variable return type in c++ class

Question

i have a class with the following structure:

class myClass
{
    private:
        int type;
        classOne objectOne;
        classTwo objectTwo;
    public:
          


        

Answer 1

You can use Boost.Variant to do this. A variant can be constructed directly from any value convertible to one of its bounded types. Similarly, a variant can be assigned any value convertible to one of its bounded types. Heres how you could use it in your class:

class myClass
{
    private:
        boost::variant obj;
    public:
        myClass(classOne object) : obj(object)
        {
        }
        myClass(classTwo object) : obj(object)
        {
        }
};

It also provides a very convenient boost::get to retrieve the value from the variant. You can use that to supply code for each bounded type you have(ie classOne and classTwo). Here is an example:

if (classOne * x = boost::get(&obj))
{
    //Code for classOne
}
else if (classTwo * x = boost::get(&obj)
{
    //Code for classTwo
}

However, such code is quite brittle, and without careful attention will likely lead to the introduction of subtle logical errors detectable only at runtime. Thus, real-world use of variant typically demands an access mechanism more robust than get. For this reason, variant supports compile-time checked visitation via apply_visitor. Visitation requires that the programmer explicitly handle (or ignore) each bounded type. Failure to do so results in a compile-time error.

Visitation of a variant requires a visitor object. Like this:

class object_visitor
: public boost::static_visitor<>
{
public:

    void operator()(classOne & x) const
    {
        //Code for classOne
    }

    void operator()(classTwo & x) const
    {
        //Code for classTwo
    }

};

With the implementation of the above visitor, we can then apply it to obj, as seen in the following:

boost::apply_visitor( object_visitor(), obj );