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class Widget {
    // ...
};
class Thingy {
    public:
        // ...
        Thingy& operator=(const Thingy& rhs);
        // ...
    private:
        Widget *w;
};
// ...
Thingy& Thingy::operator=(const Thingy& rhs) {
    delete w;                // delete the current Widget
    w = new Widget(*rhs.w);  // create a copy of rhs's Widget
    return *this;
}
// ...

Thingy& Thingy::operator=(const Thingy& rhs) {
    if (this != &rhs) {
        delete w;
        w = new Widget(*rhs.w);
    }
    return *this;
}

Thingy& Thingy::operator=(const Thingy& rhs) {
    Widget *original = w;
    w = new Widget(*rhs.w);
    delete original;
    return *this;
}

class Thingy {
    public:
        // ...
        // compiler-generated copy assignment now correct
    private:
        std::tr1::shared_ptr<Widget> w;
};