[boost] Re: Problem solved: EBO pessimization in smart_ptr not an issue anymore!

From: David B. Held (dheld_at_[hidden])
Date: 2002-05-01 23:13:12

"Andrei Alexandrescu" <andrewalex_at_[hidden]> wrote in message
news:aaqd13$8sr$1_at_main.gmane.org...
> [...]
> Now when defining smart_ptr, the policies come wrapped in
> OptionallyInherit:
>
>     template
>     <
>         typename T,
>         template <typename> class OwnershipPolicy,
>         template <typename> class ConversionPolicy,
>         template <typename> class CheckingPolicy,
>         template <typename> class StoragePolicy
>     >
>     class smart_ptr
>         : public OptionallyInherit<
>             StoragePolicy<T>,
>             OptionallyInherit<CheckingPolicy<
>                     typename StoragePolicy<T>::stored_type> >,
>                 OptionallyInherit<OwnershipPolicy<
>                         typename StoragePolicy<T>::pointer_type> >,
>                     OptionallyInherit<ConversionPolicy<
>                         typename StoragePolicy<T>::pointer_type> > > >
>     {
>         ...
>     };
> [...]

Cool.  This also looks somewhat like Gennadiy's policy
adaptor suggestion, with some optimization.  But I would
use a tree structure instead of a list. ;)  (Unless there's a good
reason not to, of course)

    class smart_ptr
        : public OptionallyInherit<
            OptionallyInherit<
                StoragePolicy<T>,
                CheckingPolicy<typename StoragePolicy<T>::stored_type>
            >,
            OptionallyInherit<
                OwnershipPolicy<typename StoragePolicy<T>::pointer_type>
                ConversionPolicy<typename StoragePolicy<T>::pointer_type>
            >
        >

I'll take a look at boost::compressed_pair, to see if it can be
re-used.  This is a relief (if it works), because even though VC6
responded to the same MI-EBO hacks that bcc did, I couldn't get
the auto_ptr-compatible SmartPtr below 5 bytes on either one.

Dave