Path: utzoo!attcan!uunet!microsoft!jimad
From: jimad@microsoft.UUCP (Jim ADCOCK)
Newsgroups: comp.lang.c++
Subject: Re: How smart is operator resolution?
Message-ID: <59579@microsoft.UUCP>
Date: 5 Dec 90 18:57:14 GMT
References: <1747@umriscc.isc.umr.edu>
Reply-To: jimad@microsoft.UUCP (Jim ADCOCK)
Organization: Microsoft Corp., Redmond WA
Lines: 37

Issues of overloading are probably too complicated to do justice here.
I refer you to pages 307 to 339 of "The Annotated C++ Reference Manual."

Consider instead the approach below -- the standard trick of introducing
an intermediate helper function to allow polymorphism on a second parameter.

const float pi = 3.14159;

class figure {            // abstract base class definition
protected:
    float r, h;
public:
    virtual float volume(void) = 0;
    friend ostream& operator<< (ostream& s, figure& self) 
        { return self.shiftout(s); }
    virtual ostream& shiftout(ostream&) = 0;
};

class sphere : public figure {    // derived class definition
public:
    sphere(float radius)  { r = radius; }
    virtual float volume(void)  { return 4.0 / 3.0 * pi * r * r * r; }
    virtual ostream& shiftout(ostream&);
};

ostream& sphere::shiftout (ostream &strm) {
    strm << "VOLUME OF SPHERE:\n";
    strm << "radius = " << r << "\n";
    strm << "volume = " << volume() << "\n";
    return strm;
}

main() {
    figure *fig = new sphere(2.0);
    cout << *fig << "\n";
    return 0;
}