[Boost-users] [iterator] unrelated type problem with iterator_facade arrow operator

Subject: [Boost-users] [iterator] unrelated type problem with iterator_facade arrow operator
From: Michael Fawcett (michael.fawcett_at_[hidden])
Date: 2009-03-19 17:47:53

Can someone confirm if the attached code doesn't compile intentionally
or if this is a bug?  I'm sorry for not posting a minimal example but
I couldn't figure out how to reduce the problem.  It requires Windows
(uses ATL::CAdapt and ATL::CComBSTR) and I've tested using VS 2005 and
VS2008.  This bug manifests when the Reference type has overloaded the
address-of operator to return a type not implicitly convertible to
Value * (I believe).

Changing lines 324-326 in iterator_facade.hpp from:

        static type make(Reference x)
        {
            return implicit_cast<type>(&x);
        }

to:

        static type make(Reference x)
        {
            return implicit_cast<type>(boost::addressof(x));
        }

and adding the appropriate include makes the attached code compile.

Full error log below:

1>c:\dev\vendor\boost\1.37.0\boost\iterator\iterator_facade.hpp(326) :
error C2664: 'boost::implicit_cast' : cannot convert parameter 1 from
'BSTR *' to 'ATL::CComBSTR *'
1>        Types pointed to are unrelated; conversion requires
reinterpret_cast, C-style cast or function-style cast
1>        c:\dev\vendor\boost\1.37.0\boost\iterator\iterator_facade.hpp(325)
: while compiling class template member function 'ATL::CComBSTR
*boost::detail::operator_arrow_result<ValueType,Reference,Pointer>::make(Reference)'
1>        with
1>        [
1>            ValueType=ATL::CComBSTR,
1>            Reference=ATL::CComBSTR &,
1>            Pointer=ATL::CComBSTR *
1>        ]
1>        c:\dev\vendor\boost\1.37.0\boost\iterator\iterator_facade.hpp(641)
: see reference to class template instantiation
'boost::detail::operator_arrow_result<ValueType,Reference,Pointer>'
being compiled
1>        with
1>        [
1>            ValueType=ATL::CComBSTR,
1>            Reference=ATL::CComBSTR &,
1>            Pointer=ATL::CComBSTR *
1>        ]
1>        c:\dev\vendor\boost\1.37.0\boost\iterator\iterator_adaptor.hpp(271)
: see reference to class template instantiation
'boost::iterator_facade<Derived,Value,CategoryOrTraversal,Reference,Difference>'
being compiled
1>        with
1>        [
1>            Derived=test::atl::CAdapt_iterator<std::_Vector_iterator<ATL::CAdapt<ATL::CComBSTR>,std::allocator<ATL::CAdapt<ATL::CComBSTR>>>>,
1>            Value=ATL::CComBSTR,
1>            CategoryOrTraversal=std::random_access_iterator_tag,
1>            Reference=ATL::CComBSTR &,
1>            Difference=__w64 int
1>        ]
1>        c:\dev\personal\boost\iterator_adaptor_bug\main.cpp(65) :
see reference to class template instantiation
'boost::iterator_adaptor<Derived,Base,Value,Traversal,Reference>'
being compiled
1>        with
1>        [
1>            Derived=test::atl::CAdapt_iterator<std::_Vector_iterator<ATL::CAdapt<ATL::CComBSTR>,std::allocator<ATL::CAdapt<ATL::CComBSTR>>>>,
1>            Base=std::_Vector_iterator<ATL::CAdapt<ATL::CComBSTR>,std::allocator<ATL::CAdapt<ATL::CComBSTR>>>,
1>            Value=ATL::CComBSTR,
1>            Traversal=std::random_access_iterator_tag,
1>            Reference=ATL::CComBSTR &
1>        ]
1>        c:\dev\personal\boost\iterator_adaptor_bug\main.cpp(103) :
see reference to class template instantiation
'test::atl::CAdapt_iterator<Iterator>' being compiled
1>        with
1>        [
1>            Iterator=std::_Vector_iterator<ATL::CAdapt<ATL::CComBSTR>,std::allocator<ATL::CAdapt<ATL::CComBSTR>>>
1>        ]

Thanks for any insight,

--Michael Fawcett