Swift associated type in nested protocol not getting inferred automatically enough

Question

Description

I have a protocol containing an associated type that needs to be inferred later and it called UIViewRepresentable

Then another protocol to add extra:

protocol UIViewRepresentableHelper: UIViewRepresentable {
    var configuration: (UIViewType) -> () { get set }
}

extension UIViewRepresentableHelper {
    func makeUIView(context: UIViewRepresentableContext<Self>) -> UIViewType { UIViewType() }
    func updateUIView(_ uiView: UIViewType, context: UIViewRepresentableContext<Self>) { configuration(uiView) }
}

So any types conforming to the second one should be able to implement the first and second protocols together.

struct LabelView: UIViewRepresentableHelper {
    typealias UIViewType = UILabel // <- Commenting  out this line confuses the Xcode about TheTypeThatShouldBeInferred
    var configuration = { (view: UILabel) in }
}

struct ButtonView: UIViewRepresentableHelper {
    typealias UIViewType = UIButton // <- Commenting  out this line confuses the Xcode about TheTypeThatShouldBeInferred
    var configuration = { (view: UIButton) in }
}

The Issue:

But as comments in the code are saying, seems like Swift can not infer UIViewType from the context of the closure. Also, Xcode confuses about the context of the already written configuration.

The Question:

What could be done to get rid of at least one of the type annotations, or one line of code, or anything else to make it more elegant and less coded?

---

One of the expectations:

I hoped atleast something like this would work:

struct TextFieldView: UIViewRepresentableHelper {
    var configuration: (UITextField)->() = { _ in }
}

Answer 1

EDIT #3

Using a single generic class :

public protocol UIViewRepresentableHelper: UIViewRepresentable {
    var configuration: (UIViewType) -> () { get set }
}

public extension UIViewRepresentableHelper {
    func makeUIView(context: UIViewRepresentableContext<Self>) -> UIViewType { UIViewType() }
    func updateUIView(_ uiView: UIViewType, context: UIViewRepresentableContext<Self>) { configuration(uiView) }
}

public struct ViewConfigurator<UIViewType: UIView>: UIViewRepresentableHelper {
    public var configuration: (UIViewType) -> ()
    public init(configuration: @escaping (UIViewType) -> ()) {
        self.configuration = configuration
    }
}

You can either use it by explicitly specifying the type of the closure argument :

let labelConfigurator = ViewConfigurator { (label: UILabel) in
    print(label.text ?? "empty")
}

var label = UILabel()
labelConfigurator.configuration(label) // Optional("")
label.text = "some text"
labelConfigurator.configuration(label) // Optional("some text")

or by explicitly specifiying the generic argument :

typealias ButtonConfigurator = ViewConfigurator<UIButton>
let buttonConfigurator = ButtonConfigurator { button in
    print(button.title(for: .normal) ?? "empty")
}

var button = UIButton()
buttonConfigurator.configuration(button) // Optional("")
button.setTitle("some title", for: .normal)
buttonConfigurator.configuration(button) // Optional("some title")

either way you have to "help" the compiler at the calling site but you do it only once.

I think it did not work when you tried my first answer because you did not declare the ViewConfigurator like that :

public struct ViewConfigurator<UIViewType: UIView>: UIViewRepresentableHelper

EDIT #2

It worked because I declared :

func updateUIView(_ uiView: UITextField, context: Context) {
    
}

but once I put UIViewType the error came back, I think my first thought was correct, the compiler does not do well with associated types and closures

EDIT #1

So the problem was actually that UIViewType and configuration were not declared in the same protocol.

I could work around that by creating a typealias of UIViewType in UIViewRepresentableHelper

like that :

protocol UIViewRepresentableHelper: UIViewRepresentable {
    typealias ViewType = UIViewType
    var configuration: (ViewType) -> () { get set }
}

struct TextFieldView: UIViewRepresentableHelper {
    var configuration: (UITextField)->()
    
}

usage :

let textFieldView = TextFieldView { textField in
    print(textField.text)
}

var textField = UITextField()
textFieldView.configuration(textField) // Optional("")
textField.text = "some text"
textFieldView.configuration(textField) // Optional("some text")

---