language: C++11 (gcc-4.7.2)
date: 362 days 15 hours ago
link:
visibility: public 
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#include <iostream>
 
using namespace std;
 
template<class T> class CBase
{
    public:
        template <class T2> CBase(const T2 &x) : _var(x) {;}
        template <class T2> CBase (const CBase<T2> &x) {_var = x.var();}
        ~CBase() {;}
        T var() const {return _var;}
    protected:
        T _var;
};
 
template<class T> class CDerived : public CBase<T>
{
    public:
        template <class T2> CDerived(const T2 &x) : CBase<T>(x) {;}
        template <class T2> CDerived(const CDerived<T2> &x) : CBase<T>(x.var()) {;}
        template <class T2> CDerived (const CBase<T2> &x) : CBase<T>(x) {;}
        ~CDerived() {;}
};
 
int main()
{
    CBase<double> bd(3);
    CBase<int> bi(bd); // <- No problem
    CDerived<double> dd1(3);
    CDerived<double> dd2(dd1);
    CDerived<int> di(dd1); // <- The problem is here
    return 0;
}