Multiple trailing closures

About 2 min

Multiple trailing closures 관련

HACKING WITH SWIFT

What's new in Swift?

Multiple trailing closures | Changes in Swift 5.3

Multiple trailing closures

Available from Swift 5.3

SE-0279 (apple/swift-evolution) 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.

Other Changes in Swift 5.3

Multi-pattern catch clauses | Changes in Swift 5.3

Multi-pattern catch clauses

Synthesized Comparable conformance for enums | Changes in Swift 5.3

Synthesized Comparable conformance for enums

self is no longer required in many places | Changes in Swift 5.3

self is no longer required in many places

Type-based program entry points | Changes in Swift 5.3

Type-based program entry points

where clauses on contextually generic declarations | Changes in Swift 5.3

where clauses on contextually generic declarations

Enum cases as protocol witnesses | Changes in Swift 5.3