CODEWITHSUNDEEP
c++
G25
G25

Reputation: 49

Covariant type error when returning a derived type

I'm trying to create a base class with a derived type; where in the base class I have a pure virtual method that returns something of the type DtBase (another class), and when overriding it in the derived class returns something of the type DtDerived (which derives from DtBase). I get an error saying that the type of the return is not identical nor covariant with the type of the overriden pure virtual function. I don't understand why does this happen, are DtBase and DtDerived not covariant?

Below is a code that presents this error:

//DtBase.h

class DtBase{
    public:
        DtBase();
        virtual ~DtBase();
};

class DtDerived: public DtBase{
    public:
        DtDerived();
        ~DtDerived();
};

//Base.h
#include "DtBase.h"

class base{
    public:
        base();
        virtual DtBase foo()=0;
        virtual ~base();
};

class derived: public base{
    public:
        derived();
        DtDerived foo(); // This is where I get the error
        ~derived();
};

Upvotes: 2

Views: 46

Answers (1)

SoronelHaetir
SoronelHaetir

Reputation: 15164

You need to return a DtBase pointer DtBase::foo() and DtDerived pointer in DtDerived::foo(), otherwise the DtDerived portion would simply get sliced off and the caller would never see that it was actually a DtDerived that was returned.

Upvotes: 2

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