Question

I have the following structure of classes and a templated wrapper class.

class A {};
class B : public A {};

template<class T>
class Foo {
  T val;
public:
  Foo(T t) {val = t};
  T get() {return val};
}

Now, I need a function to process the values stored in the template but I can not modify the template itself. What I want is a function with signature similar to

void process(Foo<A>*) {/* do something */}

and I want to use it like

B b; Foo<B> foo(b);
process(&foo);

However, this won’t work because the compiler does not know how to convert Foo<B>* to Foo<A>*. Is there any workarround to fix the process function?

Answer 1

Make process a function template:

template <typename T> void process(Foo<T>*)

Inside the function template you can use the typename T as if it was class A. The function template will then work for all calls with Foo<B> as well.