Challenge 1: A Hand-Written Move Constructor — Possible Solution
====================================================================

#include <iostream>

class Buffer {
public:
    int *data;

    Buffer(int value) {
        data = new int(value);
    }

    Buffer(Buffer &&other) {
        data = other.data;
        other.data = nullptr;
        std::cout << "Moved" << std::endl;
    }

    ~Buffer() {
        delete data;
    }
};

int main() {
    Buffer a(42);
    Buffer b = std::move(a);

    if (a.data == nullptr) {
        std::cout << "Source's pointer is now nullptr" << std::endl;
    }

    return 0;
}

Output:

    Moved
    Source's pointer is now nullptr

WHY THIS WORKS AS AN ANSWER
------------------------------
std::move(a) casts a to an rvalue reference, causing the move
constructor (not the implicit copy constructor) to be selected when
constructing b -- the move constructor copies the pointer VALUE from
a.data into b.data, then explicitly sets a.data to nullptr, exactly
the chapter's own "steal and null out" pattern that prevents both a's
and b's destructors from later trying to delete the same memory.