StaticList.swift

class List<T> {
    private let listItems: [T]
    
    init() {
        self.listItems = [T]()
    }
    
    init(listItems: [T]) {
        self.listItems = listItems
    }
    
    static func with(list: List<T>, item: T) -> List<T> {
        return list.add(item)
    }
    
    func add(item: T) -> List<T> {
        var listWithAddedItem = self.listItems
        listWithAddedItem.append(item)
        
        return List<T>(listItems: listWithAddedItem)
    }
    
    func count() -> Int {
        return self.listItems.count
    }
    
    func items() -> [T] {
        return self.listItems
    }
}

let staticExampleFirstList =
    List<Int>.with(List<Int>(), item: 1)
staticExampleFirstList.items()      // [1]

let anIntList = List<Int>(listItems: [0,9])
anIntList.items()                   // [0, 9]

let staticExampleAnotherList =
    List<Int>.with(anIntList, item: 1).add(5).add(10)
staticExampleAnotherList.items()    // [0, 9, 1, 5, 10]
staticExampleFirstList.items()      // [1]