C ++通过抽象基类在未知派生类上调用复制构造函数 [英] C++ Calling a copy constructor on an unknown derived class through an abstract base class

问题描述

我创建一个树，它有几种不同的节点类型：二进制节点，一元节点和终端节点。我有一个ABC，所有的节点继承。我想为树写一个递归复制构造函数，如下：

I'm making a tree that has several different node types: a binary node, a unary node, and a terminal node. I've got an ABC that all the nodes inherit from. I'm trying to write a recursive copy constructor for the tree like so:

class gpnode
{
public:
  gpnode() {};
  virtual ~gpnode() {};
  gpnode(const gpnode& src) {};

  gpnode* parent;
}

class bnode:gpnode
{
public:
  bnode() {//stuff};
  ~bnode() {//recursive delete};

  bnode(const bnode& src)
  {
    lnode = gpnode(src.lnode);
    rnode = gpnode(src.rnode);

    lnode->parent = this;
    rnode->parent = this;
  }

  gpnode* lnode;
  gpnode* rnode;
}

class unode:gpnode
{
public:
  unode() {//stuff};
  ~unode() {//recursive delete};

  unode(const unode& src)
  {
    node = gpnode(src.node);

    node->parent = this;
  }

  gpnode* node;
}

我的问题是我不能做

node = gpnode(src.node);

因为gpnode是一个虚拟类。我可以做

because gpnode is a virtual class. I could do

node = unode(src.node);

但是当unode的子节点是bnode时，它不工作。我如何让它智能调用我需要它的复制构造函数？

but that doesn't work when the child of a unode is a bnode. How do I get it to intelligently call the copy constructor I need it to?

推荐答案

您需要实施克隆。

   class base
   {
   public:
       virtual base* clone() const = 0;
   }

   class derived : public base
   {
   public:
       derived(){}; // default ctor
       derived(const derived&){}; // copy ctor

       virtual derived* clone() const { return new derived(*this); };
   };

Etceteras

Etceteras

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