Class hash_str_diff

tests/ordered_map_tests.cpp:1407–1411

insert x values; serialize map; deserialize in new map which has a different hash; check equal

  // insert x values; serialize map; deserialize in new map which has a
  // different hash; check equal
  struct hash_str_diff {
    std::size_t operator()(const std::string& str) const {
      return std::hash<std::string>()(str) + 123;
    }
  };

  const std::size_t nb_values = 1000;