Re: [boost] [ptr_map] iterator changes, feedback welcome

From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 2006-02-22 15:32:25

Felipe Magno de Almeida <felipe.m.almeida <at> gmail.com> writes:

> 
> On 2/20/06, Bill Buklis <boostuser <at> pbjzone.com> wrote:
> 
> [snip]
> 
> > The only point of #1 is so that the iterators behave exactly like std::map
> > iterators, right? One the one hand, that would be nice for consistency with
> > std::map, but then this is a different class with slightly different uses,
> > so I personally don't mind if it has slightly different characteristics. And
> > the usefulness of operator-> as T* outweighs the need for identical
> > behavior, IMO.
> 
> I had some issues with using std::ptr_map in generic algorithms because of 
this.
> I think that the inner typedef's of std::ptr_map, wrt iterator concept
> modelling, must be carefully choosed too. That can break a lot of
> generic code to not work on ptr_map or other ptr_containers.

What specific problems did you have?

Let's assume I simply base the implementation on std::ptr<key,T*> so
that I can just reuse the existing iterators.

It worries me that the pointer now becomes exposed. One might write
a copy-algorithm for std::map<key,T*>, std::map<key,shared_ptr<T>>
and ptr_map<key,T>.

Trying to do that leads major problems. Of course, what if the algorithm
only searches and call members, but does copy anything it works ok.

-Thorsten