Hi,
I am implementing something similar to python’s enumerate using boost iterator adapter, but I am running into two problems I am unable to solve. Both problems use my Enumerate-adaptor defined as:
#include <utility>
#include <boost/iterator/iterator_adaptor.hpp>
namespace Iterator
{
// some simple wrapper to have better names than std::pair
template<typename T, typename X>
struct Enumerated
{
Enumerated(T i, X x):
count(i),
value(x)
{
}
T count;
X value;
};
template< typename Iterator, typename T = typename Iterator::difference_type>
class Enumerator:
public boost::iterator_adaptor<Enumerator<Iterator, T>,
Iterator,
Enumerated<T, typename Iterator::value_type>,
boost::use_default,
Enumerated<T, typename Iterator::reference> >
{
public:
Enumerator():
mCount(),
mPos(),
mStep()
{
}
template<typename It>
explicit Enumerator(It i, T start=T(), T step=T(1) ):
mCount(start),
mPos(i),
mStep(step)
{
}
private:
friend class boost::iterator_core_access;
Enumerated<T, typename Iterator::reference > dereference() const
{
return Enumerated<T, typename Iterator::reference >(mCount, *mPos);
}
Enumerated<T, typename Iterator::reference > dereference()
{
return Enumerated<T, typename Iterator::reference >(mCount, mPos);
}
bool equal(Enumerator<Iterator, T> const& other) const
{
return mPos == mPos;
}
void increment()
{
mCount += mStep;
mPos += 1;
}
void decrement()
{
mCount -= mStep;
mPos -= 1;
}
void advance(typename Iterator::difference_type step)
{
mCount += step * mStep;
mPos += step;
}
typename Iterator::difference_type distance_to(Enumerator<Iterator, T> const& other) const
{
return std::distance(mPos, other.mPos);
}
T mCount;
Iterator mPos;
typename Iterator::difference_type mStep;
};
template<typename Iterator, typename T>
Enumerator<Iterator, T> enumerate(Iterator i, T start=0, T step=1)
{
return Enumerator<Iterator, T>(i, start, step);
}
When I compile the following sample program, msvc (VS2010) prints an error, but g++ does not have any problems.
#include <vector>
#include <iostream>
#include <algorithm>
void foo()
{
std::vector<int> v;
auto i = Iterator::enumerate(v.begin(), 0, 1);
auto j = Iterator::enumerate(v.end(), 0, 1);
std::for_each( i, j, [](decltype(*i) e)
{
std::cout << e.count << ", " << e.value << std::endl;
});
}
Error 1 error C2665: 'std::_Debug_range2' : none of the 2 overloads could convert all the argument types d:\programme\microsoft visual studio 10.0\vc\include\xutility 728
My second problem can be reproduced with the following sample program on both msvc and g++:
#include <vector>
#include <iostream>
#include <algorithm>
void foo()
{
std::vector<int> v;
auto i = Iterator::enumerate(v.begin(), 0, 1);
auto y = i->count;
auto z = i->value;
}
MSVC:
Error 3 error C2664: 'boost::implicit_cast' : cannot convert parameter 1 from 'Iterator::Enumerated<T,X> *' to 'boost::detail::operator_arrow_proxy<T>' c:\software development\externals\include\boost\iterator\iterator_facade.hpp 326