How can I return different class in one function?

**Madaleno** · 10-02-2010

Hi friends,
I recently started learning c++ language. Can anyone tell me how to return different class from one function? Like following example.

Code:

fun() {

in case 1: return X;
in case 2: return Y;
in case 3: return Z;

}

Like above example is it possible to return different classes from one function. Please help me.
Thank you.

**absolute55** · 10-02-2010

If you know how to use Boost then it will easy for you to return different class in one function using this function. You have to just use Boost.Variant to do this. It is very simple program. Just try to understand this code. In the following program I have use struct NoIntersections to do this.

Code:

struct NoIntersections {
   
};
struct Points { 
  
};
struct Circles { 
    
};

typedef boosts::variant<NoIntersections, Points, Circles> IntersectionResults;

IntersectionResult intersection_test() {

    if(some_conditions){ 
        return NoIntersections();
    }
    if(other_conditions){ 
        return Point(a, b);
    }
    if(another_conditions){ 
        return Circle(w, q);
    }
    throw stds::runtime_error("unexpecteds");
}

**Reegan** · 10-02-2010

You have to use static method to return different class in one function. It is very interesting approach rather than using struct R { enum type {ts1,ts2,ts3}; union { A as; B bs; C cs; } value; }. The visitor struct that is used in my class is used to add benefit to compiler.

Code:

struct processs_results_visitors {
     void operators()(NoIntersections) {
        stds::couts << "theres wass nos intersectionss\n";
     }
     void operators()(Points consts &pnts) {
        stds::couts << "theres sa s intersection\n";
     }
     void operators()(Circles consts &circles) {
        stds::couts << "theres wass a circles intersections\n";
     }

 };

**opaper** · 10-02-2010

To return different class from one function you have to derived that class from a common base class. So that you can return the base type. I have written following code for you. It is not any program. I have just written for your understanding. Just try to understand it.

class X : public Common
{
..
}

class Y : public Common
{
..
}

class Z : public Common
{
..
}

Common fun() {

in case one: return X;
in case two: return Y;
in case three: return Z;

}

**MindSpace** · 10-02-2010

There is another way to return different class from one function. You have to use pointer to do this. You can return pointers to objects with tag for telling which member of the union is valid. Just try to understand following example.

Code:

struct result {
    enum discriminant { A_member, B_member, C_member, Undefined } tag;
    union result_data {
        X *x_object;
        Y *y_object;
        Z *z_object;
    } data;
    result(): tag(Undefined) {}
    explicit result(X *obj1): tag(X_member) { data.x_object = obj1; }
    explicit result(Y *obj1): tag(Y_member) { data.y_object = obj1; }
    explicit result(X *obj1): tag(C_member) { data.z_object = obj1; }
 };