Static Types in SwiftUI

Re:Static Types in SwiftUI by Razengan on Tuesday November 05, 2019 @06:44PM (#21458154)

You're correct, part of the problem is indeed that, though I'm not completely sure myself.

But how do things like EmptyView work? How do they conform to the View protocol without having a body property (that must also be a View)?

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Re:Static Types in SwiftUI by DelightOne on Tuesday November 05, 2019 @06:58PM (#21458286)

I think it has a body type [0] (Never). And since a default implementation is provided [1] the compiler probably does not complain. This default body implementation does likely not draw anything, but that's just guessing.

[0]: https://developer.apple.com/documentation/swiftui/emptyview/... [1]: https://developer.apple.com/documentation/swiftui/view/32785...

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Re:Static Types in SwiftUI by favorited on Tuesday November 05, 2019 @07:03PM (#21458328)

It's because of Body's type:

    public struct EmptyView: View {
        @inlinable public init()
        public typealias Body = Never
    }

Because Body is Never, you can't access EmptyView's body property.

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Re:Static Types in SwiftUI by Razengan on Tuesday November 05, 2019 @07:50PM (#21458652)

Can we write a protocol + type like that?

https://forums.swift.org/t/how-do-views-like-emptyview-confo...

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Re:Static Types in SwiftUI by favorited on Tuesday November 05, 2019 @08:25PM (#21458852)

I don't see why not. When I trick it into calling `body` on an EmptyView, I get this runtime failure:

> Thread 1: Fatal error: body() should not be called on EmptyView.

So I don't think the implementation is doing anything beyond the fatalError() call from that forum thread. At least not at this point in time.

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