Adding examples on Swift.

Swift/Double.playground/Contents.swift

@@ -0,0 +1,92 @@
+import Foundation
+
+class Node {
+    var data: String
+
+    var next: Node?
+    weak var previous: Node? //  weak to avoid memory leak. ARC do the trick.
+    // Every Node knows only its neighbours
+    init(with data: String) {
+        self.data = data
+    }
+}
+
+class LinkedList {
+    private var head: Node?
+    private var tail: Node? // List knows its head and tail.
+
+    var isEmpty: Bool {
+        return head == nil
+    }
+
+    var first: Node? {
+        return head
+    }
+
+    var last: Node? {
+        return tail
+    }
+
+    func append(value: String) {
+        let newNode = Node(with: value)
+
+        if let tailNode = tail {        // if tail exist
+            newNode.previous = tailNode
+            tailNode.next = newNode
+        }
+        else {
+            head = newNode             // This is the first append
+        }
+        tail = newNode
+    }
+
+    func printList() {
+        var text = "["
+        var node = head
+
+        while node != nil {
+            text += "\(node!.data)"
+            node = node!.next
+            if node != nil { text += ", " }
+        }
+        text += "]"
+        print(text)
+    }
+
+
+    func removeAll() {    // When head and tail is nil, weak ref will automatically delete its references one by one.
+        head = nil
+        tail = nil
+    }
+
+
+    func node(at index: Int) -> Node? {
+        if index >= 0 {
+            var node = head
+            var i = index
+
+            while node != nil {
+                if i == 0 { return node } // Iterating over the List
+                i -= 1
+                node = node!.next
+            }
+        }
+        return nil
+    }
+
+}
+
+
+let myList = LinkedList()
+
+myList.append(value: "1231")
+myList.append(value: "Car")
+myList.append(value: "Dog")
+myList.append(value: "Harry Potter")
+
+myList.printList() // [1231, Car, Dog, Harry Potter]
+let secondNode = myList.node(at: 1)?.data // Car
+
+myList.removeAll()
+
+myList.printList() // []

Swift/Double.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>