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From: Alexandre Oliva <oliva@dcc.unicamp.br>
Subject: Re: my own 'pointer type'
Date: 1997/03/08
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Hyman Rosen writes:

> "Enno Rehling" <enno@uni-paderborn.de> writes:
>> At one point, I had a class B derived from A, and it dawned on me that
>> ptr<B> does not conform to ptr<A>, because it's not derived from it.

> There's a better way than the one you used, but it requires
> support for member templates:

I don't think conversion operators would do it as well as inheritance.

In fact, there are two cases I can think of where such a construction
would not do it well: when an additional user-defined conversion would
be necessary and in cases that presented covariance.

In fact, I'd love if auto_ptr were declared this way, so that
covariance would work with auto_ptr's too:

template <class T, class Base = void>
class auto_ptr : auto_ptr<Base> {
// implementation that just prevents pointers to different types
// from being assigned
};

template <class T>
class auto_ptr<T, void> {
// actual implementation
};

-- 
Alexandre Oliva
mailto:oliva@dcc.unicamp.br mailto:aoliva@acm.org
Universidade Estadual de Campinas, SP, Brasil

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