PhantomTypes.swift

enum Plain {}
enum Encoded {}
enum Decompressed {}
enum Compressed {}

struct Bytes<A, B> {
    let string: String
}

extension Bytes where A == Plain, B == Decompressed {
    func encode() -> Bytes<Encoded, Decompressed> {
        return Bytes<Encoded, Decompressed>(string: string.addingPercentEncoding(withAllowedCharacters: .urlHostAllowed) ?? "")
    }
}

extension Bytes where A == Encoded, B == Decompressed {
    func encode() -> Bytes<Plain, Decompressed> {
        return Bytes<Plain, Decompressed>(string: string.removingPercentEncoding ?? "")
    }
}