Storing multiple types of a templated class into a container

Question

If I have a class with a template:

template
class foo{
    T m_a;

    foo(T a){
        m_a = a;
    };

    ~foo(){

    };
};

Answer 1

Different instantiations of a class-template are different (from the compilers perspective completely unrelated) types, so this question applies.

Answer 2

If you want e.g. std::vector<foo<T>*>, then you need to use a non-templated base class. It will need to use dynamic dispatch, so all of the public interface should be declared virtual.

struct foo_base {
    virtual ~foo_base() {}
    virtual void something() = 0;
};

template <typename T>
struct foo : foo_base {
    // ...
    void something() { /* do something with T */ }
};

Then your container is std::vector<foo_base*>. Another, perhaps better, way, is to use boost::variant. This limits the number of types you can store, but at the same time doesn't require base class and virtual interface.

typedef boost::variant<foo<int>, foo<std::string>> foo_variants;
std::vector<foo_variants> v;

Third way is to use boost::any, but that will require boost::any_cast wherever you use them, and allow absolutely anything to be stored in the vector.

std::vector<boost::any> v;