Hi Nate, Thanks for the response. I couldn't manage to compile the first solution (with the cast) but the second worked well. Thanks again. Miklós 2013/8/29 Nathan Crookston <nathan.crookston@gmail.com>
Hi Miklós,
Sorry for missing your first email.
Miklós Tóth wrote:
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.
<snip code>
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?
Those problems are usually due to the compiler not knowing which overload of the function to use. That can be solved using a static_cast (the bind documentation explains it pretty well [1])
Here's a solution that casts appropriately:
#include <boost/range/adaptors.hpp> #include <boost/range/algorithm.hpp> #include <boost/tuple/tuple.hpp> #include <functional> #include <iostream> #include <vector>
using boost::adaptors::transformed;
void print(int i) { std::cout << i << std::endl; }
int main() { typedef boost::tuple<int, float> Tuple; std::vector<Tuple> v; v.push_back(Tuple(5, 4.)); v.push_back(Tuple(6, 3.)); v.push_back(Tuple(7, 2.));
boost::for_each(v | transformed(std::mem_fun_ref( static_cast<int& (Tuple::*)()>(&Tuple::get<0>))), print); }
(It should work the same with transform_iterator, since I believe transformed eventually just forwards to it.)
To avoid casting, you might consider the following, using fusion and phoenix:
#include <boost/fusion/adapted/boost_tuple.hpp> #include <boost/phoenix.hpp> #include <boost/phoenix/fusion/at.hpp> #include <boost/range/adaptors.hpp> #include <boost/range/algorithm.hpp> #include <boost/tuple/tuple.hpp> #include <iostream> #include <vector>
using boost::adaptors::transformed; namespace px = boost::phoenix; using px::arg_names::_1;
void print(int i) { std::cout << i << std::endl; }
int main() { typedef boost::tuple<int, float> Tuple; std::vector<Tuple> v; v.push_back(Tuple(5, 4.)); v.push_back(Tuple(6, 3.)); v.push_back(Tuple(7, 2.));
boost::for_each(v | transformed(px::at_c<0>(_1)), &print); }
HTH, Nate
[1] < http://www.boost.org/doc/libs/1_54_0/libs/bind/bind.html#err_overloaded>
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