Class custom_vec

test/ut/ut.cpp:346–360

};

struct custom_vec : std::vector<int> {
  using std::vector<int>::vector;

  friend auto operator<<(std::ostream& os, const custom_vec& c)
      -> std::ostream& {
    os << "custom_vec{";
    if (!c.empty()) {
      os << c.front();
      std::for_each(std::next(c.begin()), c.end(),
                    [&os](int const v) { os << ", " << v; });
    }
    os << '}';
    return os;
  }
};

struct custom_non_printable_type {
  int value;