What are some uses of template template parameters?

Question

I\'ve seen some examples of C++ using template template parameters (that is templates which take templates as parameters) to do policy-based class design. What other uses do

Answer 1

This is what I ran into:

template
class B
{
  A& a;
};

template
class A
{
  B b;
};

class AInstance : A>>>>>>>
{

};

Can be solved to:

template
class B
{
  A& a;
};

template< template class B>
class A
{
  B b;
};

class AInstance : A //happy
{

};

or (working code):

template
class B
{
public:
    A* a;
    int GetInt() { return a->dummy; }
};

template< template class B>
class A
{
public:
    A() : dummy(3) { b.a = this; }
    B b;
    int dummy;
};

class AInstance : public A //happy
{
public:
    void Print() { std::cout << b.GetInt(); }
};

int main()
{
    std::cout << "hello";
    AInstance test;
    test.Print();
}