Re: iterator adapters - member & memfun?

From: the_dilster (dylan_at_[hidden])
Date: 2001-12-06 17:23:12

--- In boost_at_y..., "David Abrahams" <david.abrahams_at_r...> wrote:
> 
> I presume you're talking about the iterator adapter library 
policies?
> 
> It should be pretty straightforward: You'd store the member 
function pointer
> in the policies class. A much simpler way to get there, though, 
might be to
> pass an instance of the standard adapters to transform_iterator or
> projection_iterator, whichever is appropriate.
> 
The problem was the interface - I wanted to be able to write no more 
than above to use it, or wasn't worth the effort.

> > For the curious, my initial implementation is exceedingly simple, 
ie:
> >
> > template <class T, class I, class C = I::value_type>
> > struct member_iterator : I
> > {
> >   member_iterator() { }
> >   member_iterator(const I& i, T C::* m = 0) : I(i), m_member(m) 
{ }
> >   T& operator* () { return I::operator*().*m_member; }
> > private:
> >   T C::* m_member;
> > };
> >
> > Which requires the use of a pointer_iterator wrapper for vectors 
(I
> > can't see how to avoid this anyway for certain compilers that 
don't
> > support partial specialisation).  It would be nice
> > if "pointer_iterator" was standard actually...or at least in 
boost...
> 
> ???
> Maybe you should describe what "pointer_iterator" is supposed to 
be...
> 
Um well, I thought it was kinda obvious...it's basically a wrapper 
around a raw pointer that supplies value_type, distance_type and 
iterator_category.  For implementations that use pointers for vector 
iterators, you just create pointer_vectors as needed and then 
templates that require the iterator typedef's will work correctly.
Really only needed because VC++ doesn't support iterator_traits 
properly.

Dylan