The output of the code snippet is not what i expected

I don’t understand why this code snippet using an altered version of the visitor patters is always printing the log V instead of A. Compiled using c++11 version.

#include <iostream>

using namespace std;

class A;
class B;
class Visitable;

class Visitor
{
    public:
    void visit(const A& a)
    {
        std::cout << "A" << std::endl;
    }
    
    void visit(const Visitable& v)
    {
        std::cout << "V" << std::endl;
    }
    
    void visit(const B& b)
    {
        std::cout << "B" << std::endl;
    }
};

class Visitable
{
    public:
        virtual void Accept(Visitor* visitor)
        {
            visitor->visit(*this);
        }
};

class A : public Visitable
{
};

class B : public Visitable
{
};

int main()
{
    Visitor* v = new Visitor();
    A* a = new A();
    
    a->Accept(v); // IT PRINTS V INSTEAD OF A.

    return 0;
}

I executed the code snipped, i was expecting to see the log A in the output console.

>Solution :

The type of *this is Visitable which matches the type of the parameter in the member function void Visitor::visit(const Visitable&) so that it is the only viable option and hence selected.

That is, the other two member function void Visitor::visit(const A&) and void Visitor::visit(const B&) are not viable since the passed argument in the call visitor->visit(*this); is of type Visitable while the parameter type in these member functions is const A& and const B& respectively.

why is this a pointer to Visitable instead of A

Because as per the standard, inside the body of a non-const non-static member function func of a class X, the type of pointer this is X*. This means that *this is X. This can be seen(pun intended) from this:

The expression this is a prvalue expression whose value is the address of the implicit object parameter (object on which the non-static member function is being called).