How do you pass a view builder into a view?

Question

Created Mar ’25

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I'm making a custom control, specifically a checkbox next to a "label." I want the label parameter, like many in Apple's built-in controls, to take a view-building closure.

But I can't figure out the correct syntax. I looked at the declaration of Apple's NavigationLink control for clues:

public struct NavigationLink<Label, Destination> : View where Label : View, Destination : View {

    /// Creates a navigation link that presents the destination view.
    /// - Parameters:
    ///   - destination: A view for the navigation link to present.
    ///   - label: A view builder to produce a label describing the `destination`
    ///    to present.
    public init(@ViewBuilder destination: () -> Destination, @ViewBuilder label: () -> Label)

But when I mimic this, the compiler complains about the body() function:

struct CheckboxItem<Label> : View where Label : View
{
	let stateCheck: () -> Bool
	let label: () -> any View
	let boxSize: CGFloat

	init(withStateCheck: @escaping () -> Bool, boxSize: CGFloat, @ViewBuilder label: @escaping () -> Label)
	{
		stateCheck = withStateCheck
		self.label = label
		self.boxSize = boxSize
	}

  var body: some View
	{
		HStack
		{               <-- ERROR: "Type 'any View' cannot conform to 'View'"
			Image(systemName: stateCheck() ? "checkmark.square" : "square")
				.resizable()
				.aspectRatio(contentMode: .fit)
				.frame(width: boxSize, height: boxSize)
				.foregroundColor(AppStyle.labelColor)
				.opacity(0.75)

			label()
		}
  }
}

Also, note that I had to put @escaping before my label parameter, but that's not seen in Apple's.

Any ideas?

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Answer 1

Stokestack OP

Mar ’25

Update: I found the difference. I needed to change

let label: () -> any View

to

let label: () -> Label

Now my only question is why I have to put @escaping on the label param, but Apple doesn't.

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