ClassAndEnumBasedList.swift

class Box<T>{
    let value : T
    init(_ value : T ){
        self.value = value
    }
}

enum EList<T> {
    case Cons(Box<T>, Box<EList>) // Box the value T to work around a runtime deadlock bug in Swift
    case Nil
    
    // Consumers should use this; Box is an implementation detail
    init(_ head: T, _ tail: EList) {
        self = Cons(Box(head), Box(tail))
    }
    
    // Similarly, consumers should use this property for the same reason
    var value: T? {
        switch self {
        case let Cons(x, _):
            return x.value
        case Nil:
            return nil
        }
    }
    
    func prepand(value : T)->EList{
        return EList(value, self)
    }
}

class CList<T> {
    let value: T
    let next: CList?
    init(_ value : T, next : CList? = nil){
        self.value = value
        self.next = next
    }
    
    func prepand(value : T) -> CList{
        return CList(value, next: self)
    }
}