Re: [boost] [multi_index] use cases for iterator_to()

From: Bruno Martínez Aguerre (br1_at_[hidden])
Date: 2007-06-07 23:35:00

On Thu, 17 May 2007 16:04:57 -0300, JOAQUIN LOPEZ MU?Z <joaquin_at_[hidden]>  
wrote:

> More than a year ago a request was made for
> Boost.MultiIndx to provide the ability to
> get an iterator to an element x from x alone:
>
> iterator iterator_to(const value_type& x);

It was me, I think.

> I can provide this functionality in constant time,
> and the internal implementation is trivial, but
> I got thinking about the potential use cases for
> such capability and cannot come up with something
> convincing.
>
> Do you see usefulness in having iterator_to()?
> Can you describe a potential usage scenario? At
> first blush, seems like this is at least as useful
> as the homonym functionality in Boost.Intrusive,
> but if you think about the obvious scenarios
> applying to B.I, it turns out they do not immediately
> translate to B.MI.

Yes.  My use case was  
http://thread.gmane.org/gmane.comp.lib.boost.devel/136418/focus=136955

However, now that I look at it, it seems iterator_to is not a solution to  
that problem.

I still think the feature is usefull.  For example, you may be forced to  
pass a raw pointer to a C interface.  With iterator_to you can get the  
position of the element in a collection without overhead.

Bruno