#include <type_traits>
#include <string>
 
template <typename Heir>
class SToString {
public:
    std::string toString() {
        static_assert(std::is_member_function_pointer<decltype(&Heir::toStringImpl)>::value, "class derived from SToString should implement toStringImpl()");
        return static_cast<Heir*>(this)->toStringImpl();
    }
};
 
class Foo : public SToString<Foo> {
public:
    std::string toStringImplRRRRRRRRRRRRR() {
        return "Foo";
    }
};
 
int main() {
	Foo f;
 
	return 0;
}

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