如何动态分配内存到多态数据类型？ [英] How do I dynamically allocate memory to a polymorphic data type?

问题描述

我有一个集合类，可以多态地保存和管理任何类型的Multinumber。这可以是类型为Pair，Rational或Complex的对象。我遇到的问题是，这个类需要动态内存管理，在许多情况下，如下面的功能，我不知道要分配什么类型。因为集合是类型不可知的，我不知道我应该做Multinumber * var = new Complex，Rational或Pair。有什么方法来检查我首先添加的类型，或将此信息存储在另一种数据类型，而不会产生切片效应？我有这个问题的一个函数是：

I have a set class that can polymorphically hold and manage anything of type Multinumber. This can be an object of type Pair, Rational, or Complex. The problem that I am running into is that this class requires dynamic memory management and in many cases, such as the function below, I don't know what type to allocate. Since the set is type agnostic, I can't know if I am supposed to do Multinumber* var=new Complex, Rational, or Pair. Is there any way to check the type of what I am adding first, or to store this information in another data type without the slicing effect? One function where I have this problem is this:

bool Set::addElement(Multinumber* newElement)
{
    bool success = false;
    if(isFull())
    {
        resize();
    }
    if(!isMember(newElement))
    {
        setArray[numElements] = newElement;
        numElements++;
        success = true;
    }
    return success;
}

编辑：我说的是这种情况， / em>我可能分配的地方，例如当一个操作符+被调用并且必须立即在这里发送对象，并且调用类不知道什么是类型。

I am talking about situations where this is the only place that I could possibly allocate, such as when an operator+ is called and must immediately send the object here, and the calling class does not know what the type is. It happens in my code in the Set operator+ overload, since I the Set doesn't know what it is storing.

推荐答案

我在Set运算符+重载的代码中发生了这种情况。不明白为什么你会在这里分配。但除此之外，请使用虚拟副本成语。

I don't see why you would be allocating here. But aside from that, use the virtual clone idiom.

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