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template <class T>
class Int {
public:
    T value;
    Int(const T& value_) : value(value_) {
        ;
    }
 
    friend bool operator==(const Int<T>& f, const Int<T>& s);
};
 
template <class T>
bool operator==(const Int<T>& f, const Int<T>& s) {
    return f.value == s.value;
}
 
int main() {
    int a;
    Int<int> x(a);
    x == a;
}

prog.cpp:22:7: warning: equality comparison result unused [-Wunused-comparison]
    x == a;
    ~~^~~~
prog.cpp:22:7: note: use '=' to turn this equality comparison into an assignment
    x == a;
      ^~
      =
1 warning generated.
/home/Q708ei/prog-dde773.o: In function `main':
prog.cpp:(.text+0xf): undefined reference to `operator==(Int<int> const&, Int<int> const&)'
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Standard output is empty