Perfect forwarding full example

Here is an example of how to use rvalue references for forwarding:

#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<A> a1 = factory<A>(v);

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

    return 0;
}