fork(6) download

#include <iostream>
using namespace std;
 
  template< typename LeafT>
    class ATree {
    public:
        virtual  ATree< LeafT> * branch() = 0;
    };
 
  template< typename LeafT, typename Self>
    class Tree : public ATree< LeafT> {
    public:
        Self * branch() {}
    };
 
  template< typename LeafT>
    class C : public Tree< LeafT, C< LeafT> > {};
 
int main() {
	C< int> t;
 
	return 0;
}

prog.cpp: In instantiation of 'class Tree<int, C<int> >':
prog.cpp:17:11:   required from 'class C<int>'
prog.cpp:20:10:   required from here
prog.cpp:13:16: error: invalid covariant return type for 'Self* Tree<LeafT, Self>::branch() [with LeafT = int; Self = C<int>]'
         Self * branch() {}
                ^
prog.cpp:7:34: error:   overriding 'ATree<LeafT>* ATree<LeafT>::branch() [with LeafT = int]'
         virtual  ATree< LeafT> * branch() = 0;
                                  ^

Standard output is empty