How to create a custom debug description

Swift version: 5.1

Paul Hudson @twostraws May 28th 2019

Swift lets you print all types of data, but some data is more useful than others thanks to the CustomDebugStringConvertible protocol. If you write a type conforming to that protocol, you must include a debugDescription string property that describes how instances of this type should be represented while debugging.

To test this out, we’re going to create a Player struct that stores a player’s name. When we try to debug an instance of this struct – i.e., print it out, or hover over it in the debugger – we just want the player’s name to come back, for easier debugging.

Try adding this struct to a playground:

struct Player: CustomDebugStringConvertible {
    var name: String = "@twostraws"

    var debugDescription: String {
        return name
    }
}

You can now create instances of that struct and print them out to see the player name:

let player = Player()
print(player)

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Available from iOS 8.0 – learn more in my book Pro Swift