Directly Converting Parsed String To A Type

[mergesort]

I have a URL and query parameter that I'm trying to parse into a FilterScreenTab, without the intermediate step of manually parsing out a String. I've looked across all the discussions and tried a few approaches, but none of them seem to work.

What I'm trying to do is to take this case in my app router:

/// plinky://open/filters?screen=[String]
case linksFilterScreen(screen: Screen)

And have the associated value use the FilterScreenTab type directly, like so.

/// plinky://open/filters?screen=[String]
case linksFilterScreen(tab: FilterScreenTab)

My current approach is to take the screen parameter and to convert it into a tab through an initializer.

func handleScreenDeepLink(_ screen: AppRoute.Screen) {
    switch screen {

    case .linksFilterScreen(let screen):
        let tab = FilterScreenTab(string: screen)
        self.appState.$selectedFilterTab.set(tab)

        // More code here
    }
}

private extension FilterScreenTab {
    init(string: String) {
        let tab: FilterScreenTab = switch string {

        case screenParameter(for: URL.actions.openSearchLinksScreen):
            .search

        case screenParameter(for: URL.actions.openTagsScreen):
            .tags

        case screenParameter(for: URL.actions.openFoldersScreen):
            .collections

        default:
            .search
        }

        self = tab
    }

    func screenParameter(for url: URL) -> String? {
        guard let queryItems = URLComponents(string: url.absoluteString)?.queryItems else { return nil }

        for queryItem in queryItems where queryItem.name == "screen" {
            return queryItem.value
        }

        return nil
    }
}

I came across a few solutions such as #69, but all of the approaches in there seemed to provide me different sets of errors.

While the manual conversion works, I tried tried constructing queries like so:

Query {
    Field("screen") { Parse(.string.representing(FilterScreenTab.self) ?? .search) }
}

Query {
    Field("screen") { Parse(.string.map(FilterScreenTab.init(string:))) }
}

And none of them quite worked. The last thing I tried was to conform to Conversion and see if I could get that working, but I ran into a different set of errors.

extension Conversion where Input == String, Output == FilterScreenTab {
    public func apply(_ input: Input) throws -> Output {
        let tab: FilterScreenTab = switch input {

        case screenParameter(for: URL.actions.openSearchLinksScreen):
            .search

        case screenParameter(for: URL.actions.openTagsScreen):
            .tags

        case screenParameter(for: URL.actions.openFoldersScreen):
            .collections

        default:
            .search
        }

        return tab
    }

    public func unapply(_ output: Output) throws -> Input {
        switch output {
        case .search:
            screenParameter(for: URL.actions.openSearchLinksScreen)

        case .tags:
            screenParameter(for: URL.actions.openTagsScreen)

        case .collections:
            screenParameter(for: URL.actions.openFoldersScreen)

        default:
            screenParameter(for: URL.actions.openSearchLinksScreen)
        }
    }

    func screenParameter(for url: URL) -> String? {
        guard let queryItems = URLComponents(string: url.absoluteString)?.queryItems else { return nil }

        for queryItem in queryItems where queryItem.name == "screen" {
            return queryItem.value
        }

        return nil
    }
}

It's not a huge issue but I'd like to see if there's a way for me to build this, ideally without conforming to RawRepresentable.