[boost] Re: range addition - generic constructor

From: Neal Becker (ndbecker2_at_[hidden])
Date: 2004-09-12 16:26:23

Thorsten Ottosen wrote:

> "Neal Becker" <ndbecker2_at_[hidden]> wrote in message
> news:chvoo4$qbl$1_at_sea.gmane.org...
> | It is not unusual to need to construct a container from another where
> | one or the other doesn't comply with sequence.
> |
> | When generic code needs to convert to a container of unknown type (e.g.,
> | the return container type of a function is a template parameter), a
> | generic
> | constructor is useful, and could be part of range.  Here is the idea:
> |
> | #ifndef const_from_range_hpp
> | #define const_from_range_hpp
> |
> | #include <boost/range.hpp>
> | #include <algorithm>
> | #include <boost/numeric/ublas/vector.hpp>
> |
> | namespace detail {
> |   template<typename cont_t, typename range>
> |   struct construct_from_range_impl {
> |     cont_t operator() (range const& r) {
> |       return cont_t (boost::begin (r), boost::end (r));
> |     }
> |   };
> 
> Please see the "Utility" section of the docs. You would be looking for
> copy_range().
> 
> |   template<typename T, typename range>
> |   struct construct_from_range_impl<boost::numeric::ublas::vector<T>,
> |   range>
> | {
> |     typedef typename boost::numeric::ublas::vector<T> ret_t;
> |     ret_t operator() (range const& r) {
> |       ret_t v (boost::size (r));
> |       std::copy (boost::begin (r), boost::end (r), v.begin());
> 
> this can write past the end
> 
> |       return v;
> |     }
> |   };
> | }
> 
> hm..if ublas support is needed one could either do
> 
> 1. give ublas classes a constructor that takes two iterators
> 2. overload copy_range
> 
> I would prefer 1.
> 
How would 2 work?  copy_range is a function, so can't have a partial
specialization.  How would you overload for converting an arbitrary range
to ublas::vector<T>?