Method OptionalHolder

tests/test_stl.cpp:82–82

NOLINTNEXTLINE(modernize-use-equals-default): breaks GCC 4.8

struct OptionalHolder {
    // NOLINTNEXTLINE(modernize-use-equals-default): breaks GCC 4.8
    OptionalHolder() {};
    bool member_initialized() const { return member && member->initialized; }
    OptionalImpl<T> member = T{};
};