Conditional operator issue

Question

I'm having some trouble with using the conditional operator to get a reference to an object. I have the a setup similar to this:

class D
{
    virtual void bla() = 0;
};

class D1 : public D
{
    void bla() {};
};

class D2 : public D
{
    void bla() {};
};

class C
{
public:
    C()
    {
        this->d1 = new D1();
        this->d2 = new D2();
    }

    D1& getD1() {return *d1;};
    D2& getD2() {return *d2;}
private:
    D1 *d1;
    D2 *d2;
};

int main()
{    
    C c;    
    D& d = (rand() %2 == 0 ? c.getD1() : c.getD2());    
    return 0;    
}

When compiling, this gives me the following error:

WOpenTest.cpp: In function 'int
main()': WOpenTest.cpp:91: error: no
match for conditional 'operator?:' in
'((((unsigned int)rand()) & 1u) == 0u)
? c.C::getD1() : c.C::getD2()'

I understand this is illegal according to the C++ standard (as seen in this blog post), but I don't know how to get my reference to D without using the conditional operator.

Any ideas?

Answer 1

Cast to D& within both branches:

D& d = (rand() %2 == 0 ? static_cast<D&>(c.getD1()) : static_cast<D&>(c.getD2()));

Answer 2

Btw, you don't really need to use a conditional operator,

D* dptr; if(rand() %2 == 0) dptr = &c.getD1(); else dptr = &c.getD2();
D& d = *dptr;

would work too.

Answer 3

Or you can change the return types of the functions to Base Class.