func firstMatch<T: Equatable>(in values: [T], equalTo target: T) -> T? { values.first { $0 == target } }
protocol FirstReadable { associatedtype Element; func first() -> Element? }
struct Queue<T>: FirstReadable {
    let values: [T]
    func first() -> T? { values.first }
}

@main
struct Lesson {
    static func main() {
        print(firstMatch(in: ["Cedar", "Ash", "Cedar"], equalTo: "Ash") ?? "missing")
        print(Queue(values: [2, 3]).first() ?? -1)
    }
}