Re: [boost] [iterator] Silent-but-deadly bug in iterator_facade category

Subject: Re: [boost] [iterator] Silent-but-deadly bug in iterator_facade category
From: paul Fultz (pfultz2_at_[hidden])
Date: 2013-05-06 17:22:18

> 

> Does the problem lie with iterator_category_with_traversal?  It looks
> like it's intended in this case to be convertible to either
> std::input_iterator_tag or std::random_access_iterator_tag, but
> clearly something is wrong with the latter conversion.  Any ideas?
> 

The problem lies in the fact that your iterator when it calls `dereference()`,
returns something that is not a reference(ie char). For it to be a
`std::random_access_iterator_tag` it must a reference. That is,
`iterator_traits<X>::reference` must be an actual reference. So therefore your
iterator is given the `std::input_iterator_tag`, since it is the only iterator
category that doesn't require `dereference()` to return a reference. So then
when you call:

> std::advance(it, -1);

With an input iterator, it will, depending on the implementation and the build
type, either fail with a runtime assertion, or go into an infinite loop.

Thanks,
Paul