Why doesn't :contentsOf work when appending an array to NavigationPath object?

Question

I have the following code:

@Published var path:[Screen] = []

var launchScreens:[Screen] = [.someOtherView, .launch]

init() {
    path.append(contentsOf: launchScreens)
}

It works as expected and appends launchScreens to my path variable. When I add other enum values, they are also added to the NavigationPath, and when bound to my NavigationStack, the other view show in the order added.

However; if I want to use a NavigationPath instead of a [Screen] (as below) I get an error that says "Extraneous argument label 'contentsOf:' in call"

@Published var path = NavigationPath()

var launchScreens:[Screen] = [.someOtherView, .launch]

init() {
    path.append(contentsOf: launchScreens)
}

If I remove the "contentsOf", the compiler doesn't complain, but the screens fail to load correctly. I'd like to use NavigationPath because I have different View types besides 'Screen' to add.

How can I append an array of views to NavigationPath?

Answer 1

NavigationPath simply does not have such a method. You need to call append multiple times, with a loop.

You can write an extension like this

extension NavigationPath {
    mutating func append<S: Sequence>(contentsOf sequence: S) where S.Element: Hashable {
        for elem in sequence {
            append(elem)
        }
    }
}

You should not think of NavigationPath as a "collection". It does not conform to any of the collection protocols like RangeReplaceableCollection.

---

In this specific situation, since path is empty initially, you can also initialise path like this:

@Published var path: NavigationPath

var launchScreens:[Screen] = [.someOtherView, .launch]

init() {
    path = NavigationPath(launchScreens)
}

This obviously wouldn't work if path is not empty, because it would overwrite the existing elements in path.