derivation template classes - c++

Question

I have written a template BST class with the usual operations like this:
template <class Key,class T>
class BTree {
public:
BTree():root(0){}//crea un albero vuoto
BTree<Key,T>& treeInsert(const Key& k,const T& val);
BTree<Key,T>& treeDelete(const Key& k);
Node<Key,T>& treeSearch(const Key& k);
Node<Key,T>& treeMinimum();
void treeClear();
protected:
BTree<Key,T>& transplant(Node<Key,T>& n1,Node<Key,T>& n2);
Node<Key,T>* root;
};
I would like to implements a template red-black tree class that inherits from the bst class.
The red-black class should rewrite the insertion and deletion, but I read that methods of a template class can not be virtual, and so do not know how to do this.

Answer 1

As mentioned in comments, you actually can have virtual functions in a template class, and those can be overridden by deriving classes.
Though the better choice IMHO might be, to use a CRTP (aka Static Polymorphism, Policy based design) for such case (as you're already handing on templates). It could look like this
template <class Key,class T,class Derived>
// ^^^^^^^^^^^^^^
class BTree {
public:
BTree():root(0){}//crea un albero vuoto
BTree<Key,T>& treeInsert(const Key& k,const T& val) {
return static_cast<Derived*>(this)->doTreeInsert();
}
BTree<Key,T>& treeDelete(const Key& k) {
return static_cast<Derived*>(this)->doTreeDelete();
}
Node<Key,T>& treeSearch(const Key& k);
Node<Key,T>& treeMinimum();
void treeClear();
protected:
BTree<Key,T>& transplant(Node<Key,T>& n1,Node<Key,T>& n2);
Node<Key,T>* root;
};
Derived classes must implement doTreeInsert() and doTreeDelete() functions accordingly, to let this code compile:
template <class Key,class T>
class RedBlackTree
: public BTree<Key,T,RedBlackTree> {
public:
BTree<Key,T>& doTreeInsert(const Key& k,const T& val) {
// Implement the RB specifics for insert here
return *this;
}
BTree<Key,T>& doTreeDelete(const Key& k) {
// Implement the RB specifics for delete here
return *this;
}
};