#include <iostream>
#include <vector>
 
using namespace std;
 
 
template<typename T>
struct NotARef { typedef void type; };
template<typename T>
struct NotARef<T&> { }; // specialize for references, such that the type member doesn't exist.
 
template <class T>
void foo(const T& )
{cout << "void foo(const T&)" << endl;}
template <class T, typename x = typename NotARef<T>::type >
void foo(T&& ) // Now, thanks to NotARef, this will be called only for rvalues
{cout << "void foo(T&&)" << endl;}
 
int main()
{
        vector<int> x;
        foo(x); // Calls foo(const T&) as desired
        foo(vector<int>()); // void foo(T&&)
}
 

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