New and improved diagnostics

Paul Hudson      @twostraws

Swift 5.2 introduced a new diagnostic architecture that aims to improves the quality and precision of error messages issued by Xcode when you make a coding error. This is particularly apparent when working with SwiftUI code, where Swift would often produce false positive error messages.

For an example, consider code like this:

struct ContentView: View {
    @State private var name = 0

    var body: some View {
        VStack {
            Text("What is your name?")
            TextField("Name", text: $name)
                .frame(maxWidth: 300)
        }
    }
}

That attempts to bind a TextField view to an integer @State property, which is invalid. In Swift 5.1 this caused an error for the frame() modifier saying 'Int' is not convertible to 'CGFloat?’, but in Swift 5.2 and later this correctly identifies the error is the $name binding: Cannot convert value of type Binding<Int> to expected argument type Binding<String>.

You can find out more about the new diagnostic architecture on the Swift.org blog.

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Other changes in Swift 5.2…

• Key path expressions as functions
• Callable values of user-defined nominal types
• Subscripts can now declare default arguments
• Lazy filtering order is now reversed

Download all Swift 5.2 changes as a playground Link to Swift 5.2 changes

Browse changes in all Swift versions