Simple LinkedList written in D

linkedList.d

import std.stdio;

class ListNode(T){
  ListNode!T nextNode,
             prevNode;
  T value;
  this(T arg){
    value = arg;
  }
}

class List(T){
  alias ListNode!T Node;
  Node firstNode,
       lastNode,
       thisNode;
  
  this(T arg){
    firstNode = lastNode = new Node(arg);
  }

  void addNode(Node newNode){
    if(lastNode !is null){
      lastNode.nextNode = newNode;
      newNode.prevNode  = lastNode;
      lastNode = newNode;
    } else {
      firstNode = lastNode = newNode;
      newNode.prevNode = null;
    }
  }

  void addNode(T newValue){
    Node newNode = new Node(newValue);
    this.addNode(newNode);
  }

  void printAll(){
    for(thisNode = firstNode; thisNode !is null; thisNode = thisNode.nextNode){
      thisNode.value.writeln;
    }
  }
  
  void printReAll(){
    for(thisNode = lastNode; thisNode !is null; thisNode = thisNode.prevNode){
      thisNode.value.writeln;
    }
  }

  bool findNode(T key){
    for(thisNode = firstNode; thisNode !is null; thisNode = thisNode.nextNode)
      if(thisNode.value == key)
        return true;
      return false;
  }

  Node pickupNode(T key){
    Node reNode;

    for(thisNode = firstNode; thisNode !is null; thisNode = thisNode.nextNode)
      if(thisNode.value == key)
        reNode = thisNode;
    
    return reNode;
  }

  T[] toArray(){
    T[] tArray;
    
    for(thisNode = firstNode; thisNode !is null; thisNode = thisNode.nextNode)
      tArray ~= thisNode.value;
    
    return tArray;
  }

  T[] toReArray(){
    T[] tArray;
    
    for(thisNode = lastNode; thisNode !is null; thisNode = thisNode.prevNode)
      tArray ~= thisNode.value;

    return tArray;
  }
}

void main(){
  List!int intList = new List!int(1);
  intList.addNode(2);
  intList.addNode(3);
  intList.addNode(4);

  //test
  foreach(i; 1..5){
    assert(intList.findNode(i));
    assert(intList.pickupNode(i).value == new ListNode!int(i).value);//Need to more consideration
  }

  assert(intList.toArray == [1, 2, 3, 4]);
  assert(intList.toReArray == [4, 3, 2, 1]);

  intList.printAll;
}