1

I am encountering a weird bug lately, while trying to conform a class to a given protocol the compiler rejects the typealias declaration.
My code looks like this:

/// Protocol from CareKit
public protocol OCKTaskViewSynchronizerProtocol: OCKAnyTaskViewSynchronizerProtocol {

    associatedtype View: UIView & OCKTaskDisplayable

    func makeView() -> View
    func updateView(_ view: View, context: OCKSynchronizationContext<OCKTaskEvents?>)
}

/// My own protocol
protocol ConditionalTaskViewProtocol: UIView, OCKTaskDisplayable, OCKEventUpdatable {
    init()
}

/// class that should conform to `OCKTaskViewSynchronizerProtocol`
/// Error gets thrown here:
/// Type 'ConditionalTaskViewSynchronizer<First, Second>' does not conform to protocol 'OCKTaskViewSynchronizerProtocol'"
class ConditionalTaskViewSynchronizer<First: ConditionalTaskViewProtocol, Second: ConditionalTaskViewProtocol>: OCKTaskViewSynchronizerProtocol {
    typealias View = ConditionalTaskViewProtocol

    let condition: () -> Bool

    public init(condition: @escaping () -> Bool) {
        self.condition = condition
    }

    func makeView() -> View {
        if condition() {
            return First()
        } else {
            return Second()
        }
    }

    func updateView(_ view: View, context: OCKSynchronizationContext<OCKTaskEvents?>) {
        view.updateWith(event: context.viewModel?.firstEvent, animated: context.animated)
    }
}

The fix that the compiler suggests is to conform the type of the typealias View to UIView. But I already conformed ConditionalTaskViewProtocol to both UIView and OCKTaskDisplayable.

Am I missing something here?

Help would be highly appreciated!

2

View needs to be a concrete type that inherits from UIView and conforms to OCKTaskDisplayable.

3

Thanks for the fast response @suyashsrijan!

But to be honest I am not quite sure how I can replace the protocol with a concrete type at that point.
I specifically used a protocol to be able to conform specific views to it and then present them based on a specified condition. Can I achieve the same functionality with a concrete type of some sorts?

4

I think you need to transform:

protocol ConditionalTaskViewProtocol

to

class ConditionalTaskView

which is the concrete class you need. Declaring it as a class makes it derive from UIView, which the framework wants. Then, First and Second are defined as sub-classes of ConditionalTaskView.

5

If you look at your “makeView” method, it returns two different types (First or Second) depending on whether the condition is true or false. That needs to become a single return type.

That single view type can be generic, and can simply host one of the given views, full-size, depending on the condition. So basically you sink that logic down to the view.