cpp_prac/junk/1.cc

#include <iostream>

using std::cout;

// Rule of three:
//   If a class requires a user-defined destructor, a user-defined copy
//   constructor, or a user-defined copy assignment operator, it almost
//   certainly requires all three.
//

// Rule of five:
//   Because the presence of a user-defined (include = default or = delete
//   declared) destructor, copy-constructor, or copy-assignment operator
//   prevents implicit definition of the move constructor and the move
//   assignment operator, any class for which move semantics are desirable, has
//   to declare all five special member functions:

struct A {
    A() = default;
    /* Constructor */
    A(const int &x) { val = x; }
    /* Copy constructor */
    A(A &other) { other.val = this->val; }
    /* Move constructor */
    A(A &&other) { other.val = this->val; }
    /* Copy assignment operator */
    A &operator=(const A &other) { return *this; }
    ~A() {}
    void print() { cout << "A(" << val << ")"; }
    int val;
};

struct B {
    B(int x) { a = A(x); }
    // B(int x) : a(x) {};
    void print() {
        cout << "B(";
        a.print();
        cout << ")";
    }
    A a;
};

int main() {
    B b(10);
    b.print();
    cout << "\n";
}

struct K {
    K() = default;
    /* Constructor */
    K(const int &x) { val = x; }
    /* Copy constructor */
    K(K &other) : K(other.val) {}
    /* Move constructor */
    K(K &&other) : K(other.val) {}
    /* Copy assignment operator */
    K &operator=(const K &other) { return *this; }
    ~K() {}
    void print() { cout << "K(" << val << ")"; }
    int val;
};