covariance of shared_ptr types

From: Vaclav Vesely (vaclav.vesely_at_[hidden])
Date: 2003-02-10 17:03:49

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
 

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