C++ Boost::MPL fold example - wrong number of arguments - c++

Question

I'd like to process some template arguments by using boost::mpl::fold. At the moment, I'm still stuck to the sample provided by Boost as even that does not work for me. I get the following error:
..\src\main.cpp:18:32: error: template argument 2 is invalid
..\src\main.cpp:18:37: error: wrong number of template arguments (4, should be 3)
The following code is taken from http://www.boost.org/doc/libs/1_48_0/libs/mpl/doc/refmanual/fold.html
#include <string>
#include <iostream>
#include <boost/mpl/fold.hpp>
#include <boost/mpl/plus.hpp>
#include <boost/mpl/vector.hpp>
#include <boost/type_traits.hpp>
using namespace std;
using namespace boost;
using namespace boost::mpl;
using namespace boost::type_traits;
typedef vector<long,float,short,double,float,long,long double> types;
typedef fold<
types
, int_<0>
, if_< is_float<_2>,next<_1>,_1 >
>::type number_of_floats;
BOOST_MPL_ASSERT_RELATION( number_of_floats::value, ==, 4 );
int main(){
}
I'm running mingw 4.7.0 using the flag "-std=c++11". I found some other examples on the net but have not yet been successful in compiling anything useful. Any suggestions?

Answer 1

You are messing up the namespaces. Making a lot of symbols ambiguous.
Remove the using and the example works fine for me.
...
using namespace boost;
typedef mpl::vector<long,float,short,double,float,long,long double> types;
typedef mpl::fold<
types
, mpl::int_<0>
, mpl::if_< is_float<boost::mpl::_2>,boost::mpl::next<boost::mpl::_1>,boost::mpl::_1 >
>::type number_of_floats;
...