The Human class turned out to be non-copied, since it contains a field of type unique_ptr, for which the copy constructor and the copying assignment operator have been removed. This prevents the compiler from automatically generating a copy constructor and assignment operator for the Human class. How can I implement a copy constructor and a copy assignment operator in the Human class? A copy of the human must own a copy of the cat, if the original human owned it.

struct Cat {
    Cat(const string& name, int age)
        : name_(name)
        , age_(age)  //
    {
    }
    const string& GetName() const noexcept {
        return name_;
    }
    int GetAge() const noexcept {
        return age_;
    }
    ~Cat() {
    }
    void Speak() const {
        cout << "Meow!"s << endl;
    }

private:
    string name_;
    int age_;
};

unique_ptr<Cat> CreateCat(const string& name) {
    return make_unique<Cat>(name, 2);
}

class Human {
public:
    explicit Human(const string& name)
        : name_(name) {
    }
    
    const string& GetName() const noexcept {
        return name_;
    }
    void SetCat(unique_ptr<Cat>&& cat) noexcept {
        cat_ = std::move(cat);
    }
    unique_ptr<Cat> ReleaseCat() noexcept {
        return std::move(cat_);
    }

private:
    string name_;
    unique_ptr<Cat> cat_;
}; 

CodePudding user response：

Your copy constructor might look like

Human::Human(const Human& rhs) :
    name_(rhs.name_),
    cat_(rhs.cat_ ? std::make_unique<Cat>(*rhs.cat_) : std::nullptr)
{}

but getting rid of std::unique_ptr and having Cat by value (or std::optional<Cat>) would be simpler:

Human::Human(const Human&) = default;

If Cat is polymorphic, a clone method would be required:

Human::Human(const Human& rhs) :
    name_(rhs.name_),
    animal_(rhs.animal_ ? rhs.animal_->clone() : std::nullptr)
{}