Re: [boost] Re: ublas & custom containers?

From: Kresimir Fresl (fresl_at_[hidden])
Date: 2002-03-18 08:05:10

jhrwalter wrote:

[...]
> I imagine, that we could introduce here some (array_type_?)traits 
> classes, which define the iterators for valarray via partial 
> specialization.
[...]
> Ok, if all agree, that it would be useful to have std::valarray as 
> another array_type option, I'll try to add some traits logic to 
> support it at least under the more standard conforming compilers.

Some time ago I wrote a patch that extends Dietmar Kuehl's
`boost/array_traits.hpp' for `std::valarray<>'. Here are relevant
lines (diff format):

-------------------------------------------------------------------------------------
20a21,22
 > // Feb 23, 2001  Added std::valarray<T> support. --K. F.
 >
30a33,36
 > #ifndef NO_VALARRAY_SUPPORT
 > #  include <valarray>
 > #endif
 >
98a105,150
 >
 > #ifndef NO_VALARRAY_SUPPORT
 >
 >   // --- a special version for non-const valarray<T>s 
-----------------------
 >
 >   template <typename T>
 >     struct array_traits< std::valarray<T> >
 >     {
 >       typedef T* iterator;
 >       typedef iterator iter_type; // just for backward compatibility
 >       typedef T value_type;
 >       typedef value_type& reference;
 >       typedef std::size_t size_type;
 >       static iterator begin (std::valarray<T>& va) { return &va[0]; }
 >       static iterator end (std::valarray<T>& va) {
 >          return &va[0] + va.size();
 >       }
 >       static size_type size (std::valarray<T>& va) { return va.size(); }
 >     };
 >
 >   // --- a special version for const valarray<T>s ------------------
 >
 >   template <typename T>
 >     struct array_traits<std::valarray<T> const>
 >     {
 >       typedef T const* iterator;
 >       typedef iterator iter_type; // just for backward compatibility
 >       typedef std::size_t size_type;
 >       typedef T const value_type;
 >       typedef value_type& reference;
 >       typedef value_type* pointer;
 >       static iterator begin (std::valarray<T> const& cva) {
 >          std::valarray<T>& va = const_cast<std::valarray<T>&> (cva);
 >          return &va[0];
 >       }
 >       static iterator end (std::valarray<T> const& cva) {
 >          std::valarray<T>& va = const_cast<std::valarray<T>&> (cva);
 >          return &va[0] + va.size();
 >       }
 >       static size_type size (std::valarray<T> const& cva) {
 >          return cva.size();
 >       }
 >     };
 >
 > #endif // NO_VALARRAY_SUPPORT
--------------------------------------------------------------------------------------

`const_cast<std::valarray<T>&>()' in const version is needed
because `valarray<>::operator[] const' returns `T' and not
`T const&'. I hope that this code is legal -- it works with
g++ 3.0.4 and Comeau 4.2.45.2.

Now, with following changes to `ublas/vector.h':

--------------------------------------------------------------------------------------
24a25,26
 > #include <boost/array_traits.hpp>
 >
351,352c353,357
<         typedef typename A::const_iterator const_iterator_type;
<         typedef typename A::iterator iterator_type;
---
 > #ifndef NUMERICS_USE_INDEXED_ITERATOR
 >         typedef typename boost::array_traits<A const>::iterator
 >                      const_iterator_type;
 >         typedef typename boost::array_traits<A>::iterator iterator_type;
 > #endif
520c525
<             return const_iterator (*this, data_.begin () + i);
---
 >             return const_iterator (*this, boost::begin (data_) + i);
528c533
<             return iterator (*this, data_.begin () + i);
---
 >             return iterator (*this, boost::begin (data_) + i);
---------------------------------------------------------------------------------------------
`std::valarray<>' can be used as array_type in `numerics::vector<>'
without NUMERICS_USE_INDEXED_ITERATOR defined
(at least with g++ 3.0.4 && at least in some simple examples ;o).
BTW, `std::valarray<>' hasn't `insert()', `erase()' and `clear()' member
functions, but if corresponding functions in `numerics::vector<>' are
not used, this shouldn't be a problem.
Sincerely,
fres