Function try_set_i

dlib/test/constexpr_if.cpp:167–178

    template<typename T>
    bool try_set_i(T& obj, int i)
    {
        return switch_(bools(is_detected<set_i_pred, T>{}),
            [&](true_t, auto _) {
                _(obj).set_i(i);
                return true;
            },
            [](auto...){
                return false;
            }
        );
    }

    void test_set_i()
    {