Fix for reference type deduction in join_iterator.hpp

[stheophil@…]

Changeset 70041 introduced a better reference type deduction for join_iterators (​https://svn.boost.org/trac/boost/changeset/70041) that was originally proposed by my colleague aschoedl.

The deduction contains a bug however that (I think) the attached patch fixes

[Nathan Ridge]

Could you please give an example of a piece of code that doesn't work as expected without this fix?

Thanks!

[stheophil@…]

I'm sorry it took so long for me to respond. The problem is easy to replicate:

typedef boost::join_iterator< 
   std::vector<int>::const_iterator, 
   std::vector<int>::iterator 
> JoinIterator;

static_assert( std::is_same< 
   typename JoinIterator::reference, 
   int const& 
>::value, "" );

The static_assert should not trigger but it does with the old implementation of join_iterator (using Visual Studio 2012). add_const< int& >::type is still int&. We need to remove the reference first, then add const then re-add the reference. (Or find an altogether better solution :-)

[Nathan Ridge]

(In [85400]) [range] Fixed a bug in join_iterator where joining a const range and a non-const range led to a compiler error (refs #8483).

[Nathan Ridge]

Thanks! Fixed in trunk.

[Neil Groves]

Hi Nathan! I see you have fixed this in the trunk. When you are happy would you please merge this to release and then close this ticket?

[Nathan Ridge]

I have already merged it to the 'master' branch in git: ​https://github.com/boostorg/range/commit/4c2898345972bd6c44c6b55abb386af931cc8fb5. I guess I need to close the bug manually now that we use git (with svn I would put "fixes #8483" in the commit message of the merge and it would auto-close the bug).