map insertがpush_backに分岐するときの強い例外保証

[kohkubo]

  void insert(iterator pos, size_type n, const_reference value) {
    // TODO push_backのとき、強い例外保証
    if (size() + n > capacity()) {
      size_t pos_index = pos - begin();
      reserve(__new_cap(n));
      pos = begin() + pos_index;
    }
    pointer pos_ptr = pos.base();
    std::copy_backward(pos_ptr, __end_, __end_ + n);
    std::uninitialized_fill(pos_ptr, pos_ptr + n, value);
    __end_ += n;
  }