[Boost-users] [Iterators] Change in transform_iterator from 1.31 to 1.32?

From: Nat Goodspeed (ngoodspeed_at_[hidden])
Date: 2005-07-26 14:54:03

We have a class that contains a std::map. This class wants to provide
its clients with iterators over just the values in the map, hiding the
fact that there's a map under the covers at all. transform_iterator
seems like just the ticket, and with Boost 1.31 we used these methods:

    typedef std::map<KEYTYPE, VALUETYPE> MapType;

    typedef boost::transform_iterator<
        boost::function<const MapType::mapped_type&(const
MapType::value_type&)>,
        MapType::const_iterator
    > const_iterator;

    const_iterator begin() const
    {
        return boost::make_transform_iterator(mymap.begin(),
boost::bind(&MapType::value_type::second, _1));
    }

    const_iterator end() const
    {
        return boost::make_transform_iterator(mymap.end(),
boost::bind(&MapType::value_type::second, _1));
    }

The above compiled cleanly, except when it caused a compiler ICE, and
the instances that compile seem to run okay.

Now we're trying to upgrade to Boost 1.32 -- I know, a little late in
the 1.32 lifespan. The same code now produces an ominous warning (full
text at end of message):

c:/videobranch\boost\boost\function\function_template.hpp(111) : warning
C4172: returning address of local variable or temporary

When it finally gets around to mentioning a line number in our own
source code, the indicated line is the return statement in the above
begin() method.

The reason I'm concerned is that when compiled with Boost 1.32, our
program suffers mysterious crashes that it did not when compiled with
Boost 1.31. 
:-(

I don't *know* that this warning is related, but I thought it prudent to
try to eliminate such warnings to see if that might help. I can't figure
out what temporary is driving the warning, though. I tried factoring out
our own code a couple of different ways without making the warning go
away.

Can you suggest anything?

Platform: Microsoft Windows XP Pro
Compiler: Microsoft Visual C++ .NET, aka 7.1

*** Message ends; what follows is Microsoft warning output ***

cl /EHsc /I c:/videobranch/boost $FF
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 13.10.3077 for
80x86
Copyright (C) Microsoft Corporation 1984-2002. All rights reserved.

WrapMap.cpp
c:/videobranch\boost\boost\function\function_template.hpp(111) : warning
C4172: returning address of local variable or temporary
c:/videobranch\boost\boost\function\function_template.hpp(109) : while
compiling class-template member function 'const int
boost::detail::function::function_obj_invoker1<FunctionObj,R,T0>::invoke
(boost::detail::function::any_pointer,T0)'
        with
        [
 
FunctionObj=boost::_bi::bind_t<int,boost::_mfi::dm<int,std::pair<const
std::string,int>>,boost::_bi::list1<boost::_bi::list_av_1<boost::arg<1>>
::B1>>,
            R=const int &,
            T0=const std::pair<const std::string,int> &
        ]
        c:/videobranch\boost\boost\function\function_template.hpp(482) :
see reference to class template instantiation
'boost::detail::function::function_obj_invoker1<FunctionObj,R,T0>' being
compiled
        with
        [
 
FunctionObj=boost::_bi::bind_t<int,boost::_mfi::dm<int,std::pair<const
std::string,int>>,boost::_bi::list1<boost::_bi::list_av_1<boost::arg<1>>
::B1>>,
            R=const int &,
            T0=const std::pair<const std::string,int> &
        ]
        c:/videobranch\boost\boost\function\function_template.hpp(433) :
see reference to function template instantiation 'void
boost::function1<R,T0,Allocator>::assign_to<Functor>(FunctionObj,boost::
detail::function::function_obj_tag)' being compiled
        with
        [
            R=const int &,
            T0=const std::pair<const std::string,int> &,
            Allocator=std::allocator<void>,
 
Functor=boost::_bi::bind_t<int,boost::_mfi::dm<int,std::pair<const
std::string,int>>,boost::_bi::list1<boost::_bi::list_av_1<boost::arg<1>>
::B1>>,
 
FunctionObj=boost::_bi::bind_t<int,boost::_mfi::dm<int,std::pair<const
std::string,int>>,boost::_bi::list1<boost::_bi::list_av_1<boost::arg<1>>
::B1>>
        ]
        c:/videobranch\boost\boost\function\function_template.hpp(289) :
see reference to function template instantiation 'void
boost::function1<R,T0,Allocator>::assign_to<Functor>(Functor)' being
compiled
        with
        [
            R=const int &,
            T0=const std::pair<const std::string,int> &,
            Allocator=std::allocator<void>,
 
Functor=boost::_bi::bind_t<int,boost::_mfi::dm<int,std::pair<const
std::string,int>>,boost::_bi::list1<boost::_bi::list_av_1<boost::arg<1>>
::B1>>
        ]
        c:/videobranch\boost\boost\function\function_template.hpp(649) :
see reference to function template instantiation
'boost::function1<R,T0,Allocator>::function1<UnaryFunction>(Functor,boos
t::enable_if_c<B,T>::type)' being compiled
        with
        [
            R=const int &,
            T0=const std::pair<const std::string,int> &,
            Allocator=std::allocator<void>,
 
UnaryFunction=boost::_bi::bind_t<int,boost::_mfi::dm<int,std::pair<const
std::string,int>>,boost::_bi::list1<boost::_bi::list_av_1<boost::arg<1>>
::B1>>,
 
Functor=boost::_bi::bind_t<int,boost::_mfi::dm<int,std::pair<const
std::string,int>>,boost::_bi::list1<boost::_bi::list_av_1<boost::arg<1>>
::B1>>,
            B=true,
            T=int
        ]
        c:/videobranch\boost\boost\iterator\transform_iterator.hpp(130)
: see reference to function template instantiation
'boost::function<Signature>::function<UnaryFunction>(Functor,boost::enab
le_if_c<B,T>::type)' being compiled
        with
        [
            Signature=const std::map<std::string,int>::mapped_type
&(const std::map<std::string,int>::value_type &),
 
UnaryFunction=boost::_bi::bind_t<int,boost::_mfi::dm<int,std::pair<const
std::string,int>>,boost::_bi::list1<boost::_bi::list_av_1<boost::arg<1>>
::B1>>,
 
Functor=boost::_bi::bind_t<int,boost::_mfi::dm<int,std::pair<const
std::string,int>>,boost::_bi::list1<boost::_bi::list_av_1<boost::arg<1>>
::B1>>,
            B=true,
            T=int
        ]
        WrapMap.cpp(20) : see reference to function template
instantiation
'boost::transform_iterator<UnaryFunction,Iterator>::transform_iterator<b
oost::_bi::bind_t<R,F,L>,std::_Tree<_Traits>::const_iterator,boost::use_
default,boost::use_default>(const
boost::transform_iterator<boost::_bi::bind_t<R,F,L>,Iterator,Reference,V
alue> &,boost::iterators::enabled<__formal>::base<T>::type *)' being
compiled
        with
        [
            UnaryFunction=boost::function<const
std::map<std::string,int>::mapped_type &(const
std::map<std::string,int>::value_type &)>,
            Iterator=std::map<std::string,int>::const_iterator,
            R=int,
            F=boost::_mfi::dm<int,std::pair<const std::string,int>>,
 
L=boost::_bi::list1<boost::_bi::list_av_1<boost::arg<1>>::B1>,
 
_Traits=std::_Tmap_traits<std::string,int,std::less<std::string>,std::al
locator<std::pair<const std::string,int>>,false>,
            Reference=boost::use_default,
            Value=boost::use_default,
            __formal=true,
            T=boost::detail::enable_type
        ]