[Boost-users] [boost-users][tuple] Tuple::get<0> as std::mem_fun_ref

14 Aug 2013

      Hi!

I have a problem with std::mem_fun_ref and boost::tuple. Here is my code:
I have small LevelSetter class. It makes a level vector indexed by a
transform_iterator value.

template <typename LevelType>
class LevelSetter {
private:
    int nmb_of_elements;
public:
    LevelSetter(int nmb_of_elements_) : nmb_of_elements(nmb_of_elements_) {}

    template <typename TrRange>
    std::vector<LevelType> set(TrRange range) {
        typedef typename TrRange::first_type TrIter;
        std::vector<LevelType> levels(nmb_of_elements);
        for (TrIter it = range.first; it != range.second; ++it) {
            levels[*it] = 0.0;
        }
        // much more complicated code
        return levels;
    }
};

Let's call it:

class MemFunRefTest
{
private:

    typedef float Scalar;
    typedef boost::tuple<int, Scalar> Tuple;
    typedef std::vector<Tuple> Fwd;
    typedef Fwd::iterator FwdIter;
    typedef std::pair<FwdIter, FwdIter> FwdRange;

    Fwd elements;

public:
    MemFunRefTest() {
        elements.push_back(Tuple(0, 400.0));
        elements.push_back(Tuple(1, 120.0));
        elements.push_back(Tuple(2, 150.0));
    }

    void fun() {

        FwdRange element_range = std::make_pair(elements.begin(),
elements.end());

        LevelSetter<Scalar> setter(elements.size());
        setter.set(std::make_pair(
                       boost::make_transform_iterator(
                           element_range.first,
                           std::mem_fun_ref(&Tuple::get<0>)
                           ),
                       boost::make_transform_iterator(
                           element_range.second,
                           std::mem_fun_ref(&Tuple::get<0>)
                           )
                       )
                   );
    }
};

When I try to compile i get:

error: call of overloaded 'mem_fun_ref(<unresolved overloaded function
type>)' is ambiguous
candidates are:
c:\mingw-4.6\bin\..\lib\gcc\i686-pc-mingw32\4.6.1\..\..\..\..\include\c++\4.6.1\bits\stl_function.h:697:
std::mem_fun_ref_t<_Ret, _Tp> std::mem_fun_ref(_Ret (_Tp::*)()) [with
_Ret = int&, _Tp = boost::tuples::cons<int, boost::tuples::cons<float,
boost::tuples::null_type> >]
c:\mingw-4.6\bin\..\lib\gcc\i686-pc-mingw32\4.6.1\..\..\..\..\include\c++\4.6.1\bits\stl_function.h:702:
std::const_mem_fun_ref_t<_Ret, _Tp> std::mem_fun_ref(_Ret
(_Tp::*)()const) [with _Ret = const int&, _Tp =
boost::tuples::cons<int, boost::tuples::cons<float,
boost::tuples::null_type> >]

What am I missing?

Thanks, Miklos

[Boost-users] [boost-users][tuple] Tuple::get<0> as std::mem_fun_ref

Miklós Tóth