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POHow to derive from/extend a recursive class
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Id
6416862
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6416941
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5
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CommunityOwnedDate
CreationDate
2011-06-20T20:09:51.233
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2011-06-21T12:05:19.453
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2011-06-21T12:05:19.453
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390847
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1
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ViewCount
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text
Body
I have a recursive class, a kind of tree, that has instances of itself as member variables. For example: <pre><code>template<class T> class Tree { public: /* Constructors, etc. */ protected: T m_value; Tree<T> *leftChild; Tree<T> *rightChild; }; </code></pre> If I want to add a method that prints all the values using an in-order traversal, I could do this: <pre><code>template <class T> void Tree<T>::printInOrder() { leftChild->printInOrder(); std::cout << m_value << std::endl; rightChild->printInOrder(); } </code></pre> But what if, for various reasons, I couldn't or didn't want to change Tree's implementation? If the class wasn't recursive, i.e. didn't contain instances of itself, I could just derive from Tree and implement a new method in the derived class. But this approach doesn't work for Tree. <pre><code>template <class T> class DerivedClass : public Tree<T> { public: void printInOrder(); } template <class T> void DerivedClass<T>:: printInOrder() { this->leftChild->printInOrder(); std::cout << this->m_value << std::endl; this->rightChild->printInOrder(); } </code></pre> leftChild and rightChild are instances of Tree and thus don't have a printInOrder() method. Can anyone suggest a way to do this in a modular way without changing Tree's implementation. It's ok to change how it is implemented in general, as long as you don't have to change it whenever you want to extend/derive from the class. I can see a possible way to do it by making the template class T have methods to do the things I want, but that just seems ugly. There must be a better way. I'm perfectly happy for someone to point out how I've overlooked something obvious. It certainly feels like I have. Edit: The point is not how to implement printInOrder(). That was just an example. The point is how to derive a class so that the children are also the derived class.
Tags
<c++><inheritance><recursion><derived-class>
Title
How to derive from/extend a recursive class
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