C++ - Extract template parameter from derived class

Question

Can I extract the type parameter from the derived class? Something like this:

template<typename T>
class A {
...
};

struct TheType {};

class B : public A<TheType> {
...
};

template<typename DerivedClass>
class C {
  // If DerivedClass is B
  // Can I extract the type parameter T of B:A<T> inside of C?
  DerivedClass elem;
};

Answer 1

You can add a type in A:

template<typename T>
class A {
protected:
    using type = T;
    ...
};

Then you can use typename DerivedClass::type in C.