#include <cassert>
#include <memory>
#include <utility>
#include <vector>

struct Values {
    std::vector<int> items;
};

class DeepBox {
    std::unique_ptr<int> value_;
public:
    explicit DeepBox(int value) : value_(new int(value)) {}
    DeepBox(const DeepBox& other)
        : value_(other.value_ ? new int(*other.value_) : nullptr) {}
    DeepBox& operator=(const DeepBox& other) {
        DeepBox temporary(other);
        value_.swap(temporary.value_);
        return *this;
    }
    DeepBox(DeepBox&&) noexcept = default;
    DeepBox& operator=(DeepBox&&) noexcept = default;
    ~DeepBox() = default;
    int value() const { return value_ ? *value_ : 0; }
    void set(int value) {
        if (value_) *value_ = value;
        else value_.reset(new int(value));
    }
};

int main() {
    Values a{{1, 2}};
    Values b = a;
    b.items[0] = 8;
    assert(a.items[0] == 1);
    DeepBox original(3);
    DeepBox copy = original;
    copy.set(7);
    assert(original.value() == 3 && copy.value() == 7);
    original = original;
    DeepBox moved = std::move(copy);
    assert(original.value() == 3);
    assert(moved.value() == 7 && copy.value() == 0);
}