Re: Enable functions in the derived class with the same function name but different return type?

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Wed, 23 May 2007 11:03:39 -0400

Message-ID:

<f31l4c$o0t$1@news.datemas.de>

PengYu.UT@gmail.com wrote:

Are there any walkaround to enable functions in the derived class with
the same function name but different return type?

In the following example, D1 and D2 are B's derived class. I want both
D1 and D2 have the function "doit". But there return type should be
different. Is it possible?

Generally final overriders are allowed to have different return value
types, but only if their return value types are _covariant_ with the
return value type of the function they override. Since 'B::doit' has
the return value type 'int', the only covariant type to it is 'int'
itself. So, if you stick with 'int', the answer is, then, "no".

Thanks,
Peng

#include <iostream>

class B {
public:
   B() { }
   virtual ~B() { }
   virtual int doit() const = 0;
};

class D1 : public B {
public:
   D1() { }
   int doit() const {
     return 42;
   }
};

class D2 : public B {
public:
   D2() { }
   virtual double doit() const {
     return -42;
   }
};

int main() {
B* b = new D1;
std::cout << b->doit() << std::endl;
}

V
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