RE: [boost] filter iterator adaptor

From: Gary Powell (Gary.Powell_at_[hidden])
Date: 2001-01-23 13:12:35

> Looking forward to supporting more of the adaptors from the VTL,
> how about we add filter iterator to the iterator adaptors?
> 
Sounds like a good idea to me!
(Martin and I would like to convert VTL to use this design.
Martin is busy with his Ph.d. and I am busy with LL, but soon.)

> It looks like we need to add an initialize() function to the
> policies interface in order to do this.
> 
>   template <class Predicate, class Iterator>
>   class filter_iterator_policies : public default_iterator_policies {
>   public:
>     filter_iterator_policies() { }
> 
>     filter_iterator_policies(const Predicate& p, const Iterator& end) 
>       : m_predicate(p), m_end(end) { }
> 
>     void initialize(Iterator& x) {
>       while (!m_predicate(*x) && x != m_end)
>         ++x;
>     }
>     void increment(Iterator& x) {
>       ++x;
>       while (!m_predicate(*x) && x != m_end)	// if x == m_end *x is
> undefined.
>         ++x;
>     }
>   private:
>     Predicate m_predicate;
>     Iterator m_end;
>   };
> 
// Better to write an "advance"

void advance(itertype iter)
{
   while (m.end != iter &&	// test that it is valid first.
          !pred(*iter) ))
   ++iter;
}

  Yours,
 -gary-

gary.powell_at_[hidden]