[Boost-users] Re: indirect_iterator_generator and std::distanceambiguity

24 Sep 2003


      "Jeff Flinn"  writes:
...
Dave,
"David Abrahams"  wrote in message > "Jeff Flinn"
 writes:
...
...
I'm having problems compiling the code below with boost_1_30_2 and VC71
complaining about:
...\Microsoft Visual Studio .NET 2003\Vc7\include\xutility(489)
: error C2665: 'std::_Distance2'
: none of the 4 overloads can convert parameter 4
from type 'std::iterator_traits<_Iter>::iterator_category'
        with
        [
            _Iter=CDictionary::tVarConstItr
        ]
...
Replacing with std::distance( lBeg.base(), lItr.base() ) does compile
...
...
work properly. Am I missing something in the typedef of tVarConstItr
and
that
...
...
would allow direct usage?
No, you've got the order of the parameters to
indirect_iterator_generator wrong.
Thanks for spotting that. I entered them in the order listed in the Template
Parameters table rather than in the order specified in the Synopsis in the
documentation.
...
I suggest you let the library defaults take effect instead.
typedef boost::indirect_iterator_generator
< tVars::const_iterator
, tVar const
...
::type tVarConstItr;
typedef boost::indirect_iterator_generator
< tVars::const_iterator
, tVar
::iterator_category
...
::type tVarItr;
But you'll have a bigger problem.  IIRC the version of iterator
adaptors in 1.30.2 doesn't support indirect iterators over shared_ptr.
Go ahead and try it, but if you have trouble you may want to switch to
the (much easier-to-use) version of the library in the CVS, which
explicitly *does* support that usage.
Explicitly specifying all template parameters is what allows 1.30.2 to work
with shared_ptr's. I'm far from smart enough to figure this out on my own,
and took this tack based on one of your responses that I found doing a
search on relevant topics.
I gather that the new iterator adaptors will not have these issues. Will
they be in 1.31.0 recently brought up by Beman?
Absolutely.  You can preview them at
http://www.boost-consulting.com/boost/libs/iterator/doc

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com