Jens Theisen writes:

Hello,

I'm wondering what the reference member in the iterator_traits of an iterator is required to be. I couldn't find any requirement at all in the C++98 standard,

Bingo.

and more surprisingly, I can't see any requirement in the new iterator proposal either.

In particular, operator* does not seem to be required to return the iterator_traits< Iterator >::reference for lvalue iterators.

Interesting point. IIRC we were trying to stay compatible with the existing standard iterators; one of the iterators (istream_iterator?) has a very strange reference type. OTOH, for lvalue iterators, the reference member is redundant: the result of operator* is reqiured to be value_type&

At one point, however, the proposal suggests that this was the intention:

"...would have a return type of reference; the same as operator*."

where reference has a font style indicating that it's the iterator_traits's notion of reference.

I'm looking at the proposal version currently published along in the documentation of the boost iterator library.

So my questions:

- Am I right in my suspicion that in the STL, the reference iterator_trait is entirely useless if taken strictly?

Yes.

- Should the proposal not better require the reference to match with operator*'s return type for lvalue iterators? If not, what's its use?

Maybe, but that particular proposal is sorta dead. Some people have been working on a new one to address these issues, but I don't know where it's going.

- Is this off-topic here? :)

It's marginally on-topic, I s'pose. -- Dave Abrahams Boost Consulting www.boost-consulting.com