int main()
{
  try
  {
    std::list<int> lst1;
    std::list<int> lst2;

    if(!std::equal(lst1.begin(),lst1.end(),lst2.begin()))
      throw std::logic_error("Error: 2 empty lists should always be equal");

    lst2.push_back(5);

    if(std::equal(lst1.begin(),lst2.begin()))
      throw std::logic_error("Error: comparing 2 lists where one is not empty should not be equal");
  }
  catch(std::exception& e)
  {
    std::cerr << e.what();
  }  
}

输出(给我一个惊喜)：

Error: comparing 2 lists where one is not empty should not be equal

观察：为什么std::equal不首先检查2个容器是否具有相同的尺寸()？有合理的理由吗？