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