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Copy and replace base and derived class

I recently read about copy and swap , and now I'm trying to implement ctors in a base and derived class. I have four constructors in both my base and the derived class, however, I am not sure how to implement the assignment operator of the derived class.

explicit Base(int i) : m_i{i} {}
Base(const Base & other) : m_i{other.m_i}
Base(Base && other) : Base(0) { swap(*this, other); }
Base & operator=(Base other) { swap(*this, other); return *this; }
friend void swap(Base & a, Base & b) noexcept {
    using std::swap;
    swap(a.m_i, b.m_i);
}

explicit Derived(int j) : Base(42), m_j(j) {}
Derived(const Derived & other) : Derived(other.m_j) {}
Derived(Derived && other) : Derived(other.m_j) { swap(*this, other); }
Derived & operator=(Derived other) { /*???*/ }
friend void swap(Derived & a, Derived & b) noexcept {
    using std::swap;
    swap(a.m_j, b.m_j);
}
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2 answers

Use if possible = default. And if we are talking about public inheritance, you really need a virtual destructor.

Here's what your looks like Basewith the copy / swap style:

class Base
{
    int m_i;
public:
    virtual ~Base() = default;
    Base(const Base& other) = default;
    Base& operator=(Base other) noexcept
    {
        swap(*this, other);
        return *this;
    }
    Base(Base&& other) noexcept
        : Base(0)
    {
        swap(*this, other);
    }

    explicit Base(int i) noexcept
        : m_i{i}
        {}

    friend void swap(Base& a, Base& b) noexcept
    {
        using std::swap;
        swap(a.m_i, b.m_i);
    }
};

, , , = default .

Derived:

class Derived
    : public Base
{
    int m_j;
public:
    Derived(const Derived& other) = default;
    Derived& operator=(Derived other) noexcept
    {
        swap(*this, other);
        return *this;
    }
    Derived(Derived&& other) noexcept
        : Derived(0)
    {
        swap(*this, other);
    }

    explicit Derived(int j) noexcept
        : Base(42)
        , m_j{j}
        {}

    friend void swap(Derived& a, Derived& b) noexcept
    {
        using std::swap;
        swap(static_cast<Base&>(a), static_cast<Base&>(b));
        swap(a.m_j, b.m_j);
    }
};

, , .

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operator= , Base.

Derived - other, swap other.

Derived swap Base, Derived.

, copy/swap. , .

Base = default 5 :

class Base
{
    int m_i;
public:
    virtual ~Base() = default;
    Base(const Base&) = default;
    Base& operator=(const Base&) = default;
    Base(Base&&) = default;
    Base& operator=(Base&&) = default;

    explicit Base(int i) noexcept
        : m_i{i}
        {}

    friend void swap(Base& a, Base& b) noexcept
    {
        using std::swap;
        swap(a.m_i, b.m_i);
    }
};

, , swap.

Derived :

class Derived
    : public Base
{
    int m_j;
public:
    explicit Derived(int j) noexcept
        : Base(42)
        , m_j{j}
        {}

    friend void swap(Derived& a, Derived& b) noexcept
    {
        using std::swap;
        swap(static_cast<Base&>(a), static_cast<Base&>(b));
        swap(a.m_j, b.m_j);
    }
};

5 !

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copy/swap - , , , .

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+6

op= , Derived, Base:

Derived& operator=(Derived other) { swap(*this, other); return *this; }

, , :

  • : .
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, :

  • : Single-argument non-copy/move ctors explicit: int Base...
  • swap Derived ( -, , ). , Derived .
+3

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