Method operator()

tests/ordered_map_tests.cpp:1535–1538

    using is_transparent = std::true_type;

    bool operator()(const std::unique_ptr<int>& p1,
                    const std::unique_ptr<int>& p2) const {
      return p1 == p2;
    }

    bool operator()(const std::unique_ptr<int>& p1, std::uintptr_t p2) const {
      return reinterpret_cast<std::uintptr_t>(p1.get()) == p2;