#49: Pattern Matching with guard case in Swift

guard case is the early-exit sibling of if case. It is great when the rest of the function only makes sense for one specific pattern.

enum APIResponse {
    case success(Data)
    case failure(Int)
}

func handle(_ response: APIResponse) {
    guard case let .success(data) = response else {
        return
    }

    print(data.count)
}

This keeps the happy path unindented and makes the intent clear: continue only if the value matches the pattern.

You can also combine it with extra conditions, which makes it handy for compact validation code.