Can a template object change its type?

Question

I have the following class

template <typename T> class Item {

public:

    T item;
    Item () : item( T() ) {}
    Item (T arg) { this->item = arg;}

    operator T () const {
        return item;
    }

};

Now I want to write an assignment operator that also changes the type of the object. Is that even possible? I have googled it, but nothing relevant came out of this (which, btw, makes me think that maybe I`m a bit out of my mind).

To make this clear, let`s say I have the 2 following objects:

Item <int> intItem = 3;
Item <double> doubleItem = 3.4;

I want to be able to write

intItem = doubleItem;

And, after this, I want the type of intItem to be Item<double>.

If I only wanted a "classic" assignment operator, it would work just fine if, inside my class, I would have something like

Item<int>& operator= (const Item<double> & var) {
    this->item = var.item;
    return *this;
}

The double value would be rounded, but it would work. Oh, and the type of intItem would remain Item<int>

P.S.: I know about unions and tagged unions, I don't want to use that. My Item class should behave "something like" tagged unions.

So please give me an answer, or tell me I`m dreaming.

Answer 1

No you can't change the type during runtime, as templates are a compile-time thing.

In fact, it would be like having a variable declared as int and try to change it to a float. Yes you can assign the variable to another float variable, but you can't change the type of the actual variable.