C++: What is the Rule of Three/Five/Zero?

1class MyClass {
2private:
3    int* data;
4
5public:
6    // Constructor
7    MyClass(int value) {
8        data = new int(value);
9    }
10
11    // Destructor
12    ~MyClass() {
13        delete data;
14    }
15
16    // Copy constructor
17    MyClass(const MyClass& other) {
18        data = new int(*other.data);
19    }
20
21    // Copy assignment
22    MyClass& operator=(const MyClass& other) {
23        if (this != &other) {
24            *data = *other.data;
25        }
26        return *this;
27    }
28};

1class MyClass {
2    std::unique_ptr<int> data;
3public:
4    MyClass(int value) : data(std::make_unique<int>(value)) {}
5    // Destructor, copy, move — all auto-generated!
6};