocol MTMathKeyboard.

I've tried,

var keyboard: (UIView & MTMathKeyboard)
var keyboard: UIView<MTMathKeyboard>

What's the syntax for a non-generic class instance that implements a protocol?

I think there is no simple solution for this yet in Swift. Check out this blog post: http://chris.eidhof.nl/post/classes-and-protocols/ — tonisuter, Mar 15 '17 at 11:46
Related (duplicate?) http://stackoverflow.com/questions/25623761/swift-property-with-type-and-protocol — Martin R, Mar 15 '17 at 11:48

score 6 · Answer 1 · answered Jun 06 '17 at 23:05

6

In Swift 4 you can use:

let keyboard: UIView & MTMathKeyboard

answered Jun 06 '17 at 23:05

Jeroen Bakker

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very helpful, what's the name of this feature? I've been looking for documentation. – Juanmi Feb 19 '20 at 17:45

score 3 · Answer 2 · answered Mar 15 '17 at 11:49

3

I think you should go this way:

protocol MTMathKeyboard: class {

}

class YourClass<MTMathKeyboard where T:UIView> {
    var keyboard: T!
}

answered Mar 15 '17 at 11:49

Grzegorz Krukowski

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score 0 · Answer 3 · answered Mar 15 '17 at 21:06

0

You could use protocol composition and extend UIView to meet a placeholder protocol:

protocol UIViewClass {}
extension UIView:UIViewClass {}


var keyboard :  UIViewClass & MTMathKeyboard

answered Mar 15 '17 at 21:06

Alain T.

40,517
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score -1 · Answer 4 · edited Mar 13 '19 at 15:01

-1

typealias KeyboardView = UIView & MTMathKeyboard

protocol MTMathKeyboard: class {
}

private func updateController(with view: KeyboardView) {
        someView = view
}

edited Mar 13 '19 at 15:01

vikingosegundo

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answered Mar 11 '19 at 08:55

Wasim

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a good example why sticking to code formatting guidelines is helpful: `someView = keyboard` here an object called `keyboard` does not exists, but it is a type name. – vikingosegundo Mar 12 '19 at 11:50

Swift Typealias for Class and Protocol

4 Answers4