ATL / WTL / STL

template <class Type> class CMy_Array 
{

    private:
		std::vector<Type> m_vItems;

	public:

		CMy_Array()
		{
		}
		virtual ~CMy_Array ()
		{
			m_vItems.clear();
		}
        void InsertAt(int index)
        {

       	//	THE LINE IN QUESTION - trying to acquire an iterator...
        // this worked w/ std:c++17   -

            std::vector<Type>::iterator p =  m_vItems.begin();

        // With c++20, 2 errors occur; 
        // C2760 - syntax error: unexpected token 'identifier', expected ';' , and 
        // C7510 - 'iterator': use of dependent type name must be prefixed with 'typename'

        // Using the documentation for C2760, I modified the line in question as so -

    		std::vector<Type>::iterator p =  static_cast <std::vector<Type>::iterator> m_vItems.begin();

        // This eliminated the C7510 error, but C2760 remains.


        }      
}

// To write a memory efficient linked list
#include <iostream>
using namespace std;

// Node structure of a memory efficient doubly linked list
class Node {
public:
    int data;
    Node *npx;      //  XOR of next and previous node
};

// return XORed value of the node address
Node *XOR(Node *a, Node *b){
    return ((Node *)( (uintptr_t)(a) ^ (uintptr_t)(b) ));
}

// insert a node at the beggining of the XORed linked list and makes the newly inserted node as head
void insert(Node **head_ref, int data){
    // allocate memory for new node
    Node *new_node = new Node();
    new_node->data = data;

    // since node is inserted at the beggining, npx of the new node will always be XOR of curent head and null
    new_node->npx = XOR((*head_ref), nullptr);

    // if the linked list is not empty, then npx of current head node will be XOR of new node and node next to current head
    if(*head_ref != nullptr){
        // (*head_ref)->npx is XOR of null and next.
        // so if we do XOR of it with null, we get next
        Node *next = XOR((*head_ref)->npx, nullptr);
        (*head_ref)->npx = XOR(new_node, next);
    }

    // change head
    *head_ref = new_node;
}

// prints contents of doubly linked list in forward direction
void printList(Node *head){
    Node *curr = head, *prev = nullptr, *next;

    cout << "Following are the nodes of Linked List: \n";

    while(curr != nullptr) {
        // print current node
        cout << curr->data << " ";

        // get the address of next node : curr->npa is next^prev,
        // so curr->npx^prev will be next^prev^prev which is next
        next = XOR(prev, curr->npx);

        // update prev and curr for next iteration
        prev = curr;
        curr = next;
    }
}

// Driver function
int main(){
    Node *head = nullptr;
    insert(&head, 10);
    insert(&head, 20);
    insert(&head, 30);
    insert(&head, 40);
    insert(&head, 50);
    insert(&head, 60);

    printList(head);

    return 0;
}

Node *insert(Node **last, int data){
    // allocate memory for new node
    Node *new_node = new Node();
    new_node->data = data;

	new_node->npx = XOR(*last, nullptr);

	if(*last != nullptr) {
		Node *prev = XOR((*last)->npx, nullptr);
		(*last)->npx = XOR(prev, new_node);
	}

	// *last = new_node;
	return (new_node);
}

// Driver function
int main(){
    Node *head = nullptr;
    head = insert(&head, 10);
    head = insert(&head, 20);
    head = insert(&head, 30);
    head = insert(&head, 40);
    head = insert(&head, 50);
    head = insert(&head, 60);

    printList(head);

    return 0;
}

template <typename ParamType>
void Template_universal_ref(ParamType&& param)
{
    cout << "Template_universal_ref, param : " << param << endl;
}

void NonTemplate_universal_ref(int&& param)
{
    cout << "NonTemplate_universal_ref, param : " << param << endl;
}

int main()
{
    int x=5;
    Template_universal_ref(x);
    //NonTemplate_universal_ref(x); // This is giving compilation error
    return 0
}

NonTemplate_universal_ref(x);

Template_universal_ref(x);