how to assign to Binding<String>

I have a custom view that is passed a Binding to a String. The custom view renders a TextField. I can't find the right syntax to modify the binding after focus leaves the TextField. The code is something like this:

struct MyURL: View {
    private let title: String
    @Binding var url: String
    @State private var tempUrl: String

    init(_ title: String, url: Binding<String>) {
        self.title = title
        _url = url
        _tempUrl = State(initialValue: url.wrappedValue)
    }

    var body: some View {
        TextField(title, text: $tempUrl, onEditingChanged: editingChanged)
            .autocapitalization(.none)
            .disableAutocorrection(true)
        }
    }

    private func editingChanged(hasFocus: Bool) {
        guard !hasFocus else { return }

        if !tempUrl.starts(with: "https://"),
           !tempUrl.starts(with: "http://") {
            tempUrl = "https://" + tempUrl
        }

        url.wrappedValue = tempUrl // THIS LINE IS WRONG!
    }
}