Re: [boost] Question and idea for smart pointers

From: Jonathan Wakely (cow_at_[hidden])
Date: 2005-01-07 07:22:55

On Fri, Jan 07, 2005 at 11:30:34AM +0100, Ion Gazta?aga wrote:

> >>template< class P, class V > struct pointer_to_other;
> >>template< template<class> class P, class U, class V >
> >>struct pointer_to_other< P<U>, V >
> >>{
> >>   typedef P<V> type;
> >>};
> 
> >>#include <boost/shared_ptr.hpp>
> >>#include <typeinfo>
> >>#include <iostream>
> 
> >>int main()
> >>{
> >>   typedef pointer_to_other< boost::shared_ptr<int>, double >::type
> >>pointer;
> >>   std::cout << typeid(pointer).name() << std::endl;
> >>}
> 
> >>On compilers that can't handle the above, just add partial specializations
> >>for "well known" pointer types (auto_ptr, shared_ptr).
> 
> I think this would work only with template classes with only one template
> parameter, like shared_ptr, but not with other smart pointers (offset_ptr or
> others, or future smart pointers that have some extra policy template
> parameters).

Then you can add other partial specialisations:

    template< template<class,class> class P, class U, class V, class W >
    struct pointer_to_other< P<U,W>, V >
    {
       typedef P<V,W> type;
    };

This will work with all two-parameter smart pointer templates without
having to change them. If you need it for smart pointer templates that
take three parameters, add another specialisation.

jon

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