关于使用用户定义方法扩展 C++ STL 容器的更好方法的建议

2022-01-07 00:00:00 c++ stl

我从 C++ STL 容器继承并添加了我自己的方法.其基本原理是，对于客户端来说，它看起来像一个常规列表，但具有可以轻松调用的特定于应用程序的方法.

I inherited from C++ STL container and add my own methods to it. The rationale was such that to the clients, it will look act a regular list, yet has application-specific methods they can readily be called.

这很好用，但我已经阅读了很多关于不继承 STL 的帖子.有人可以就我如何以更好的方式编写下面的代码提供具体建议吗?

This works fine, but I have read numerous posts about not inheriting from STL. Can someone provide a concrete advice of how I might write the code below in a better way? 

class Item
{
  int a;
  int b;
  int c;

  int SpecialB()
  {
    return a * b + c;
  }
};

class ItemList : public std::vector<Item>
{
  int MaxA()
  {
    if( this->empty() )
      throw;

    int maxA = (*this)[0].a;

    for( int idx = 1; idx < this->size(); idx++ )
    {
      if( (*this)[idx].a > maxA )
      {
        maxA = (*this)[idx].a;
      }
    }
    return maxA;
  }

  int SpecialB()
  {
    if( this->empty() )
      throw;

    int specialB = (*this)[0].SpecialB();

    for( int idx = 1; idx < this->size(); idx++ )
    {
      if( (*this)[idx].SpecialB() < specialB )
      {
        specialB -= (*this)[idx].c;
      }
    }
    return specialB;
  }

  int AvgC()
  {
    if( this->empty() )
      throw;

    int cSum = 0;
    for( int idx = 0; idx < this->size(); idx++ )
    {
      cSum += (*this)[idx].c;
    }

    return cSum / this->size(); // average
  }
};

编辑:感谢您提供一系列深思熟虑的答案.我将改为创建辅助函数，从现在开始不再继承 STL 容器.

EDIT: Thanks for a bunch of thoughtful answers. I will create helper functions instead and from now on will never inherit from STL containers.

推荐答案

为什么需要以这种方式扩展向量?

why you need extend vector in this way?

对您的函子使用标准 .
例如

use standard <algorithm> with your functors.
e.g.

std::min_element, std::max_element 

int max_a = std::max_element
        ( 
            v.begin(), 
            v.end(), 
            boost::bind( 
                std::less< int >(),
                bind( &Item::a, _1 ), 
                bind( &Item::a, _2 ) 
            )
        )->a;

std::accumulate - 对于计算平均值

std::accumulate - for calculate avarage 

const double avg_c = std::accumulate( v.begin(), v.end(), double( 0 ), boost::bind( Item::c, _1 ) ) / v.size(); // ofcourse check size before divide

您的 ItemList::SpecialB() 可以重写为:

your ItemList::SpecialB() could be rewrited as: 

int accumulate_func( int start_from, int result, const Item& item )
{
   if ( item.SpecialB() < start_from )
   {
       result -= item.SpecialB();
   }
   return result;
}

if ( v.empty() )
{
    throw sometghing( "empty vector" );
}
const int result = std::accumulate( v.begin(), v.end(), v.front(), boost::bind( &accumulate_func, v.front(), _1, _2 ) );

顺便说一句:如果您不需要访问成员，则不需要继承.

BTW: if you don't need access to members, you don't need inheritance.

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