Expected object construction is missing [duplicate]

Question

class A
{
public:

    A ()
    {
        wcout << L"Empty constructed." << endl;
    }

    A (LPCWSTR Name)
        : m_Name(Name)
    {
        wcout << L"Constructed." << endl;
    }

    friend void swap (A& Lhs, A& Rhs)
    {
        using std::swap;

        swap(Lhs.m_Name, Rhs.m_Name);
    }

    A (A&& Other)
    {
        wcout << L"Move constructed." << endl;

        swap(*this, Other);
    }

    A (const A& Other)
        : m_Name(Other.m_Name)
    {
        wcout << L"Copy constructed." << endl;
    }

    A& operator= (A Other)
    {
        wcout << L"Assignment." << endl;

        swap(*this, Other);

        return *this;
    }

    ~A ()
    {
        wcout << L"Destroyed: " << m_Name.GetString() << endl;
    }

private:

    CString m_Name;
};


int
wmain ()
{
    A a;

    a = A(L"Name"); // Where is the construction of this temp object?

    return 0;
}

This is the output I get for the above code:

Empty constructed.
Constructed.
Assignment.
Destroyed:
Destroyed: Name

See the line with the comment. What I expected is for a temp object to get constructed there, and the argument Other in the operator= would get move-constructed from that temp-object. What's happening here?

Answer 1

The output that says "Constructed" is actually the feedback from the construction of that temporary object.

If you are looking for an additional copy-construction (or move-construction) of Other parameter of copy-assignment operator, it was probably eliminated by copy elision. Your A(L"Name") is immediately constructed and used as that Other parameter. No extra copying (or moving) is performed.

Answer 2

You can use an interactive debugger to see for yourself. However, your answer to where "Name" got constructed is this:

A (LPCWSTR Name) 
    : m_Name(Name) 
{ 
    wcout << L"Constructed." << endl; 
} 

and

 a = A(L"Name");

Your code constructed an empty object at the code line A a;.

It then constructed "Name".

Then it swapped the two's CString m_Name; (shown by the output Assignment).

Then it destructed the original object holding "Name" (A(L"Name")).

Then it destructed the original empty object that is now holding "Name" in its m_Name.