Constructors Demo

prog.cpp

#include <iostream>

struct A
{
    //A() = delete;
    A()
    {
        std::cout << "A::A()\n";
    }
    A(int)
    {
        std::cout << "A::A(int)\n";
    }
    ~A()
    {
        std::cout << "A::~A()\n";
    }
    A(const A&)
    {
        std::cout << "A::A(const A&)\n";
    }
    A(A&&)
    {
        std::cout << "A::A(A&&)\n";
    }
    A& operator= (const A&)
    {
        std::cout << "A::operator= (const A&)\n";
        return *this;
    }
    A& operator= (A&&)
    {
        std::cout << "A::operator= (A&&)\n";
        return *this;
    }
};

struct B
{
    B()
    {
        std::cout << "B::B()\n";
    }
    B(const A& a)
    {
        std::cout << "B::B(const A&)\n";
        value = a;
    }
    B(A&& a)
    {
        std::cout << "B::B(const A&)\n";
        value = std::move(a);
    }
    ~B()
    {
        std::cout << "B::~B()\n";
    }
    
    B(const B& b)
    {
        std::cout << "B::B(const B&)\n";
        value = b.value;
    }
    B(B&& b)
    {
        std::cout << "B::B(B&&)\n";
        value = std::move(b.value);
    }
    B& operator= (const B& b)
    {
        std::cout << "B::operator= (const B&)\n";
        value = b.value;
        return *this;
    }
    B& operator= (B&& b)
    {
        std::cout << "B::operator= (B&&)\n";
        value = std::move(b.value);
        return *this;
    }
    
private:
    A value;
};

int main()
{
    std::cout << "Case 1:\n";
    {
        auto x = B(A(1));
    }
    std::cout << "\nCase 2:\n";
    {
        A a(1);
        B b(a);
    }
    std::cout << "\nCase 3:\n";
    {
        A a(1);
        B b(std::move(a));
    }
    std::cout << "\nCase 4:\n";
    {
        B b(A{1});
    }
    std::cout << "\nCase 5:\n";
    {
        A a{A{A{1}}};
    }
    std::cout << "\nCase 6:\n";
    {
        B b;
    }
}
/*
Output:
    Start
    Case 1:
    A::A(int)
    A::A()
    B::B(const A&)
    A::operator= (A&&)
    A::~A()
    B::~B()
    A::~A()

    Case 2:
    A::A(int)
    A::A()
    B::B(const A&)
    A::operator= (const A&)
    B::~B()
    A::~A()
    A::~A()

    Case 3:
    A::A(int)
    A::A()
    B::B(const A&)
    A::operator= (A&&)
    B::~B()
    A::~A()
    A::~A()

    Case 4:
    A::A(int)
    A::A()
    B::B(const A&)
    A::operator= (A&&)
    A::~A()
    B::~B()
    A::~A()

    Case 5:
    A::A(int)
    A::~A()

    Case 6:
    A::A()
    B::B()
    B::~B()
    A::~A()
    0
    Finish
*/