struct Tuple<T, U> {
    let first: T
    let second: U
}

extension Tuple where U == String {
    var secondLowercased: String {
        second.lowercased()
    }
}

typealias TupleString<T> = Tuple<T, String>

extension TupleString {
    var secondUppercased: String {
        second.uppercased()
    }
}