Re: [Boost-users] boost.iterators - iterator_facade issue with aligned types.

Subject: Re: [Boost-users] boost.iterators - iterator_facade issue with aligned types.
From: Dave Abrahams (dave_at_[hidden])
Date: 2011-01-19 13:12:19

At Wed, 19 Jan 2011 14:36:24 +0100,
Christoph Heindl wrote:
> 
> It seems to me that boost::iterator_facade cannot cope with aligned types
> when the 'Reference = use_default' template argument is not a reference,
> which can happen if transform_iterator is used to return the result of a
> temporay calculation (by value of course).
> 
> Inside iterator_facade.hpp
> 
> struct operator_arrow_result {
>   //...
>         static type make(Reference x)
>         {
>             return implicit_cast<type>(&x);
>         }
> };
> 
> Reference here is passed by value. Since Reference has alignment the compiler
> reports an error.
> 
> The issue was resolved once i changed that code to
> 
> struct operator_arrow_result {
>   //...
>         typedef typename mpl::if_<
>             is_reference<Reference>
>           , Reference
>           , typename add_reference<Reference>::type
>         >::type input_type;
> 
>         static type make(input_type x)
>         {
>             return implicit_cast<type>(&x);
>         }
> };
> 
> I wonder about any side effects this would cause? My lousy research is based
> boost 1.43. That part of the code seems to be unchanged for the current trunk.

I *think* that change is safe to make.  Care to submit it as a patch
at http://svn.boost.org/ ?

Thanks!

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com