Re: [Boost-users] Another sub_range problem

From: abir basak (abirbasak_at_[hidden])
Date: 2006-12-04 01:00:18

abir basak wrote:
> Hi,
>    I am facing some more range problem from boost::range;
> According to the CVS RC_1_34 works. Revision 1.21 version specified by 
> Thorsten Ottosen , most of the classes work.
> What is my interest is to have a get_range function inside some of the 
> container class like std::vector  and boost::circular_buffer (from boost 
> CVS)
> Here I have test class to show the problem I am facing.
> First, when I inherit from a vector , and specify a range function just 
> like iterator functions ( begin() and end() )
> 
> template<typename T>
> class range_vector : public std::vector<T>{
> public:
>    typedef boost::sub_range<range_vector> range;
>    typedef boost::sub_range<const range_vector> const_range;
>    range get_range(size_type from,size_type to){
> 	std::cout<<"range"<<std::endl;
> 	return range(begin()+from,begin()+to);
>    }
>    const_range get_range(size_type from,size_type to)const{
> 	std::cout<<"const range"<<std::endl;
> 	return const_range(begin()+from,begin()+to);
>    }
> };
> int main(){
>    range_vector<int> v;
>    int x[] = {0,1,2,3,4,5,6,7,8};
>    v.insert(v.end(),x,x+9);
>    std::copy(v.begin(),v.end(),std::ostream_iterator<int>(std::cout," "));
>    std::cout<<std::endl;
>    range_vector<int>::range r = v.get_range(1,5);
>    r[0] = 100;
>    copy(r.begin(),r.end(),std::ostream_iterator<int>(std::cout," "));
>    std::cout<<std::endl;
>    range_vector<int>::const_range cr = v.get_range(1,5);
>    copy(cr.begin(),cr.end(),std::ostream_iterator<int>(std::cout," "));
>    std::cout<<std::endl;
>    const range_vector<int>& cv = v;
>    range_vector<int>::const_range cr1 = cv.get_range(1,5);
>    copy(cr.begin(),cr.end(),std::ostream_iterator<int>(std::cout," "));
>    std::cout<<std::endl;
> }
> This code compiles perfectly and gives result as expected. It also works 
> with deque .
> 
> However when I compile the same code for boost::circular_buffer,i.e
> template<typename T>
> class range_vector : public boost::circular_buffer<T>{
> public:
>    typedef boost::sub_range<range_vector> range;
>    typedef boost::sub_range<const range_vector> const_range;
>    range get_range(size_type from,size_type to){
> 	std::cout<<"range"<<std::endl;
> 	return range(begin()+from,begin()+to);
>    }
>    const_range get_range(size_type from,size_type to)const{
> 	std::cout<<"const range"<<std::endl;
> 	return const_range(begin()+from,begin()+to);
>    }
> };
> It has a same interface that of a vector, it fails to compile when I 
> call the non-const get_range function.
> i.e
> //Initialized the circular_buffer with a few elements.
> range_vector<int> v;
>    int x[] = {0,1,2,3,4,5,6,7,8};
>    v.insert(v.end(),x,x+9);
>    std::copy(v.begin(),v.end(),std::ostream_iterator<int>(std::cout," "));
>    std::cout<<std::endl;
> 
> ///got a const reference and invoking const version of get_range. works 
> fine.
> const range_vector<int>& cv = v;
>    range_vector<int>::const_range cr1 = cv.get_range(1,5);
>    copy(cr1.begin(),cr1.end(),std::ostream_iterator<int>(std::cout," "));
>    std::cout<<std::endl;
> ///now trying to get a non-const version
>   range_vector<int>::range r = v.get_range(1,5);
> Here it gives error in Visual Studio
> e:\boost_1_33_1\boost\range\iterator_range.hpp(60): error C2440: 'type 
> cast' : cannot convert from 'boost::range_iterator<C>::type' to 
> 'boost::range_iterator<C>::type'
>          with
>          [
>              C=const boost::sub_range<range_vector<int>>
>          ]
>          and
>          [
>              C=range_vector<int>
>          ]
> 
> 
> ///now trying to get a non-version and assign it to const version
>   range_vector<int>::const_range r = v.get_range(1,5);
> It gives the same error.
> Here C (container) is passed as correct one. begin() and end() are too 
> executes correct version (non-const one).
> Not getting why it won't work.
> 
> Any kind of help is highly appreciated.
> Thanks to boost community in advance.
> 
> abir basak
To make the problem little clearer,
typedef boost::circular_buffer<int> cbi;
typedef std::vector<int> vi;
This code works,
boost::sub_range<vi> get_range(vi& v,int from,int to){
   return boost::sub_range<vi>(v.begin()+from,v.begin()+to);
}
But this don't.
boost::sub_range<cbi> get_range(cbi& v,int from,int to){
   return boost::sub_range<cbi>(v.begin()+from,v.begin()+to);
}

-- 
Abir Basak, Member IEEE
Software Engineer, Read Ink Technologies
B. Tech, IIT Kharagpur
email: abir_at_[hidden]
homepage: www.abirbasak.com