Unable to infer complex closure return type with SwiftUI

user_672989 0
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Following part 3 of Apple's tutorial on SwiftUI, Handling User Input, I get this error:

Unable to infer complex closure return type; add explicit type to disambiguate

I'm using the same code as the tutorial (even coping from the 'Complete' sample code doesn't resolve the error).

Does anyone have a cue what is going wrong here?

enter image description here

struct LandmarkRow: View {
    var landmark: Landmark

    var body: some View {
        HStack {
            landmark.image(forSize: 50)
            Text(verbatim: landmark.name)
            Spacer()

            if landmark.isFavorite {
                Image(systemName: "star.fill")
                    .imageScale(.medium)
            }
        }
    }
}

Regardless of the cause of the issue, how could you indeed add an explicit type to disambiguate here? What would the return type in such a case be?

--

Update

Apparently you should not continue with your result of the 2nd tutorial with the 3rd. Some things changed in between of the tutorials that is not documented in the tutorial. I've added the project files to Github so you can check out the diff.

It's better to start the 3rd tutorial fresh with a fresh download of the Project files of the 3rd tutorial.

xcode11 swiftui
5 Answers

The issue is not with the closure, but with the isFavorite property on landmark.

It is not declared on the Landmark type, and the compiler instead of showing the undeclared property error, unable to resolve the stacks build closure return type, so it shows and error there.

Great job Apple tutorial writers and even better one Xcode11 compiler.

To fix:

  1. Declare isFavorite variable on the Landmark type.
  2. Make sure you update the landmarkData.json for every landmark record with the isFavorite = false entry, otherwise the app will crash at runtime.
user_33272100

Some background to this problem

Like @dirtydanee already answered there is a difference between those two tutorials. But the problem behind the problem is that while it looks like you're doing a configuration it's actually just functions nested in functions using generics and protocols to "magically" parse everything into a compiling function.

However conformance to these generics and protocols need to be pretty precise because if not the whole tree of functions cannot compile anymore. But it's hard to determine for the compiler what conformance actually failed. This is why you see an error at the top rather than at the point where it actually happens.

It's strongly advised to make sure your views are decomposed into natural and simple blocks so you're not pouring over hundreds of lines of View code to find that one bug.

Dave DeLong had a really great talk about how to compose Views from ViewControllers that still holds true until today: basically you never use View as a subview inside another View but you need to decompose your View of many, simple Views. Otherwise these errors'll drive you nuts.

user_28045850

For people getting this error on SwiftUI and looking for a way to debug their view stack

This error happens mainly when there is a compilation issue on one child View.

1 - Make sure your parent view can support multiple subviews (VStack, ZStack) and you have less than 10 subviews. Sometime you may want to add a Group wrapper.

2 - If this is not the problem, there is probably an issue with one subview. Try to isolate the one you suspect to have the issue. Usually I copy the subview into a property and a different error appears

var debug: some View {
        MyViewWithError(property: self.property)
}

Most of the time you'll encounter this because you pass the property (self.property) instead of a binding (self.$property)

Hope this can help some people

user_28431960

I have run into this error when made a typo. Also this error appears when a code has syntax issues. Just check if your changes are correct

user_47708770

I encountered the problem in a subview where a @Binding prop was of a different type of the @Binding source.

user_21924830
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