Perfect forwarding full example

#include <functional>
#include <iostream>
#include <memory>

class V
{
public: 
    explicit V(int x) :x(x) 
    {
       std::cout < <  "V()n"; 
    }
    int x;
protected:
   V(const V&){}
   V& operator=(const V&){}
};

class A
{
public:
    A(V& v) 
    {
       std::cout < <  "A(V&) x = " < <  v.x < <  "n"; 
    }
};

template< typename T, typename Arg> std::shared_ptr< T> factory(Arg arg)
{
    return std::shared_ptr< T>(new T(arg));
} 

template< typename T, typename Arg> std::shared_ptr< T> factory2(Arg&& arg)
{
    // you can't use std::move for forwarding - compiler error 
    return std::shared_ptr< T>(new T(std::forward< V>(arg)));
} 

int main(int argc, char* argv[])
{
    V v(1);

    A a(v);

   // compiler error //std::shared_ptr a1 = factory(v);

    std::shared_ptr< A> a1 = factory2< A>(v);

    return 0;
}