At Sat, 16 Apr 2011 21:35:29 +0900, Andrej van der Zee wrote:

Hi Dave,

Thank you for your email.

...

You misspelled "distance_to."  Fix the spelling and it should work better.

Indeed a typo. Unfortunately, changing it to the method below does not change anything. The method is never called even though I explicitly call std::distance(), which, I assume, should call eventually distance_to(),

facade_t::difference_type distance_to(const data_stream::const_iterator & to) const { abort(); }

Not unless yours is a random access iterator. Is it? -- Dave Abrahams BoostPro Computing http://www.boostpro.com

At Sun, 17 Apr 2011 08:43:00 +0900, Andrej van der Zee wrote:

Hi Dave,

Thanks for your email.

...

Not unless yours is a random access iterator.  Is it?

Its a forward iterator. Changing it to a random access iterator solves it indeed.

This is my first iterator that I am writing, but why is it not possible to implement a custom distance method for forward iterators?

The implementation of std::distance only has the iterator category to go on when deciding whether to move by many steps or by one jump. There isn't any other information it can use.

Am I doing something conceptually wrong?

Could be. If you can move your iterator by N steps in one jump, maybe it should be a random access iterator.

Or should I specialize the std::distance() function?

You could specialize that function for specific iterator types. There's no partial specialization of function templates, and you're not allowed to add an overload to namespace std. -- Dave Abrahams BoostPro Computing http://www.boostpro.com