Re: [boost] [fusion] [intro] ADAPT_STRUCT extensions

Subject: Re: [boost] [fusion] [intro] ADAPT_STRUCT extensions
From: David Sankel (camior_at_[hidden])
Date: 2010-08-11 21:46:54

On Sat, Jul 31, 2010 at 9:02 AM, Christopher Schmidt <
mr.chr.schmidt_at_[hidden]> wrote:

> Joel de Guzman schrieb:
> > On 7/30/2010 6:35 AM, Stefan Strasser wrote:
> >> Zitat von Hartmut Kaiser <hartmut.kaiser_at_[hidden]>:
> >>> Have you seen the new BOOST_FUSION_ADAPT_CLASS() family of utilities
> >>> which
> >>> allow using (member-) functions instead of direct access to the data
> >>> members
> >>> of a class/struct?
> >>
> >> no I had not, I was using 1.41. where can I see those? can't seem to
> >> find them in 1.43 or
> >> the trunk.
>
> The BOOST_FUSION_ADAPT_xxxCLASSxxx-macros are not documented yet. For
> more information, refer to the code and the testcases:
>
> https://svn.boost.org/trac/boost/browser/trunk/boost/fusion/adapted/class
> https://svn.boost.org/trac/boost/browser/trunk/libs/fusion/test/sequence
>
> https://svn.boost.org/trac/boost/browser/trunk/libs/fusion/test/sequence/adapt_class.cpp

I think the ADAPT_CLASS macros fundamentally change the expected behavior of
struct adaptation in a negative way. A non-template class/struct is a
collection of

 a) types (declared as nested typedefs or other structs)
 b) values of the following variety
      i) static member variables (values that are non-functions)
      ii) static member functions (values that are functions)
      iii) member functions (values that are "special" functions over the
instance record)
 c) an instance record, which includes member variables

Up until this point, struct adaptation has exclusively been over the
instance record, point c) above. This is very simple to understand and
implies exactly one canonical adaptation for every struct/class.

ADAPT_CLASS mixes point c) and point iii) in an arbitrary way. Stefan's
suggestions, on the other hand, are a straightforward extension of the
original semantics. I'd personally like to see the latter incorporated and
the former removed.

David

-- 
David Sankel
Sankel Software
www.sankelsoftware.com
585 617 4748 (Office)