A memory-safe bare-minimum binary tree implementation in c++

ref_counted_binary_tree.cc

#include <functional>
#include <iostream>
#include <memory>
#include <optional>

template <int T>
struct S {
  int _[T];
};

template <typename T>
class Node {
public:
  Node() : parent{*this}, data{} {}
  Node(Node &parent, T &&data) : parent{parent}, data{std::move(data)} {}

  bool isRoot() const { return this == &parent; }

public:
  std::unique_ptr<Node<T>> left, right;
  Node &parent;
  T data;
};

void test_data_in_node() {
  using namespace std::literals;

  using NodeType = Node<std::optional<std::string>>;

  NodeType root;
  root.left = std::make_unique<NodeType>(root, "left data"s);
  root.right = std::make_unique<NodeType>(root, "right data"s);

  std::cout << root.isRoot() << std::endl;
  std::cout << root.data.value_or("nothing") << std::endl;
  std::cout << root.left->data.value() << std::endl;
  std::cout << root.right->data.value() << std::endl;
  std::cout << root.right->parent.isRoot() << std::endl;

  std::cout << sizeof(NodeType) << std::endl;
  std::cout << sizeof(Node<std::optional<S<2>>>) << std::endl;
  std::cout << sizeof(Node<std::optional<S<8>>>) << std::endl;
  std::cout << sizeof(Node<std::optional<S<64>>>) << std::endl;
}

void test_data_ptr_in_node() {
  using namespace std::literals;

  using NodeType = Node<std::unique_ptr<std::string>>;

  NodeType root;
  root.left = std::make_unique<NodeType>(root, std::make_unique<std::string>("left data"s));
  root.right = std::make_unique<NodeType>(root, std::make_unique<std::string>("righ data"s));

  std::cout << root.isRoot() << std::endl;
  std::cout << root.data << std::endl;
  std::cout << *root.left->data << std::endl;
  std::cout << *root.right->data << std::endl;
  std::cout << root.right->parent.isRoot() << std::endl;

  std::cout << sizeof(NodeType) << std::endl;
  std::cout << sizeof(Node<std::unique_ptr<S<2>>>) << std::endl;
  std::cout << sizeof(Node<std::unique_ptr<S<8>>>) << std::endl;
  std::cout << sizeof(Node<std::unique_ptr<S<64>>>) << std::endl;
}

int main()
{
  std::cout << std::boolalpha;

  std::cout << std::string(80, '-') << "\n\tWith std::optional\n";
  test_data_in_node();

  std::cout << std::string(80, '-') << "\n\tWith std::unique_ptr\n";
  test_data_ptr_in_node();
}