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Multiple trailing closures

Available from Swift 5.3

Paul Hudson      @twostraws

SE-0279 introduced multiple trailing closures, making for a simpler way to call a function with several closures.

This will be particularly welcome in SwiftUI, where code like this:

struct OldContentView: View {
    @State private var showOptions = false

    var body: some View {
        Button(action: {
            self.showOptions.toggle()
        }) {
            Image(systemName: "gear")
        }
    }
}

Can now be written as this:

struct NewContentView: View {
    @State private var showOptions = false

    var body: some View {
        Button {
            self.showOptions.toggle()
        } label: {
            Image(systemName: "gear")
        }
    }
}

Technically there is no reason why label: needs to be on the same line as the preceding }, so you could even write this if you wanted:

struct BadContentView: View {
    @State private var showOptions = false

    var body: some View {
        Button {
            self.showOptions.toggle()
        }

        label: {
            Image(systemName: "gear")
        }
    }
}

However, I would caution against that for readability – a floating piece of code like that is never pleasant, and in Swift it looks like a labeled block rather than a second parameter to the Button initializer.

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