template<typename OwnerType, typename ResultType, typename ... ArgTypes>
consteval auto function_signature(auto(OwnerType::*)(ArgTypes...)-> ResultType) noexcept {

struct result {


using result_type                    = ResultType;


using owner_type                     = OwnerType;

};

return result{};
}

struct s {

size_t operator()(int, double) {


return 4;

}
};
void f(int,double) {

using testlambda = decltype([](int, double) -> size_t { return 4; });

using testfuncinfo = decltype(function_signature(&s::operator()));          // работает
   using testfuncinfo = decltype(function_signature(&testlambda::operator())); // не работает
}