Implementing Vector<T> Front() and Back()

template <typename T>
T&  Vector<T>::Front() const
{
  if (size_ == 0)
  {
    std::cerr << "** Vector error:: invalid Front() called on empty vector\n";
    exit (EXIT_FAILURE);
  }
  return content_[0];
}

template <typename T>
T&  Vector<T>::Back() const
{
  if (size_ == 0)
  {
    std::cerr << "** Vector error: invalid Back() called on empty vector\n";
    exit (EXIT_FAILURE);
  }
  return content_[size_ - 1];
}