How can I change the textual representation displayed for a type in Swift?

Question

How can I modify the textual output that gets displayed in string interpolation?

The Printable protocol looks the most obvious but it\'s ignored in both

Answer 1

Relevant Apple Swift Docs

Apple provides this example:

struct MyType: Printable {
    var name = "Untitled"
    var description: String {
        return "MyType: \(name)"
    }
}

let value = MyType()
println("Created a \(value)")
// prints "Created a MyType: Untitled"

If you try this in playground, you will get the same issue that you're getting (V11lldb_expr...). In playground, you get the description on the right hand side when you call the initializer, but the println doesn't return something legible.

Out of playground, however, this code behaves as you would expect. Both your code and the sample code from Apple above print the correct description when used in a non-playground context.

I don't think you can change this behavior in playground. It could also just be a bug.

EDIT: I'm pretty sure that this is a bug; I submitted a bug report to Apple.

UPDATE: In Swift 2, instead of Printable, use CustomStringConvertible (relevant doc link).

struct MyType: CustomStringConvertible {
    var name = "Untitled"
    var description: String {
        return "MyType: \(name)"
    }
}

let value = MyType()
println("Created a \(value)")
// prints "Created a MyType: Untitled"