covariance of shared_ptr types

10 Feb 2003

      Hi,

in C++ it's possible to write this:

class A {};

class B: public A {};

class X {
    virtual A* f() { ... };
};

class Y: public X {
    virtual B* f() { ... };    // B* is covariant from A*
};

However it is NOT possible to write that with shared_ptr:

class X {
    shared_ptr<A> f() { ... };
};

class Y: public X {
    virtual shared_ptr<B> f() { ... };    // Error: shared_ptr<B> is NOT
covariant from shared_ptr<A>
};

I don't know C++ standard very well (in fact I've never read it). So my
question is: it's possible to adjust shared_ptr to allow such constructions?

Thank you,
Wasek

[Non-text portions of this message have been removed]

covariance of shared_ptr types

Vaclav Vesely