Alternative to switch statement in SwiftUI ViewBuilder block?

⚠️ 23 June 2020 Edit: From Xcode 12, both switch and if let statements will be supported in the ViewBuilder!

Thanks for the answers, guys. I’ve found a solution on Apple’s Dev Forums. It’s answered by Kiel Gillard. The solution is to extract the switch in a function as Lu_, Linus and Mo suggested, but we have to wrap the views in AnyView for it to work – like this:

struct RootView: View {
  @State var containedViewType: ContainedViewType = .home

  var body: some View {
     VStack {
       // custom header goes here
       containedView()
     }
  }

  func containedView() -> AnyView {
     switch containedViewType {
     case .home: return AnyView(HomeView())
     case .categories: return AnyView(CategoriesView())
     ... 
  }
}

Update: SwiftUI 2 now includes support for switch statements in function builders, https://github.com/apple/swift/pull/30174

Adding to Nikolai's answer, which got the switch compiling but not working with transitions, here's a version of his example that does support transitions.

struct RootView: View {
  @State var containedViewType: ContainedViewType = .home

  var body: some View {
     VStack {
       // custom header goes here
       containedView()
     }
  }

  func containedView() -> some View {
     switch containedViewType {
     case .home: return AnyView(HomeView()).id("HomeView")
     case .categories: return AnyView(CategoriesView()).id("CategoriesView")
     ... 
  }
}

Note the id(...) that has been added to each AnyView. This allows SwiftUI to identify the view within it's view hierarchy allowing it to apply the transition animations correctly.

It looks like you don't need to extract the switch statement into a separate function if you specify the return type of a ViewBuilder. For example:

Group { () -> Text in
    switch status {
    case .on:
        return Text("On")
    case .off:
        return Text("Off")
    }
}

Note: You can also return arbitrary view types if you wrap them in AnyView and specify that as the return type.

You must wrap your code in a View, such as VStack, or Group:

var body: some View {
   Group {
       switch containedView {
          case .home: HomeView()
          case .categories: CategoriesView()
          ...
       }
   }
}

or, adding return values should work:

var body: some View {
    switch containedView {
        case .home: return HomeView()
        case .categories: return CategoriesView()
        ...
    }
}

The best-practice way to solve this issue, however, would be to create a method that returns a view:

func nextView(for containedView: YourViewEnum) -> some AnyView {
    switch containedView {
        case .home: return HomeView()
        case .categories: return CategoriesView()
        ...
    }
}

var body: some View {
    nextView(for: containedView)
}