Before Swift 5.8, if you try to print a keypath via a print() or po command, it will print out general output for a Swift class.

struct User {
    let firstName: String
    let lastName: String
    var nickName: String
}

print(\User.firstName)
// Swift.KeyPath<ModuleName.User, Swift.String>

print(\User.lastName)
// Swift.KeyPath<ModuleName.User, Swift.String>

print(\User.nickName)
// Swift.WritableKeyPath<ModuleName.User, Swift.String>

In this example, Swift will print a class name and a type of that key path.

This isn't very useful since you can't distinguish one property from another.

You can easily support sarunw.com by checking out this sponsor.

Add CustomDebugStringConvertible conformance to AnyKeyPath

Swift 5.8 ([SE-0369]) make AnyKeyPath conform to CustomDebugStringConvertible protocol and provide more useful information when print.

The followings are the output for the same keypaths.

print(\User.firstName)
// \User.firstName

print(\User.lastName)
// \User.lastName

print(\User.nickName)
// \User.nickName

As you can see, we know at a glance what the keypaths are referring to.

Enjoy the read?

If you enjoy this article, you can subscribe to the weekly newsletter.
Every Friday, you'll get a quick recap of all articles and tips posted on this site. No strings attached. Unsubscribe anytime.