为什么我们不能声明一个std :: vector< AbstractClass&gt ;? [英] Why can't we declare a std::vector<AbstractClass>?

问题描述

在C＃中花了很多时间，我注意到，如果你声明一个抽象类，以使用它作为一个接口，你不能实例化这个抽象类的向量来存储孩子类的实例。

Having spent quite some time developping in C#, I noticed that if you declare an abstract class for the purpose of using it as an interface you cannot instantiate a vector of this abstract class to store instances of the children classes.

#pragma once
#include <iostream>
#include <vector>

using namespace std;

class IFunnyInterface
{
public:
    virtual void IamFunny()  = 0;
};

class FunnyImpl: IFunnyInterface
{
public:
    virtual void IamFunny()
    {
        cout << "<INSERT JOKE HERE>";
    }
};

class FunnyContainer
{
private:
    std::vector <IFunnyInterface> funnyItems;
};

在MS VS2005中声明抽象类向量的行会导致此错误：

The line declaring the vector of abstract class causes this error in MS VS2005:

error C2259: 'IFunnyInterface' : cannot instantiate abstract class

我看到一个显而易见的解决方法，即用以下代替IFunnyInterface：

I see an obvious workaround, which is to replace IFunnyInterface with the following:

class IFunnyInterface
{
public:
    virtual void IamFunny()
    {
        throw new std::exception("not implemented");
    }
};

如果没有，是否有任何第三方库，如boost，可以帮助我解决这个问题？

Is this an acceptable workaround C++ wise ? If not, is there any third party library like boost which could help me to get around this ?

感谢您阅读！

Anthony

推荐答案

您不能实例化抽象类，

You can't instantiate abstract classes, thus a vector of abstract classes can't work.

然而，您可以使用指针向量来抽象类：

You can however use a vector of pointers to abstract classes:

std::vector<IFunnyInterface*> ifVec;

这也允许你实际使用多态行为 - 即使该类不抽象，值会导致对象切片的问题。

This also allows you to actually use polymorphic behaviour - even if the class wasn't abstract, storing by value would lead to the problem of object slicing.

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