Re: [Boost-bugs] [Boost C++ Libraries] #8489: Unnecessary Definition of iterator_adaptor.hpp class Has Dangerous Return of Temporary Object

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #8489: Unnecessary Definition of iterator_adaptor.hpp class Has Dangerous Return of Temporary Object
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-06-10 04:58:31

#8489: Unnecessary Definition of iterator_adaptor.hpp class Has Dangerous Return
of Temporary Object
-------------------------------------------+------------------------------
  Reporter:  Jeffrey D. Oldham <oldham@…>  |      Owner:  jeffrey.hellrung
      Type:  Bugs                          |     Status:  new
 Milestone:  To Be Determined              |  Component:  iterator
   Version:  Boost 1.53.0                  |   Severity:  Problem
Resolution:                                |   Keywords:
-------------------------------------------+------------------------------

Comment (by dave):

 The problem here is that the underlying iterator of the
 {{{iterator_adaptor}}} is an {{{istreambuf_iterator<char>}}}, which quite
 legitimately (for an input iterator) returns a non-reference type from its
 {{{operator*}}}.  This should be filed as a bug against Spirit.

 To debug it, I applied this patch to iterator_adaptor.hpp, and ran the
 failing program through stlfilt:

 {{{
 #!diff
 --- iterator_adaptor.hpp        2013-06-09 20:32:52.000000000 -0700
 +++
 /Users/dave/src/boost/release/boost_1_53_0/boost/iterator/iterator_adaptor.hpp
 2013-06-09 21:42:48.000000000 -0700
 @@ -18,9 +18,11 @@
  #include <boost/mpl/and.hpp>
  #include <boost/mpl/not.hpp>
  #include <boost/mpl/or.hpp>
 +#include <boost/mpl/assert.hpp>

  #include <boost/type_traits/is_same.hpp>
  #include <boost/type_traits/is_convertible.hpp>
 +#include <boost/type_traits/is_reference.hpp>

  #ifdef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY
  # include <boost/type_traits/remove_reference.hpp>
 @@ -303,7 +305,20 @@
        // base_reference(), above, to get direct access to m_iterator.
        //
        typename super_t::reference dereference() const
 -        { return *m_iterator; }
 +      {
 +          BOOST_MPL_ASSERT((
 +              mpl::or_<
 +                  mpl::not_<is_reference<typename super_t::reference> >
 +                , is_reference<
 +#ifdef BOOST_NO_CXX11_DECLTYPE
 +                    typename boost::iterator_reference<Base>::type
 +#else
 +                    decltype(*m_iterator)
 +#endif
 +                  >
 +              >));
 +          return *m_iterator;
 +      }

        template <
        class OtherDerived, class OtherIterator, class V, class C, class R,
 class D
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/8489#comment:7>
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