Hold any kind of C++ template class in member variable

Question

I have got two classes.

The first class (A) is builded with an template.

template <class T>
class A
{
    public:
        T value;
};

The second class (B) should have an object of class A as member variable. Like this:

class B
{
    public:
        A<int> value;
};

But now i want to use any kind of template-class in class A. Not only int. Apparent I can't declare a (member-)variable which contains any kind of a class. So, I need something like this:

class B
{
    public:
        A<*> value;
};

Is there any (clean) solution for this problem?

-- Greeting from Germany, Bastian

Answer 1

You cannot have a single class B with "any" member object, because B has to be a well-defined class, and A<T> is a different type for different types T. You can either make B a template itself:

template <typename T>
class B
{
  A<T> value;
};

or you can take a look at boost::any, which is type-erasing container for arbitrary types (but making use of it requires a certain amount of extra work). The any class only works for value types, though, it's not completely arbitrary.