Re: [boost] Smart Pointer Feature Model

From: Kevlin Henney (kevlin_at_[hidden])
Date: 2000-07-12 11:11:05

In message <4.3.2.7.2.20000712104116.00b89d98_at_[hidden]>, Beman
Dawes <beman_at_[hidden]> writes
>Using the technique described in 
>http://www.egroups.com/files/boost/Feature+Modeling/feature_modeling.htm, I 
>have taken a first cut at building a smart pointer feature diagram.

Thanks for putting this summary up. Have been following the C&E stuff
from a distance, and what with these postings and the timely arrival of
the book, even now staring at me across the table in its distinctive B&W
cover, seems I ought to give it a deeper look.

[...]
>----- Smart Pointer Feature Diagram  ----
>
>Draft of 12 July 2000
>
>smart-pointer  ( ownership
>                  release
>                  T-visability
>                  operations                     // dereference, get, etc.

I think that dereferencing will open up a whole set of possibilities, ie
result as raw pointer, some other kind of proxy (eg for locking), etc.

>                  size
>                  [multi-ptr-aquisition-safe]    // shared-in-ptr
>                )
>
>ownership      ( tightly-held    // scoped_ptr
>                | transferable    // auto_ptr
>                | shared          // shared_ptr, linked_ptr, etc.
>                | weak            // ??? weak_ptr
>                | copyable        // copy_ptr

Also: 'unowned'.

Would 'copyable' read better as 'copied'?

>                          )    
>
>release        ( non-array
>                | array
>                | user-supplied

Also: 'none' -- not all SPs have anything to do with ownership.

>                )
>
>T-visability   ( complete
>                | incomplete-OK-if-trivial-dtor
>                | incomplete-OK
>                )

sp: T-visibility?

>operations     ( with-conversion-to-T-star
>                | without-conversion-to-T-star
>                )                              

Is this to be extended to include the shopping list of possibilities
available for smart pointers or is it just for conversions?

>//  Choosing a size forces some of the other features.
>//  Likewise, Choosing some of the other features forces size.
>//  This may be an example of an "aspect"; I need to read C&E more
>//  to be sure
>size           ( one-ptr         // scoped_ptr, auto_ptr, copy_ptr
>                | two_ptr         // shared_ptr
>                | three_ptr       // linked_ptr
>                )
>
>shared         ( invasive-reference-count     // shared_in_ptr
>                | separate-reference-count     // shared_ptr
>                | linked-list                  // linked_ptr
>                )

Following slightly more traditional classification, and extending:

shared         ( attached-reference-count
                | detached-reference-count
                | linked-handles
                )

attached-reference-count
               ( invasive
                | non-invasive
                )

countable_ptr at http://www.boost.org/more/count_bdy.htm is an example
of a non-invasive attached-reference-count in this reckoning.

And where detached-reference-count == separate-reference-count.

>separate-reference-count
>                ( direct      // shared_ptr
>                | indirect    // like shared_ptr but ptr stored with count
>                )

There is another possibility for truly separate counting, where the
count is maintained quite independently of the handle, the body, or an
additional counter body, ie a manager object deals with the count and
the object.

This closely follows the reference counting classification I sketched
out and revised with Jim Coplien earlier this year on the back of an
envelope (or moral equivalent) in a bar at OT2000. Don't know whether
that's a good sign or not!
____________________________________________________________

  Kevlin Henney                   phone:  [phone]
  Curbralan Ltd                   mobile: [phone]
  kevlin_at_[hidden]            fax:    [phone]
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