example that shows off a function that can accept a lvalue reference as well as a rvalue

referencecollapse.cpp

#include <iostream>

template<typename T>
void fnc(T&& x)
{
    // std::cout << x;
    x++;
}

int main()
{
    fnc(10);  // Nope!
    // This works instead:
    int x = 10;
    fnc(x);
    std::cout << x;
    
}