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#include <iostream>
using namespace std;
 
template <typename Derived>
struct Comparisons
{
};
 
 
template <typename Derived>
bool operator!=(const Comparisons<Derived>& lhs, const Comparisons<Derived>& rhs)
{
    const Derived& d1 = static_cast<const Derived&>(lhs);
    const Derived& d2 = static_cast<const Derived&>(rhs);
 
    return !(d1 == d2);
}
 
int main()
{
    Comparisons<int> c1, c2;	
 
    bool b = c1 != c2;
 
    return 0;
}

prog.cpp: In instantiation of ‘bool operator!=(const Comparisons<Derived>&, const Comparisons<Derived>&) [with Derived = int]’:
prog.cpp:23:20:   required from here
prog.cpp:13:25: error: invalid static_cast from type ‘const Comparisons<int>’ to type ‘const int&’
     const Derived& d1 = static_cast<const Derived&>(lhs);
                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
prog.cpp:14:25: error: invalid static_cast from type ‘const Comparisons<int>’ to type ‘const int&’
     const Derived& d2 = static_cast<const Derived&>(rhs);
                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Standard output is empty