Re: [Boost-users] zip_iterator and sTL algorithms like random_shuffle

Subject: Re: [Boost-users] zip_iterator and sTL algorithms like random_shuffle
From: Andreas Fabri (andreas.fabri_at_[hidden])
Date: 2009-03-31 06:59:03

Hi Steven,

Adding a specialization for iter_swap

typedef boost::tuple<
   std::vector<int>::iterator,
   std::vector<int>::iterator
   > iterator_tuple;

typedef boost::zip_iterator<
   iterator_tuple
   > ziterator;

namespace std {

   void
   iter_swap(ziterator a, ziterator b)
   {
     std::swap(a->get<0>(), b->get<0>());
     std::swap(a->get<1>(), b->get<1>());
   }

}

solved the problem for std::random_shuffle.

For std::sort  I provide a comparison functor for the tuple.
but the compiler (VC8) complains about no match for _Rotate

Any hint would be appreciated.

andreas

C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1719) : error C2665: 'std::_Rotate' : none of the 3 overloads could convert all the argument types
         C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1649): could be 'void std::_Rotate<_FwdIt>(_FwdIt,_FwdIt,_FwdIt,std::forward_iterator_tag)'
         with
         [
             _FwdIt=boost::zip_iterator<iterator_tuple>
         ]
         C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1666): or 'void std::_Rotate<_FwdIt>(_BidIt,_BidIt,_BidIt,std::bidirectional_iterator_tag)'
         with
         [
             _FwdIt=boost::zip_iterator<iterator_tuple>,
             _BidIt=boost::zip_iterator<iterator_tuple>
         ]
         C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1709): or 'void std::_Rotate<_FwdIt>(_RanIt,_RanIt,_RanIt,std::random_access_iterator_tag)'
         with
         [
             _FwdIt=boost::zip_iterator<iterator_tuple>,
             _RanIt=boost::zip_iterator<iterator_tuple>
         ]
         while trying to match the argument list '(boost::zip_iterator<IteratorTuple>, boost::zip_iterator<IteratorTuple>, boost::zip_iterator<IteratorTuple>, 
boost::detail::iterator_category_with_traversal<Category,Traversal>)'
         with
         [
             IteratorTuple=iterator_tuple
         ]
         and
         [
             IteratorTuple=iterator_tuple
         ]
         and
         [
             IteratorTuple=iterator_tuple
         ]
         and
         [
             Category=std::input_iterator_tag,
             Traversal=boost::random_access_traversal_tag
         ]
         C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(3125) : see reference to function template instantiation 'void 
std::rotate<_BidIt>(_FwdIt,_FwdIt,_FwdIt)' being compiled
         with
         [
             _BidIt=boost::zip_iterator<iterator_tuple>,
             _FwdIt=boost::zip_iterator<iterator_tuple>
         ]
         C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(3252) : see reference to function template instantiation 'void 
std::_Insertion_sort<_RanIt,_Pr>(_BidIt,_BidIt,_Pr)' being compiled
         with
         [
             _RanIt=boost::zip_iterator<iterator_tuple>,
             _Pr=Compare,
             _BidIt=boost::zip_iterator<iterator_tuple>
         ]
         C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(3261) : see reference to function template instantiation 'void 
std::_Sort<_RanIt,__int64,_Pr>(_RanIt,_RanIt,_Diff,_Pr)' being compiled
         with
         [
             _RanIt=boost::zip_iterator<iterator_tuple>,
             _Pr=Compare,
             _Diff=__int64
         ]

Steven Watanabe wrote:
> AMDG
> 
> Andreas Fabri wrote:
>> I have two vectors and want to random_shuffle them the same way
>> using the zip_iterator.  I thought the code below would do it,
>> but when I execute it I see that both sequences get screwded up.
>>
>> What do I wrong?
> 
> The problem is that std::iter_swap doesn't work
> for zip_iterator and there is no standard compliant
> way to fix it.
> 
> In Christ,
> Steven Watanabe
> 
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