Cannot assign value of type 'some View' to type 'some View' - why not?

Question

I am trying to create a structure that's holding the dynamic configuration of a popup view. That includes an array of actionButtons as well as a body property that will make up the later popup. The body can be seen as the "child views" of the popup, such as text for example. I want to be able to specify child views at will, using the @ViewBuilder in my initializer.

However, I am getting the following error:

Cannot assign value of type 'some View' to type 'some View' (type of 'PopupConfiguration.body')

public struct PopupConfiguration {
    let headline: String
    private(set) var body: some View = EmptyView()
    let actionButtons: [ActionButtonDefinition]

    init(headline: String, @ViewBuilder bodyContent: () -> some View, actionButtons: [ActionButtonDefinition]) {
        self.headline = headline
        self.body = bodyContent() // Cannot assign value of type 'some View' to type 'some View' (type of 'PopupConfiguration.body')
        self.actionButtons = actionButtons
    }
}

I am confused now, since the compiler should be able to assign some View to some View , right? It's literally the same type, or not?

Can anyone please explain why this generates above shown error?

Answer 1

You need to make use of generics in this case:

public struct PopupConfiguration<Content: View> {
    let headline: String
    private(set) var body: Content
    let actionButtons: [ActionButtonDefinition]

    init(headline: String, @ViewBuilder bodyContent: () -> Content, actionButtons: [ActionButtonDefinition]) {
        self.headline = headline
        self.body = bodyContent()
        self.actionButtons = actionButtons
    }
}

I recommend you read the opaque types documentation , especially the section "Differences Between Opaque Types and Protocol Types":)

The main takeaway is that an opaque type refers to one specific type and retains said type informations. In your case, there is no guarantee that var body: some View and content: () -> some View will have the same type.