Document best practices for shared stores

[bbrk24]

Checklist

• I searched the existing GitHub issues and this hasn't already been reported.

Request

When sharing an @Store object from a view to its subview, this is legal with an implicit initializer:

struct Superview: View {
    @Store var object: StoreType

    var body: some View {
        Subview(object: self.object)
    }
}

struct Subview: View {
    @Store var object: StoreType

    var body: some View {
        // ...
    }
}

but it's not clear from the documentation whether this is good practice or not. Furthermore, this becomes more complicated with an explicit initializer, since Store.wrappedValue is get-only:

struct Superview: View {
    @Store var object: StoreType

    var body: some View {
        Subview(object: self._object)
    }
}

struct Subview: View {
    @Store var object: StoreType

    init(object: Store<StoreType>) {
        self._object = object

        // then, property access must be done as either
        self.object.someThing
        // or
        object.wrappedValue.someThing
    }

    var body: some View {
        // ...
    }
}

In some cases, it may not be necessary for them to both be @Store, but this prevents both views from accessing the projected value $object.

[bbrk24]

While it does work with both of them marked @Store, I don't think that's something we should encourage. Perhaps we should add a property wrapper like @SuperviewStore, which can be constructed from Store.projectedValue -- so as to mirror @State and @Binding:

struct Superview: View {
    @State var state: Int
    @Store var store: ObjectType

    var body: some View {
        Subview(state: $state, store: $store)
    }
}

struct Subview: View {
    @Binding var state: Int
    @SuperviewStore var store: ObjectType

    init(state: Binding<Int>, store: Store<ObjectType>.Wrapper) {
        self._state = state
        self._store = .init(store)
    }

    var body: some View {
        // ...
    }
}

@wboyd600 What do you think?

[bbrk24]

Upon further thought, we may be able to make Store.Wrapper itself a property wrapper, and then either rename it or provide a typealias so that it can be spelled @SuperviewStore (though I'm open to suggestions) rather than @Store.Wrapper.

[wboyd600]

Hey, sorry for the late reply -- I'm really not sure. I might be missing the bulk of the issue -- but it seems like @Binding and @State are different property wrappers because they actually do different things. Would @SuperviewStore actually behave differently, or just have a different initializer?

[bbrk24]

Coming back to this later, I don't think there actually would need to be a difference. After all, Binding still conforms to DynamicProperty. Binding only needs to be different because the value type can only live in one place (the place marked @State). @Store wraps a reference type, so it can be used in multiple views at once.

TL;DR: There doesn't actually need to be @SuperviewStore or similar.

[wboyd600]

Okay, so we're really just looking at adding another initializer to @Store.