Question

Let’s say I have the classes:

class Base{};

class A: public Base{
    int i;
};

class B:public Base{
    bool b;
};

And now I want to define a templated class:

template < typename T1, typename T2 >
class BasePair{
    T1 first;
    T2 second;
};

But I want to define it such that only decendants of class Base can be used as templateparameters.

How can I do that?

Answer 1

More exactly:

class B {};
class D1 : public B {};
class D2 : public B {};
class U {};

template <class X, class Y> class P {
    X x;
    Y y;
public:
    P() {
        (void)static_cast<B*>((X*)0);
        (void)static_cast<B*>((Y*)0);
    }
};

int main() {
    P<D1, D2> ok;
    P<U, U> nok; //error
}