Re: [Boost-users] [iterator] reverse_iterator from iterators thatreturn references to data in self.

15 Jul 2006

      "David Abrahams"  wrote in message
news:...
...
"Seb Martel"  writes:
...
Hello,
given something like:
class ProxyIterator
    : public boost::iterator_facade
{
public:
    ProxyIterator(FactoryOfCostly* pF, int i ) : m_pFactory( pF ),
m_index( i )
    {}
private:
    friend class boost::iterator_core_access;
    void decrement() {--m_index;}
    // ... and others
Costly& dereference() const
    {   
        m_value = m_pFactory->MakeCostlyAtIndex( m_index );
        return m_value;
    }
private:
    FactoryOfCostly* m_pFactory;
    int m_index;
    mutable Costly m_value;
};
You might need to do something to prevent this from being reported as
a valid random access (or even forward) iterator.  24.1.3:
--- If a and b are both dereferenceable, then a == b if and only if *a
      and *b are the same object.
As in &(*a) == &(*b) ? That's just cruel. But then again, vector<bool> 
comes to mind... Which reminds me: 

Is http://boost.org/libs/iterator/doc/new-iter-concepts.html making 
any progress ?
...
You could build a reverse_iterator like the one you propose by storing
the inner iterator within a boost::optional wrapper, and only
initializing it upon dereference.
I might just name it the DamnYou2413ReverseIterator.

Tx!

-seb