Re: [Boost-users] boost::variant and SGI's compose1 cause constnesserror

From: Peter Dimov (pdimov_at_[hidden])
Date: 2005-07-06 12:23:20

junkmail.hoefling_at_[hidden] wrote:
> Hi there,
>
> I have a problem using boost::variant. I want apply_visitor to go
> through a list of pairs whose first type is a variant.
> Using compose1 and select1st from the SGI extensions to the STL
> yields a constness error. The problem is illustrated by
> the attached code which shoud be compiled with the g++ (the SGI
> extensions are here available via __gnu_cxx).
>
> What's wrong? Is it my fault using the library or is it a missing
> const version in apply_visitor_delayed_t()?

Judging by the comments in apply_visitor_delayed.hpp, it may be missing the 
const overloads on purpose... but I think that this is a mistake. FWIW,

for_each( v.begin(), v.end(),

  bind( apply_visitor(_dummy), bind<TMixed&>( &TPair::first, _1 ) )

);

works (when using boost/bind.hpp), but it isn't particularly elegant.