[iterator]counting_iterator question
I encountered some problems while using counting_iterator. Suppose we have a range called RangeType, and we define: typedef boost::counting_iterator< boost::range_value< RangeType >::type
MyCountingIterator;
if I do: std::vector< int > vec( 100 ); std::vector< int >:: iterator iter = vec.begin() + ( countingIter2 - counitingIter1 ); VC8 would then complain about a conversion from __int64 to int because the difference type of MyCountingIterator (using default) is __int64. Since we treat warnings as errors. I then changed MyCountingIterator to typedef boost::counting_iterator< boost::range_value< RangeType >::type, boost::use_default, boost::range_difference< RangeType >::type > MyCountingIterator; This time I got a different error: iterator_facade.hpp(554) : error C2784: '__w64 int boost::counting_iterator<Incrementable,CategoryOrTraversal,Difference>::distance_to(const boost::counting_iterator<OtherIncrementable> &) const' : could not deduce template argument for 'const boost::counting_iterator<OtherIncrementable> &' from 'const boost::counting_iterator<Incrementable,CategoryOrTraversal,Difference>' My question is why limiting the last three template parameters to default in counting_iterator::distance_to. Thanks, Sean
"Sean Huang" <huangsean@hotmail.com> writes:
My question is why limiting the last three template parameters to default in counting_iterator::distance_to.
Sorry, I don't understand the question. The only thing that's limited here is that you can only compare counting iterators that have the same CategoryOrTraversal and Difference parameters. That might be a bit shortsighted; maybe we should have additional template arguments to distance_to. -- Dave Abrahams Boost Consulting www.boost-consulting.com
From: "David Abrahams" dave@boost-consulting.com
"Sean Huang" <huangsean@hotmail.com> writes:
My question is why limiting the last three template parameters to default in counting_iterator::distance_to.
Sorry, I don't understand the question.
The only thing that's limited here is that you can only compare counting iterators that have the same CategoryOrTraversal and Difference parameters. That might be a bit shortsighted; maybe we should have additional template arguments to distance_to. Sorry, I meant the last TWO template parameters.
The distance_to is declared as: template < class OtherIncrementable > difference_type distance_to(counting_iterator<OtherIncrementable > const& y) const; My understanding is this is equivent to (correct me if I am wrong): template < class OtherIncrementable > difference_type distance_to(counting_iterator<OtherIncrementable, boost::use_default, boost::use_default > const& y) const; To do what you want, shouldn't it be: template < class OtherIncrementable > difference_type distance_to(counting_iterator<OtherIncrementable, CategoryOrTraversal, Difference > const& y) const; Maybe the compiler is wrong? Thanks, Sean
"Sean Huang" <huangsean@hotmail.com> writes:
To do what you want, shouldn't it be:
template < class OtherIncrementable > difference_type distance_to(counting_iterator<OtherIncrementable, CategoryOrTraversal, Difference > const& y) const;
Maybe the compiler is wrong?
You're right; this is certainly a bug. Would you care to submit a bug report at sourceforge? Thank you! -- Dave Abrahams Boost Consulting www.boost-consulting.com
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